This is probably the most important factor discussed in the concept of sleep therapy. The amount of sunlight that enters your eyes has a great impact on your sleep rhythm.
* Exposure to high intensity light increases our body temperature. Rise in our body temperature decreases out melatonin levels.
* When exposed to natural sunlight, our body delays the temperature drop, thus allowing us to be awake and aware for longer times.
* Lack of enough natural sunlight results in more melatonin level leading to lower temperature levels, sleepiness and tiredness.
Lack of sunlight will create a flat-line effect in your body temperature, because it will not get a chance to rise high enough, your body temperature won't fall low enough during the night either. If your body temperature is flat-lined, this could cause major sleeping problems, and it will be very difficult for you to sleep deeply for long periods of time. A lot of people who complain about “poor sleep” usually don't get enough sunlight.
Consider how for the most part of our evolution we were always outside during the day, it seemed that nature intended us to be this way, then suddenly over the past 100 years we drastically changed our exposure to natural sunlight. Most of us hardly get any sun today at all! We drive to work in a car, we wear sunglasses, we work in offices, what kind of effect do you think this has on our sleep clock?