An astronaut's view of urban lights glowing over Spain and Portugal. NASA

They’re “significantly associated with sleep disturbances,” say researchers.

The next time you’re tossing and turning at 2 a.m., it might not be because of work stress or that afternoon coffee. Street lights outside your window could be affecting your sleep, leading to fatigue and even bouts of late-night disorientation, according to new research.

Maurice Ohayon, who heads up Stanford’s Sleep Epidemiology Research Center, queried nearly 16,000 people over eight years on their nocturnal habits and quality of sleep. His team then looked at satellite images from the Defense Meteorological Satellite Program to determine who lived near cities with more than 500,000 residents—areas where the illumination is up to six times brighter than towns and rural plats, they say.

What they found is a purported link between beaming lights and sleep disturbances. Here’s more from an American Academy of Neurology press release:

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.

Folks in light-washed neighborhoods were also 6 percent more likely to be jolted awake with no idea what’s happening—something the researchers call waking up “confused.” And they were reportedly 4 percent more likely to suffer from tiredness and mental impairment the next day.

There’s no mention of other potential sleep-disrupting sources in the urban environment, such as traffic or noisy apartment neighbors. Still, Ohayon and his crew suggest one easy way to sleep better is kill the lights, whether by blackout curtains, blindfolds, or hacking an annoying street light with a laser so it turns off. (All right, they didn’t say that last one, and you certainly shouldn’t do it, but here’s a tutorial for informational purposes only.)

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