Comparison of lifetime predictions with LED lamps and light source modules in accelerated aging tests
In order to investigate the difference of the lifetime predictions between LED lamps and light source modules, different types of accelerated aging tests have been done in this paper. The accelerated temperatures are 85 °C, 80 °C and 60 °C for three aging tests, respectively. Luminous flux, as evaluation criteria of degradation, is measured at accelerated aging temperatures. Fitted by the exponential decay law of luminous flux, decay rate of each sample is acquired. Under the condition of Weibull distribution, two-stage method is used to solve the degradation model and to calculate the accelerated lifetimes of LED. The lifetimes at room temperature of 25 °C are then calculated by use of the Arrhenius model. It is shown that the widths of confidence intervals of parameters of Weibull distribution are improved greatly by the second stage of simulation. The averaged confidence interval of shape parameter is about 3% of that in the first stage of estimate. The medium lifetime at room temperature of LED lamp declines by 5.6% as compared with light source module. This implies that the aging of driver module has small influence on lifetime of LED lamp.