Decay of radiation pattern and spectrum of high-power LED modules in aging test

High-power light-emitting diodes (LEDs) modules encapsulated with different lens shapes after a thermal-aging test were studied experimentally and numerically. Samples from different manufacturers were aged at 65, 85, and 95degC under a constant driving current of 350 mA. The results showed that the optical power of the LED modules at the two view angles of plusmn (45deg~75deg) decreased more than the other view angles as the aging time increased. This was due to the reduction of radiation pattern from the corner effect of lens shape, resulted in lower output power. The simulation of the corner effect of lens shape is in good agreement with the experiment result. Results also showed that the center wavelength of the LED spectrum shift 5 nm after thermal aging 600 hours at 95degC because of degradation the lens material. The key module package related failure modes under thermal-aging may be due to the corner effect of lens shape and the degradation of the lens material. Therefore, improving the lens structure and lens material is essential to extend the operating life of the phosphor-based white LEDs modules.