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High-power LEDs have been widely used and have a big potential market due to the many advantages compared to conventional light sources. Reliability is one of the most important issues for the application of LEDs. In order to study the degradation mechanism and the stability of LED withstanding cyclical exposures to temperature variations, life test was carried out under temperature cycle testing. The experiment was designed basing on the EIAJ ED-4701/100. Four groups of 1 W high power LEDs adopting different material and structures were utilized. The temperature cycle accelerated life test under the condition of −25°C/125°C. After the accelerated test, the optical performance of the four kinds of devices were compared and analyzed, and the thermal performance of the LEDs was also tested, analyzed and discussed. At last, the reliability differences of high-power LEDs were analyzed and degradation mechanism of high power LEDs under temperature cycling was discussed.

In this paper, GaN-based blue light emitting diodes with double roughened surfaces were fabricated and compared with planar LEDs and these with single roughened layer. The double roughened surfaces were fulfilled by patterned sapphire substrates (PSS) and roughened p-GaN surface. Magnesium treatment during the growth process was used to produce p-GaN surface roughening. After the epitaxial growth, the four group samples were fabricated using the standard process (four mask steps) with a mesa area of 10×23 mil2. At last, 25 LED devices were packaged for each group using the same packaging material and by the same method. It was found that import of PSS and roughened p-GaN surface may lead to a little higher voltage by simply copying the epitaxial process of planar LED. However, even fabricated by the non-optimized epitaxial process, comparing with planar LEDs, the optical power of the package can be increased by 40.1% by using the patterned sapphire substrate, 10.2% by using p-GaN surface roughing, and 44.9% by using double roughing technologies.

In this paper, the reliability issue of the LED lamp in high temperature and moisture condition was investigated. Thermal stress and hygroscopic stress in the LED package were obtained by coupled-field analysis using Finite element analysis (FEA). The results demonstrate that the temperature of the module can reach saturation in tens of seconds while the moisture field needs longer to reach balance. 85°C/85RH can reach the same distribution of relative humidity with 65°C/65RH, but the time spent is half. So temperature is the important factor to affect the humidity distribution. The moisture concentration is better than the relative humidity response to the material moisture level. So we made further research on hygroscopic stress. Both the thermal stress and hygroscopic stress contributed to the delaminations in LED packages.