Aging tendencies of power leds under different humidity conditions during thermal reliability testing

The standard LED characterization methods do not consider changes in relative humidity of the test environment. This paper describes the effects of a high relative humidity drop on the measured light output of undomed test LED samples. The related investigation is carried out in controlled ambient conditions. Spectra of the test LED samples and of a reference light source were captured in discrete relative humidity steps. The relative humidity dependence is identified for both the light output of the undomed LED samples and for the reflectance of the optical measurement system itself. 2-2.5% of change is found in the optical parameters in the 35-80% and 35-100% ranges of relative humidity.