Color Control System for RGB LED Light Sources Using Junction Temperature Measurement

The efficiency of LED lights is approaching that of fluorescent lamps. LED light sources are finding more applications than conventional light bulbs due to their compactness, lower heat dissipation, and most importantly, real-time color changing capability. Accurate control of colors for RGB LED lights is a challenging task, which includes optical color mixing, color light intensity control and color point maintenance due to LED junction temperature change and device aging. In this paper , we present a LED junction temperature measurement technique for a pulse width modulation (PWM) diode forward current controlled RGB LED lighting system. The technique can control the color effectively without the need for using expensive feedback systems involving light sensors. Performance of chromaticity and luminance stability for a temperature compensated RGB LED system will be presented.