What role do light and darkness play in regulating sleep?
Light activates special receptor cells at the back of the eye (retina), which in turn affect the suprachiasmatic nucleus. This has link to other parts of the brain that regulate sleep and wakefulness, including the pineal gland, which produces melatonin. Exposure to light increase wakefulness while darkness has the opposite effect. Light is thus important to the regulation of sleep and wakefulness and helps our circadian rhythm on track. Light is an effective cue for wakefulness in all humans, except those who lack light receptors in the eyes (certain forms of profound blindness).
