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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Quantities of brightness
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.
Quantities of brightness
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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.
Quantities of brightness
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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
Optics for Multi Chip LEDs
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Optics for Multi-Chip LEDs
20mm
26.5mm
Optics for Multi Chip LEDs
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Optics for Multi-Chip LEDs
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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Continuous Strip Optic
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
Continuous Strip Optic
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Continuous Strip Optic
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
Lead Time: 4-6 weeks
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
Lead Time: 6-8 weeks
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
724-244-1976jim.oconnor@carclo-usa.com
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Thank You
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