Set by the sun: An escape from electrical lights synchs our circadian clocks to the solar day

A weeklong wilderness escape from the electrical lights that illuminate most of our daily lives is enough to reset our internal circadian clocks to synchronize with sunrise and sunset, according to new research from the University of Colorado Boulder.

Eight hardy study participants spent a week camping in Colorado’s Eagles Nest Wilderness with just the blaze of the sun and the glow of a campfire for light. At the end of the trip researchers found that the campers’ biological nighttimes shifted to start when the sun went down and end when the sun came back up.

The shift happened for all the participants, even though some are night owls in their normal lives and others are early birds.


Electrical lighting, widely available beginning in the 1930s, has affected our internal circadian clocks, which tell our bodies when to prepare for sleep and when to prepare for wakefulness. The ability to flip a switch and flood a room with light allows humans to be exposed to light much later into the night than is possible naturally.

Even when people are exposed to electrical lights during daylight hours, the intensity of indoor lighting is much lower than sunlight and the color of electrical light also differs from natural light, which changes shade throughout the day.

To quantify the effects of electrical lighting, a research team led by Wright, and including undergraduate and doctoral students, monitored the study participants for one week as they went about their normal daily lives. The participants wore wrist monitors that recorded the intensity of light they were exposed to, the timing of that light, and their activity, allowing the researchers to infer when they were sleeping.


The same metrics were recorded during and after a second week when the participants—six men and two women with a mean age of 30—went camping in the Rocky Mountains. During the week, flashlights and personal electronic devices were not allowed.



“When people are living in the modern world—living in these constructed environments—we have the opportunity to have a lot of differences among individuals,” said Wright, who also is the director of CU-Boulder’s Sleep and Chronobiology Laboratory. “Some people are morning types and others like to stay up later. What we found is that natural light-dark cycles provide a strong signal that reduces the differences that we see among people—night owls and early birds—dramatically.”

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