Developing a standard measurement and calculation procedure for high brightness LED junction temperature

Abstract

White light emitting diodes (LEDs) are appearing in general illumination applications. Clusters of such LEDs can replace an incandescent light bulb of equal luminosity on the merit of considerably low power consumption. However the optical performance and working life of these LED packages are strongly dependent on the temperature of the p-n junction of the LED. Hence it is very critical to determine the temperature of the junction. Three methods - forward voltage change, peak wavelength shift and infrared thermal imaging are employed to determine the junction temperature. Forward voltage change method is found to be the most accurate method (± 3 °C) for an optimized set of parameters. Analytical model is proposed for the thermal transient behavior of the LED junction and the predictions are compared with experimental results. A good agreement is observed between that of two experimental methods. Thermal resistance of the LED package is estimated analytically and experimentally. Experimental values show a larger variation than expected through material property variation.