Wide-Range, Open-Loop, CCT and Illuminance Control of an LED Lamp Using Two-Component Color Blending

This paper proposes a wide-range control scheme of correlated color temperature (CCT) and illuminance of a light-emitting diode (LED) lamp, using two-component color blending. A simple control algorithm is implemented by using Grassmann's law of color mixing and McCamy's formula of CCT. Light from a white LED source is blended with that from a blue LED or a red LED to get, respectively, a CCT value higher or lower than that of the white CCT. The prototype LED lighting system can independently produce a variable CCT ranging from 2500 to 12500 K and a variable illuminance ranging from 5 to 120 lx. The algorithm is experimentally validated by hardware implementation. An empirical model to estimate the luminous parameters of the individual LED is also implemented. Experimental results show that although the system is an open-loop one, it is quite accurate with respect to set point CCT and illuminance. Despite acceptable performance in respect of these two quantities, a large deviation from the color of an ideal black body radiator is noticeable in a part of the CCT range, and a remedy of the problem has been suggested.