How does the SCN know when it time to be awake or asleep?The SCN is very responsive to light changes and take its cue from your eyes. When your eyes transmit light information to the SCN, they are in essence telling it whether it is light or dark inside. The light information helps the SCN direct the release of melatonin, the hormone that facilitates sleep. Melatonin regulates your circadian rhythm and help you get to sleep. As darkness increases, so does the production of melatonin in your body. For this reason, it is called the “Dracula hormone” because it come out at night.