Effect study of silicone amount on the lumen maintenance of high power LED under accelerated stress test

In our previous study, we investigated the effects of different packaging materials (silicone and phosphor layer) on the reliability of high power light-emitting diodes (HPLEDs) by highly accelerated stress test (HAST). The experimental results showed that the LED samples' lumen maintenance property might have dependence on the silicone amount in the package. In this paper, we further studied the effect of silicone amount on the lumen maintenance under HAST. Five categories of LED specimens specified by silicone amount were prepared and subjected to an isothermal chamber whose temperature was set at 125 °C. An online testing system was used to monitor and record the light outputs in real time during the experimental process. After 400 hours of aging, the largest attenuating range reached 6.17% and different groups display different degradation behaviors. An exponential decay model was adopted to calculate the decay rate of each lumen maintenance curve. The decay rate differs as the silicone amount inside the package modules changes. This phenomenon is well explained and Monte Carlo ray-tracing simulations are carried out to validate the explanation. The interaction effect of both silicone amount and temperature is also found and more researches need to be done for further study.