Study of humidity reliability of high power LEDs

High power Light-emitting Diode (LED) as Solid-state Lighting (SSL) is a promising light source, and one of the crucial factors for its wide acceptance is its reliability. However, humidity reliability study of the high power LED reliability is rare despite that they are also susceptible to high humidity environments in many of their applications. In this work, we present the various humidity reliability of the high power LEDs, and we found that there are several failure mechanisms that render LED failure under humid conditions. These mechanisms do not cause a sudden black out of the LED, and the mechanisms that cause a continuous degradation of the lumen output are also changing with time. Furthermore, the mechanisms are distinctly different from that for integrated circuit (ICs), and thus the humidity models used for the extrapolation of the lifetime of IC under different humid condition cannot be applied to the high power LEDs, and new model that also account for the changing failure mechanisms must be developed if the time to failure of LED under humid condition is to be predicted as an important reliability index for the LEDs.