Lifetime predictions of LED-based light bars by accelerated degradation test

The accelerated degradation of light bars was tested under different stresses called junction temperatures, which result from the combination of current and ambient temperature. Light bars are used as a light source in laptops. A general procedure for an accelerated degradation test was used to analyze the useful lifetime of light bars under operating conditions. The degradation behavior for each light bar was fitted by an exponential function. The impact of parameter variations and measurement errors were also considered. The failure criterion was defined as the 50% decrease of the emitted optical power, when compared with the initial level. The failure time is, accordingly, the time required to achieve that failure criterion. A response model based on an inverse power (exponential) law for the failure time under different stresses was then calculated to predict the lifetime under operating conditions. The results show that the failure time of a light bar under operating conditions is about 11,571 h.