The same thing that keeps us safe on the street may be bad for us in the bedroom. Scientists say light pollution from outdoor lighting can leak into our bedrooms, messing with our sleep patterns. These findings from a recently released study will be presented at the annual meeting of the American Academy of Neurology next month.

Human beings have been around for millions of years, but we’ve only had electric light for less than two centuries. Our brains are still wired to equate light with wakefulness and darkness with sleep, but these days when the sun goes down, the lights come on, both indoors and out.

"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," study author Maurice Ohayon said in a press release. "The concern is that we have reduced our exposure to darkness and it could be affecting our sleep."

Ohayon and his colleagues collected data via phone survey of 15,863 people over the course of eight years. They asked participants about their medical histories, sleep habits, and sleep quality, as well as where they lived. Their addresses were then compared with nighttime data from the Defense Meteorological Satellite Program, which allowed the researchers to measure light pollution near each participant’s home.

They found that people living in large cities were exposed to three to six times more light pollution than people in small towns and rural areas. Sure enough, urban participants reported 2 percent more fatigue and 10 minutes less sleep per night than those living in areas with less light pollution. They were 6 percent more likely to get less than six hours of sleep per night, and 13 percent more likely to be dissatisfied with their sleep. They were also 6 percent more likely to wake up confused in the middle of the night, and were 4 percent more affected by daytime sleepiness and impaired functioning.

But city dwellers shouldn't start packing up just yet. All of these percentage differences are pretty small. There’s also no evidence of causality. It may be that the sleep of city-dwellers is disrupted for other reasons: noise, for example. Still, the researchers believe their hypothesis is sound.

"Light pollution can be found in any sizable city in the world," Ohayon said in the press release. "Yet, excessive exposure to light at night may affect how we function during the day and increase the risks of excessive sleepiness. 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."