For a long time, science has assumed that visual stimuli are processed through the two photosensitive sensory cells of the rods and cones. Only recently in 2002, Berson, Dunn, and Takao discovered a third photoreceptor whose strongest action potential is caused by light of bluish color. With this discovery, research in the effects of artificial light has increased enormously. The development of efficient LEDs, both white light LEDs and monochromatic LEDs, has also made a great contribution to science by broadening their possibilities.
This article provides a chronological overview of some studies and findings in the field of artificial light effects on humans.