Abstract

This paper presents one of the first studies on degradation of retrofit lamps based on white GaN light emitting diodes. The results indicate that lifetime of LED lamps depends mostly on stability of driver and optical elements, rather than on degradation of LED chips, that have a constant output over stress time. By comparing lamps from four different manufacturers stressed at room and high temperature, we found that (i) long-term stress changes chromatic properties of lamps, which is attributed to degradation of phosphors or to the inner LED reflector; (ii) LED driver may degrade gradually and/or catastrophically, causing reduced output optical power, or complete failure; (iii) proper thermal management and heat dissipation reduce the degradation rate; (iv) spectral transmissivity measurements and visual inspection reveal the degradation of diffusive optical elements, which is induced by the short wavelength side of the LED emission spectrum.