'Besides adjusting the timing of the clock, bright light has another effect. It directly inhibits the release of melatonin. That is why melatonin is sometimes called the "Dracula of hormones" - it only comes out in the dark. Even if the pineal gland is switched "on" by the clock, it will not produce melatonin unless the person is in a dimly lit environment. In addition to sunlight, artificial indoor lighting can be bright enough to prevent the release of melatonin.
The amount of melatonin released at night varies among individuals, but it is somewhat related to age. Children on average secrete more melatonin than adults, which decreases further with age. However, research has shown that older people with sleep problems do not always have lower melatonin levels than people who experience normal sleep.(utk kterangan lanjut,sila click d'cni --> melatonin+breast cancer)