Advanced Thermal Management of LEDs
SBIR FY03.2 Topic A03-217
Department of Defense (DoD)/ARMY - Tank Automotive RD&E Center (TARDEC)
The entire solicitation may be viewed at http://www.acq.osd.mil/sadbu/sbir/solicitations/sbir032/index.htm
A03-217 TITLE: Advanced Thermal Management of LEDs
TECHNOLOGY AREAS: Sensors
ACQUISITION PROGRAM: PM Future Combat Systems
OBJECTIVE: Develop LED packaging and interface technologies that would minimize the thermal resistance of LEDs while at the same time increase LED durability and lower total product cost.
DESCRIPTION: LEDs are quickly replacing incandescent lamps for many applications because of their tenfold increase in luminous efficacy, robust construction, longer service life, lighter weight, and the wide variety of wavelengths available. In particular, LEDs have jumped to the forefront in lighting applications such as traffic lights, pedestrian signals and tail lights in vehicles. The military has also begun to investigate the advantage of LEDs in Identification, Friend or Foe (IFF), near infra-red illuminator/search lights, and covert communication. Unfortunately, the life and luminous efficacy is bounded by the junction temperature of the LED, therefore limiting their functionality. Elevated temperatures, as is common with vehicular and outdoor applications, can reduce the life of high performance LEDs from the rated 100,000 hours of service to less than 5,000 hours. Empirical data shows that for every 17 degree C rise in LED junction temperature, service life is decreased by one half. However, if the luminous intensity versus the junction temperature can be characterized and monitored, and the temperature rise controlled, the lifetime of the LED would be greatly extended.
Optimally, the LEDs would be characterized by measuring the radiation angle, maximum output vs. current and thermal resistance before being placed in an array. This determination would allow for correct placement of LEDs in the array. Additionally, continuous monitoring of the junction temperature would result in an essentially constant luminous intensity throughout the life of the LED. Monitoring the junction temperature would also enable the user to determine the remaining life of the LED. The technology to monitor the junction temperature is limited and as of yet, still very costly. An innovative design for continuous monitoring of the junction temperature would greatly improve lifetime and therefore the life-cycle costs in future IFF and covert communication systems.
PHASE I: The contractor shall research methodologies for continuous monitoring of LED junction temperatures. This phase will identify the current state of technology and designate reasonable goals for such a program.
PHASE II: The contractor shall utilize the goals and methodologies from Phase I to design a computer driven instrumentation system to measure the thermal characteristics of LEDs. Fabricate and test sample low thermal resistance LEDs for durability under various environmental conditions. Design tooling and produce production prototypes of these low thermal resistance LEDs and the low thermal resistance interface for mounting the LEDs.
PHASE III: A highly efficient LED allows for immediate commercial use. Some applications such as stop lights have already been converted to LEDs because of the lower incurred life cycle costs. A highly efficient, thermally optimized LED and ancillary mounting system could be used in a wide variety of commercial applications because of extended service life and cost efficiencies. Typical uses would include commercial signage, military lighting systems, emergency lighting, marine and aviation illumination systems.
KEYWORDS: LED, thermal resistance, low cost
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