Melatonin is a hormone that is a precursor to good sleep.  In most people, endogenous melatonin levels are highest during the normal hours of sleep, increasing rapidly in the late evening, then peaking after midnight and decreasing toward morning.”19

Functions of melatonin include: the synchronization of “circadian and circannual rhythms, that stimulate immune function, and, have recently been shown is a potent hydroxyl radical scavenger and antioxidant.”20

Melatonin release naturally increases in the late evening.  If we arrange our schedules so that we can go to bed in sync with this natural increase, we will maximize its release and the subsequent benefits.  On the other hand, if we keep the lights on and stay up in the evening, melatonin release will be reduced and it will be more difficult to enjoy quality sleep.