LIGHTING DESIGN PROCESS - wtgzik.pairserver.comwtgzik.pairserver.com/courses/273s18/273-LightDesign.pdf · US, this source would commonly be the IESNA Lighting Design Guide) ... design

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Ball State Architecture | ENVIRONMENTAL SYSTEMS 1 | Grondzik 1

LIGHTING DESIGN PROCESS

illustration by James Benya


LIGHTING DESIGN PROCESS

illustration by James Benya

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Lighting Design Process: IESNA

“Lighting design is the creative process for developing safe, productive, and enjoyable lighting solutions within the built environment. In the past, emphasis was placed on simply delivering an appropriate quantity of light. The quality of light was considered mainly in terms of controlling direct or reflected glare. But as this Design Guide reveals, lighting design now extends far beyond these basic factors. This Guide explains that many factors influence the quantity and quality of light. Thus there is no one perfect solution to a single lighting problem. Instead there are multiple solutions, each more or less successful depending on the judging criteria.”

The “judging criteria” would ideally be the OPR


Lighting Design Process: IESNAcontinued …

“And the design must also be appropriate in terms of cost, energy, maintenance, style, availability, and a dozen other considerations. Though not a predictable, linear process, lighting design as revealed by this Guide begins with a concept selected from a myriad of alternatives. Then, as the process proceeds, it is filled with cross-checking. Like many architectural projects, most lighting designs can be circumscribed by the following seven-step process: Programming, Schematic Design, Design Development, Contract Documents, Bidding and Negotiation, Construction, and Post-occupancy Evaluation. These elements are discussed in full detail in this Guide.”

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Lighting Design Process: Lam

“A new process of design …

This is the diametric opposite of the typical ‘engineered’ approach, which starts with the selection of light fixtures and then, taking them as givens, places them in patterns to achieve predetermined illumination levels.”

William Lam

Perception and Lighting as Formgivers for Architecture


A Holistic (Lam-like)Lighting Design Process

Would be entered into with a big picture view:

– The designer would clearly understand the desired overall result (the collective lighting effect) and work iteratively to make it happen

– The designer essentially envisions an effect and works backward to institute appropriate causes

– The designer cycles through possible methods and validations

– The designer selects the best (or at least an acceptable) solution

– This design process requires experience and confidence

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An Incremental (IES?)Lighting Design Process

Would be entered into sequentially:– The designer would establish OPR (intent and criteria)– The designer (through observation/precedent/intuition)

would establish some aspects of the proposed system (perhaps basic delivery approach or lighting fixture type)

– The designer addresses specific design issues (illuminance, glare, energy, color, …) individually

– The designer selects the best (or acceptable) solutions for each of the individual issues

– The designer integrates potential solutions to the various design problems into a good overall solution

– This process can succeed in the face of limited experience and confidence


Some Design Issues to Consider

issues considered very important in an office with computers are flagged

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Some Design Issues … cont’d

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We’ll Follow the Incremental Trail …

So, let’s look, in more detail, first at:

Illuminance (a “quantity”)

and then

Glare (a “quality”)

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Illuminances to be Considered

• Design illuminance (DI)– The design criterion (a target; defines success)

• Initial illuminance (II)– Illuminance at the time the lighting system is

first used (at the start of owner occupancy)

• Maintained illuminance (MI)– Illuminance after some defined time (typically

several years) of usage; after wear and tear takes a toll on the system

MI must be >= DI II will be > DI


Sources for Illuminance Values

• Codes = formal, mandatory, government-enforced (not much help – in fact, close to useless in the US)

• Standards = formal, voluntary (contract-enforced, or lawyer-enforced) (rare in the US)

• Guidelines = less formal than a standard (in the US, this source would commonly be the IESNA Lighting Design Guide)

• Recommendations = even less formal (perhaps coming from an owner or a colleague)

• General practice = real informal (“everybody does this” use with caution)

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Design Illuminance Code (an example)

http://ecodes.biz/ecodes_support/free_resources/14FloridaDraft/Building/PDFs/

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Design Illuminance Code

Florida Building Code (2014)

SECTION 1205: LIGHTING

Comments: although compliance with codes is mandatory, there is not much in this code section to truly inform design beyond a specific minimum illuminance for emergency conditions;

Terminology is awkward: “natural” and “artificial”

The specified minimum non-emergency illuminance (107 lux or 10 fc) would be quite unacceptable to most owners/users in many common space types

Codes are not written to ensure satisfaction—but to ensure life safety

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Design Illuminance Guideline

room/task-specificilluminance values;generally above the

107 lux code minimum

see next slide


DesignIlluminances Guideline

Illuminance categories

From IESNA LightingHandbook (9th edition)

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Note: the 10th (current) edition of the IES Lighting Handbook substantially revised the design illuminance selection information; this older table is shown here because the concept is similar and the information is easier to digest.

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DesignIlluminances

contrast andtask size…with judgment

eye condition (age) ?

task speed ?

validation ?… and judgment

Addressing …

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A Comment on Illuminances

UK and European lighting standards generallyrequire substantially lower design

illuminances than the IESNA guidelines. Thisdoes not reflect a lack of concern across theocean for human health and comfort. This

does not reflect a difference in humanphysiology. It does reflect a difference in culture and history. We’ll see where this difference leads

the US in the future (perhaps for green or carbon-neutral projects).

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Direct Glare Guidance*

Design Patterns**– Maximum luminance rule– Maximum contrast rule

* there are no known US code requirements regarding glare mitigation

** these are simple patterns to help guide design decisions toward direct glare avoidance


Maximum Luminance “Rule”

• 2500 cd/sq m – Is the maximum luminance recommended for

large light sources (such as a fluorescent fixture, window, or skylight) that will be seen

• 7500 cd/sq m – Is the maximum luminance recommended for

small light sources (such as a recessed downlight fixture) that will be seen

although glare is a perception associated with brightness, luminanceis measurable and therefore easily verifiable and specifiable

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Maximum Contrast “Rule”

Recommended Maximum LUMINANCE RATIOS**

• 3 : 1– Between task and surround

• 10 : 1– Between task and more distant surroundings

• 20 : 1– Between light sources and surroundings

• 40 : 1– Anywhere in field of view

** with opaque surfaces under equal illuminance, this becomes simply the ratio of surface reflectances


A Numeric Index for Direct Glare

Visual Comfort Probability (VCP)– VCP represents the percentage of occupants who,

when using a space as intended, would say that they do NOT sense direct glare

– 70 or greater is considered a “good” value– VCP varies from lighting design to lighting design;

and from location to location within a given space– Can be “measured” in an occupied space (as a POE

tool) or simulated using computers (as a design tool)– Generic data are provided by some electric luminaire

manufacturers for typical room layouts (but not by window manufacturers for daylighting)

POE: post-occupancy evaluation

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Direct Glare and Daylighting

occupant’s response occupant’s response

recod.net/daylighting/


Reflected Glare “Rules”

The “common sense” geometry rule (which involves identifying the “offending zone”)

– Look at the geometry of tasks and lighting elements during design and avoid potentially poor design decisions involving reflective surfaces (see next slide)

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The “Offending Zone”

bottom line: to avoid introducing the potential for reflected glare, do not place lighting fixtures (electric or daylighting luminaires) in this zone;or limit fixture brightness (luminance) if you do so locate fixtures


Light Sources and Glare Potential

potential for reflectedglare if highluminance

potential for directglare if highluminance

less potential forglare if highluminance

ceiling

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Reducing Glare with Daylighting


Two Numeric Indices for Reflected Glare

• Contrast rendition factor (CRF)

• Equivalent spherical illuminance (ESI)

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Contrast Rendition Factor (CRF)

• CRF is the ratio of contrast at a task under a proposed (or given) lighting system to the contrast under a reference spherical (“glare-free”) lighting system Cprop/Cref

• CRF could possibly range from 1.0 to 0.0• The higher the CRF the better (with respect to

reducing reflected glare potential)• No generally-accepted design standards or

guidelines for appropriate CRF values are currently available


Equivalent Spherical Illuminance (ESI)

ESI = (E) (CRF)where E = “raw” illuminance (as in, just dumping some light on a surface) ESI = equivalent spherical illuminance (as in good—without much reflected glare potential—light) CRF = contrast rendition factor

• ESI was briefly the basis for design criteria published by IESNA, but the concept was dropped—at the time there was no ESI meter, so design criteria could not be readily verified in the field

• ESI is still an interesting and valid concept

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color rendering: four pieces of the same cloth; on the left under four differentlamp types, on the right under the same lamp—which color is “real”?

Illuminance and Glare are not the only Lighting Issues


energy use for lighting: in residences (left) and offices (right)–the first best design moves are building-type specific

Energy and Environmental Impactare also Lighting Design Issues