Shane P. Robinson

Polychromatic optical feedback control, stability, and dimming

The use of RGB and RGBA LEDs in luminaires enables a variety of features, such as color temperature-controllable white light, that have not been available in traditional sources. The general illumination market requires that lamp chromaticity be accurately maintained, and therefore an advanced control scheme must be used. Feeding back tristimulus values alone is not enough to maintain precise color control, given the variability of LEDs during changes in ambient temperature, degradation over life, and manufacturing tolerances. In this paper, we discuss a solution based on photodiodes with color filters combined with feedforward temperature compensation and empirical LED data. We also discuss a method to maintain control feedback loop stability and accuracy over the full dimming range.