Prediction of lifetime by lumen degradation and color shift for LED lamps, in a non-accelerated reliability test over 20,000 h.

Abstract

Although the predicted lifetime of the classical 6000h test given by Energy Star is taken as the normal lifetime of LED products in most research and applications, the aim of this study is to explore the error in lifetime prediction of LED lamps based on the 6000h test. A non-accelerated aging test with 10 LED lamps is conducted for 20,000h (from March 2016 to now) under room temperature, which is long enough for this kind of lamp reaching the real lifetime with the normalized luminous flux dropping to 70% naturally. At different aging periods, the correspondent lifetime of each sample is predicted by the lumen degradation, and the median lifetime τ0.5 of 10 samples is obtained by applying the Weibull distribution. Result shows that the τ0.5 of the real lifetime is 16,867h in this work, and the aging time should be at least 9000h to make the error in predicting the lifetime less than 3%. On the other hand, the Du'v' values of 0.006, 0.007, and 0.008 are taken as the three thresholds for predicting the lifetime by color shift. For the case of 0.008, the calculated shape parameter of 8.4 in Weibull distribution is similar with that of the real lifetime, which means the Du'v' of 0.008 for this kind of lamp gives the same failure mechanism as that of lumen degradation of 70%.