Study on the effect of the relative position of the phosphor layer in the LED package on the high power LED lifetime

For the case of the white LED (phosphor converted), the temperature affects phosphor in addition to chip and package. The heat can cause the decrease of the phosphor performance as well as the irreversible damage to the phosphor. In this study, the effect of phosphor thermal configuration on the degradation rate has been investigated experimentally and verified by the theoretical simulations. Two different configurations have been tested. One is die-contact phosphor layer and the other is remote case. The experimental result shows that the LEDs of the die-contact phosphor layers exhibit lower degradation rate than those of the remote phosphor layers. The thermal simulation considering the heat generation from the phosphor (energy converting loss) shows similar results. The temperature of remote phosphor layer is higher than the die-contact case. High temperature causes rapid degradation of phosphor. As the power consumption of LEDs increases, the heat generation from the phosphor becomes no more negligible. For the higher performance and longer lifetime, we have to consider phosphor layer as the heat generator and design the layer with sufficient thermal paths. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)