DESIGN NOTE 1 - REFLECTOR FLASHLIGHTS

Design Note 1 Copyright BrightBurst
Technologies, LLC
1
BrightBurst
Technologies, 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 BrightBurst
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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 forward
Single
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
simulation graphics
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 1
Refraction 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
simulation graphics
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
Glass
Protective
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 at
Infinity
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
into
target
FWHM
lighting
region
Wasted
light….
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 BrightBurst
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• 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
Spillbeam
plateau
Mainbeam
Rays which form
spillbeam of flashlight
Rays directed
by 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!
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S&W reflector
in red
Eco-LensTM reflector
in green
Eco-Lens Reflector has same height and diameter as the S&W reflector
Both curves have
FWHM = 13.9 deg
Wasted light
Reduced!
Eco-Lens reflector
yields 25% greater
Lum 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
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S&W reflector
in red
in green
Eco-Lens Reflector has same height but larger diameter than the S&W reflector
Both curves have
FWHM = 13.9 deg
Unprecedented
top-hat distribution
provides smooth
illumination spot
Wasted light
Reduced!
Extended
spillbeam

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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
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S&W reflector
in red
in green
Eco-Lens Reflector has same height but smaller diameter than the S&W reflector
Both curves have
FWHM = 13.9 deg
Wasted light
Reduced!
top-hat distribution
provides smooth
illumination 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
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Eco-Lens Reflector is half the size of the S&W reflector
S&W reflector
in red
in green
S&W curve has
FWHM = 13.9 deg
Eco-Lens curve has
FWHM = 12.9 deg
Brightness peak
Is matched with
less but better
directed power
Spillbeam
extended 10
deg 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
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Eco-Lens Reflector is half the size of the S&W reflector
S&W reflector
in red
in green
S&W curve has
FWHM = 13.9 deg
Eco-Lens curve has
FWHM = 9.5 deg
Spillbeam
extended 10
deg 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
info@BrightBurstTech.com
Tel: 908-359-5851
Fax: 908-566-0775

DESIGN NOTE 1 - REFLECTOR FLASHLIGHTS

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