Step-down accelerated aging test for LED lamps based on nelson models

In order to quickly acquire the lifetime and reliability prediction for LED lighting products, the method of step-down accelerated aging test based on Nelson models is experimentally studied in this paper. Ten Lide lamps and ten Philips lamps are used in the accelerated aging tests, with humidity less than 50%. The ambient temperatures are 90°C and 70°C for Lide lamps, and are 90°C and 80°C for Philips lamps. The models, the equal cumulative amount of degradation and the equal cumulative failure probability, are used to obtain the equivalent test time from one stress to another. The maximum likelihood function method is used to obtain two unknown parameters of Weibull distribution at the accelerated ambient temperatures. Then the distribution of the failure probability of LED lamp at ambient temperature of 25°C is obtained by Arrhenius model. The lifetime tests recommended by Energy Star standard are conducted to verify the accuracy of the models. It is shown that the model of equal cumulative amount of degradation is with a smaller error of lifetime estimation which is respectively 1.74%, 2.41% and 6.57% at the failure probability of 63.2%, 10% and 1% for Lide lamps, and is respectively 8.19%, 1.06% and 5.89% for Philips lamps in this research. The total accelerated aging time about 1000h is achieved in this experiment, which is quite satisfactory for a quick lifetime prediction of LED lamps recently.