An experimental and analytical investigation of the photo-thermal-electro characteristics of a high power InGaN LED module

The photo-thermal-electro characteristics of a high power InGaN LED module were studied both experimentally and theoretically. Three types of heat sink substrate composed of two layers of materials were used to investigate the coupled relationships between chip temperature, thermal resistance, input electric power and light emission efficiency. The results showed that the thermal spreading resistance accounts for a significant fraction of the total substrate thermal resistance. The measured thermal resistance of the LED module increased with rising electric power input. Luminescent efficacy measurements revealed that this increase of thermal resistance was the result of increased heat dissipation from the chip due to less efficient conversion of electric power to light output. Furthermore, experimental results showed that the radiant efficiency of the LED decreases with increasing input electric power. The coupled effects of chip temperature, input power and thermal resistance of the substrate are responsible for this efficiency droop. A revised model for estimating the luminous efficacy that takes both thermal and electrical effects into consideration is proposed. It is shown that the efficiency droop of the LED module for all three types of substrates can be clearly demonstrated by using the proposed analysis.