A Low-Cost, Wide-Range, CCT-Tunable, Variable-Illuminance LED Lighting System

This article proposes a cost-effective, wide-range, open-loop, and decoupled control scheme of correlated color temperature (CCT) and illuminance of a light emitting diode (LED) lamp, based on two-component color blending. Light from a phosphor-converted white LED source is blended with that from a blue/cyan LED or a red/amber LED to get a CCT value higher or lower than that of the phosphor-converted white LED CCT. Based on Grassmann's law of color mixing and McCamy's formula of CCT, a simple control algorithm has been implemented to manipulate the duty cycles for driving two different LED strings in pulse-width modulation (PWM) mode. The prototype lighting system has the capability to independently produce a flexible CCT ranging from 2500 K to 12,500 K and a flexible illuminance ranging from 1 lx to 100 lx at a distance of 1 m. The algorithm is experimentally validated by hardware implementation. Experimental results show that although the system is an open-loop one, it is quite accurate with respect to set point CCT and illuminance. In this two-component color blending process, mixing is possible on a straight chromatic line. A deviation from the ideal black-body radiator (i.e., increase in D-uv) may be noticeable based upon the two selected LEDs' color coordinates. This kind of dynamic LED lighting system can be used in diverse applications like road lighting, mood lighting, human photobiology research, museum lighting, etc.