DESIGN NOTE 2 - TIR Lenses

Design Note 2 Copyright BrightBurst Technologies, LLC

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BrightBurstTechnologies, LLC

Eco-TIRTM Lens Designs for Small Output Angle Illumination

BrightBurst Technologies Optical Engineering Design Series

Design Note 2

• Flashlights• Spotlights


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• Presented Previously:– Flashlight Types– The Eco-LensTM Design System

The reader is referred to Design Note 1 (available from our website – www.BrightBurstTech.com) for a full treatment of these topics

• TIR Lenses– Function illustrated– Best platform for forming narrow beams from LED emission– These narrow beams frequently exhibit “hotspot” non-uniformities due to the square LED

emitter geometry

• Three Production “Spot” TIR Lenses Are Analyzed Through Optical Simulation– MCAD and IES files are used to analyze the outputs of

• Polycarbonate TIR lenses of 20 and 26.5 mm diameter and • A PMMA TIR lens of 20 mm diameter with a micro-textured output feature

– Eco-LensTM TIR (Eco-TIRTM) designs of equivalent form factors show• Brightness increases of as much as 2.7 X!• Uniform illuminance (spot) distributions with no hotspots or emitter imaging

• Summary of Results and Benefits to TIR Lens Manufacturers

Design Note 2 Outline BrightBurstTechnologies, LLC


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Total Internal Reflector (TIR) Lenses

• TIR lenses mix refraction and reflection in their operating mode– Light which leaves the lens undergoes two refractions and one reflection (TIR Walls), or– Two refractions when passing through the central lens– All light is directed by an optical interface

• The output quality of the illumination depends on the care devoted to the TIR lens design– The TIR spotlight lens is noted for hotspots and irregularities in output distributions

• TIR lenses are made by injection molding of materials such as– PMMA,– Polycarbonate, and – Cycloolefin CoPolymer (COC)

TIR lens function is illustrated with optical

simulation graphics

Output rays (red) are emitted from an LED,

refract into the TIR lens then reflect off the outer wall and leave through the front of the optic

PMMA TIR lens shown in the head of

a flashlight

Refraction 1Refraction 2

Total Internal Reflection

TIR Walls

CentralLens


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Example 1 – Luminous Intensity Comparison

9.9 mm

21.4 mm

9.9 mm

21.4 mm

20 mm Platform

TIR 1 Eco-TIR 1

• Production lens TIR 1(red) is made from single-side injection molded polycarbonate– Optical features in MCAD show smoothly varying TIR walls and a central lens as illustrated on page 3

• Eco-TIR 1 (green) lens is designed in polycarbonate with the same features and to the same form factor– The Eco-LensTM design system was used to optimize for best tight angle, spotlight output

• Luminous intensity output of TIR 1 is shown at right above and indicates a distribution of FWHM = 14 deg with 20% spill

– Spill is defined in this Design Note as the percentage of the luminous intensity distribution which falls outside of the FWHM cone

• The luminous intensity output of the Eco-TIR 1 lens shows a peak 2.4 X greater than TIR 1!– FWHM has been reduced from 14 deg to 8.4 deg - Spill remains the same– Spotlight penetration is significantly increased for the same drive current dollars!

Peak of Eco-TIR 1 is 2.4 X brighter than thatof TIR 1

TIR 1FWHM = 14 degSpill = 20%

Eco-TIR 1FWHM = 8.4 degSpill = 20%

Example 1 - Normalized Intensity Comparisons

Luxeon K2*

The Eco-TIR 1 produces a spotlight output superior to all other TIR lenses of this size!


*Mechancial CAD and optical ray data for the for the Luxeon K2 LED were used for all simulations in this Design Note


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Example 1 – Illuminance at 1 m Comparison

TIR 1 Spot Illuminance at 1 m Eco-TIR 1 Spot Illuminance at 1 m

Hotspots

Spill = 20%Spill = 20%

• The illuminance distribution of TIR 1 at 1 meter shows indications of hotspots or non-uniformities in the image– This is the most common drawback of tight angle, spot TIR lenses produced with imaging/freeform optical design – The square features of the LED emitter are “imaged” (poorly) and corrupt the integrity of the spotlight

• By contrast the illuminance distribution of Eco-TIR 1 shows more uniform illumination– The Eco-LensTM design system was formulated specifically to better direct LED emission for illumination applications– It is not based on an image producing paradigm

• Both TIR 1 and Eco-TIR 1 have the same 20% output spill– The 20% spill of TIR 1 is part of a broader distribution and it’s relatively slow spatial variation is apparent in the illuminance

distribution (green grading to blue)

• By contrast the 20% spill of Eco-TIR 1 is part of a much tighter and brighter distribution– It’s spatial variation is much faster (green grading to blue)

• The result is a more uniform, well defined output spot!


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Example 2 – Luminous Intensity Comparison BrightBurstTechnologies, LLC

26 mm Platform

13.8 mm13.8 mm

26.5 mm 26.5 mm

TIR 2 Eco-TIR 2 TIR 2FWHM = 11.3 degSpill = 22%


Peak of Eco-TIR 2 is 2.7 X brighter than thatof TIR 2


Hotspot

Luxeon K2

• Larger TIR lenses are employed to produce even tighter angle spotlights– Increase in size of the TIR optic allows any design system to better direct LED emission

• Increasing diameter with TIR 2 produces a luminous intensity distribution with FWHM = 11.3 deg and Spill = 22%– Increasing size decreases FWHM by 2.7 deg from that of TIR 1– Spill remains nominally unchanged– The decrease in FWHM and concomitant increase in brightness also results in a luminous intensity tip which indicates a hotspot

• Eco-TIR 2 of the same dimensions produces a distribution 2.7 X brighter than that of TIR 2!– FWHM has decreased by 1.8 deg– Spill is unchanged

The Eco-TIR 2 lens gives spotlight performance usually found in LED optics several times it’s diameter!


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Example 2 – Illuminance at 1m Comparison


PronouncedHotspots


• The illuminance distribution of TIR 2 at 1 meter shows very pronounced hotspots– Reducing the output FWHM has increased the effect of the square LED emitter on the output spot

• The illuminance distribution of Eco-TIR 2 shows uniform illumination– The Eco-LensTM design system will always best traditional optical design in producing uniform output spots

• Both TIR 2 and Eco-TIR 2 have nominally the same output spill– Note that the same spatial variation effect described on page 5 is also present with these distributions– The spill of Eco-TIR 2 rolls off much faster than TIR 2 as evidenced by the outputs grading from green to blue

• This once again results in a tighter, more desirable output spot!


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19.7 mm

9.9 mm10.3 mm

21.4 mm


20 mm Platform

TIR 3 Eco-TIR 1



TIR 3FWHM = 8.7 degSpill = 31%


Luxeon K2

Peak of Eco-TIR 1 is 1.6X brighter than thatof TIR 3

• TIR 3 shows a design to achieve tighter spotlight distributions with no hotspots– This lens is produced in double-sided injection molded PMMA– Input face to TIR walls is contoured to optimize effectiveness of TIR walls in directing light– Cavity over lens is textured to diffuse light and reduce effect of hotspots

• TIR 3 luminous intensity output shows a smaller FWHM = 8.7 deg but dramatically increased Spill of 31%– The combination of lens features has produced a tighter output distribution– Increase in spill means less light driven into target FWHM cone

• Eco-TIR 1 output luminous intensity is 1.6 X brighter than the output of TIR 3– Spill is 13% less than TIR 3– Output indicates more light is being directed into FWHM by the Eco-TIR 1 curves– Fullness of Eco-TIR 1 luminous intensity curve indicates a more uniform spot

Superior Eco-TIR 1 performance is produced by a simpler, single-sided injection molded design consisting of 2 Eco-LensTM curves!


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• The illuminance distribution of TIR 3 at 1 meter shows no indication of hotspots– This is due to the combination of increased lens features and diffusion– The penalty for this illuminance uniformity is an increase in spill to 31%– Using diffusion to smooth outputs is a common optical design option but it also results in wasted light

• The illuminance distribution of Eco-TIR 1 shows a broader, “crisper” illumination for a slightly smaller FWHM– FWHM is 8.4 deg vs 8.7 deg for TIR 3

• The faster spatial variation of luminous intensity for Eco-TIR 1 produces– A brighter spot,– Illustrates superior light direction, and– Is available in a simpler design!


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TIR 1TIR 3 Eco-TIR 1

Summary of 20 mm TIR Lenses


TIR 3FWHM = 8.7 degSpill = 31% TIR 1

FWHM = 14 degSpill = 20%

Summary of 20mm Normalized Intensity Comparisons• The 20 mm TIR lens platform is the most popular• TIR 1 produces the broadest distribution

– All results are normalized to it’s luminous intensity curve– Output is broadest and is produced by two curves based on traditional optical design

• Single-sided injection molded Polycarbonate – Spot at 1 m shows hotspots and emitter imaging

• TIR 3 produces an output 1.5 X brighter than TIR 1– Lens features and diffusion added

• Double-sided injection molded PMMA– Spot at 1m is brighter and shows no hotspots– Increase in spill indicates light is wasted

• Eco-TIR 1 produces the smoothest output and is 2.4 X brighter than TIR 1– Output is produced by 2 Eco-LensTM curves positioned similarly to TIR 1

• Design option shown is single-sided injection molded Polycarbonate– Spot at 1 m is brightest and most distinct due to

• Superior light direction• Faster spatial roll-off of spill



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Summary of Results and Benefits

• The Eco-LensTM design system was used to illustrate Eco-TIRTM lenses for reduced angle, spotlight applications

• Eco-TIR 1 was designed on the popular 20 mm platform – Comparisons of luminous intensity (brightness) distributions revealed

• Increases in brightness of– 2.4 X as compared to production lens TIR 1 and– 1.6 X as compared to production lens TIR 3

– Spot image at 1 meter (illuminance) • TIR 1 produced hotspots• TIR 3 employed diffusion to eliminate hotspots

– Diffusion increased spill and wasted light• Eco-TIR 1 produced brighter, more uniform spot images due to

– Superior light direction and– Faster spatial roll-off of spill

• Eco-TIR 2 was developed to match a larger (26 mm) TIR 2– Luminous Intensity

• Eco-TIR 2 brightness exceeded that of TIR 2 by 2.7 X• Output of TIR 2 indicated a very pronounced hotspot

– Illuminance• Spot image of TIR 2 at 1 m indicates hotspots

– Square LED emitter features • Spot image of Eco-TIR 2 is uniform and tight due to

– Superior light direction and – Faster spatial roll-off



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Summary of Results and Benefits (cont)

• The Eco-TIRTM spotlight lenses illustrated in this Design Note are single sided designs and can be moved directly into production for the least cost

• The results presented in this Design Note clearly illustrate that the Eco-LensTM

design system used to develop the lenses can provide superior performance over other single and double sided TIR designs

• Eco-TIRTM spot lenses can be quickly designed for any injection molded material– PMMA– Polycarbonate– Cyclic Olefin Copolymer (COC)– Proprietary Blends

• Eco-TIRTM spot lenses can be quickly designed for use with any LED– Osram– Cree– Lumileds– Nichia– Custom LEDs



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• The Eco-TIRTM spotlight represents a quantum leap forward in LED spotlighting– Significantly brighter beams can be produced for the same drive current dollars– Illumination level requirements can be met for less cost

• Significant product differentiation can be provided for markets like– Retail lighting– Show and stage lighting– Parking lot illumination– Municipal lighting– Handheld lighting

• Commercial• LE/Military

– Automotive headlights– Shipboard lighting



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For more information on how the Eco-LensTM design system can distinguish your lighting products and increase your profitability in today’s tough marketplace please feel free to contact us immediately!

BrightBurst Techologies, LLC

[email protected]

Tel: 908-359-5851Fax: 908-566-0775


mailto:[email protected]

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DESIGN NOTE 2 - TIR Lenses