Luminotherapy

A bright light shining in the direction of your eyes (you do not have to look at the light) for 30 minutes to 2 hours, depending on the intensity of the lamp and your distance from it, stops your production of melatonin, a neurohormone produced by the pineal gland. This neurohormone helps you feel sleepy at night. Some people feeling sleepy during the day still have too much of this neurohormone in their blood. The amount you have is in part piloted by the presence / absence of light and is supposed to go up at night and go way down in the morning. Luminotherapy and dawn simulation may help you get rid of too much melatonin.
Your circadian rhythm is influenced in part by the presence / absence of light. More light ==> less melatonin==>less sleepy.