Useful lifetime analysis for high-power white LEDs

• The degradation-data-driven method is used to analyze the lifetime of HPWLEDs.
• We present a bi-exponential model to improve the fit accuracy for the data.
• The two-stage method provides the highest ability to explain variation.
• A response model was used to predict the useful lifetime.

An accelerated degradation test is used to analyze the useful lifetime of high-power white light-emitting diodes (HPWLEDs) as the point at which the light output declines to 70% of the initial flux in lumens, called L70 In this study, the degradation-data-driven method (DDDM), including the approximation method, the analytical method, and the two-staged method, is used to analyze the useful lifetime of HPWLEDs. A response model based on an inverse power (exponential) law under different stresses is used to predict the useful lifetime under operating conditions. However, the degradation model for each HPWLED is usually fitted to an exponential function. In order to improve the fit accuracy, we present a bi-exponential model for the degradation curve of HPWLEDs. The estimation of the model parameters are easily obtained by using the nonlinear least square method. Through numerical examples, the results show that the bi-exponential model performs better than the exponential model based on the two-staged method. The extrapolation algorithm for L70 should be fitted to a bi-exponential extrapolation model and two-staged method.