Useful lifetime analysis for high-power white LEDs

Keywords: Accelerated degradation test HPWLED Useful lifetime Bi-exponential model Degradation-data-driven method. a b s t r a c t 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 L 70 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 L 70 should be fitted to a bi-exponential extrapolation model and two-staged method. Lighting systems play a significant role in life, affecting visual conditions, comfort, health, well-being, and work performance [1–3]. Light-emitting diodes (LEDs) were developed in 1993 and have been continuously improved. LEDs have attracted increasing interest in the field of lighting systems owing to their having superior characteristics to conventional light sources in terms of guaranteed longer lifetime, lower power consumption, higher brightness and being less harmful [4]. These merits of LEDs forced them to be used for high-power applications, such as general lighting , back lighting (small to large size), strobe lighting (cell phones and cameras), automotive, and large outdoor displays [5]. In recent years, LEDs have been increasingly used in display back lighting, communications, medical services, signage, and general illumination [6–9] due to their small exterior outline dimensions, often less than 10 mm  10 mm. LEDs, when designed properly, offer higher energy efficiency that results in lower power consumption (energy savings) with low voltage (generally less than 4 volts) and low current operation (usually less than 700 mA). LEDs can have a longer lifetime (50,000–100,000 h) [10] with better thermal management than conventional lighting sources (e.g., fluorescent lamps and incandescent lamps). LEDs provide high performance, such as ultra-high-speed response time (microsecond-level on–off switching), a wider range …