design note 1 - reflector flashlights

Design Note 1 Copyright BrightBurst Technologies, LLC

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BrightBurstTechnologies, LLC

Improved Optical Performance of LED Flashlights Using the Eco-LensTM

Design System

BrightBurst Technologies Optical Engineering Design Series

Reflector Based Flashlights

Design Note 1


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• Flashlight Types are Reviewed– Lensed LED flashlights– Flashlights based on TIR lenses– Traditional reflector designs

• The Eco-Lens Design System is Introduced– Imaging optic designs waste light– The limits of the standard lens design system is discussed

• Improvements in Reflectors for LED Flashlights are Demonstrated– Results are referenced against the performance of a Smith & Wesson tactical flashlight– Eco-Lens designs which match the S&W reflector height show significant improvements in

• Brightness (in the same FWHM),• Output uniformity (in the same FWHM), and • Can immediately be used in existing flashlight heads with little or no packaging modifications

– Half-size Eco-Lens designs show substantial improvements in• Brightness (60%),• Spillbeam tailoring, and• Allow reduced flashlight head packaging limited only by LED electrode position

• Summary of Results and Benefits to Flashlight Manufacturers

Design Note 1 Outline BrightBurstTechnologies, LLC


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Flashlights utilizing three different LED optical designs have become popular

Flashlight Types

Lensed LED Flashlight Total Internal Reflector Flashlight Standard Reflector Flashlight

Each type is briefly described


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Lensed LED Flashlights

• Individual light emitting diodes are encapsulated in PMMA (plexi-glass) lenses– Light which leaves the lens undergoes refraction at only one interface

• These individual LED units are arranged into compact arrays to form a flashlight

• The optical output of the flashlight is the sum contribution of the individual LED’s optical outputs– Rounded lens shape yields outputs which are too broad and diffuse for adequate beam penetration

Lensed LEDs housed in an array

form the head of this flashlight purchased

in an area home center

Lensed LED function is illustrated with optical

simulation graphics

Output rays (red) are emitted from a p-n

junction embedded in PMMA

The rounded edge forms a lens designed to direct

the rays forwardSingle refraction


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

• The output quality of the flashlight depends on the care devoted to the TIR lens design– The TIR lens design is noted for hotspots and bright rings in output distributions

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


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Reflectors

• The reflector cup is the most common flashlight design– Light output undergoes one reflective bounce then forms an illumination pattern

• High reflectivity coatings can be applied to the reflector wall to maximize output efficiency– Glass discs are used to protect the reflector and LED from dirt and humidity

• The optical output of the standard reflector forms two beams– The main beam is the light focused by the reflector – The light which misses the reflector forms a halo around the main beam and is called spillbeam

An aluminized reflector cup and

LED form the head of this tactical

flashlight marketed for law enforcement

Reflector function is illustrated with optical

simulation graphics

Output rays (red) are emitted from an LED and

then reflect off of the highly reflective wall surface

(green) and leave through the open front of the optic

Single reflection

GlassProtective

Disc

Spillbeam

Mainbeam


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All Flashlight Types Use Imaging Optic Designs

• The optics in the three types of flashlights described were designed by using the standard lens formula

• Standard lens curves were developed to produce optics for imaging systems– This means they map object points to image points as in the camera lens shown above

Object Points atInfinity

Focused Points Form

An Image

Double Gauss Design

Imaging System Design Based on Standard Lens Curves

When used in illumination products such as flashlights, standard lens optics waste light!


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Standard Lens Systems Waste Light

FWHM

Light intotargetFWHM lighting region

Wastedlight….wasted money!

• All current LED flashlights are designed with standard lens optical curves

• The design goal is to direct output power into a target angular region (FWHM)

• Light which does not fall inside the FWHM region is disregarded as background and is wasted– The graph above illustrates this effect

The drive current dollars which produced this wasted light have also been wasted!


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The Eco-LensTM Advantage

• The Eco-LensTM design system was developed to produce optics for LED applications which– Reduce wasted light,– Provide brighter distributions,– Create more uniform outputs, and– Save energy dollars by establishing desired light levels for less drive current

• The remainder of this Design Note will show how the Eco-LensTM design system can provide compelling and unique flashlight products based on enhanced reflector designs

• The point of departure will be a standard lens design reflector found on a Smith & Wesson tactical flashlight

– The output of the reflector will be characterized with optical simulation and will be used as a reference baseline

• Tier 1 Eco-LensTM reflector designs will be referenced to that of the S&W reflector to show improvements in

– Brightness– Uniformity, and – Spillbeam tailoring


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S & W Tactical Flashlight BrightBurstTechnologies, LLC

• The flashlight pictured above is sold under the Smith & Wesson brand and is typical of units sold as tactical flashlights. It features

– High brightness LED (of unknown origin)– Standard lens reflector with protective glass disc– Powered by 2 AA batteries (or CR123 Lithium)– Durable, aluminum housing

• Purchase price was $30.00 at Trexpo East 2007

• The flashlight beam illuminance (image “on the wall”) at 0.5 meters is shown at right

– This output is typical of reflector based flashlights

Flashlight reflector Tactical flashlight sold under Smith & Wesson brand

Flashlight output on wall 0.5 meters away

Mainbeam

Spillbeam


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Optical Simulation to Establish Reference

• The flashlight reflector was parameterized to find the standard lens reflector curve pictured above– Protective glass disc was added to the simulation to model the effect of Fresnel reflections

• High brightness LED is of unknown origin (probably offshore)– Luxeon K2 was used to model LED output

• K2 popular choice for reflector flashlights• Output typical of domed LEDs

– Mechanical CAD and optical ray data for Luxeon K2 incorporated in simulation

• Normalized luminous intensity baseline distribution was established (presented above right)– Same ray simulation parameters were used for all design comparisons– Comparison to the baseline will illustrate Eco-LensTM design improvements

Flashlight reflector Reflector and LED simulation

FWHM = 13.9 deg

Spillbeam

Main beam


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Is the Simulation Accurate?

• Need to “check” the integrity of the reflector model and choice of K2 LED

• The illuminance at 0.5 meters from the simulation is compared to the flashlight’s output at the same distance

• The mainbeam and spillbeam features correspond indicating that the model is an excellent representation of the flashlight’s optical performance

– Simulation output graphed on logarithmic scale to better match the saturation region of the photograph

Mainbeam

Spillbeam

Mainbeam

Spillbeam

Reflector and K2 LED simulation Flashlight illuminance photograph at 0.5 m Illuminance of model at 0.5 m – logarithmic scale


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Note - Spillbeam is Not Wasted Light

• The rays which form the spillbeam portion of the output distribution never hit the reflector mirror and are not considered wasted light under the Eco-LensTM definition

– The entire spillbeam contribution forms a plateau (luminous intensity “bias”) upon which the mainbeam sits– Spillbeam provides peripheral illumination in flashlight applications

• This is an essential feature in law enforcement applications

• Wasted light is that portion of directed light (by an optic) which does not fall into the FWHM cone angle which defines the targeted illumination goal

– This concept is completely new to illumination optics

Reflector and LED simulation

FWHM = 13.9 deg

Spillbeamplateau

MainbeamRays which form

spillbeam of flashlight

Rays directedby mirror form mainbeam Wasted light

The Eco-LensTM design system is the only method available to reduce wasted light and provide superior flashlight performance


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Example 1

• Spillbeam is matched because the front diameter of the mirror remains the same as S&W the reflector

• Power redirected by the Eco-LensTM reflector provides 25% greater brightness for the same drive current

– To achieve the same brightness as the S&W reference drive current can be reduced and battery life can be extended

• Dimensions allow for immediate replacement into the existing S&W flashlight housing– No packaging redesign is necessary!


S&W reflectorin red

Eco-LensTM reflectorin green

Eco-Lens Reflector has same height and diameter as the S&W reflector

Both curves haveFWHM = 13.9 deg

Wasted lightReduced!

Eco-Lens reflectoryields 25% greaterLum Int!


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Example 2

• Spillbeam is extended by 7 deg on either side of Eco-LensTM curve– Peripheral illumination has been enhanced

• The decreased power available to the mirror is redirected by the Eco-LensTM curve into the same brightness level as the S&W output

– brightness level is maintained but with a more uniform output

• Dimensions allow for immediate insertion into flashlight housings designed for larger diameter reflector heads

– This type of reflector can be tailored to any size flashlight head


S&W reflectorin red


Eco-Lens Reflector has same height but larger diameter than the S&W reflector


Unprecedentedtop-hat distributionprovides smoothillumination spot


Extendedspillbeam


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Example 3

• Spillbeam is reduced due to the smaller diameter of the Eco-LensTM curve– More power becomes available for direction by the reflector mirror

• Power redirected by the Eco-LensTM curve achieves 25% greater brightness with a vastly more uniform output

– Reducing drive current to achieve previous S&W brightness level will extend battery life

• Smaller radial dimensions allow for immediate insertion into flashlight housings with minimal redesign

– This advantage means quicker time to market and profitability


S&W reflectorin red


Eco-Lens Reflector has same height but smaller diameter than the S&W reflector



top-hat distributionprovides smoothillumination spot


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Example 4

• Spillbeam is increased by 10 deg on both sides by the smaller size of the Eco-LensTM curve– Peripheral illumination is greatly enhanced, a huge benefit for law enforcement

• Even with the reduced power available to the reflector the amount re-directed by the Eco-LensTM

curve achieves – the same peak brightness as the full size S&W reflector – with a one degree tighter FWHM output cone

• Smaller reflector dimensions allow for more compact packaging of powerful and versatile flashlights

– Reflector head packaging would be limited by the electrodes of the Luxeon K2 LED


Eco-Lens Reflector is half the size of the S&W reflector

S&W reflectorin red


S&W curve hasFWHM = 13.9 degEco-Lens curve hasFWHM = 12.9 deg

Brightness peakIs matched with less but better directed power

Spillbeamextended 10deg either side


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Example 5

• Spillbeam is still 10 deg wider on both sides

• The Eco-Lens reflector is now designed to deliver 60% greater brightness in a reduced FWHM cone

– Increased brightness significantly extends the lighting penetration depth of the flashlight– Increased brightness can more effectively dazzle suspects in law enforcement situations– Reducing brightness to the S&W level (as a design option) will extend battery life dramatically

• Enhanced peak brightness with extended spillbeam cannot be offered with standard lens designs

• Packaging options are the same as for example 4


Eco-Lens Reflector is half the size of the S&W reflector

S&W reflectorin red


S&W curve hasFWHM = 13.9 degEco-Lens curve hasFWHM = 9.5 deg

Spillbeamextended 10deg either side

Peak brightness increased by 60%!


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Summary of Results and Benefits

• All current flashlights illustrate the limitations of the standard lens design system:– Output distributions which do not direct enough of the LED emission into the targeted design

region causing– Drive current levels to be set higher to achieve lighting goals

• The Eco-LensTM design system was developed by BrightBurst Technologies to more effectively direct LED emissions for flashlight applications

• Examples 1 – 3 illustrate the advantages of reflectors designed with a Tier 1 Eco- LensTM curve which matches the height of a S&W reflector

– Brightness distributions are 25% higher than the S&W reference,– Illumination spots are much more uniform,– The ability to tailor spillbeam, – The option to run at the lower S&W brightness level to extend battery life, and– Reflector dimensions which allow immediate replacement in existing flashlight packages

• Quicker market penetration means quicker profitability


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Summary of Results and Benefits (cont)

• Examples 4 - 5 illustrate the versatility and range of the Eco-LensTM design system in producing powerful, effective reduced size reflectors. At half the height of the S&W reference reflector the Eco-LensTM design produces

– Output brightness which can match the S&W reference,– Output brightness which exceeds it by 60% in a narrower beam, – Greatly expanded spillbeam (10 deg) to enhance peripheral lighting, and – The option for compact packaging limited only by the electrodes of the LED

• All this means big flashlight performance in a much smaller package!

• The design options detailed in this Design Note are unique and powerful and offer substantial product differentiation to flashlights targeted for markets such as

– Law Enforcement– Military hand held lighting– Consumer hand held lighting– Camping– Hunting– Hiking– Specialty Products


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Summary of Results and Benefits (cont)

For more information on how the Eco-LensTM design system can distinguish your hand held 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]

design note 1 - reflector flashlights

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