Thermal resistance analysis of high power light emitting diodes

Thermal characteristic of light emitting diodes is one of primary reliability parameters. In this paper, the thermal resistances of different kinds of blue and white high power LEDs are measured by the forward voltage based method. The relationships between thermal resistance and heat time at measurement currents 1mA, 5mA and 10mA are obtained respectively. The results show that there is optimum heat balance time of 300∼1200s to measure the thermal resistances at room temperature. The influence of current crowding, the phosphor and heat sink to the thermal resistance has been demonstrated.