Experimental analysis of LEDs´reliability under combined stress conditions

There are many practical situations in which the reliability of a device cannot be correctly predicted by considering only a single stress. In these cases, the use of a more complicated life model working with multi-stress is needed: in practice, taking into account two stresses provides good results in several real applications. In this paper, the problem of deriving a life model for LEDs that can be usefully employed in actual operating conditions is faced. The combination of thermal stress and forward current is considered and a test system used to carry out an exhaustive measurement campaign is presented. The results of some experiments are also presented and discussed.