LightTools IntroTutorial

Introductory Tutorial

July 2007

3280 East Foothill Boulevard, Suite 300Pasadena, California 91107 USA

Tel: (626) 795-9101Fax: (626) 795-0184

E-mail: [email protected]://www.opticalres.com

mailto:[email protected]

http://www.opticalres.com

The information in this document is subject to change without notice and should not be construed as a commitment by Optical Research Associates (ORA®). ORA assumes no liability for any errors that may appear in this document.

The software described in this document is furnished under license and may be used or copied only in accordance with the terms of such license. The LightTools output shown (plotted and printed) may vary in different versions.

Copyright © 2007 by Optical Research Associates. All rights reserved.

Proprietary Software Notification

LightTools® is the proprietary and confidential property of ORA and/or its suppliers. It is licensed for use on the designated equipment on which it was originally installed and cannot be modified, duplicated, or copied in any form without prior written consent of ORA. If supplied under a U.S. Government contract the following also applies:

Restricted Rights Legend

Use, duplication, or disclosure by the Government is subject to restrictions as set forth in subparagraph (c)(1)(ii) of the Rights in Technical Data and Computer Software clause at DFARS 252.227-7013 or in subparagraph (c) of the Commercial Computer Software - Restricted Rights clause at FARS 52.227-19.

ORA, CODE V, and LightTools are registered trademarks of Optical Research Associates. Other trademarks or marks are the property of their respective companies.

LightTools Introductory Tutorial • iii

Contents

Introduction .........................................................................................................1What This Tutorial Covers ..................................................................................................1A Note About Modules........................................................................................................2Contacting Customer Support..............................................................................................3

Chapter 1 The LightTools User Interface........................................................5Interface Elements ...............................................................................................................6

The LightTools Window ...............................................................................................6Windows Standard Features .........................................................................................8The Properties Dialog Box ...........................................................................................9What’s This? and Other Help .....................................................................................10

The 3D Design View .........................................................................................................11Selecting Elements in a Design ..................................................................................11The Command Panel...................................................................................................15Design View Panes .....................................................................................................16Design View Tools .....................................................................................................17

Starting, Saving, and Stopping ..........................................................................................19Installing LightTools...................................................................................................19Starting LightTools .....................................................................................................19Saving LightTools Files..............................................................................................20Stopping LightTools ...................................................................................................20

Using Libraries, Utilities, and Macros...............................................................................21

Chapter 2 Before You Begin ..........................................................................23

Chapter 3 Learn by Doing: Analyze a Light Pipe.........................................25What is a Light Pipe?.........................................................................................................26Opening, Viewing, and Selecting ......................................................................................27

Opening the Model .....................................................................................................27Viewing the Model .....................................................................................................28Selecting Objects and Surfaces...................................................................................30

iv • LightTools Introductory Tutorial

Contents

Tracing Rays and Modifying the Light Pipe .....................................................................32“Point-and-Shoot” Ray Tracing..................................................................................32Using the Command Panel .........................................................................................33Trace a Ray Fan ..........................................................................................................33Make a Cut..................................................................................................................35Name the Object .........................................................................................................37Changing Properties....................................................................................................38

Performing Illumination Analysis .....................................................................................40Layers .........................................................................................................................40Sources and Receivers ................................................................................................41Simulation Info and Ray Preview...............................................................................42Understanding Charts .................................................................................................44Making the Big Run ...................................................................................................46Analysis Results and Re-binning................................................................................47

Optical Properties Example: Paint It White.......................................................................49Conclusions........................................................................................................................51

Chapter 4 Starting from Scratch: Build a Virtual Flashlight .......................53What is a Wide-Angle Flashlight?.....................................................................................54

Start with the Reflector...............................................................................................54Use the Place Reflector Buttons .................................................................................55Curve the Back Surface ..............................................................................................57Trace Some Rays ........................................................................................................58

Point Source and Receiver .................................................................................................59Place a Point Source ...................................................................................................59Run a Quick Illumination Simulation.........................................................................64

Adding a Detailed Source Model.......................................................................................66Delete the Point Source ..............................................................................................67Insert the Library Element ..........................................................................................67Make a Hole for the Lamp Base .................................................................................69Re-run the Simulation.................................................................................................71Save Your Work .........................................................................................................71

Create a Faceted Reflector .................................................................................................72Delete the Smooth Reflector.......................................................................................72Running Utilities.........................................................................................................72Run an Illumination Simulation .................................................................................75

Create the Flashlight Body ................................................................................................77Collar ..........................................................................................................................77Create the Battery Compartment ................................................................................78Join the Parts Using a Boolean Operation ..................................................................79

Conclusions........................................................................................................................80

LightTools Introductory Tutorial • v

Contents

Chapter 5 Introduction to Backlight Design.................................................81About Backlighting............................................................................................................82

Information Displays ..................................................................................................82Designing a Digital Picture Viewer ...................................................................................83

Using the Backlight Utility.........................................................................................84Creating the Light Guide ............................................................................................84Defining a Texture of Spherical Bumps .....................................................................86Parts Summary............................................................................................................87Parameterize the Bumps .............................................................................................88Examining Surface Properties ....................................................................................90Viewing the Texture Property Zone ...........................................................................91Add a Luminance Meter .............................................................................................92

Illumination Analysis.........................................................................................................94Turn Off the BEFs ......................................................................................................95Run a Quick Preview Simulation ...............................................................................96Run a Simulation with More Rays .............................................................................97View Illuminance Results...........................................................................................97View Luminance Results ............................................................................................98

Performing a Final Analysis ..............................................................................................99Turn On the BEFs.......................................................................................................99Specify More Rays .....................................................................................................99View the Improved Luminance ................................................................................100

Evaluating Spatial Luminance .........................................................................................100Controlling the Angular Coordinate Rotation ..........................................................101

Changing the Material of the Block.................................................................................103Conclusions......................................................................................................................104

Index .................................................................................................................105

vi • LightTools Introductory Tutorial

Contents

LightTools Introductory Tutorial • 1

Introduction

Thank you for trying LightTools from Optical Research Associates. We are sure you will find the program easy to learn and use, as well as extremely powerful and flexible for all your optical modeling and simulation needs.

LightTools can be used to create virtual prototypes of optical systems for a wide range of applications. Because of this flexibility, LightTools has many features, only a subset of which are typically used for any one application. We have tried to make these features as easy as possible to learn and use, by providing a user interface similar to many common Windows®-based applications. If you have used applications such as Microsoft® Excel, you will find the menus, spread sheets, windows, dialog boxes, and other interface features to be quite familiar. Preference settings allow you to tailor various aspects of the interface, and, beyond this, LightTools also includes a command language and powerful programming facilities. A variety of supplied utilities extend the basic capabilities of LightTools without requiring any knowledge of programming.

What This Tutorial CoversUsing three independent sample sessions, the LightTools Introductory Tutorial is designed to acquaint you with a few of LightTools’ basic capabilities for optical modeling, design, and illumination analysis. The first session uses a simple pre-defined plastic light pipe model. It describes the steps needed to modify the geometry and surface properties of the light pipe and analyze it to evaluate illumination uniformity on a specified surface. This shows the power of interactive point-and-shoot ray tracing as a design tool, and introduces basic illumination analysis.

In the second session, you will set up a wide-angle flashlight. This chapter leads you through the process of entering a completely new optical system model, defining solid objects, combining them with Boolean operations, modifying optical and material properties, and using various interface features and utilities. Additional illumination features are also introduced.

2 • LightTools Introductory Tutorial

Introduction

The third session starts with the use of a supplied utility to quickly create and analyze a backlight model for a liquid crystal display (LCD) for a portable digital photo viewer, a device similar to a personal digital assistant (PDA). This demonstrates the power of supplied utilities to help you create and modify sophisticated models.

When you have completed these sample sessions, you will have a good idea of how LightTools is used to solve optical problems. While these sessions are relatively simple, LightTools can handle systems of great complexity, including optical and mechanical geometry imported from computer-aided design (CAD) software or created within the program, and with a wide range of optical properties, including scattering, polarization, coatings, and much more. The techniques are the same as those used in this manual (the same types of steps, just a lot more of them).

Chapter 1 of this tutorial briefly describes the features of LightTools’ user interface. We strongly urge you to read this section before trying the examples. Familiarity with the assumptions and techniques of the user interface will make your later use simpler and more productive.

If this is your first experience with LightTools, we hope it is an interesting and pleasant one for you. We’d like to hear your comments on the program and its documentation. We are always working to improve our product to make it a better tool for all our customers’ needs.

A Note About ModulesLightTools is modular, meaning that its specialized features are separately licensed. The Core module is always required and includes the basic capabilities of geometry creation, modification, and ray tracing. The Illumination module includes features for creating sources and receivers, running Monte Carlo simulations, and displaying these results with various charting features. The Data Exchange modules are used to import and export CAD models in several specific formats. The Image Path module is primarily for customers who also use ORA’s CODE V optical design software. Any licensed modules are integrated in the LightTools user interface.

Trial licenses of LightTools normally include the Core and Illumination modules, and these are covered by this tutorial; trial licenses may also include other modules not covered here. If you are working with a licensed (that is, non-trial) version of LightTools that does not include the Illumination Module, you will not be able to do some of the steps described in this manual.


Introduction

Contacting Customer SupportIf you have questions or problems with the tasks in this tutorial, or with program installation or other issues, please feel free to contact Customer Support at Optical Research Associates. You can contact ORA in several ways:

E-mail: [email protected]: http://www.opticalres.comTelephone: (626) 795-9101 8 a.m. to 6 p.m. U.S. Pacific Time

mailto:[email protected]

http://www.opticalres.com


Introduction


Chapter 1 The LightTools User Interface

This section presents the main features of the LightTools user interface.

Contents

Interface Elements.....................................................................................................6

The 3D Design View...............................................................................................11

Starting, Saving, and Stopping................................................................................19

Using Libraries, Utilities, and Macros ....................................................................21


CHAPTER 1 The LightTools User Interface

Interface Elements

The LightTools WindowLike most Windows-based applications, LightTools runs in a main window that contains various other windows and controls. The three navigation windows and the output window are initially docked (located at a fixed position) inside the main window, but you can disconnect them from the main window and let them float as separate windows or close them, if desired.

From the menu bar, you can show or hide any of these windows by selecting View menu and then the name of the window listed on the pull-down menu. For example, when the Window Navigator is displayed, selecting View > Window Navigator hides it; selecting View > Window Navigator a second time shows the Window Navigator again.

• Menu bar. Provides access to most of the functions of the program. The menu options vary depending on the active window.

Menu bar

System Navigator

3D Design View

Window Navigator

Preferences dialog box

Console Window Properties dialog box

Output Window

Preferences Navigator



LightTools windows display various types of data and perform quite different functions; for example, 3D Design views are like CAD programs, table views are like spreadsheets, LumViewer windows are interactive data display/explora-tion windows, the Console window displays text messages. Rather than define menus that would apply to all possible types of windows, LightTools changes the displayed menus depending on the active window.

In most cases, the common menus File, Edit, View, Window, and Help are displayed, although their contents will change depending on the active window. Properties are displayed in dialog boxes that, for convenience, behave some-what like windows (i.e., they can stay open when not in use and can be moved and resized). While they may act like windows, Properties are displayed in self-contained dialog boxes, so they have no menus associated with them.

• System Navigator. Shows the names and hierarchal relationships of all the objects in the current LightTools session in a collapsible tree structure. From this window, you can view objects, select them (by left-clicking), or modify them (by right-clicking and selecting the Properties menu to open a dialog box). Use plus and minus symbols to expand and collapse the levels of the tree structure.

• Preferences Navigator. Provides access to the Preferences dialog box, which enables you to set and save general and view preferences, as well as default values.

• Window Navigator. Provides a way to keep track of all the windows you are working with. The Window Navigator lists all of the open LightTools windows. Click on the name of a window to bring it to the front and make it active, or right-click on the name of a window to see a shortcut menu of other operations you can perform (e.g., minimize, maximize, close).

• 3D Design view window. Displays the model in 3D form, with many options for changing views (including free rotation with the right mouse button), rendering (wire frame, solid, translucent), selecting, and editing through the palette of command buttons on the right side of the window.

• Properties dialog box. This dialog box is something like a window, in that it can stay open between operations, and it can be moved and resized as needed. Its content varies depending on what is selected.

Tip: If there is no menu bar displayed, you probably have a Properties dialog box active. Click on an actual window to activate it, and the menu bar for that window will be displayed.



• Console window. Displays a log of the commands generated by all operations in the current sessions, as well as error messages. (Note that error messages may be easier to read in the Output window, docked at the bottom of the screen). You must make the Console window active when you want to close or open a system file (an .lts file), although you can save the current model with any window active. This text window remains open at all times, although it can be obscured by other windows, as it is here.

• Output window. The Output window is where all LightTools output messages are displayed, including separate information, error, and warning messages for:

– Message Log

– Ray Report (Simulations)

– Data Exchange

– Macro output

– Optimization

– Photorealistic rendering

The Message Log tab is displayed when you start a LightTools session; other tabs are displayed as needed (as messages are printed to them).

• Miscellaneous windows and dialog boxes. Specialized windows or dialog boxes are displayed as needed. The example shown at the bottom of the sample screen on page 6 is the Preferences dialog box (Edit > Preferences), used to specify display preferences and default settings for various properties and modes.

Windows Standard FeaturesIf you are familiar with other Windows-based applications such as Microsoft Excel, you will find the basic operation of LightTools to be quite familiar. Operations such as moving and resizing windows, editing spreadsheets, selecting items (text, numbers, rows, columns), and copying and pasting, are performed in a way that is commonly seen in other Windows-based applications. Most of these operations use the left mouse button. As in many other programs, the right mouse button is used to display shortcut menus that vary, based on your current situation.

Although standards are followed to a great extent, optical design is a specialized application, so there are a number of special features in the interface that are specific to LightTools. Most of them are covered in this section, along with some standard features that are useful to know about in more detail.



The Properties Dialog BoxThe Properties dialog box allows you to view and edit object and surface properties of every type of object in a LightTools model. Only one Properties dialog box is displayed at a time, but it automatically reconfigures itself to display the data for the selected object(s).

The parts of the Properties dialog box are described below.

• Object Navigator. A collapsible tree-structure, similar to the System Navigator, but restricted to the currently selected object and its subordinate objects or children, allowing convenient access to all aspects of the current object. In the Object Navigator, you can select multiple items (Shift-click or Ctrl-click), which results in the display of only those properties shared by the selected items.

Tabs

Action Buttons

Object Navigator



• Property Tabs. Tabbed pages place properties in logical groups for easy viewing and editing. Note that, in some cases (especially receiver properties for illumination), tabs display read-only data, indicated by gray, non-editable text fields. Other pages may include buttons for saving or loading data or spreadsheets for displaying or editing 2D data. For example, illumination raw data is read-only, while spline surface data is editable.

• Action Buttons. The Apply button allows you to apply the current settings without closing the dialog box. The OK button applies the settings and closes the dialog box. The Cancel button cancels all changes that haven’t been applied. The Help button displays Help for the current tab and provides access to the LightTools Help system.

What’s This? and Other HelpLightTools has extensive help capabilities, including What's This? help. When you select the menu Help > What's This?, the cursor changes to a question mark. When you click on most interface objects, a pop-up description is displayed. There is also extensive how-to help (available from Help > Contents and Index) and a complete online documentation library (available from the Help > Document Library menu.)



The 3D Design ViewThe 3D Design view is where you will spend most of your time with LightTools. This interactive graphics window resembles a 3D mechanical computer-aided design (CAD) window, although it has special features not found in most Windows applications.

Selecting Elements in a DesignBefore you can specify the characteristics of any part of your model, you must select it.

Selecting Objects and Surfaces

Most elements in LightTools are modeled as solid, 3D objects with surfaces. Objects such as rays, ray fans, and text, are not solids, but they can be selected and modified as well. Selecting objects and surfaces is a fundamental step in modeling tasks, because many commands are not available until you select something. You cannot move an object, for example, until you select it, so the Move command

ToolbarCommand panel

Layout pane (one-pane layout shown)

Command line



button is grayed out to show that it is unavailable; if you enter Move on the command line when nothing is selected, LightTools displays an error message that states the command is unavailable.

To select an item, you can click on it in the design view or the System Navigator. When you click on an item in either place, LightTools shows that it is selected in both places. In the System Navigator, the selected item is surrounded by grey box. In the design view, LightTools highlights the selected item by changing the color of its outline or its surface. When you select a surface, LightTools also displays a dark block or tag point near the center of the selected surface.

Some items can be selected only in the System Navigator, however. If you click on a block in the design view, for example, you select a surface on the block; to select the entire block object, you must click on the block (e.g., Cube_1) in the System Navigator.

Tip: In complex systems, it is often easier to select desired objects and surfaces in the System Navigator. When you create an object, LightTools assigns it a default name, such as Cylinder_21. If there are many similar objects in a model, a name such as RedFilter is more useful than Cylinder_21. To change an object’s name, right-click on it in System Navigator and select Rename.

Surface is selected



As with most Windows-based programs, you can Shift-click to select multiple objects in either the 3D Design view, the System Navigator, or other tree-structure navigation views. Use Ctrl-click for discontinuous multiple selection in navigation views. The 3D Design view also provides commands for multiple selection (e.g., More for adding to existing selected objects, Inside for selecting objects in a defined area, etc.).

Selecting Multiple Elements

When multiple elements are selected in the Object Navigator of the Properties dialog box, changes will apply to all the selected elements, allowing you to make the same property change to all selected elements.

Tip: No matter which tool you have selected in the 3D Design view, you can use the mouse to single select by holding down the Ctrl key while clicking (Ctrl-clicking), or to a select more by holding down the Shift and Ctrl keys while clicking (Shift-Ctrl-clicking).

Object is selected



If the elements selected are of different types, the Properties dialog box shows only the tabs and properties that the selected elements have in common. If there are no properties in common, the Properties dialog box can be blank.



The Command PanelThis array of buttons is where most actions start. Initially, you can see only one of three tiers of buttons.

Many of the command buttons have a small diagram of the steps required to perform the command. These steps are also prompted above the Command line.

Selecting a button in the first tier opens the second tier.

Selecting a sub-category on the second tier opens the third tier of buttons, which correspond to commands.



Design View PanesThis is where the graphics are displayed, either in single-pane or four-pane mode. In four-pane mode, a red border is displayed around the active pane. Selecting an object or a surface in the design view automatically selects its name in the System Navigator window (if open), and vice versa.

In many cases, it’s easier to work with one pane, and you can quickly switch to a single-pane view using the 1-Pane button in the design window’s toolbar.

Toggle between 1-Pane and 4-Pane views from the toolbar.



Design View Tools

Undo

The Undo feature (Edit > Undo) keeps track of virtually all changes that you make, allowing you to track down and correct many mistakes. Actions that affect only the interface, such as moving or resizing windows, cannot be undone.

The Zoom Tool

You can zoom in on a particular portion of a design using the zoom tool.

1. Click the Zoom button on the toolbar.

2. Specify the corners of the area you want to display larger.

Zoom toolbar button

Two clicks define the corners of the zoom area



The Reset Command

After you rotate, pan or zoom a design, you can reset the view to the original orientation. To reset a view, select Viewing > Viewpoint > ResetViewpoint on the Command panel.

The Command Line

Text commands are displayed in the Command line as you click the mouse. You can also type commands directly into the Command line instead of using the mouse.

Click this button to display the Viewpoint command buttons.

Click the Reset command button.

Click this button to display the Viewing options.



The two methods of input co-exist in the program; in fact, you can start a command using the mouse (click a command button, click to define a location, etc.) and continue it with text entry in the command line (enter precise coordinates, text labels, etc.). This is demonstrated in a later example.

LightTools has a complete command language that you can use to write macros or for use with Visual Basic (or other COM-enabled) programs to control operations in LightTools. However, programming skills are not needed for most routine design and analysis.

The Toolbar

Frequently used commands are available in the form of small icons called toolbar buttons, which are always available along the top of the design view. You can place the cursor over a toolbar button to see a tool tip that shows its name.

Starting, Saving, and Stopping

Installing LightToolsThis tutorial assumes that LightTools is already properly installed on your computer and that your security key is attached, if one is required for your LightTools installation. If you have problems, see Contacting Customer Support on page 3.

Starting LightToolsTo start LightTools, click the Windows Start menu to locate the program shortcut or double-click the desktop shortcut. Then, in the main LightTools window, select the menu File > New Model > 3D Design to start a new LightTools model. Select the menu File > Open to locate and open an existing file.

Tip: If you know the name of a command (shown here as bold italics, e.g., Move), you can type it in the command line of the appropriate window (most often the 3D Design view), and the palette will switch to that command button, allowing you to use the mouse or input text to complete the command.



Saving LightTools Files LightTools saves system models in specially structured text-based files with .lts as the file extension. It also saves multiple versions of each file name, using a number between the file name and the file extension (e.g., mybacklight.3.lts), where higher numbers are newer versions. Use the menu item File > Save As, to assign a name, or File > Save to save a new version of the current name. If you want to save simulation ray data along with your LightTools model, select File > Save With Ray Data. This menu option enables you to later re-open the model and analyze the ray data without having to re-run the simulation. Saving is available from any window that displays a File menu. (For details, see Saving a LightTools Model on page 14 in the LightTools Core Module User’s Guide.)

If you want to save some components as a library object (to insert in another LightTools model), you can select the desired object(s) in the design view and select File > Save Library. Follow the displayed prompts to create an entity (.ent) file.

LightTools also allows you to save specialized or user-defined data for use with other system models. For example, you can save user materials (.mat files), user coatings (.coa files), and optical properties (.opr files). You can import or export data from an active Illumination chart data window using the File menu.

In addition, if you have licensed one or more of the Data Exchange modules, the menu options File > Import and File > Export are active so that you can import and export specially formatted CAD data files with appropriate file extensions (e.g., .sat, .stp).

Stopping LightToolsActivate the Console window (bring it to the front) and select File > Exit to exit LightTools.



Using Libraries, Utilities, and MacrosLightTools has many built-in features for creating, modifying, and analyzing optical system models. These features are supplemented by a number of supplied model libraries, utilities, and pre-written macros, which are accessible from the Tools menu (when a design window is active) or the AddIns menu (when the Console window is active).

The first three libraries provide access to LightTools models and associated files that can help to accelerate your design process or experiment with various LightTools features. These are described in the LightTools Core Module User’s Guide.

The fourth library, the Utility Library, provides access to utilities written by ORA Technical Support using Microsoft Visual Basic and the LightTools Macro Function Library. This LightTools Utility Library window, shown in the following figure, allows you to browse through the various utilities, see brief descriptions, and run them.



Some utilities are relatively simple, such as Move and Copy, which extends the capabilities of built-in commands. Others are specialized mini-applications, powerful tools for setting up complete backlight models, designing faceted reflectors, or creating source models of various types. These utilities are introduced in this tutorial.

In addition to the ORA-written utilities, LightTools includes programmable features that allow you to create tools and utilities that expand upon the built-in features to accommodate specialized needs. The component object modeler (COM) interface allows LightTools to be controlled by other Windows programs, such as Excel or Visual Basic. (The supplied utilities are compiled Visual Basic applications that use COM to communicate with LightTools.) LightTools also has its own built-in macro language, based on an earlier version of BASIC.


Chapter 2 Before You Begin

This section describes how to set the preferences that are used in the examples.

LightTools has various settings for default parameters, new object creation, etc. Most of them are matters of personal taste, such as color schemes. Many people just start with the default settings, but the examples in this tutorial assume certain technical settings in order for your results to match what’s shown in the samples.

1. Start LightTools.To do this, locate LightTools on the Windows Start menu, or double-click the desktop shortcut, shown below.

When the program opens, the main window displayed is the Console window, where commands and messages are displayed. This window must be active (selected) when you open and close files. You will also see three navigation windows docked at the left side of the main window, and an Output window docked at the bottom.

2. Open a new 3D Design view by selecting File > New Model > 3D Design.

3. Select Edit > Preferences to display the Preferences dialog box.

4. Expand the General Preferences list (click the plus sign next to the heading), and click on System.

5. On the System tab, set the Units to Millimeters, set the Radius Mode to Radius, and click Apply.

6. Expand the Defaults list, and click on Receiver.

7. Set the Units to Photometric Flux and the Illuminance units to Lux, as shown in the following figure, and click Apply.


CHAPTER 2 Before You Begin

8. Click on Source, set the Units to Photometric Flux (Lumens), and click Apply.

9. Right-click on Defaults and select the menu Save General and Defaults to retain these settings in future sessions.

10. Expand the View Preferences list and click on 3D_untitled.

11. Click on the Grid tab.

12. Make sure that the Snap to Grid box is checked, set the XValue and YValue below that to 0.1 mm, and click Apply.

13. Optional: Click on the Colors tab, select the Color Scheme Black on White, and click Apply. (This scheme works best for documentation purposes, so this is used for the examples in this book. You may prefer another combination.)

14. Optional: Click on the Visibility tab, click the Show Annotation check box to clear it, and click Apply. (This setting is used to simplify the illustrations in this book. You may prefer to display annotations in your model.)

15. Right-click on 3D_untitled and select the menu Save View Environment.

16. Click OK to close the Preferences dialog box.

17. Close the model. To do this, click on the Console window to make it active, and select File > Close Model. Click OK when LightTools warns you that you haven’t saved it.


Chapter 3 Learn by Doing: Analyze a Light Pipe

In this chapter, you open, view, ray trace, and modify a simple plastic light pipe. Then, you do some basic illumination analysis, introduce a scattering surface, and see the effect of this on the illumination distribution. This introduces you to many of the basic techniques needed to use LightTools.

Contents

What is a Light Pipe? ..............................................................................................26

Opening, Viewing, and Selecting............................................................................27

Tracing Rays and Modifying the Light Pipe...........................................................32

Performing Illumination Analysis...........................................................................40

Optical Properties Example: Paint It White ............................................................49

Conclusions .............................................................................................................51


CHAPTER 3 Learn by Doing: Analyze a Light Pipe

What is a Light Pipe?Light pipes are used in many applications where light must be guided from a source to one or more illuminated areas. Light pipes in automobile dashboards can be very complex, and LightTools is a great tool for designing and analyzing such systems.

You will start with a simple L-shaped plastic light pipe with a single flat surface to illuminate. This is similar to light pipes used to illuminate buttons or indicator lights in various devices.

When you are finished, the light pipe will look something like this:

In this chapter, you learn how to:

• Open an existing LightTools model.

• Use 3D viewing selection tools.

• Trace a fan of rays and modify the light pipe to redirect the rays to illuminate the target surface.

• Use a pre-defined light source (simulating an LED) and a receiver (collection surface) to run a simple Monte Carlo illumination simulation.

• Apply an optical property (Lambertian scattering) to a surface and rerun the illumination simulation.



This will allow you to exercise many powerful LightTools features in a short time. Some of these features are briefly explained as they are introduced here, and additional explanation is included in subsequent chapters. The main purpose of this chapter is to get familiar with the interface and with typical tasks and procedures.

This is a very simple system, but it allows you to explore some of LightTools basic features.

Opening, Viewing, and SelectingThe starting point for this light pipe model is supplied with the sample models in the LightTools installation directory. It is made of plastic (polycarbonate) and consists of two blocks joined using Boolean operations, with a simple light source, and a rectangular dummy element (that is, an element that has no optical effect) with a receiver for illumination analysis. The source and receiver are on a hidden layer, so you won't see them at first.

Opening the Model

1. Select File > Open on the menu bar.

If you didn’t close your model after you finished setting preferences, a LightTools message is displayed warning that your model hasn’t been saved. Click OK to close it now and continue.

2. On the Open dialog box, browse to the \Tutorial folder of the LightTools installation directory, shown in the following figure.

Note: Be sure that you have set your preferences as described in Chapter 2.



3. Click the file name TD_Lpipe_start.1.lts and click the Open button.

LightTools models are saved in files with the file extension .lts (for LightTools System).

Viewing the ModelThe model opens, and the 3D Design view is displayed, showing four panes (nominally, top, right, front, and isometric views, but you can change each pane as desired). Note that one of the panes has a red border around it, indicating that this is the active pane for any operations that depend on view-based coordinates. (In LightTools, you can use several different coordinate systems in various types of tasks.)

Now that a model is open, the navigation windows contain structured lists, which you will soon use to keep track of the parts of the system you are modeling and the various windows you will open. If you would like to explore the lists, click on plus signs (+) to expand hidden levels, and click on minus signs (-) to collapse a list.



1. Make sure the lower right pane is active (has a red border), then click on the 1 Pane button on the toolbar:

The right side view now fills the entire display area, and the 4 Pane toolbar button is available to return to the 4-pane view when desired. Although you now see only a single view of the model, the right mouse button and the toolbar let you quickly change that view as needed.

2. Use these view operations to set up a view similar to the following picture. To do this, you can:

– Rotate the View. Place the cursor over the model, hold down the right mouse button, and slowly move the mouse around to spin the 3D Design view.

– Zoom. Hold down the Control key and the right mouse button and move the mouse up or down. Move the mouse up to zoom in, or move the mouse down to zoom out.

– Pan. Hold down the Shift key and the right mouse button and move the mouse to move the view around (pan up, down, left, right).



Selecting Objects and SurfacesAs explained in Chapter 1, there are two aspects to selection: the object itself, and (in most cases) the surface of the object. Some operations affect the object as a whole, while others (e.g., setting optical properties) operate on the selected surface(s).

There are several tools that you can use to select objects, but because selection is needed so frequently, it is also the default operation, DefaultSelect. You will see this command in the 3D Design view command line whenever no other tool is selected.

1. Click with the left mouse button on any visible surface of the light pipe.

The wireframe outline of the model is highlighted to show that it is selected. The surface you click on changes color and a tag point (a small square) is displayed on that surface. The name of the selected surface is also highlighted in the System Navigator.

Note: These view operations do not change any aspect of the model itself; you are simply “walking around” the model to view it from different virtual positions in space. Note that the coordinate axis rotates when you rotate the view. The objects in the model are fixed with respect to this global coordinate system. LightTools provides commands (such as Move) to change the position of selected object(s) within the model.



2. Click on the name of a different surface in the System Navigator.

The corresponding surface is highlighted in the 3D Design view. If you click a surface that is not directly visible (e.g., the back surface or bottom surface), you won't see the highlighting when the model is displayed in translucent mode. If you use the right mouse button to rotate the view, you will see the highlighting.

To get ready for ray tracing, the next step restores the original side view and changes the rendering mode from translucent to wireframe.

3. To restore the YZ plane view and set the scale to fit all objects in the visible plane, click these toolbar buttons:

Y-Z Plane and then Fit .

4. Select View > Render Mode > Wireframe to display only the edges of the objects.

Tag point



Wireframe render mode makes it easier to see and work with rays, but in this mode, you can select objects only by clicking on an edge. With translucent and solid rendering, you can click anywhere on a rendered surface to select it.

Tracing Rays and Modifying the Light PipeThe basic operation of LightTools is ray tracing. Everything else is based to some extent on tracing one or many rays and doing some calculations with them. LightTools’ Monte Carlo simulation traces many rays (thousands, sometimes millions, from defined sources) to predict illumination distributions.

“Point-and-Shoot” Ray TracingPoint-and-shoot rays are defined graphically, interactively, by clicking a starting point and then making additional clicks to define the direction and, in the case of fans and grids, the extent of the ray bundle. These rays are called non-sequential (NS) rays, because you do not have to define the order of surfaces that the rays will hit. You typically trace a relatively small number of point-and-shoot rays to view and understand the behavior of light in the system and to instantly see the optical effect when you make changes to the model. Going beyond the requirements of a simulation tool, this capability helps to make LightTools an excellent design tool. Once you begin running illumination simulations, you must explicitly re-run the simulation when you make changes to the model.



Using the Command PanelThe command panel is the array of buttons down the right side of the 3D Design view, arranged by function. As described inThe Command Panel on page 15, you click one of the six category buttons to open a sub-category tier of buttons. You click a button in the middle to choose a sub-category, and the panel of Command buttons, is displayed.

In this tutorial, the category, sub-category, and command button sequence are shown side by side, as shown here:

After you click a command button, use the diagram on the button as a general guide to its use. Most commands require one or more clicks, numbered in order in the diagram. The Command line shows the command name (NSFanFromPoint, in this case), and, above the command line, you will see prompts for the input. As you click points using the mouse, or enter data directly in the Command line, the command is built, and, when complete, it is executed.

Trace a Ray FanYou can trace single rays, a fan of rays, or a grid of rays. There are several types of fans and grids: parallel, diverging, and converging. In this example, you will have a light source located 0.5 mm to the left of the entering face of the light pipe. Use the cursor coordinates displayed at the lower right of the 3D Design view for the following steps.

Note: If you followed the setup instructions in Chapter 2, there is a 0.1 mm snap grid active, which restricts the mouse motion to 0.1 mm increments, making it easier to hit specific points.



1. Click the Ray Fan button (NSFanFromPoint). The command panel button sequence is shown below.

2. Click at the point (X = 0, Y = 0, Z = -0.5) to start the ray fan. Be sure to release the mouse button after clicking. Each point is discrete.

3. Click at (0, 1, 1) to define the top of the fan, then click at (0, -1, 1) to define the bottom of the fan.

Follow the prompts and watch the cursor coordinates to track the cursor location.

Prompts

Cursor coordinates



The fan is displayed. As you might expect, no light makes it to the desired output surface on top of the larger cube. You will have to modify the light pipe to get the light there. Note that the command button is no longer highlighted; to trace another ray fan, you would have to click the command button again.

Make a CutTo reflect light to the top of the light pipe, you must introduce an angled surface. If the trim angle is correct, total internal reflection (TIR) will direct most of the light to the top surface without requiring any sort of coating. (TIR is the default surface property, but there are many others, as you will see.)

1. Select the light pipe by clicking on any edge.

2. Select the Trim button (TrimSolid), shown below.

To find out what the Trim button is for, you can use What’s This? help.

Tip: The snap grid is not your only guide for precisely entering points. During any operation, you can right-click to display a shortcut menu with a Snap menu item. You can snap points to objects, surfaces, coordinate axes, and even lines or rays.



3. Select Help > What's This? on the main menu.

The cursor changes to a question mark.

4. Click on the Trim button.

A pop-up window is displayed, with a description of the command button.

5. Click on the help pop-up to close it.

6. Click the point (0, 0, 6.5) to define the section point, as prompted.

The exact coordinate is not critical, because you will change it later to try to get more rays on the target surface. A “rubber band” line is displayed, along with text showing you the length and angle of the vector leading to the second point.

7. Aim the normal vector at the lower right corner, making an angle of about -34º (the length is not critical), and then click to create the trim surface.



If you make a mistake and trim away too much, select Edit > Undo and try again. It should look something like this:

Name the ObjectIn the System Navigator, the Trim operation has created the new object PlanePrimitive_n (where n is an integer). This is essentially an infinite “block” that has been Boolean subtracted from the light pipe to form the trim plane surface, which is labeled HalfPlane (this is where the surface properties reside). You can keep the default name, but it is a good idea to give important objects a descriptive name, so they are easy to recognize later. In this case, you should rename the PlanePrimitive, because you will later modify the trim angle of this 3D object. Renaming is easy.

1. In the System Navigator, right-click on PlanePrimitive_n and select Rename on the shortcut menu.



2. Type a new name, such as TIR_fold, and press Enter.

3. Save the modified system:

a. Select File > Save As... .

b. Navigate to the \LTUser (or other) directory.

c. Key in a new name, such as Tut_Lpipe_trimmed.1.lts, and click Save.

Note that the file name displays in the title bar (top edge) of the 3D Design view window.

Changing PropertiesNow the light is getting to the collection surface, but it doesn't fill the surface and it isn’t very uniform. This is just a rough judgment based on a small number of rays, but it's often part of the iterative design process to use a few rays to make decisions about parameters, then do a Monte Carlo simulation to predict the illumination more precisely. It may not be possible to get a great distribution with a simple TIR surface, but it's easy to experiment with the angle and position of the trim surface.

1. In the System Navigator, right-click on TIR_fold (the recently renamed PlanePrimitive_n) and select Properties on the shortcut menu.

The Properties dialog box gives you access to every detail of a model, and it changes, depending on the type of object selected. Right now, it displays the Coordinates tab, which applies to the entire selected object. (There is also a navigation tree in the dialog box, which provides access to specific surfaces, but you don’t need to use it at this time.)



2. Move the Properties dialog box so that you can see the 3D Design view.

3. Change the Absolute values of Z and Alpha to several different values, clicking Apply each time.

Can you get the ray fan to cover most of the top surface? The values shown (Z = 6 and Alpha = 139º) are not necessarily optimum.

4. Close the Properties dialog box. To do this, you can click the Cancel button or the X in the top right corner.

5. Click on the design view to make sure it is active.

6. Save your modified file. This time, you can use File > Save, because you gave it a name when you saved it earlier.

Tip: You can also click on the name of a window in the Window Manager to bring it forward and make it active.

Tip: If the File menu is not displayed, the Properties dialog box may still be the active window. To re-display the menu bar, make the 3D Design view active.



Performing Illumination AnalysisPoint-and-shoot ray fans are great for simple analysis and design, because they instantly show you what the light does, but eventually you will want to simulate the illumination performance, which requires several additions to the model:

• One or more sources

• One or more receivers

• A few decisions, such as how many rays to trace, and whether or not to display them

• Various charting features, which enable you to look at analysis results

The light pipe model already has a source and receiver, but they are on a hidden layer. Next, you will display them and do some quick illumination simulations. Later examples will explain the illumination results more extensively.

LayersLightTools models can become very complex, with optical elements, mechanical parts, rays, sources, receivers, etc. The layer feature provides a way of managing this complexity, allowing you to separate objects on as many as 32 layers, any of which can be visible or hidden. A layer number is one of the properties assigned to a LightTools object. To see or set the layer number, right-click the object’s name in the System Navigation window, select the Properties shortcut menu and click on the Display tab.

In this model, a light source and receiver for illumination analysis have already been defined and hidden on layer 2. Follow these steps to make them visible.

1. Click on the design view.

2. Select Edit > Preferences to display the Preferences dialog box.

This dialog box controls many program parameters, with sections for General preferences, various defaults, and view-specific parameters for any views that are currently open (only the 3D Design view, in this case).

Note: Making a layer visible or hidden affects only the display of objects, not their optical behavior. For example, a mirror on a hidden layer still reflects rays. To make 3D objects “invisible” to rays, you must use another option: the Ray Traceable check box on the Ray Trace tab of the Properties dialog box.



3. In the navigation tree of the dialog box, click the plus sign (+) next to the View Preferences heading, and then click on the name of the 3D Design view below it.

4. Click on the Layers tab to bring it to the front.

5. Click the check box for layer 2 (Lum_Objects) to make it visible.

6. Click OK.

Clicking OK applies changes and closes the dialog box.

The source and receiver symbols are now visible in the 3D Design view.

Sources and ReceiversThis section briefly describes sources and receivers. Please see LightTools Illumination Module User’s Guide, Chapter 2 and Chapter 3 for detailed information about these types of objects.

Sources. LightTools supports a variety of sources, from point sources to surface or volume emitters, in simple shapes to detailed lamp models made up of multiple sources and mechanical parts. You can also use simple sources with angular and

Tip: You can go directly to the Preferences dialog box for the active design view by choosing View > View Preferences or by right-clicking in the design view and selecting View Preferences on the shortcut menu.



spatial distributions (apodization files) applied to match measured or desired distributions, as well as ray data sources created from measurements of real sources.

Receivers. Receivers are special objects created to collect ray trace data for illumination calculations. LightTools supports spatial and angular receivers, and they are usually attached to a surface of an object. (A far-field angular receiver is not attached to any object.) Receivers assign ray energy (weighted ray data) to bins (cells) in a collection mesh, and this allows the irradiance and other properties to be determined. There is a trade-off between radiometric accuracy (based on the number of rays per bin) and spatial accuracy (based on the number of bins across the receiver). LightTools allows you to re-bin the data without re-tracing the rays.

In this sample model, a source and surface receiver are already defined. The source is a 1.0 watt point source with an apodization file attached to simulate the Gaussian intensity of an LED. The receiver is attached to the rectangular dummy element (named AirLens in this model, because that's its material) defined for this purpose. You can attach receivers to surfaces of real objects or to dummy elements, depending on your goals.

Simulation Info and Ray PreviewA Monte Carlo simulation requires a large number of samples for accurate statistical estimates of illumination. Samples in LightTools are traced rays, but unlike point-and-shoot rays, rays in an illumination simulation are traced in random directions from randomly selected points in or on the defined sources. Apodization and other factors affect the selection of random points so source behavior can be accurately simulated.

Before tracing large numbers of Monte Carlo rays, it’s a good idea to trace a smaller number with the Ray Preview option turned on. When Ray Preview is on, LightTools draws the rays in the design view, allowing you to see whether or not things are working correctly. Drawing many rays may slow down the ray trace, so it makes sense to turn it off when you’re tracing thousands of rays (or more).

1. Select Illumination > Simulation Info to display the Illumination Simulation Properties dialog box.

2. Change the Total Rays to Trace to 200.



3. Check the Preview Rays box and click OK.

No rays are traced yet. You have just defined the parameters for the simulation.

You can run the simulation from Illumination menu or from the toolbar.

4. Click the Start Simulation button or select Illumination > Start Simulation to trace and display the rays.

Your 3D Design view should look something like the figure below. (The design view has been rotated in this example.



Understanding ChartsWhen you run a simulation, all of the output data is stored in memory; you see the results when you open an illumination chart. Because there are many ways to view and analyze illumination results, the best chart to display depends on your goals. In this example, you will look only at the illuminance (spatial) distribution on the predefined surface receiver. Other available analyses and charts (including the interactive LumViewer) will be discussed in later examples.

Scatter charts are always a good starting point, because they are the closest thing to a view of the raw ray data. They don't tell you anything about the energy or statistics, but they allow you to see how completely you have covered the receiver.

1. With the 3D Design view active, select Illumination > Illuminance Display > Scatter Chart.

With only 200 rays for preview, the scatter chart is not very dense, but it can help you understand the relationship between chart coordinates and system coordinates. In the figure below, the 3D Design view has been rotated so that the receiver surface has the same orientation as the chart. You can see that the scatter chart is a kind of “ray diagram,” showing where the rays fall on the receiver surface.

Note: The menus always use the term illuminance, although, strictly speaking, this term applies only when photometric units are in use. In this example, the spatial distribution is in radiometric units of watts/mm2.



Tip: Chart coordinates are receiver coordinates. If you are not sure of the relationship between the chart coordinates and what you see in the design view, you can attach a local coordinate system to the surface holding the receiver. This was done in the figure above.

To attach a local coordinate system, click the UCSOnSurface toolbar button, shown at left, and then click on the receiver surface. (UCS means user coordinate system. This is also the rotation point for right-mouse view operations.)A local coordinate system diagram is displayed on the surface. To return the UCS to the global origin, click the UCSToGLobalOrigin toolbar button, shown at left.



Making the Big RunIf the simulation with a few rays doesn't show any major problems, you can try a bigger run.

1. Click on the 3D Design view to make it active.

2. Select Illumination > Simulation Info to display the Illumination Simulation properties dialog box.

3. Change the Total Rays to Trace to 10000.

4. Uncheck the Preview Rays box (click the check box to clear it) and click OK.

5. Click the Start Simulation button to trace the rays.

This calculation will probably take a little longer (a few seconds or more, depending on your CPU’s speed). You will probably see a small Interrupt Operation dialog box and the Progress dialog box, shown below.

Tip: If a calculation ever takes too long, you can interrupt the simulation by clicking the Interrupt button. You can then look at other windows, and even open new analysis windows to see if you have enough data. Then, click Resume or Cancel in the Progress dialog box, as needed.



Analysis Results and Re-binningAt this point, your scatter chart should be quite dense with rays. With more rays, illumination calculations make sense, so take a look at a pseudo-color raster chart of the illuminance (actually, irradiance, in this case, with units of W/mm2 and no photometric weighting. Please see Chapter 2 of the LightTools Illumination Module User’s Guide for information on radiometric vs. photometric calculations). To display a raster chart, make the design view the active window, and select Illumination > Illuminance Display > Raster Chart on the main menu.

The raster chart shows a pseudo-color coded, graphically smoothed map of irradiance (spatial) distribution on the receiver, along with a histogram showing the energy levels. You can see a fairly “hot” region in the center, with dark edges. How much data is here? How accurate is it? As with most objects in LightTools, receivers and charts have properties, and you can look to them to answer these questions.

1. Right-click near the center of the raster chart (on the shaded area).

The Properties dialog box for the Illumination Mesh_shade is displayed. Like other property dialog boxes, it has a small navigation tree. (You can also access mesh and other properties from the Illumination Manager section of the System Navigator, even if no charts are open.)



2. Click on the plus sign (+) to expand the tree chart, then click on the sub-item illuminanceMesh_n, (where n is an integer).

This dialog box has three tabs containing data.The Properties tab shows that the Mesh Dimensions have been set to 9 bins by 15 bins. (Auto Size Mesh, turned off in this case, is the default. It normally sets the number of bins to try to get a required accuracy level.) The Results tab contains read-only (calculated) values, including a (radiometric) Error Estimate at Peak, which should be about 9-11% for the 9x15 mesh. What if you have fewer bins?

3. In the Properties tab, change the bins to X = 5 and Y = 9 and click Apply.

The Error Estimate on the Results tab changes to around 6%. (Due to the statistical nature of Monte Carlo simulation, your numbers will not exactly match these.) This is called re-binning and is very useful for understanding the statistics of your illumination data. Note that in this case (with a TIR angled surface, with no coating), the total power is about 0.67 watts. The total power of the source is 1 watt.

Tip: If you would like to see the content of two or more tabs at once, you can open them in separate windows. To do this, right-click on the tab title, and select Open Tab in New Window on the shortcut menu, as shown above.



Optical Properties Example: Paint It WhiteTo improve the uniformity of illumination in this case, you could try a number of techniques: “stair-step” extrusions, a curved surface, patterns of paint dots, or 3D textures (bumps or grooves), for example.

One quick option to try is to paint it white. LightTools provides a number of pre-defined optical properties, including one called White Paint, in an easy-to-use library of properties. These library properties are created by combining several basic properties; for example, the White Paint property creates a Lambertian scatterer with 92% reflectance. You can, of course, set basic properties directly, and you can save and name your own combinations in .opr (for optical property) files.

1. In the 3D Design view, rotate the view so that you can click on the TIR_fold surface.

2. Right-click, and select Optical Properties on the shortcut menu.

The Properties dialog box is displayed, with the Optical Properties tab in the foreground.

3. Click the radio button for Load From Library.

4. Select Surface Finishes from the first drop-down list, shown in the following figure.



5. In the second drop-down list, select WhitePaint.1.opr.

6. Click OK.

Scattering causes a lot of, well, scattering, and you may see some warning messages about maximum hits for the NS rays in your model (the rays bounce and re-scatter, and if they hit a surface more than the default “max hits” of 10 times, a warning is displayed in the Console window).

Now you can re-run the illumination simulation with a single click.

7. Activate the design view and click the Start Simulation button to re-run the simulation.

8. Check the charts again. To bring a chart to the foreground, you can click on the chart window or click on the name of the chart in the Window Navigator.



The Scatter Chart looks pretty well covered now, and the Raster Chart looks more uniform over a larger area of the receiver, as shown in the following figure.

What’s the bad news? Right-click the raster chart and look at the Results tab. The total power is now about 0.3 watts. (Again, your values will not exactly match these due to Monte Carlo sampling and statistics.) Lambertian scattering is non-directional, so a lot of light is scattered in other directions (e.g., back toward the source). This is probably not the best solution.

9. Save your work again (File > Save).

10. Close the model if you are ready to go on to the next example. To do this, make the Console window active and select File > Close Model.

ConclusionsThis example showed how LightTools is organized and demonstrated some of its basic capabilities. This is a simple example, but the techniques are general.

The next session shows you how to build a 3D model of a wide-angle flashlight from scratch.




Chapter 4 Starting from Scratch: Build a Virtual Flashlight

This chapter describes the steps needed to create and analyze a model of a wide-angle flashlight. You will start with a smooth parabolic reflector and a point source, introduce a detailed lamp source, and finally use a supplied utility to create a faceted reflector tailored for the desired pattern (i.e., a uniform beam over a 100 mm disk at a distance of 300 mm from the source). You will also learn how to use Boolean operations to build a mechanical model of the flashlight body.

Contents

What is a Wide-Angle Flashlight? ..........................................................................54

Point Source and Receiver ......................................................................................59

Adding a Detailed Source Model............................................................................66

Create a Faceted Reflector ......................................................................................72

Create the Flashlight Body......................................................................................77

Conclusions .............................................................................................................80


CHAPTER 4 Starting from Scratch: Build a Virtual Flashlight

What is a Wide-Angle Flashlight?In this example, you will create a virtual prototype of a wide-angle flashlight, using an incandescent lamp and a reflector. What is a wide-angle flashlight? A typical flashlight tries to produce a fairly concentrated beam of light, without much concern for uniformity. A point source at the focus of a perfect parabolic reflector would produce a collimated beam the same size as the reflector, with a Gaussian illuminance profile. In this design example, the flashlight will produce fairly uniform illuminance over a 100 mm diameter circle at a distance of 300 mm from the source.

Because you will be starting from scratch, this example has more steps than the light pipe example. Be sure to follow all the steps and save your work frequently (File > Save) so you can get back on track if you should take a wrong turn.

Start with the ReflectorOptically speaking, a flashlight is just a light source and a reflector, so you’ll start with the essentials, and then add the shiny metallic flashlight body at the end, mainly for show.



Use the Place Reflector ButtonsFirst, you’ll create a smooth, parabolic reflector.

1. Start LightTools.

2. With the Console window active, start a new model in a 3D Design view (File > New Model > 3D Design).

3. With the Right Side View active (indicated by a red border), click the One Pane button on the toolbar:

4. On the command panel, click the following buttons to display the Place Reflector buttons:

The Place Reflector buttons are different from other command buttons because they each launch a macro. The only functional difference you should notice, however, is that the prompts for these commands are displayed in small dialog boxes, rather than above the command line.

5. Click the Spun Parabola button:

The first of three prompting dialog boxes is displayed, shown in the following figure.

Note: Be sure that you have set the default preferences as described in Chapter 2.



6. Key in 12 for the distance from the focus to the reflector apex and click OK.

The next dialog box prompts you to enter either the reflector diameter or an input code (-1) to indicate that you want to define the depth of the reflector instead.

7. Key in -1 and click OK.

8. In the third dialog box, key in 60 for the depth of the parabola and click OK.

The reflector is displayed, as shown in the following figure.

Tip: If you click on the Console window, which logs all events in your session, you can see that the macro issues the Wireframe rendering and FitAll scaling commands.



Curve the Back SurfaceThis step is not optically important, but it makes the reflector look a little more realistic. The reflector has a parabolic front surface (a conic surface with a conic constant of -1), and a flat rear surface. It's easy to give the rear surface the same profile as the front.

1. Select the reflector. You can do this in the design view or the System Navigator.

– In the design view, click anywhere on the reflector to select it.

– In the System Navigator window, select refl.

2. Open the Properties dialog box by right-clicking and selecting Properties on the shortcut menu.

3. In the navigation tree of the dialog box, click on LensFrontSurface.

On the Geometry tab, you can see that the surface shape is Conic, with Conic Constant of -1 and (vertex) Radius of 24 mm.

4. Click on LensRearSurface, and change the following parameters, as shown in the following figure:



a. For the Shape, select Conic from the drop-down list, and click Apply.

b. For the Conic Constant, key -1.

c. For the Radius, key in 24.

The Concavity option is automatically set to Convex.

5. Click OK.

The rear surface is redrawn.

Trace Some RaysHow can you show that this really is a parabolic reflector? If it is, a bundle of point-and-shoot rays traced parallel to the Z-axis should focus to a single point, which, because of the design of the reflector macro, is located at (0,0,0).

1. Pan and zoom the view so that you have about 300 mm of space to the right of the reflector. To do this, use the Shift and Control keys with the right mouse button, with the cursor coordinates in the lower-right corner as a guide.

2. Select the ray fan button (NSFanAim):

3. Click the points needed to define the ray fan (locations do not have to be exact):

– Click 1: to the right of the reflector, at approximately Z = 200, Y = 0, for example.

– Click 2: above the first point, at approximately Z = 200, Y = 45, to define the width of a half-fan of parallel rays.

– Click 3: The third click defines the direction. Use a snap operation to make it precise. Right-click anywhere and select Snap > 90 Degrees; then, move your cursor to the left to aim the bundle of rays at the reflector and click to trace the rays.



Note that the rays focus precisely at (0,0,0), as expected for an on-axis parallel ray bundle with a parabolic reflector.

If you’d like, select Edit > Undo and try creating the fan of rays without using the snap feature to see how a small off-axis angle can lead to big aberrations.

4. Delete the fan of rays. To do this, click on any part of the fan to select it; then, right-click and select Delete on the shortcut menu, or click the Delete toolbar button, shown here:

Point Source and Receiver

Place a Point SourceIf a parallel fan of rays focuses at (0,0,0), then a point source at this point should produce collimated light (parallel rays) after reflection.

1. Click the Point source button (PtSource):



You could zoom in and click at the point (0,0,0), but since you know the coordinates, it’s easier to enter them on the command line, following the command PtSource, which is already displayed.

2. In the command line, key in the string xyz 0,0,0 with spaces and commas as shown, followed by a space.

A 1-lumen photometric point source is created, shown below, after zooming in.

Enlarging (zooming in) for a specific area is described in The Zoom Tool on page 17.

The wireframe sphere represents the aim sphere of the point source. It was created using the default source properties, which are acceptable for now. If you would like to see the properties, click to select the source, then right-click and select Properties.

Note: LightTools starts evaluating the command when you input the final space. You do not need to press the <Enter> key.

Note: The aim sphere for the source determines the directions in which the source can emit. By default, it's a full sphere. For more details about aim spheres, see Defining Aim Entities for Importance Sampling on page 38 in the LightTools Illumination Module User’s Guide. To display this book, select Help > Document Library > Illumination Module User’s Guide from the main menu.



Create a Dummy Surface

Illumination analysis requires at least one receiver, where rays are collected, displayed, and analyzed. A surface receiver can be attached to a surface of any 3D object. (Far-field receivers for angular calculations are not attached to a surface, but it’s not necessary to perform angular analysis right now). In many cases, a dummy surface or a flat (no-power) “lens” element is created to hold a receiver, but if there is a convenient real object, you can attach a receiver there. In this case, the goal is a certain illuminance at 300 mm from the source. So, you need to define a square dummy surface with a full-width of 150 mm at a distance Z=300 mm.

1. Select the dummy surface button (DummyPlane):

2. Since you know the required coordinates, key in the string xyz 0,0,300 with spaces and commas as shown, followed by a space.

3. Right-click and select Snap > Z-axis.

4. Using the rubber band guide (L value for length), click about 75 mm to the left of the starting point.

This point defines the dummy’s surface normal vector, and the length of the vector sets the half-size of the dummy. By default, a square dummy plane is created. You can use the Properties dialog box to adjust its (full) width and height to exactly 150 mm.

5. Click to select the new dummy plane, right-click, select Properties, and click the Controls tab.



6. Change Width and Height to 150 mm each, as shown.

7. Under Ray Trace, make sure that the box for Clip Rays to Boundary is checked.

This is useful when a dummy surface is used to hold a receiver, since you are only interested in the light collected by the receiver. (By default, the receiver is the same size as the dummy surface it is attached to). Note that the default name for the dummy surface is PlaneInterface. You can rename it if you like.

8. Click OK to apply these changes.

Place the Receiver

Now you can attach a surface receiver to the dummy surface. Surface receivers are displayed as a triangular symbol. A right-click menu is the easiest way to do this.

1. Click anywhere on the dummy surface to select it, then right-click and select Add Receiver.

A receiver symbol and label are displayed, shown above (after zooming in).



Understanding Surface Receivers and Far Field Receivers

LightTools offers two types of receivers, surface and far field. Surface receivers can measure illuminance and intensity on a given surface. Therefore, a surface receiver always exists on a given surface and only measures the light that interacts with the surface it is attached to. Surface receivers are always located at a finite distance from the source.

The far field receivers are located at infinity. Therefore, they measure only intensity, and not illuminance. The illuminance on a given surface is given by the following equation:

From this, it is clear that the illuminance is inversely proportional to the square of the distance between the source and the receiver. This is known as the inverse square law. When the distance becomes infinitely large, the illuminance approaches zero. The intensity, however, is independent of the distance and, therefore, remains unchanged. Most light sources follow the inverse square law. However, when the output beam is highly collimated (spot lamps, laser, etc.), they tend to deviate from this behavior.

Tip: You can also add a receiver to a surface from the System Navigator. To do this, select the PlaneInterface object listed under the Components heading in the System Navigator, right-click, and select Add Receiver on the shortcut menu.

whereE – illuminance on a given surface (lumens per unit area)I – intensity of the source in the given direction (flux per unit solid angle)D – the distance between the source and the receiver

E ID2------=



Run a Quick Illumination Simulation1. Select Illumination > Simulation Info to display the Illumination Simulation

Properties dialog box.

2. Change Total Rays to Trace to 100, check the Preview Rays box, and click OK.

3. Select the Start Simulation button on the toolbar.

The results should resemble the figure below, although the colors in your model may be different.



Trace More Rays and Check Results in the LumViewer

The preview rays are collimated, as expected (although you may see some non-parallel direct-radiation rays that don't hit the reflector). Now, you can increase the number of rays and look at an analysis.

1. Select Illumination > Simulation Info.

2. Change Total Rays to Trace to 10000 (ten thousand), uncheck the Preview Rays box, and click OK.

3. Click the button on the toolbar.

The interrupt and progress dialog boxes are displayed. It will take a few seconds to trace, depending on your CPU speed.

4. Select Illumination > Illuminance Display > Scatter Chart.

The ray density looks good. You could open an illuminance raster chart as well, as in the light pipe chapter, but you can see the properties of the ray data directly from the System Navigator.

5. In the System Navigator, expand the Illumination Manager items as shown in the following figure.

6. Right-click on the illuminanceMesh_n item, and select Properties.

The Properties tab should show an auto-sized mesh of 17 x 17 bins. The Results tab should show a peak error of under 5% (the 17 x 17 was chosen to provide this) and total flux of about 0.85 Lumens.

You can use the LumViewer feature to see how the illuminance distribution looks. LumViewer is interactive and can only display one receiver at a time, so you must select the receiver of interest (the only one, in this case).

7. Click on the receiver to select it. You can either select the name of the receiver in the System Navigator or select the receiver symbol in the design view.



8. Select Illumination > Illuminance Display > LumViewer.

The LumViewer opens an interactive Illuminance Chart, as shown below. This view has been rotated and modified as described in the following steps.

9. Right-click anywhere on the chart to display the Chart Properties dialog box.

10. Check the Grid Lines box on the View tab of the Chart Properties dialog box.

Note that this tab also gives you graphic smoothing, contour plots, and other controls.

11. Click OK.

12. Place the cursor over the 3D chart, press and hold the right mouse button, and move the mouse to rotate the view.

13. Drag with the left mouse button to move the chart cursor that selects the X and Y slices that are displayed.

The illuminance cross-section plots look like Gaussian curves, which they are for a point source at the focus of a parabolic mirror.

Adding a Detailed Source ModelYou could experiment with the position of the point source, but you wouldn’t be able to get a very uniform distribution. Instead, this section describes how you can replace the point source with a pre-defined lamp model that has been saved as a



library element. This lamp model was created for this example and is similar in geometry and illumination properties to actual flashlight bulbs used with larger (3 D-cell) flashlights. It includes a toroidal filament for the actual source, as well as objects to define the bulb and base of the lamp.

Delete the Point Source 1. In the System Navigator, locate and expand the Illumination Manager section as

shown below.

2. Right-click on the pointSource_n item under Sources, and select Delete.

Insert the Library ElementMost sources are placed from the source palette, but since this source has been saved as a multi-object library entity (an .ent file), you load it using the File > Restore Library menu.

1. Select File > Restore Library.



2. In the Open dialog box, navigate to the \Tutorial folder in the LightTools installation directory. Click on the file name KPR103.1.ent and click Open.

Watch the command line text prompts (noted below) for the following steps, entering the values or clicking as required.

3. Enter scale factor for element: Enter 1 for the scale factor, followed by a space.

4. Indicate position: Enter xyz 0,0,0, followed by a space.

5. Indicate Z axis direction: Right-click and select Snap > Z-axis, then click anywhere to the right of the source position.

6. Indicate Y axis direction: Right-click and select Snap > 90 degrees, then click anywhere above the point just entered.

LightTools .ent files are similar to .lts files, in that they can contain multiple objects of various types (e.g., sources, optical parts, mechanical parts), but they are meant to be inserted into an existing model. Inserting the lamp file takes a few seconds.



Make a Hole for the Lamp BaseRight now, the lamp base occupies the same space as a portion of the reflector. LightTools has no problem with this, but it's not physically correct. It's easy to use a Boolean operation to “drill a hole” in the lamp base. Boolean operations are used to combine simple 3D objects into more complex objects. To make the hole, you will create a mechanical cylinder and subtract it from the mirror.

You can be as precise as necessary with dimensions, but in this case, you can visually estimate the size.

Before you begin these steps, you may want to zoom in on the lightbulb because you will be drawing a cylinder around it. And you can use the Y-Z Plane button to adjust the view if you had rotated it earlier.

1. Select the mechanical Cylinder button (Mcylinder):

2. Right-click anywhere in the design view and select Snap > Z-axis.

3. Click somewhere to the right of the front surface of the reflector (over the lamp is OK, around z = 0 is fine).

4. Use the lamp base and displayed radius (R, in a red font on the screen) as a guide and click to define the radius of the cylinder. A value of 6 for example, is bigger than the lamp base but smaller than the flange.

5. Right-click and select Snap > Z-axis, then click somewhere to the left of the rear surface of the reflector (a Z of about -25 will work).

The cylinder is created, as shown in the following figure.



6. In the System Navigator, select the refl object. Then, control-click on the name of the cylinder to add it to the selection. The order in which you do this is important.

7. Select the Boolean Subtract button:

Note that this command operates immediately on the selected objects; no input points or data are required.

Try switching to translucent rendering mode and rotating the view with the right mouse button to see the hole. By default, mechanical objects are rendered in red, optical absorbers are yellow, reflectors are silver, and refracting objects are translucent blue. In the picture below, absorbing and reflecting objects have been made translucent for illustration. They are opaque by default.

You can set these properties on the Surface Color and Surface Rendering tabs on the Preferences dialog box. To display this dialog box, right-click anywhere in the design view and select View Preferences on the shortcut menu.

Tip: Commands are useful shortcuts for some tasks. Try typing Wireframe (or just Wir) and Translucent (or just Tra) in the command line of the design view to change the rendering mode. Fit is the same command as is used by the Fit toolbar button; it puts all of the components into view. The View menu is always available for these tasks as well.



Re-run the SimulationNow you have a more complex source. Re-running the simulation run is simple. If you would like, you can first run a small simulation (100 rays) with Ray Preview turned on, as shown earlier. (Use Illumination > Simulation Info to change the settings.) Or, you can just re-run with the most recent settings.

1. Click on the toolbar.

2. Check the results in the LumViewer chart. If you still have a chart window open, click the name in the Window Navigator to bring it to the front. Otherwise, select the receiver again (in the System Navigator or the design view) and select Illumination > Illuminance Display > LumViewer.

The following chart was created with 20,000 rays.

Note that the distribution is somewhat flattened out because of the extended source, and there is a dip in the middle due to the lamp base and hole in the reflector. It's still not very uniform.

Save Your WorkIf you haven’t done so recently, save your work before moving on to the next steps.

To do this, select File > Save As, enter a new name such as SmoothReflLamp.1.lts, and click Save.



Create a Faceted ReflectorOne solution to the problem of uniformity is to use a faceted reflector. Provided with LightTools is a powerful Faceted Reflector utility that you can use to create faceted reflectors with specified properties.

LightTools provides a number of utility programs and macros that make certain tasks easier. Although they are written using the same programming tools available to you (the COM/Visual Basic interface and the earlier LightTools Basic macro language), no programming is required to use these utilities. They generally run in a separate window through a user interface that is different from that of LightTools, but still very easy to use.

Delete the Smooth ReflectorTo prepare for the next step (using a faceted reflector) first delete the smooth reflector.

1. Select the reflector.

2. Right-click and select Delete on the shortcut menu.

Running Utilities Although utilities are actually separate programs that communicate with LightTools when they run, you can launch the Utility Library from the Tools menu.

1. Select Tools > Utility Library.

This launches a new window from which you can browse, select, and run utilities.

Tip: To make sure nothing else is selected for deletion, click a blank area to clear the selection buffer, and then select the reflector.



You can access the supplied utilities from this window using the Run Utility menu at the top or the navigation tree on the left.

2. Expand the Geometry category in the browser panel.

3. To launch the Faceted Reflector utility, you can either:

– Double-click on the Faceted Reflectors item.

– Click once on the Faceted Reflectors item to select it click on the Run Application button.

This utility has a picture of a typical faceted reflector, an information area, several buttons, and two tabbed pages.

4. Click on the Source/Receiver tab and uncheck all the check boxes that are checked by default, as shown below.



This utility can create sources and receivers and do other special tasks. Since your model already has a source and receiver, you don't need these features now.

5. Click on the Reflector Geometry tab.

6. Enter 53 for the Rim Radius, 5.6 for the Hole Radius, and 60 degrees (default) for the Rim Angle.

These values approximate the geometry of the original smooth parabola. The program automatically places the focus of the reflector at the point (0,0,0), which is the location of the source filament.

This program has many options for the type of reflector, facet geometry, etc., but the default settings are adequate for this example. You need to provide performance specifications, however (in the lower left corner), based on the goals originally stated (i.e., uniformity over a 100 mm diameter disk at a distance of Z=300 mm). The utility uses the target information (plus default values) to determine the necessary facet geometry.

7. Enter 300 for the Target Z and 50 for the Target Half Size.

8. Click the Create Facets button.



The facet creation operation can take a little time (maybe a minute or so), and you can switch over to LightTools and watch as the command panel flashes and the geometry is created. The utility is actually a separate program that runs LightTools by “remote control,” sending commands to it via the Windows COM facility. When the Interrupt dialog box is no longer displayed, the creation process is complete.

Run an Illumination SimulationThe source and receiver are still in place from before, so it's easy to run another simulation on this system. But since the geometry has changed quite a bit, you should do a small run with Ray Preview turned on to prove that the rays are doing what they should.

1. Select Illumination > Simulation Info, change Total Rays to Trace to 200, check the Preview Rays box, and click OK.

2. Click the button on the toolbar.

Your model should resemble the following figure (after right-click rotation).



If it looks OK (did you delete the smooth reflector?), go ahead and select Illumination > Simulation Info to define more rays (10,000) and turn off the Ray Preview. Re-run the simulation, then select the receiver and open a LumViewer chart to examine the illuminance. Open an Illuminance Raster Chart too, and look at the numerical results. The LumViewer output shown below is for 20,000 rays.

The uniformity is much improved over the smooth reflector case. Try running with even more rays (50,000 or so) to get better spatial resolution.

3. Select File > Save As and save this faceted reflector version with a new name.



Create the Flashlight BodyAlthough it doesn’t affect the optical performance, adding a simple mechanical model for the flashlight body will make the model look more realistic and complete. This can be done with a few mechanical cylinders (one tapered) and a few Boolean subtract and union operations.

Since the objective is to present a quick visual impression, you don’t have to be too precise about measurements, but it’s still a good idea to use the Snap feature to be sure things line up properly. Some steps (e.g., Boolean subtract) are described just briefly because they are similar to the procedure for making a hole in the smooth reflector a few pages back.

CollarYou could certainly trim the reflector to be a little smaller, but you don’t need to bother in this case. Just make the collar big enough to house the reflector. Make sure you are in wireframe mode in the right side view.

1. Select the mechanical Cylinder button (Mcylinder) as follows:

2. Right-click and select Snap > Z-axis; then, click a little to the left of the rear (left) surface of the reflector (around Z = -30).

3. Click to make the radius of the cylinder about 66 mm.

4. Right-click and select Snap > Z-axis; then, click just to the right of the reflector (around Z = 34).

This is the outer ring of the collar.

5. Click the cylinder tool again and repeat steps 2, 3, and 4 with the following values: left Z = -40, radius 62 mm, right Z = +40.

The model should resemble the following example.



6. Select the larger-radius (66mm) cylinder; then, shift-click the inner cylinder. The order in which you select the cylinders is important.

7. Select the Boolean Subtract button (or type the command Sub for Subtract on the command line and press Enter).

The collar now surrounds the reflector.

Create the Battery CompartmentNext, you need to make a tapered cylinder to connect the collar to the battery compartment of the flashlight.

1. Select the Mcylinder button again (or, type Mcyl in the command line and press Enter).

2. Right-click and select Snap > Object; then, place the mouse near the axis at the left side of the collar assembly. z = -30 is good.

Snap-to-object finds the nearest object vertex, helping you to line up the next cylinder with the collar assembly.

3. Click to define the axis of the new cylinder. Make its radius (R) 66 mm, using Snap-to-Z (z will be around -97) to make its length (L) 66 mm.



4. Select the new cylinder, right-click, and select Properties.

5. In the Object Navigator, select the CylinderPrimitive, and enter 0.5 for the Taper parameter.

Taper is the ratio of the end diameters. (It would be 2.0 if you had started the cylinder from the other end.) It should look like this:

Before you create the final cylinder, you may want to zoom out.

6. Type Mcyl, then start at the left end of the tapered cylinder (Snap-object), radius 33, length 300 (snap-Z).

If you are off on any of the measurements, use the Properties dialog box to correct the values. Visually speaking, you are finished, but, because the flashlight body can be considered one unit, you can use a Boolean union to join all the body parts.

Join the Parts Using a Boolean Operation1. Change to translucent mode (View > Render Mode > Translucent).

This makes it easier to select the body parts. Note that, using default surface rendering settings, mechanical parts are not translucent, even in translucent mode.

2. Click on the collar assembly, then Shift-click on the tapered cylinder, then Shift-click the long cylinder.

Note that, in shaded views, selected objects highlight with both wire frame color and surface shading. (The default color is purple.) Check the System Navigator to be sure that all mechanical cylinders are selected (and that the reflector assembly and lamp are not selected).

3. Select the Union button:



4. Try this simple test to verify that the objects were unioned:

a. Select the flashlight body, type Move in the command line, and click somewhere in the design view to specify a new location.

The flashlight body should move as a unit.

b. Select Edit > Undo to return the flashlight body to its original position.

5. Save your work!

ConclusionsThe final model should resemble the picture below. For this example, a small simulation was run with the Ray Preview turned on, and the color of the rays was changed to yellow in the Properties dialog box.

In this chapter, you learned even more about how systems are built and analyzed in LightTools. The final chapter introduces the concepts of backlight design using another powerful utility that is supplied with LightTools.


Chapter 5 Introduction to Backlight Design

This section presents an introduction to the design and analysis of backlights for information display devices. It briefly describes the components of a backlight system, and then demonstrates how to use the Backlight Utility to create a backlight model for a hypothetical portable “digital photo viewer.” It also introduces the concept of luminance meters and describes how to perform an illumination analysis.

Contents

About Backlighting .................................................................................................82

Designing a Digital Picture Viewer ........................................................................83

Illumination Analysis ..............................................................................................94

Performing a Final Analysis ...................................................................................99

Evaluating Spatial Luminance ..............................................................................100

Changing the Material of the Block......................................................................103

Conclusions ...........................................................................................................104


CHAPTER 5 Introduction to Backlight Design

About Backlighting

Information DisplaysThere are various information display technologies, some of which use luminous display elements. But the majority of flat panel displays in use today are based on LCD technology and require a lighting system often referred to as backlighting. This chapter introduces backlight design through a single example, using a small subset of the program’s capabilities.

The major components of a backlight system are shown in the following schematic:

• Light source. Often a cold cathode fluorescent (CCFL) tube with a reflector, as in this chapter's example. Smaller displays often use one or more LEDs.

• Rectangular light guide. Often called a light pipe, designed to extract the light from the edge-mounted source to illuminate the panel.

• Additional layers. Many backlight systems use diffusing or brightness-enhancing films (BEFs) between the light guide and the LCD to help tailor the uniformity or angular properties.

The design challenge is to extract the light in a direction perpendicular to the direction of propagation to illuminate the LCD panel. There are a variety of light extraction methods, several of which are described and demonstrated in Designing Backlight Displays in LightTools. The two major approaches are printed light extraction (paint dots) and molded light extraction (3D textures). Both approaches are well-supported by property zone features of LightTools.

Reflector

Diffuser

Light guideLight source

Brightness-enhancement film (BEF)

LCD



Designing a Digital Picture ViewerThe premise for the example in this chapter is a hypothetical, low-cost device for viewing digital photographs. It would consist of an illuminated 3.5 x 5 inch (88.9 x 127 mm) LCD display with a memory card slot, allowing you to view digital photos saved in a memory card by a digital camera or a personal computer. It would have computing power sufficient for displaying photos, controlling settings, etc. This example won't address the packaging, electronics, or computing aspects of this device, only the display, which is to be made as compact as possible.

You can assume that a suitable fluorescent source and reflector would be available, and use a molded pattern of 3D spheres for light extraction. You will analyze the uniformity (luminance distribution) and the brightness variation as a function of angle (angular luminance), with and without brightness-enhancing films (BEFs).

The final model is shown above, with a bitmap pattern (a family portrait converted to a monochrome .bmp file) applied to the top surface to simulate a displayed photo (otherwise not used in this example). The close-up on the right shows part of the lamp, reflector, and the 3D texture pattern. The Backlight Utility supplied with LightTools can be used to quickly define and build a backlight model of these specifications, and to modify it, if desired.



Using the Backlight UtilityThe basic procedure to run the backlight utility is to start LightTools, create a new 3D Design view, then run the Backlight Utility from the LightTools Utility Library. Next, you specify the dimensions and any special properties of the light guide, modify the source/receiver and BEF tabs, if necessary, then choose the light extraction method from the other tabs (paint dots, three 3D texture options, and a sawtooth extruded solid method). In this case, you will use a 3D Sphere texture.

Creating the Light GuideYou will begin by starting LightTools and defining the size of the light guide for the photo viewer.

1. Start LightTools.

2. Start a new model in a 3D Design view (File > New Model > 3D Design).

3. Click the One Pane button on the toolbar:

4. Select Tools > Utility Library.

5. Click the plus sign next to Geometry to expand the list.

6. Select the Backlights item and click the Run Application button, shown in the following figure.

Note: Be sure that you have set the default preferences as described in Chapter 2.



7. Click on the Light Guide tab.

Note that, in addition to dimensions, there are other settings for reflectance of the three non-source “edge” surfaces, and a couple of controls for tilting the bottom surface with respect to the top surface. In this example, you will modify just the dimensions, and accept defaults for other parameters, including the height (the thickness of the light guide, for which the default is a very thin 5 mm). The length and width are for a typical photographic print size of 3.5 inches by 5 inches, expressed in millimeters.

8. Enter 88.9 for the Width and 127 for Length. Do not change the value for the Height (5 mm).



For this example, you can accept the defaults for Source/Receiver and BEF, but you will need to change the defaults for the array of spherical bumps on the bottom surface of the light guide. Do this in the next task.

Defining a Texture of Spherical Bumps1. Click on the Texture (3D) tab.

Note that “Sphere” is the default selection in the drop-down box. Let us assume that we need bumps with radius = 0.05 mm. For this, change the “Bump Height” to 0.05.



The Backlight Utility creates all necessary components: the light guide, the BEFs, and the reflective layer at the bottom. It also adds a property zone with the 3D bumps to the bottom surface of the light guide, which can be changed later in LightTools.

2. If possible, move the Utilities and LightTools windows so you can keep the Utilities window in front and see some of the LightTools window (if possible with your screen size).

3. Click the Create Backlight button.

The utility generates commands and sends them to LightTools. You will see parts of the LightTools window flash as the program starts to create the backlight model. When it needs to insert the CCFL (source) model, it will prompt you (with an Open dialog box) to select the library entity (.ent) file, which is supplied with the Utilities.

4. In the Open dialog box, navigate to the folder \Utilities\Backlights in the LightTools installation directory, select the file LampReflectorSystem.1.ent, and click Open.

The Backlight Utility will complete the backlight model in a few seconds. Note that it reports its progress in the status bar at the lower left corner of the Utilities window. The process is finished when the message Model Complete is displayed.

Parts SummaryHere’s a summary of what the Backlight Utility built using the input you provided and default values for the rest of the parameters. Although the purpose of this backlight is to illuminate an LCD display, the LCD itself, located on top of the light guide, doesn't need to be modeled. The Backlight Utility has defined all the needed properties of these objects, including object names:

• Source. A CCFL fluorescent lamp with a cylindrical reflector, imported as a predefined library (.ent) file. The lamp luminance was specified (as a default value in the utility) as 26,000 cd/m2, and converted by the utility to photometric flux of 68.4 lumens, by assuming the lamp to be a Lambertian cylindrical surface emitter. The default name is used (starts with CylinderSource).

• Backing Film. Located below the light guide is a sheet (actually a very thin cube) whose top surface is a 98% reflecting Lambertian scattering surface, something like a piece of white paper. This is used to collect and “re-scatter” light that fails to TIR and “leaks” from the bottom of the light guide. Object name: ReflectiveFilm.



• Light Guide. The light guide and its array of 3D spherical bumps on the bottom surface were described and pictured in the previous section. Object name is LightGuide.

• Brightness Enhancement Films. These are two thin sheets with prismatic surface textures, located above the light guide. Object names: PrimaryBEF and SecondaryBEF.

• Dummy Surface. Located just above the two BEF layers, this is a rectangular object with no volume. It is used to establish the location of and hold the receiver. Object name: ReceiverPlane.

• Surface Receiver. The utility’s default settings for the receiver were used, resulting in a 10 x 10 mesh. Object name: SurfaceReceiver.

Your model should resemble the following picture (after right-mouse rotation and rendering in translucent mode).

You can close the LightTools Utilities window, and this is a good time to save your model (File > Save As…).

Parameterize the BumpsThe Backlight Utility was helpful to build the backlight system quickly. However, the bumps must be parameterized in order to get the desired output distribution. You can do this easily using the LightTools Properties dialog box.



1. In the System Navigator, expand the items LightGuide, CubePrimitive_1, BottomSurface, and Zones. Then, select Texture, as shown in the following figure.

2. Right-click and select Properties on the shortcut menu.

3. Select the Geometry tab.

4. Select the arrow next to the Placement drop-down list, and select Bezier. Click Apply.

The default number of bumps is 100 (10 X 10). You need to change these parameters to match your design. Note that LightTools allows many other placement options, but you will use the Bezier placement option for this example.

5. On both the X Placement tab and Y Placement tab, change the Number of Bumps parameter to 300, as shown in the following figure. Click Apply after each change.



6. Click OK to close the dialog box.

Note that the number of bumps is 300 X 300, which results in about 90,000 bumps on the surface (~ 5143 bumps/in2). These bumps are arranged in a manner defined by the Bezier parameterization option. Please see Chapter 5 of the LightTools Core Module User’s Guide for more information. With the current parameter values, the Bezier option varies the bump spacing along the length of the light guide. The spacing in the orthogonal direction is constant. The X and Y refer to the local coordinate system of the surface.

Examining Surface PropertiesUsing the methods described in previous chapters, you may want to check your model before you run a simulation.

Click on various parts of the model in the 3D Design view. Or, use the System Navigator to select different surfaces and view their properties.

1. In the System Navigator, click to open BottomSurface of the LightGuide, click Zones, and then click Texture.

2. Select SphericalElement, and then right-click and select Properties from the shortcut menu. The Shape tab shows you a graphical representation of the spherical bump shape that is on the bottom of the light guide.



Viewing the Texture Property ZoneYou might be curious as to why you cannot see the 3D texture property zones you defined. They are invisible by default, because drawing thousands of texture elements can make displaying and exploring the model somewhat slow. If you choose to make them visible, 3D textures are displayed in wireframe, even if the display mode is set to translucent. Wireframe rendering displays a bit faster and shows more of the technical details.

1. Rotate and zoom the model so that you can see something like the illustration below.

.

2. To display the property zones:

a. Right-click in the design view and select View Preferences to display this dialog box.

b. On the Visibility tab, click the Show Property Zone check box to turn it on.



c. Click OK.

You will see the wireframe rendering of the spherical bumps on the bottom surface and a solid color above it. The solid color is the BEFs (brightness-enhancing films) built automatically by the utility.

3. Zoom in further to see the texture elements.

These are very dense arrays of prismatic texture elements. The small features are necessary for the optical performance, but they are too detailed to display. It can be useful to conceal such densely-drawn features on a hidden layer, but for now, just hide all the property zones, knowing that they are optically there, but hidden from view.

4. Go back to the Visibility tab, click to uncheck the Show Property Zone box, and click Apply.

Add a Luminance MeterFor display devices, it is important to consider how “bright” the display looks from different viewing angles. As defined in the handbook Illumination Fundamentals (Lighting Research Center, Troy, New York, 2000, available by request from Optical Research Associates), “Luminance is the illuminance per unit solid angle,



measured in lm/m2/sr. In other words, luminance is the density of visible radiation in a given direction. Luminance is the measurable quantity that most resembles a person’s perception of brightness, although they are not quite the same.”

Luminance meters are physical devices used to measure luminance. LightTools provides simulated angular and spatial luminance meters which can be attached to surface receivers to analyze and display luminance. In this example, you will add an angular luminance meter.

1. Select the receiver. To do this in the System Navigator, under Components, click to open ReceiverPlane, then click on Receivers, and then select SurfaceReceiver.

2. Zoom in on the receiver, if necessary, to be sure you can place the luminance meter on the correct object.

3. Select the LumAngular button:

4. Right-click in the design view and select Snap > Object.

5. Place the cursor over the selected receiver and click to place the center point of the luminance meter.

The cursor snaps to the receiver. A rubber band rectangle, shown below, lets you preview the size and position of the metered area as you move the mouse.

To view and set the approximate size of the meter area, use the right mouse button to zoom out and rotate the view. You will check and adjust the properties in a moment, so just approximate the narrow dimension of the receiver surface. The meter area is a square, so it will not fill the entire receiver.



6. Click to define the size of the luminance meter area.

7. Click on the wireframe hemisphere of the meter, or select the angularLumMeter in the System Navigator. Right-click and select Properties from the shortcut menu.

8. In the Properties dialog box, select the Controls tab. Set the Meter Half Size to 88.9/2.

9. Set the X and Y displacement values to 0.0, and then click OK.

The luminance meter will look like this:

Illumination AnalysisLightTools enables you to turn off the ray traceability of any selected object, while still allowing it to be included and displayed in the model. This allows you to include objects in your model that are purely illustrative, although you must be sure that they truly have no optical effect if you designate them as non-traceable. For example, nominally mechanical objects can have scattering or blocking effects on stray light paths, and LightTools will correctly include these effects if the mechanical objects are traceable, but it may make incorrect predictions if you exclude a relevant object by turning off its ray trace properties.

This feature is also convenient for studying the effects of removing certain objects without actually deleting them from the model.

Tip: Arithmetic operations (such as dividing by two, entered as /2) are allowed in numeric fields.

Note: Placing objects on hidden layers does not affect their ray trace properties. Visibility and ray traceability are completely independent properties.



Turn Off the BEFsIn the backlight model, the Backlight Utility defined two brightness-enhancing films, named PrimaryBEF and SecondaryBEF. To see if they are needed, you can turn off their ray trace properties, perform an illumination simulation, then later turn them on and compare the results.

1. In the System Navigator, right-click the PrimaryBEF, and then select Properties.

2. Select the Ray Trace tab on the Properties dialog box.

3. Uncheck the box labeled Ray Traceable, shown below.

4. Click OK.

5. In the System Navigator, select SecondaryBEF and turn off its ray trace property as well. Click OK.

6. Save your work. Select File > Save As and give the model a name.

Tip: Would you like to hide the BEFs? Do this by turning off the “Layer” controls. The BEFs are assigned to Layer2 when they were created by the Utility. Open the Preferences dialog box, click the Layers tab, enter a name (BEFs) for layer 2, uncheck the Visible box for this layer, and click Apply.



Run a Quick Preview SimulationIf you have gone through the earlier chapters of this manual, you know the basic procedures for illumination simulation. Start with a small preview run.


2. Change the Total Rays to 100, check the Preview Rays button, and click OK.

3. Select Illumination > Start Simulation, or click the toolbar button:

4. Select Illumination > Illuminance Display > Scatter Chart.

If the results looks reasonable, you can trace a larger number of rays to see some illumination estimates.



Run a Simulation with More RaysThis system is more complex than the earlier examples, and ray trace time will be longer. Depending on the speed and memory (RAM) of your PC, the simulations may take several minutes for every 10,000 rays. As usual, there is a trade-off between spatial resolution (more bins) and photometric accuracy (fewer bins, more rays per bin). It’s easy to add more rays to a simulation and to re-bin the results, so start with a fairly small number, around 20,000 rays. Note that, by default, the Backlight Utility assigns a 10 x 10 mesh of bins to the receiver. You can change this in the Backlight Utility dialog box or in LightTools.


2. Change the Total Rays to 20000, uncheck the Preview Rays button, and click OK.

3. Select Illumination > Start Simulation, or click the toolbar button:

If you view the properties of the illuminance mesh (most conveniently from the System Navigator), you will find that for 20,000 rays (with the 10 x 10 grid), you have a peak error of around 11%, and total flux of about 30 lumens. The plots can provide more information.

View Illuminance ResultsTo view illuminance results, select the receiver (SurfaceReceiver in the System Navigator) and select Illumination > Illuminance Display > LumViewer or Raster Chart (both shown below).

Although it is “noisy,” the data looks fairly uniform.



View Luminance ResultsWhat about the luminance meter results? Select Illumination > Angular Luminance Display > Line Chart, which produces a flat polar plot. Line charts illustrate latitude data at a given longitude; the solid line (0º) corresponds to longitude 0, while the dotted line can be considered latitude 90. Note that because of the orientation of the receiver on the dummy surface, the up direction (the desired direction for most light) is 180º.

The basic conclusion is that very little light is being coupled in the desired near-vertical directions. Therefore, more light must be “squeezed” into the near normal direction in order to increase the luminance in that direction. This can be done using BEFs.



Performing a Final AnalysisAs seen above, the 3D spheres extract the light efficiently, but the direction of extraction is not ideal, due to grazing incidence. Most of the light is propagating along the length of the light guide. This situation can be improved with BEFs. The term “brightness” correctly suggests that these devices manipulate the angular distribution of light. Adding BEFs generally reduces the efficiency, while increasing the luminance.

Turn On the BEFsThe first step of this illumination section was to turn OFF the ray traceability of the BEFs. Now that you have seen the luminance results, it’s time to see if the BEFs can improve the coupling of light into the useful (near vertical) angles.

1. In the System Navigator, right-click the PrimaryBEF item and select Properties.

2. Select the Ray Trace tab on the Properties dialog box.

3. Check the box labeled Ray Traceable and click OK.

4. In the System Navigator, select the SecondaryBEF and turn on its Ray Traceable property as well. Click OK.

Specify More RaysFor final results, try tracing 500,000 rays. This may take 20 to 50 minutes (or more, depending on the speed of your computer).



View the Improved Luminance With the receiver property Auto Size Mesh turned on (shown here), 500,000 rays results in a 23 x 23 mesh of bins, with about 5% peak error and total flux of about 27 lumens, as shown in the following figures. The angular luminance line chart shows a clear improvement in the directionality.

Evaluating Spatial LuminanceThe raster chart shown above is for illuminance. However, the illuminance does not characterize the “appearance” of the display to the human eye. For this, spatial luminance can be used (the command for this is LumSpatial). In order to measure the spatial luminance, you can add a spatial luminance meter to the receiver. Instead of adding a spatial luminance meter and re-analyzing the system in this example, you can use the following method for quick luminance analysis.

You can use the receiver angular coordinate controls to limit the acceptance angle for the illuminance results, as shown in the following figure.



This produces the same luminance distribution except for the magnitude. For this example, you can see that the luminance results do not deviate much from the illuminance results shown in the figure above. However, if you increase the spatial resolution of the chart, the results can differ, depending on the location on the light guide. This is a useful way to get a rough idea of luminance variations during design stages without having to add a separate luminance meter. The same is true for the angular luminance, where the intensity mesh can be used to find the distribution.

Controlling the Angular Coordinate Rotation You can use these controls to manipulate the receiver meshes so that the “poles” can be oriented “away” from the data. This can help avoid triangular bins near poles, and it also helps to generate smoother, more continuous charts. For example, the following chart results occur when you set Alpha = -90, Beta = 0, Gamma = 0. Note that the LumViewer chart data is more centered and line charts are continuous.





Changing the Material of the BlockYou can change from the default material to any of the other materials supplied with LightTools. If the material is not available, then you can create your own material. Such materials are called User Materials.

Light guides are commonly made of plastics (also known as polymers, acrylics, etc.). LightTools provides typical plastic materials such as Acrylic, Polycarbonate, and Polystyrene. To use these materials, you must first import them into the current design. The materials are located in a folder called Materials in the LightTools program folder (e.g., C:\Program Files\Optical Research Associates \LightTools5.3.0\Materials). In this example, you will use Acrylic as the material for the light guide. To import and apply this material, follow the steps below.

1. Select Edit > User Materials from the main menu.

2. In the User Material dialog box, click Import.

3. Navigate to the Materials folder, select acrylic.1.mat, and click Open. .

The material is imported to the current design. The User Material dialog box now shows two user materials: air and acrylic and air. The following message is displayed in the console window to confirm the import process: Material named acrylic loaded.

4. Click OK to complete the import.

The User Material is now available for use in your model.

5. Select Cube_1, and then right-click and select Properties from the shortcut menu.

6. Select the Material tab.



7. Click the arrow next to Catalog and select User Material on the drop-down list.

8. From the Material drop-down list, select acrylic.

9. Click OK to change the material of the block to acrylic and close the dialog box.

ConclusionsLightTools allows you to create and analyze various backlight system configurations of using its 3D Texture capabilities. The Backlight Utility is an easy-to-use tool that helps you set up backlights with many possible variations. Illumination analyses, including those in which luminance meters are used, allow you to predict the quality of the backlight display before it is built. Although this example does not include all possible factors in backlight design, it provides a reasonable starting point for using LightTools for such design and analysis.


Index

Numerics3D Design view 7, 113D texture

for improving illumination uniformity 49for light extraction 82illustrated 83, 91

Aaction buttons 10adding a luminance meter to the backlight

example 92annotation, showing or hiding 24

Bbacklight example

adding a luminance meter 92charts with 20,000 rays 97creating the light guide 84parts summary 87specifying parameters for spherical

bumps 86tracing 100 rays 96

backlight system, described 82Backlight Utility 84

running 84Bezier geometry

creating bump parameters with 88Brightness Enhancement Films

created in the backlight example 88turning off ray traceability 95

bumpsmodeling with optical property 88

buttons on dialog boxes 10

Cchanging properties 38color scheme, setting 24command line 16command panel 15, 33

commandsusing as shortcuts 70

Console window 8coordinates, illustrated 34cursor coordinates, illustrated 34

Ddefault settings

saving 24desktop shortcut for LightTools 23documentation library, accessing online 10dummy surface

creating for the flashlight example 61in the backlight example 88

Eexiting LightTools 20

FFaceted Reflector Utility, running 72file extension for LightTools models 28File menu, displaying 39Fit toolbar button 31flashlight example

charts with 20,000 rays 70creating the dummy surface 61creating the flashlight body 77creating the receiver 62creating the reflector 54curving the back surface 55inserting the library element 67making a hole for the lamp base 69placing a point source 59scatter chart with 10,000 rays 65tracing 100 rays 64tracing 200 rays with faceted reflector 75tracing point-and-shoot rays 58

fluorescent lamp, source for the backlight example 87

Index


Ggeneral preferences

saving 24grid snap, setting 24

Hhelp system 10

Iinterface elements 6

LLambertian scatterer

as white paint in light pipe example 49effects of 51

layersusing to hide or show objects 40

layout panes 16library element, inserting 67light guide

creating 84light pipe example 26

after Trim 37before Trim 36charts after white paint 51charts with 10,000 rays 47scatter chart with 200 rays 44tracing 200 rays 43

LightTools main window 6LightTools Utilities dialog box 73line chart for backlight example with 20,000

rayswith BEFs turned off 98

LumAngular command button 93luminance

described 92spatial 100

luminance meterattaching to a surface receiver 92

LumViewer chartin backlight example 97in flashlight example 66, 71, 76

Mmacros 21materials

saving 20maximum hits

warning messages about 50mechanical Cylinder command button 69, 77menu bar 6

Nnon-sequential rays 32NS rays 32

OObject Navigator 9One Pane toolbar button 55

Ppanning the view 29parabola

creating a spun parabola 55parts summary for backlight example 87point source, creating 59point-and-shoot rays 32preferences

saving 24setting before you begin 23

Preferences Navigator 7preview, ray

turning on or off 42properties

changing 38saving 20

Properties dialog box 7, 9property zone

displaying 91

Rraster chart for backlight example 100ray fan, tracing 33ray preview, turning on or off 42

Index


ray traceabilityturning on or off 95

rays, nonsequential 32receiver

attaching a luminance meter to 92creating for the flashlight example 62

receiver for backlight example 88receiver units, setting 23receivers, described 42reflectance, percentage for Lambertian

scatterer 49Reflector command buttons 54Rename 12, 37rotating the view 29

Ssaving your work 71scatterer, Lambertian

effects of 51in light pipe example 49

scatteringwarning messages about 50

selectionmultiple selection and smart properties 11objects and surfaces 11

simulation info 42source units, setting 23source, creating for the flashlight example 59sources, described 41spatial luminance 100Spun Parabola command button 55starting LightTools 19stopping LightTools 20Subtract command button 70, 78System Navigator 7system units, setting 23systems, saving 20

Ttabbed property pages 10tag point, illustrated 30texture, 3D

illustrated 83, 91technique for illumination uniformity 49technique for light extraction 82

toolbar 19toolbar buttons

Fit 31One Pane 55Y-Z Plane 31

Uundo 17uniformity

achieving with a faceted reflector 72, 74, 76

for the flashlight example 54improving in the light pipe example 49

Union command button 79units, setting 23Utility Library 21

running the Faceted Reflector Utility 72

Vview

panning 29rotating 29zooming 29

view environment, saving 24

WWhat’s This? help 10, 36Window Navigator 7

YY-Z Plane toolbar button 31

Zzooming the view 29

Index


Documents

LightTools IntroTutorial