You might not have yet heard the phrase "human-centric lighting" (HCL). But it's one of the oldest concepts under the Sun. Ever since humankind first yawned and stretched at dawn, and lay down to sleep at night, a 24-hour pattern of natural light that changes throughout the day and gives way to darkness has paced and conditioned our movements. Some 2.5 million years of the genus Homo's wakefulness under the blue-enriched wavelengths of daytime, and of tiredness in the reds and ambers of dusk, have conditioned the human circadian rhythm so that blues stimulate; reds, ambers, and darkness relax.
Yet in 120 or so years of artificial, electric lighting, manufacturers of lamps and luminaires have paid little attention to its color. The industry has existed for one main function: to illuminate. It has given little thought to how it might alter patterns of illumination and change wavelengths and colors to suit humans' daily cycle. While architects have paid homage , the lighting industry has largely ignored it. But that is all beginning to change.