http://www.livescience.com/12891-natural-sleep.html http://www.livescience.com/12891-natural-sleep.html http://www.livescience.com/12891-natural-sleep.html changing people’s sleep patterns exposure to natural light http://www.livescience.com/12891-natural-sleep.... http://www.livescience.com/12891-natural-sleep.html http://www.livescience.com/12891-natural-sleep.html exposure to natural light biphasic sleep http://www.livescience.com/12891-natural-sleep.html