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.