Initial rapid lumen degradation for high-power white packaged LEDs

High--power packaged LEDs experience three-stage lumen degradation behavior under MET test shown in Chapter 3. A rapid lumen degradation is observed in the first stage followed by a lumen recovery in the second stage, and the third stage shows a wear and tear out final degradation stage. This chapter investigates the physics underlying the first stage when tested under high moisture, electric, and temperature stress (MET). Light scattering due to moisture penetration inside the silicone encapsulant of packaged LED is found to be the dominant degradation mechanism.