Light influences humans at all levels – it sets our circadian clock, controls our hormones, sleep, mood, and adapts brain-body physiology to the natural day-night cycles. However, nowadays, in modern societies, with abundant use of artificial light at night, human completely disregards the natural light/dark cycles. We stay awake later and later. This means that we are active late, we eat late, and also we sleep less. The reciprocal aspect, insufficient light during the day, is generally overlooked but is also very problematic; we spend nearly 90% of the day indoor, under low intensity, artificial light.
There is now mounting evidence that this untimely, either excessive or insufficient, and nearly continuous exposure to artificial light is a major factor in sleep and circadian rhythm disruption and has deleterious consequences on health; from acute, temporary impairments to major chronic diseases like metabolic syndrome or depression.
Left: Multi-electrode array recording of light responses in the retina. Right: Immunostaining against Melanospsin, the photopigment expressed by ipRGCs.