Design of power cycling for reliability testing of LED systems: Numerical and analytical approach

Power cycling tests are often used for the development of lifetime models for LED devices, where the number of cycles to failure defines their performance. In this work, we take a closer look at the thermal transients of the devices during testing and their temperature accumulation, as they are the driving forces for LED's aging behavior. Measurements have been performed and compared against analytical and numerical calculations. It is shown that setting up a three-dimensional numerical model is a cost and time-intensive method. It helps to understand the heat penetration at different times and hence also to visualize which materials in the LED experience thermal stresses at certain power cycle conditions. However, for predicting the average temperature and the temperature response during cycling, the analytical calculation is superior in terms of computation time and accuracy. These values can be used as input parameters for lifetime estimations and furthermore as refinements of the lifetime model.