During the darker winter months the function of the bodies circadian rhythm (24 hour body clock) can become disrupted by the lack of the gradually rising brightness that comes with dawn at the end of the night. The idea of an artificial sunrise was first patented in 1890 as a technique intended to help treat seasonal affective disorder, but can also be used as a soundless alarm clock timing lights in the bedroom to come on gradually over a period of 30~120 minutes causing the body to wake naturally.
When using a sunrise simulator light enters the body through the eyelids triggering the body to begin its wake-up cycle. This gradual wake-up cycle includes the release of cortisol, so that by the time the light is at full brightness, sleepers wake up on their own, without the need for an alarm. Some sunrise simulator lights also have a sunset simulation sequence which gradually dims the light at night and helps you go to sleep.