Holiday lights are getting brighter—and messing with our sleep
Researchers say that choosing better bulbs and being intentional about where you place them can make a real difference.
It was just after 7 p.m. on December 6, long after darkness had settled over north Seattle. But on Candy Cane Lane everything was quite merry and bright. The University of Washington marching band filled the street with “Feliz Navidad,” the brass instruments coiled with golden strings of light. Dogs with LED collars wove between stroller wheels. A towering inflatable Grinch nodded in the breeze beside a brick home traced by a single strand of multicolored lights.
For more than 70 years, residents of Northeast Park Road have illuminated the darkest weeks of winter with intention, but not with the same Clark Griswold-level exuberance that you see elsewhere in the city and around the U.S. They lean into original décor, including a historic wooden carousel and a fleet of six-foot-tall stovepipe candy canes. And they keep their illumination modest and timed, generally choosing warm bulbs and shielded lighting to limit spillover on neighbors, garden plants, migrating birds—and anyone trying to sleep.
That kind of restraint is increasingly rare. Satellite images show some communities shine up to 50 percent brighter during the holidays, adding to a global baseline of light pollution already increasing by as much as 10 percent each year. The rise of inexpensive, energy-efficient LEDs has made it easier than ever to bathe winter nights in light. Just across town from Candy Cane Lane, one home now boasts more than 250,000 bulbs. That extra glow spills through neighborhoods and ecosystems.
(Want to help wildlife? Turn off your lights.)
“It’s fun to see these lights. That itself likely has positive health effects,” says Phyllis Zee, a circadian and sleep medicine doctor at Northwestern University. “But we can also be mindful and decrease the potentially harmful effects.”
All life evolved with bright days and dark nights. Humans are wired for only dim, amber light after sunset. The glare of modern LEDs—brighter and bluer than moonlight or fire—sends a conflicting signal, suppressing melatonin and keeping the brain on alert. Low levels of ambient light—equivalent to streetlight glow through a bedroom window or a hallway light—can be enough to trigger that response. Even those who sleep through the glow may experience effects. “Cortisol levels are elevated. Heart rate is elevated,” says Zee. “It’s as if your body senses something unusual in your environment and is ready to get up at any time.”
Exposure to light at night has been linked with higher risks of depression, diabetes, and obesity. A study published in late October found that people exposed to greater light at night faced significantly higher risks of heart attack, stroke, heart failure, and atrial fibrillation, even after accounting for factors like sleep duration.
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Winter makes matters worse. Snow and clouds amplify nighttime brightness, while shorter, dimmer days mean less exposure to the strong daylight cues that help set the body’s internal clocks.
(Why dark skies are good for your health.)
Still, scientists say there’s no need to be a Grinch. Simple choices can keep festivities bright without overwhelming people or wildlife. “Celebrating with lights is a pretty universal inclination,” says Travis Longcore, an environment and sustainability professor at the University of California, Los Angeles. “And light can be used in a way that makes its presence special. Like music, rests are as important as notes.”
Choose warmer light
When Michael Vaschillo and his wife moved to Candy Cane Lane earlier this year, they knew about the neighborhood’s long-standing holiday tradition. There was no requirement to participate, but Vaschillo says they were happy to join in. They sought warm-hued LED strings reminiscent of childhood holidays and outlined their roof and pathway with 300 of the bulbs. “People often ask if they’re incandescent,” he says.
Standard cool-white LEDs are brighter and bluer than the old school incandescent bulbs that have been phased out of use. Blue light is a particularly potent daytime signal. It also scatters farther, making streetlights—or a neighbor’s cool-white roofline—more likely to reach your bedroom window.
Many of Vaschillo’s neighbors have likewise gravitated to warmer LEDs and kept incandescent bulbs glowing as long as possible. Electric candles still warm the windows of one house. “We’re considerably less sensitive in the yellow-red end of the spectrum,” says Michael Siminovitch, emeritus director of the California Lighting Technology Center at the University of California, Davis. “Candles go back to before blue lights. It’s Christmas-y.”
Still, too much of any color of light can mess with sleep and circadian rhythms. “It’s better to put temporal and spatial controls on the 24-hour day and on the calendar,” says Longcore.
Light only the moments and places that matter
The Candy Cane Lane display is on a timer. Residents synchronize their lights, and on weeknights everything goes dark at 9:30 p.m.
The calendar window is brief too: December 6 through New Year’s Day. “Christmas is a season,” says Vincent Miller, who has lived on the street for more than three decades. “People keep extending it, and all they do is cheapen it.”
Year-round illumination has become trendy, much to the chagrin of scientists and advocates. Some leave up winter lights; others hang displays for new holidays. “Orange for Halloween, green for St. Patrick’s Day, pink for Valentine’s Day,” says Ruskin Hartley, executive director of the nonprofit DarkSky International. But color can be misleading. Researchers at the Detroit Zoo recently discovered that pink LEDs still emitted substantial blue light, prompting a redesign of their nighttime lighting, says Grace Fuller, senior director of animal welfare and research at the zoo.
(Dark sky tourism is on the rise across the U.S. Here's where to go.)
Some municipalities are countering with their own limits. Rancho Santa Fe, California, requires lights to be off by 11 p.m. and allows displays for only six consecutive weeks per year.
Scientists also recommend considering where lights land. Many Candy Cane Lane lights are tucked under eaves, preventing spillover for occupants or neighbors.
But a few LED spotlights shine up at decorations. “No light should ever go upwards,” says Siminovitch. Much of that light, he notes, is simply wasted—spilling across property lines and into tree canopies, where it affects neither safety nor beauty, only the night itself.
Think about your wildlife neighbors too
Candy Cane Lane borders a 50-acre wooded city park. Residents regularly see coyotes, owls, hawks, turkeys, bears, and abundant squirrels—none of which can draw curtains against the light.
In one study, scientists at a Texas university found that campus squirrels foraged more at night—and were more likely to be eaten by predators—during weeks when bright bluish holiday lights decorated campus trees. Other studies document light pollution impacts ranging from altered plant metabolism to shifts in slug and insect populations and changes in West Nile virus spread.
What concerns many scientists most, however, is the surge in brightly lit holiday events at zoos and botanical gardens. “The animals won’t fall over dead,” says Longcore. “But I bet you would find increased cortisol and disrupted sleep. All of us do better with natural light and dark cycles.”
Hartley argues that nighttime events can also be teachable moments. “You have people outside at night to experience the beauty of these lights,” he says. “But then turn them off, so people can experience the real beauty of the night: the starry canopy overhead.”
His advice applies broadly: “Celebrate. But do it responsibly. There are simple steps you can take to be part of the solution, year-round. Turn off the porch light when you go to bed.”
