System-Level Lifetime Prediction for LED Lighting Applications Considering Thermal Coupling Between LED Sources and Drivers

An accurate lifetime prediction method of light-emitting diode (LED) lighting systems is important to guide designers to fulfill design specifications and to benchmark cost-competitiveness of different lighting technologies. Currently, the lifetime of an LED system is typically predicted from the source and driver separately, and then the thermal design is also optimized independently. In practice, LED sources and drivers are usually compacted in a single fixture. The heat dissipated from LED sources and drivers are coupled and further affect heat transfer performances, which may degrade the whole system and accelerate the failure. In this paper, a thermal model concerning thermal coupling is proposed with the finite-element method (FEM) simulation to acquire key parameters in the thermal path. The proposed model shows a better estimation of thermal stresses of key components in the LED system, and therefore an improved lifetime prediction method for the LED system is proposed. Moreover, with a given lifetime requirement, this method can be used to guide the thermal design of LED systems. A case study of an outdoor lighting application is demonstrated by both FEM simulation and experimental verification.