Electricity is sapping our sleep.

Science Magazine examines our internal clock, and the power that sunlight has in saving us from being so tired of waking up tired:

Turning lights on at night can delay melatonin release and shift the timing of our internal clock, says sleep physiologist Derk-Jan Dijk of the University of Surrey in the United Kingdom, who was not involved in the work. But it wasn’t clear just what would happen in modern, electricity-adapted humans if all artificial light were suddenly taken away. “This is the first time that somebody has done the obvious but important experiment,” he says.

Wright and his colleagues outfitted eight subjects with activity-tracking watches that carry light intensity detectors and motion sensors to keep tabs on sleep and wake times. For the first week, the participants went about their lives, spent mostly in artificially lit buildings. They then spent 24 hours in a lab, where the researchers periodically tested the melatonin levels in their saliva. In the second week, the group went camping in the Colorado Rockies, where they could sleep and wake up whenever they wanted but had no access to TV, cell phones, or even flashlights. Their world was illuminated only by sunlight and campfires. The group returned from their excursion for another stint of saliva sampling.

Data from the watches showed that subjects got about the same amount of sleep in the two settings. But the shift from artificial to natural light, which nearly quadrupled their total light exposure, also tinkered with their internal clocks. After camping, the subject’s biological cycles had shifted to align with the sun. Their bodies released melatonin right at sunset—2 hours earlier than under artificial light conditions—and shut it off again just after sunrise, the team reports online today in Current Biology.