Achim Hilgers

Control of LEDs

There is a strong interest in using LEDs for general illumination due to the potential they offer for energy saving, environmental friendliness, new opportunities in lighting design, and control of the intensity, color, and spatial distribution of light. General illumination requires primarily white light that can be obtained by mixing e.g. the light of red, green, and blue LEDs. This enables also color adjustability, which is considered to be a most attractive feature of future LED lamps. There is common consent that when using color mixing some kind of feedback control must be applied in order to meet color accuracy requirements. In this paper color control concepts are briefly reviewed and control of a lamp with more than 4 primary LED colors is reduced to the known control of 3 primary LED colors. Measurements are provided for the temperature dependence of LED and color sensor characteristics. Color control implementation is outlined using a laboratory setup based on a rapid color control prototyping system which uses commercially available software and digital hardware amended by custom in-house developed hardware. The rapid control prototyping system is applied to control the color of an experimental RGB LED lamp