Humans evolved spending bright days outdoors and nights in relative darkness. Our physiological systems have functioned for millennia around this distinct daily cycle. But now we spend most of the time indoors, with artificial light enabling varying degrees of light at any time of day or night. We're well adapted psychologically to artificial light, harnessing it to elongate our days and to enhance convenience, productivity, and entertainment. But it comes at some cost to human health and wellbeing.  

This white paper is part 1 of 3, taking a deep dive into the science of photobiology as the basis for why humancentric lighting is so important. Topics include the composition of light, how light affects human physiology, and the developing standards for how to optimize light at different times of day and night.