2011 Volume 35 Issue 3 Pages 255-266
Digitally controlled lighting systems equipped with colored LEDs can produce a range of different qualities of light, adjustable to users' requirements. In this context, we explore a lighting control concept which involves strategic control of RYGB LEDs forming white light, employed to increase energy efficiency. There is a fundamental trade-off between color rendering (CR) and luminous efficacy. Specifically, we can reduce CR and increase efficacy when we redistribute spectral energy intensity in favor of wavelengths where the eye response is greatest, the yellow/green region of the spectrum. The notable point is that while changing CR, the light level and color temperature can stay constant, and hence the appearance of the modified white light remains unchanged. The strategy is to bring the lighting of unoccupied spaces to minimum color rendering to save energy without altering the appearance or light levels of the illumination, when the LED system dynamically shifts to 'energy saving mode' (low CR) from 'quality mode' (high CR) according to occupancy. This paper reports and discusses the results of an ongoing research project involving the exercise of LED color mixing re-working the spectrum of white light according to this fundamental energy vs. rendering trade-off. The research work encompasses two main domains: (a) a tunable LED light source with accompanying control equipment; and (b) human factors studies concerning how surfaces and spaces are perceived under a light source with changing spectral components. Results so far have supported the two fundamental hypotheses: (a) when fully developed, color rendering modulation could potentially enable significant power reductions; (b) the majority of subjects did not detect the color rendering changes.