title: Analysis of junction temperature and modification of luminous flux degradation for white LEDs in a thermal accelerated reliability test.
abstract: An accelerated aging test is the main method in evaluation of the reliability of light-emitting diodes (LEDs), and the first goal of this study is to investigate how the junction temperature (Tj) of the LED varies during accelerated aging. The Tj measured by the forward voltage method shows an upward trend over the aging time, which gives a variation about 6°C-8°C after 3,000 h of aging under an ambient temperature of 80°C. The second goal is to investigate how the variation of Tj affects the lifetime estimation. It is verified that at a certain aging stage, as Tj increases, the normalized luminous flux linearly decreases with variation rate of microns (μ) (1/°C). Then, we propose a method to modify the luminous flux degradation with the Tj and μ to meet the requirements of a constant degradation rate in the data fitting. The experimental results show that with the proposed method, the accelerated lifetimes of samples are bigger than that of the current method with increment values from 8.8% to 21.4% in this research.
authors: Hong-Liang
authors: HL
authors: Ke
authors: Lei
authors: L
authors: Jing
authors: Jian
authors: J
authors: Hao
authors: Qun
authors: Q
authors: Gao
authors: Yao
authors: Y
authors: Wang
authors: Xiao-Xun
authors: XX
authors: Wang
authors: Qiang
authors: Q
authors: Sun
authors: Zhi-Jun
authors: ZJ
authors: Xu