Life tests of Nichia AlGaN/InGaN/GaN blue-light-emitting diodes

We report on the results of life testing Nichia NLPB500 blue LEDs. All tests were performed with the LEDs in a temperature controlled chamber, and all equipment operation and data collection was computer automated. The tests began with 18 newer (Nichia batch 4B0001) and two older (Nichia batch S402024, acquired a year earlier) LEDs, operated at 20 mA continuous wave (CW) and 23 degree(s)C. Light from each LED was coupled to an optical fiber and fed directly to individual photodetectors. The general trend for the 18 newer LEDs was for the output intensity to increase at a faster rate within the first 50 h and then at a slower rate over the remainder of the first test. The output intensity of the two older LEDs increased within the first 50 h then decreased during the remainder of the first 1000 h. All 20 of the LEDs in the first 1000-h test were subjected to a second 1650-h test at 23 degree(s)C and at currents ranging from 20 mA to 70 mA CW. Only one LED, an older device, suffered a soft failure during this second test. The remaining LEDs underwent a third test at 30 degree(s)C and a fourth test at 35 degree(s)C, all at various currents. We will perform failure analysis on all sufficiently degraded devices and report those results elsewhere.