Can’t sleep? Street lights may be keeping you awake

"Our world has become a 24/7 society. We use outdoor lighting, such a street lights, to be more active at night and to increase our safety and security," said study author Maurice Ohayon, MD, DSC, PhD, of Stanford University in Stanford, Calif. "The concern is that we have reduced our exposure to darkness and it could be affecting our sleep."

For the study, 15,863 people were interviewed by phone over an eight-year period. They were asked about sleep habits, quality of sleep as well as medical and psychiatric disorders. Then, with nighttime data from the Defense Meteorological Satellite Program, the researchers looked at how much outdoor light those people were exposed to at night. People living in urban areas of 500,000 people or more were exposed to nighttime lights that were three to six times more intense than people living in small towns and rural areas.

The study shows that nighttime light affects sleep duration and was significantly associated with sleep disturbances. People living in more intense light areas were six percent more likely to sleep less than six hours per night than people in less intense light areas. People living in more intense light areas were more likely to be dissatisfied with their sleep quantity or quality than people in less intense light areas, with 29 percent dissatisfied compared to 16 percent.

People with high light exposure were also more likely to report fatigue than those with low light exposure, with 9 percent compared to 7 percent. People with high light exposure also slept less per night than those with low light exposure, with an average of 412 minutes per night compared to 402 minutes per night.

In addition, people with high light exposure were more likely to wake up confused during the night than people with low light exposure, with 19 percent experiencing this compared to 13 percent. They were also more likely to have excessive sleepiness and impaired functioning, at 6 percent compared to 2 percent.

"Light pollution can be found in any sizable city in the world. Yet, excessive exposure to light at night may affect how we function during the day and increase the risks of excessive sleepiness," said Ohayon. "If this association is confirmed by other studies, people may want to consider room darkening shades, sleep masks or other options to reduce their exposure."

The study was supported by the John Arrillaga Foundation, the Peter Bing Foundation and the Philip Stein Foundation.