1. a Primer on LED Optics

8/3/2019 1. a Primer on LED Optics

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Future-Lumileds Engineering Meeting November 2007

Designing with LEDs September 2011

Putting the lightonly where it's needed

A Primer on LED Optics


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Outline

Understanding Light

How We See and Measure Light

How Are Optics Tested What Can We Do With Light

Standard Optics New Developments in LED Optics

Custom Optics


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UnderstandingLight

(lite)

Optics 101


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The Electromagnetic Spectrum


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The speed of light

How fast does light travel?

300 000 000 meters per second in vacuum

Inside a material it travels slower!

In ordinary glass the velocity is about two-thirds of the velocity in free space.

The ratio of the velocity in vacuum to the velocity in a medium is called the

index of refraction of that medium, denoted by the letter n.

Index of refraction n = Velocity in vacuum

Velocity in medium


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Light propagation

LED = Point Source Emitter

We are used to visualising waves from

point sources on 2D surfaces.

Light waves radiating from a point sourcetake a spherical form

Radius of curvature of the wave front = distanc

e from the point source.

Path of a point on the wave front is a

light ray.

In a medium a light ray is a straight line.


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Lambertian Emission

What is a perfect emitter?

A perfectly matt surface or an ideal emitter looks

the same brightness regardless of what angle it

is viewed from.

This type of emitter is called a Lambertian

emitter and to be equally bright at all viewing

angles its emission with angle must vary as the

cosine of the angle.

WHITE LED chips are nearly perfect

Lambertian emitters. However the packaging

will often modify the output by refracting,

clipping or reflecting the light leaving the

device.


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Inverse Square Law

The intensity of light changes as it travels outwards from a perfect point source.

Light waves radiating outwards cover an increasingly large area the further they

travel.

This can be written as:

The area that the light covers increases as the square of the distance.

The power per area falls as the

inverse of the distance squared.


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Lagrangian Invariant - Etendue

Smaller Areas (optics) = Wider Angular Spread (Beam Angles)

Wider Areas (optics) = Narrow Angular Spread (Beam Angles)


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Refraction

The speed of light is lower inside a

material than when travelling through air.

The wave front has to change direction

when it enters a material.

The new direction that the light travels in

is given by Snells Law

n1x sin(I1) = n2x sin(I2)

Were n is the refractive index


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Total Internal Reflection

Amazing things can happen when light leaves a material!

At incidence angles > this critical angle

Light is reflected back into the material!

This is Total Internal Reflection (TIR).

As the angle of the wave front increases,

the refracted light angle increases

until the refracted light virtually travels

along the surface!

No loss of optical power in TIR.

Total Internal Reflection

The most efficient means of reflecting light!

more efficient than any metal mirror


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Simple lenses and prisms

What happens as light travels through a prism?

What happens inside a lens?

Wave front diagrams of light passing

through a lens are complex.

A simpler way is to use a ray

diagram.

The rays shown are straight lines

whose direction is normal to the

wave front.


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Dispersion

The speed of light in a vacuum is the same for all wavelengths.

This is isnt true when travelling through a material.

The refractive index of a material is a function of the wavelength of light.

For White Light:

The various wavelengths

dont bend by the same amount.

Thus we see Rainbow Effects.

The technical term for this effect is dispersion.


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How we see andmeasure Light

Optics 101


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The Human Eye

An Incredible Device!

Adapts to a light intensity that

ranges from

100,000 lux

Bright sunlight

0.00005 lux

Starlight

The eye can see even 1 photon!

Brain suppresses as noise

2 or 3 photons over a small area will

produce an impression.

The eye is an excellent edge detector.


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How the eye responds to light


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Photodiodes vs. the Human Eye

Sensitivity of a photodiode to light of different

wavelengths is not like that of the eye.

Maximum sensitivity is in the near infra-red region.

To replicate the sensitivity of the eye

Filters are needed to cut-off the near infra-red and reduce

sensitivity in the red.

Photodiodes are the most widely used device for detecting visible light.


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Measuring Light

PhotometryThe science of measuring light as thehuman eye sees it.

RadiometryThe absolute measurement of light(regardless of wavelength)

For every radiometric measurementthere is a photometric equivalent.


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Optical Measurement Matrix


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Quantities of brightness

LUMENSLuminous Flux

The total amount of visible light emitted.

This is measured by collecting all the lightemitted by the source into a full sphere.

Use this to compare sources or todetermine how efficient your source is.


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LUXIlluminance

The amount of visible light per unit area.

Use this in the Near Field to definehow dense you want the light to be.

Specifying lighting levels on surfaces.

Lighting levels in buildings.


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CANDELALuminous Flux

The amount of visible light per unit solid angle.

Use this in the Far Field to define howintense you want the light to be.

Specifying light intensity into free space.The brightness of beacons or traffic signals.



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NITS(Candela per m2)

Luminance

The amount of visible lightper unit area per unit solid angle .

Use this to define the brightness of a display.

Combination of Near Field and Far FieldUsed to measure the brightness of a surfaceemitting in to free space.



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Summary On Light Measurement

Lumens are for the total amount of visible light

Candela are for light emitted in to free space

.think solid angle

Lux are for light incident on surfaces

.think area

Nits are for light emitted from a large area in to free space.think area into solid angle

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Candela to Lux Conversion

REMEMBER THIS ONE IMPORTANT FACT !!

At a distance of 1 meter, the values of Candela and Lux are the same.

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To convert from Candela to Lux:

Divide by the distance squared.

To convert from Lux to Candela :

Multiply by the distance squared.

Then use the inverse square law to get from one to the other


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Optics 101

Testing LED Optics at Carclo


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Optical Testing Key Parameters

LED luminous flux in Lumens

Optic coupling efficiency % LED package output

Luminous intensity FWHM Full Width beam angle in degrees

at Half Maximum intensity

Peak intensity / LED lumens output Candelas/Lumen

Measured at 350mA


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Labsphere Integrating Sphere (9 Diameter)

LED luminous flux (in lumens)

Optic coupling efficiency (%)

E% = 100 x [Lumens (LED+Optic) / Lumens (LED)

9 LabsphereIntegrating Sphere

LED optic under test


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Luminous intensity FWHM (Full Width in degrees at Half Maximum intensity)Peak intensity / LED lumens output ( i.e.Cd / lumen)

Prometric Imaging Photometry


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FWHM - Specifying Beam Width

Beam widths are usually

Full Width Half Maximum(FWHM)

OR

Half Width Half Maximum(HWHM)

FWHM or HWHM is just a single figure. It doesnt give the whole picture.


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Graphs and Contour Maps

If you want to know

how far the light will spread

how it changes across the beam

you need

Intensity Distribution Graphs

Contour Maps

Graph of Candela

per lumen

Contour map of Lux

per lumen at 2.5m


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Data For Optical Designers

ProSource Files Models LED output

Generates ray data for optical ray tracing programs.

Used to design and simulate the effect of additional

optics

Ray Files

Information on the large number of light rays leaving

an LED

Optical ray tracing programs will follow the paths of

these rays through the optical component being

designed

Used to calculate the beam intensity


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Software For Optical Designers

Zemax Optical Design

ASAP Software

Photopia Photometric

Lightools Software AGi32


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Data For Lighting Designers

Excel Spreadsheets Lab Data

Calculate Intensity and Illuminance profiles Specified LED output (in lumens)

Specified distance

2-D Graphs

3-D Models

IES Type C Files Import into photometric applications

Light level/Beam contour simulations


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Click 'Illuminance' tab to change Target Distance or LED Output Flux.Illuminance & Intensity Distributions are recalculated.

Display graphs are automatically updated.

Carclo Spreadsheet Data


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Illuminance Graphical Output


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Luminous Intensity Graphical Output


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Illuminance in XY Plane


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Luminous Intensity in XYPlane


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Elliptical Optic with Rebel White LED.Text file for import into photometric applications.

IES Type C Files


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BASIC OPTICAL

SYSTEMS

Optics 101

h C i h i h ?


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Reflect From metallized surfaces

Using Total Internal Reflection (TIR)

From white diffuse surfaces

What Can You Do With Light?

Refract Bend it using prisms.

Focus it using lenses.

Spread it using diffusers.

Absorb Using black surfaces

Using structured surfaces


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No Optics

Main Uses

Area Illumination

Advantages

What could be simpler!

Even Wide Output Pattern

Disadvantages

Low intensity

Uncomfortably Bright

Tip

Make sure you have enough Lumens available.

Shade areas where you dont want light.

Si l L


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Main Uses

Spot Lights

Simple LensesEither (Conventional or Fresnel)

Advantages

Low cost

Can be fabricated as large arrays

Disadvantages

Poor Efficiency ~50%

Tip

Dont try too produce a very tight spot of light.

This will produce an image of the LED chip.

Either deliberately defocus or use a diffuser.


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Main Uses Area Illumination, spots, wall wash

Simple Reflectors

Advantages

Produce a sharp cut-off.

Even output.

Disadvantages

Cant produce narrow angle beams

Need secondary windows

Tip

Dont put the LED at the focus of a parabolic reflector.

Produces a bright spot in the center of the output beam.

TIR O i


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Main Uses Almost everything!

TIR Optics(A Total Internal Reflector Combined With A Lens)

Advantages

Very efficient ~85%

Compact

Robust

Can be used as window

Disadvantages

Cant produce very narrow beams Fixed focus

Tip

Make sure the optic is properly centered.

Otherwise, dark holes can appear in the image.

Buy from Carclo!


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ANATOMY OF A TIR OPTIC

Planar output face canbe replaced with aripple insert or afrosted insert togenerate widerintensity distributions

Total InternalReflection (TIR) of

high angle light rays atouter optic faceoptic

face

Rays over a narrower

angle range arerefracted by inner lens

Light rays collimatedin this example

Light rays from LEDare output over a wideangular range

(typically 120 deg)

Optic holder holds

LED optic at correctheight above LED


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Ripple Lenses

Main Uses

Widening and shaping beams

Advantages

Can be incorporated into optics and windows

Can create a wide range of beam shapes

Disadvantages

Used on exterior surfaces they are difficult to clean

Cant spread light out by more than 40 degrees


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Side Emitting Optics

Main Uses

Beacons

Backlighting for signage/displays

Landscape/Architectural Lighting

Advantages Compact.

Narrow 5x360 beam.

Disadvantages

Needs a window.

Output divergence varies slightly around the axis.

Tip

Alignment with the horizontal plane is critical.


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Side-Emitter Raytrace

Sid E itti O ti


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Side Emitting Opticswith light guide

Main Uses

Backlights

Advantages

Efficient coupling.

Very little forward illumination.

Disadvantages

Needs a reflective edge to the light guide.

Output divergence varies around the axis.

Tip

Works best with light guides between 8 - 12mm thick.

Side Emitting Optics


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Side Emitting OpticsWith Reflector

Main Uses

Spot lights

Automotive rear lights

Advantages

Retrofit to existing reflectors possible. Produces Narrow beams.

Disadvantages

Needs a window.

Sensitive to mirror misalignment.

Tip

Unless you are retrofitting an LED in to an existing product

there may be other ways to produce a narrow beam.


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Catadioptric Reflectors

Main Uses Very narrow spot lights or lines when combined with linear

spreaders

Advantages

Compact Produce very tight beams.

Disadvantages

Expensive

Tip

When used with secondary linear ripple windows

they can produce very narrow lines.


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Light Boxes

Main Uses

Back Illumination of floors, walls and ceilings

Advantages

Large area illumination.

Even illumination.

Disadvantages

Inefficient.

Requires lots of LEDs.

Tip

Small changes in reflectivity of the internal surfaces

make a big difference to the total efficiency.


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Diffusers

Main Uses Smoothing and widening light output

Advantages

Simple.

Effective.

Disadvantages

Reduces efficiency.

Additional component that increases cost/complexity.

Tip

Use the minimum diffusion to avoid wasting light.

Usually they have a rough and a smooth side.

Make sure you orient correctly.

Summary of selecting optics


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Summary of selecting optics

No Optics - too bright to look at and too dim to use

TIR Optics - great all rounders, not for special requirements

Reflectors - great for wide beams but not narrow ones

Side emitters - often overlooked but do things others cant

Simple Lenses - simple but inefficient

Light Boxes - good for large areas or for uniform illumination

Double Reflectors expensive, but best for narrow beams

Before You Start Selecting


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Always do a light budget before you start any new job.

Before You Start Selecting

Optics

Be realistic about the amount of Lumens you will get from your

LEDs.

Dont forget to specify where you dont want illumination.

Tip

You can increase the concentration of light within a system using

optics -but you cant create light!


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Typical Standard Optics

N O ti


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Narrow Optic

Flat fronted

Narrow beam

Tightly controlled light

Ideal for spot lighting& machine lighting

R di l Ri l O i


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Radial Ripple Optics

Front surface is a radial ripple

Output cones of 30deg &50deg (Medium & Wide)

Output is center-weighted

Provides very even outputwhen used in large numbers

Used on Airbus/Boeing forreading lights

Color mixing lights

Elli i l O i


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Elliptical Optic

Gives a linear output of45deg in one direction and10-15 deg in the other

The output is extremelyeven along the length ofthis strip of light

Used on obstructionbeacons, wall washing

F t d O ti


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Frosted Optics

Beam AnglesNarrowMedium

Wide

Available in 10mm,20mm and 26.5mm

Proprietary Coating

Soft Diffused LightArchitectural

Commercial

Theatrical

R t N O ti


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Recent New Optics

S ll F t i t" O ti


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Small Footprint" Optic

10 O ti


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10mm Optic

Designed for:

Lumileds RebelCree XP-E/XP-GNichia 119

Osram Oslon

B d ith O ti


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Board with Optics

S ll F t i t O ti


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Small Footprint Optic

Efficiency 90.03% FWHM ~17 Degrees FWHM Peak intensity / LED lumens output 7.1 Cd/lm

Additional optics in the range Elliptical (linear) 18x46 degrees

Wider Beam Angles Medium Frosted - 22 Degrees FWHM Wide Frosted 30 Degrees FWHM

SuperWide Frosted 42 Degrees FWHM

Optics for Multi Chip LEDs


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Optics for Multi-Chip LEDs

New Large Sources Provide High Lumen Output

2K lumens+

Multi-Color Color Mixing

Require Large Optics

Efficient Collimation

Narrow(er) Beams

Good Color Mixing

Less Overall Efficiency



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20mm

26.5mm



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Seoul Semi P7

30mm Optic

New Material

Makrolon LED2643

13.3 FWHM

Efficiency = 92.3%

Peak Intensity = 13.8Cd/lm

Bubble Optic


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Bubble Optic

Wide Area Illumination Even Illumination Pattern

Designed for

Luxeon Rebel Seoul Semi P4

Cree XP-E/XP-C/XP-G

Nichia 119 Osram Oslon

120/130/180 Degrees

Downlight

Bubble Optic Output Pattern


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Bubble Optic Output Pattern

Hemi Spherical Bubble Optic


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Hemi-Spherical Bubble Optic

Downlight Bubble Optic


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Downlight Bubble Optic

Continuous Strip Optic


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Single piece optic that can be made in lengths to suit your needsStandard in 4 foot & 1 foot lengthsDesigned for small footprint LEDs

Luxeon Rebel, Cree XP-E/XP-C, Nichia 119, Osram Oslon

Diffused front surface means mounting height tolerance less critical



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An epoxy resin can be used to join or mount the lensIdeal for florescent replacement applicationsRefrigeration lighting, Cove lighting, Under cupboard lighting, Wall washingCan be used in both single color and RGB mixing.Light is mixed in the long plane - Less need to same color bin LEDsMay be mounted to an aluminium extruded housing/heat sink which can be themain basis of the light engine module or fixture

FWHM: 37.91deg

Peak INT. = 64.1 Cd

Cd/lm: 64.1/46= 1.4 @ 350mAEfficiency: >80%

C t O ti


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Custom Optics

Pro Exactly What You Want

Difficult to Duplicate

Competitive Advantage

Con Expensive

Time Consuming

IP Issues Manufacturability

Obsolescence

C stom Optics


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Custom Optics

Routes to a Custom Optic

Do It Yourself Optical Design Firm

Full-Service Optics Company

Rapid Protot ping


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Rapid Prototyping

Direct Machining + Hand Polishing 75% confidence of RP optic matching simulation

Cost: ~$500 per part

Lead Time: 2-4 weeks

Diamond Turning

95% confidence of RP optic matching simulation

Cost: ~$750 per part


Rapid Prototyping


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Rapid Prototyping

Soft Tooling 75% confidence of RP optic matching simulation

Cost: ~$5000 for tooling Lower part cost

Lead Time: 4 weeks

Single Cavity Prototyping Tool

99% confidence of RP optic matching simulation

Cost: ~$10K for tooling Lower part cost


Can be used for low volume manufacturing

Almost Finall


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Almost Finally

Understand LEDs Play to the strengths of LEDs. Be aware of the weaknesses of LEDs.

When selecting optics

There are many different types of optics that can be used. Dont just think about where you want the light Remember to consider where you dont want it.

Optics that were designed for conventional light sources are

unlikely to give good performance.Designers Tip

Always start with the design of the optics with the smallest divergence first.

Its much easier to widen the divergence rather than to narrow it.

Contact Information


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Contact Information

Jim OConnorBusiness Development Manager

Carclo Technical Plastics USA

600 Depot StreetLatrobe PA 15650

724-539-6982

[email protected]


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Thank You

Documents

1. a Primer on LED Optics