Light surrounds us throughout every part of every day. Even when night falls, and we prepare to bed down and hit the hay, some form of light weaves its way through the atmosphere. Different types of light exist, and perform different functions for the surrounding environment. Some forms of light keep our circadian rhythm in check, ensuring that we can awaken and fall asleep at appropriate times of the day. Other forms of light provide us with certain types of vitamins that only our skin can properly absorb. Still, others cause some negative health effects, including cancer or insomnia.