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Clark School

Design of LED-based lighting systems

More High Power Light Emitting Diode (HP-LED) Research

Optical performance characterization of high power LEDs

Design of LED-based lighting systems

Reliability analysis of LEDs and LED-based luminaires


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High power light emitting diodes (HP LEDs) are expected to become a general light source of the next generation.  High power LEDs have higher luminous efficacy and power efficiency than conventional general light sources such as incandescent light and fluorescent light.  Yet, nearly 90% of an input power is dissipated as heat during operation, which poses inherent challenges in thermal management and reliability.

Unlike the conventional semiconductor electronic devices whose failure mechanisms are well-known and thus their contributions to the PoF-based life prediction models are well-established, the reliability issues of packaged HP LEDs is so package-dependent that it would be difficult to develop a generalized PoF model from the life test data of commercially available packaged LEDs.  Another distinct difference is that LEDs usually do not fail catastrophically.  Whereas the failure of the electronic devices is sudden “short or open” circuits in the devices, the LED failure is usually defined by its time-dependent lumen maintenance.  Although both failures are related to the certain wear-out mechanisms, the prediction of LED lifetime can vary significantly with the method of interpreting the results of the accelerated tests.

Research tasks which are conducted in LOMSS include: (1) reliability assessment and (2) design solutions for enhanced reliability.  Reliability assessment are tackled in two levels: (i) device reliability - intrinsic light output reduction under normal operating condition and (i) package reliability- package failures caused by thermal stresses and aging, eventually leading to device failure.  In the area of design solutions, thermally enhanced LED packaging solutions as well as enhanced thermal designs with advanced cooling solutions are investigated.

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