Method for in-situ thermal load testing of high-brightness LED arrays

Frequently the direct assessment of the LEDs´ junction temperature as one of the main parameters to evaluate the extent of the thermal load is possible only under laboratory conditions. In this paper we present the development of a cheap and reliable experimental method to establish the junction temperature of high-brightness LED arrays under operating conditions. It is based on the in-situ determination of the temperature dependence of the LEDs´ forward voltage drop. Three different types of high-flux LED arrays are investigated (nominal forward voltage between 18 and 45 V) at various ambient conditions (air temperatures from 20°C to 45°C) and values of forward current ranging from 270 mA to 720 mA. Recommendations on calibration, calculation and junctions´ temperatures evaluation are presented. The developed method also allows to achieve reliable results of the in situ thermal performance of the entire lamps consisting of high-flux LED arrays mounted on a cooler.