Recent studies indicate that it may also be the central regulator of the hormonal component of the aging process. It is likely that this is only partly true. The pineal gland receives information from the optic nerve about the ambient light level and adjusts its melatonin output accordingly.
Bright light suppresses the output of melatonin.
Ordinary indoor lighting does not. After sunset, the pineal gland responds to the decreased light levels by greatly increasing its output of melatonin. After a few hours, blood melatonin levels reach a point where sleep is induced. Melatonin levels usually peak two to four hours after the onset of sleep and decrease gradually during the remaining sleep period. Daylight inhibits the production of melatonin, and levels of melatonin usually reach a minimum sometime during the afternoon.