Darkness is needed for a good night's sleep. And the more darkness, the better. If you are having trouble sleeping and your bedroom is not totally dark when you try to sleep, you should take steps to eliminate or, at least, reduce the light.
Sleeping in complete darkness is important to getting a good night's sleep because darkness or night increases the production of melatonin. Melatonin is a hormone produced by the pineal gland in the brain and controls the bodys sleeping cycle. Melatonin is believed to cause a person to fall asleep faster and sleep better.
If you are exposed to light while you are trying to sleep, melatonin may not rise to high enough levels to do its job. Light coming in from the window, light entering from another room, or even a night light can disrupt the production of melatonin. In other words, if you want the best opportunity to fall asleep quickly and sleep soundly, you must have darkness.
A lack of darkness at night has even been linked to an increased risk in cancer for women.