Circadian rhythm
Exposure to light during traditional sleeping hours are documented to cause disruptions in the circadian rhythm that regulate human sleep cycles. Biologists have noted a decrease in the amount of melatonin, a natural hormone that regulates the Circadian rhythm, in humans that are exposed to light pollution of the night sky. In order to prevent major impact, biologists suggest increasing the amount of natural light exposure during the day and decreasing the amount of electrical light consumed at night.