Darkness in a room is the basis of a proper sleep. The hormone melatonin is responsible for sound sleep, it is produced by the endocrine gland by the pineal gland and sends signals to the brain that it is time to relax. Melatonin levels naturally rise every night after dark. Thanks to melatonin, our muscles relax, the feeling of drowsiness intensifies, and the body temperature decreases slightly. The peak production of melatonin occurs at three in the morning, then its level begins to fall and remains at a low level all daylight hours.
Evening exposure to light prevents melatonin from being produced in the right amount. If the light is on in your room before bedtime, then melatonin will be produced ninety minutes less than than when the lights are off in the evening. Due to the low level of melatonin, there are problems with falling asleep and shallow sleep during the night. In addition to feeling overwhelmed the next morning, sleep with light sources can provoke a increase in insulin , increase the risk of depression and even set excess weight.