The objective of this paper is to investigate the effect of rapid thermal cycling on microstructure and optical property (luminous flux and luminous efficiency) of high power light emitting diode (LED) by thermal fatigue testing from −40 to 125. Under an application of thermal fatigue device as a heating source, the specimens that were being non-operating and thermal fatigue testing in the experiment were rapidly heated and cooled based on a control system that employs a fuzzy logic algorithm, respectively. The optical performances, including ...