You may already know the importance of shutting off lights and powering down devices if you want deep, uninterrupted sleep. But what you may not know is that the light outside your home could be just as bad for your rest.
The streetlights that are so helpful when you're walking along a dark road at night can disrupt your sleep patterns, according to a study released this week from the American Academy of Neurology.
"We live in a 24/7 society, and outdoor lighting helps us be safer at night, but it comes with a tradeoff," Dr. Maurice Ohayon, a Stanford University sleep scientist who authored the study, told The Huffington Post. "That fact that we encounter less darkness as we go about our day may be affecting our sleep."
Researchers interviewed more than 15,000 people over the course of eight years about their sleep quality and bedtime habits, then cross-referenced participants' reports with data from the Defense Meteorological Satellite Program to determine how much outdoor light they were exposed to at night.
The nighttime environment of people in urban areas was three to six times brighter than that of people in small towns and rural areas, scientists found. And residents of bright areas were more likely than those in low-light areas to sleep less than six hours per night, be dissatisfied with their rest and report fatigue.
Light is the most powerful cue for our circadian clocks, our roughly 24-hour sleep-wake cycles, according to Harvard University neuroscientist Anne-Marie Chang. Its presence suppresses the hormone melatonin, which induces sleep.
The worst offenders, according to Ohayon, are the new generation of LED streetlights. They give off a bluish light and are brighter than traditional sodium-vapor streetlights, which have an orange tint.
"The blue light emanated by the streetlights in most big cities provides more safety because it's like daylight, and allows people to see more clearly at night," Ohayon said. "But it is uniquely disruptive to human sleep."
Research, including a 2014 study on eReaders and sleep, has shown that blue light has a greater effect on circadian rhythms and melatonin suppression than naturally occurring light, which has a longer wavelength.
LED streetlights have become steadily more prevalent in major cities. New York City's 250,000 streetlights, for instance, are expected to be replaced by LEDs within the next year.
Ohayon said ambient blue light from modern street lights is basically as bad for your sleep as having screens and gadgets in the bedroom.
"We spend our lives in a bath of artificial light," he said.
So what's an urbanite to do, short of moving to a farm?
Oyahon recommended using blackout shades or sleep masks in the bedroom and limiting LED light exposure from cell phones and computers near bedtime.
This isn't new advice, and it may seem easier said than done, but Ohayon acknowledged that unnatural environments call for the extra effort.
"Darkness in the bedroom must be commanded," he said.