Effects and exploitation of tunable white light for circadian rhythm and human-centric lighting

After an introduction on the effects of light on human wellness, circadian rhythm and perception of objects with this work we propose an innovative white LED lighting system able to smoothly change CCT (Correlated Color Temperature) while sensibly changing the spectral power density in the blue region (460–480 nm). Designing methodology, photometrical, electrical, optical and thermal results will be discussed. The proposed tunable white LED system is able to achieve high CRI (Color Rendering Index) (above 90) in a large CCT range (2800 – 5500 K), thus allowing a high comfort light in different conditions. Results from thermal design indicate a maximum junction temperature of 85°C at 700 mA, with an equivalent thermal resistance junction to ambient of 1.6 K/W for the series of LEDs used in the light engine. The optical emission has been designed by means of a color mixing chamber and a parabolic reflector thus achieving a good color uniformity at different emission angles and 18° beam divergence. The Light engine is engineered to be efficient (above 85 lm/W) and cost effective while working with a standard commercially available constant current LED driver. The specific control gear can be programmed to control the intensity and CCT of several lamps connected together.