Design Note 1 Copyright BrightBurst Technologies, LLC 1 BrightBurst Technologies, LLC Improved Optical Performance of LED Flashlights Using the Eco-Lens TM 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
• 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
• 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
• 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
• 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!
• 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
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
• 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
• 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
• 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
BrightBurstTechnologies, LLC
Eco-Lens Reflector is half the size of the S&W reflector
• 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
BrightBurstTechnologies, LLC
Eco-Lens Reflector is half the size of the S&W reflector
• 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
• 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
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!