Influence of optical power calculation on LED thermal resistance test

Thermal resistance is an important parameter to measure the performance of LED. In the LED thermal resistance test, the electrical energy not only into heat energy, there are 20% or more energy into light energy. At present, most of the thermal resistance testers are not specifically designed for testing LED, and the standard for calculating the optical power is not uniform. In this paper, the optical power and thermal resistance of different packages 1W dress chip LED, the flip and dress chip structure LED with the same package and output power were investigated under different temperatures and currents by the electrical test method. Results show that the LED's different dissipation capability due to different package, resulting in the optical power of different. Flip chip LED optical power with the same package conditions and output power was significantly higher than that of formal structure. Under the same environmental temperature and output power, the thermal resistance Rth of the calculated optical power is not equivalent to the thermal resistance Rth' for calculating the optical power, Rth can not reflect the true thermal resistance of LED, Therefore, the optical power should be calculated in LED thermal resistance testing.