• Publisher-DOI

The typical human indoor light environment strongly deviates from the natural light–dark cycle outdoors, both in terms of spectrum and amount of light exposure. The ubiquitous availability of electric light enables us to spend large parts of our day indoors, in conditions with limited, or sometimes even without, any natural daylight. Across daytime, we therefore expose ourselves to light conditions that are relatively dim, with daytime illuminances that frequently do not exceed civil twilight on a semi-overcast day, while during the evening and at nighttime the abundant use of electric light deprives us of natural darkness. Consequently, in our 24/7 society, we are exposed to dimmer days, brighter nights and lower day–night contrasts as compared to the natural light–dark cycle outdoors. This has negative consequences for our mental and physical health, sleep and performance.