Accelerated aging test and failure analysis of high brightness light emitting diodes

The degradation of high power white and blue light-emitting diodes (LEDs) was investigated by considering the electrical, optical and phosphor conversion. The LED samples were tested at the elevated temperature of 40°C with 700mA, 900mA, 1200mA. In order to research the degradation rule of fluorescent power in white LED, aging studies using white and blue LEDs with same batch of chips under same invariableness current and same conditions were performed. It has indicated that from blue light to yellow light the transition rate reduced by following the rule of exponential function. And it reduced faster when the electrical current was higher. The yellowing of the optical lens and structural degradations, such as phosphor carbonization in high temperature, causes the light output attenuation. Meanwhile, the relationship and interplay of electrical, optical and phosphor characteristics were found in experiments.