Light plays a crucial role in regulating many of the body’s internal processes, including the circadian rhythms that govern sleep. Among night-shift workers, fatigue, insomnia, and performance impairments are so common that experts have coined the term “shift work disorder” to encapsulate the symptoms. Research has even linked some forms of cancer and heart disease to the internal disruptions that stem from ignoring the sun’s sleep-wake cues.
So it makes sense that holding a light-emitting device a few inches from your eyeballs would disrupt your sleep. And there’s some evidence to support this theory. Studies have shown that exposing a person to blue light — a type of short wavelength light commonly emitted by digital devices — can suppress the body’s release of melatonin, a hormone that helps regulate sleep. And research from Harvard Medical School has found that people who read traditional paper books fall asleep faster and feel more alert the next morning than those who go to bed with an e-reader.
Experts say blue light isn’t the only thing — or even the primary thing — linking your bedtime device use to sleep issues.
A blue light–blocking filter or one of those light-mellowing programs built into most smartphones should remove any sleep risks, right? That would be a convenient solution (especially for device makers and app sellers who want you to stay glued to your screens), experts say blue light isn’t the only thing — or even the primary thing — linking your bedtime device use to sleep issues.
“Based on my research and that of others, we have consistently found that the blue-enriched light from screens tested in a single night in a sleep laboratory does not affect sleep,” says Michael Gradisar, a sleep researcher and professor of psychology at Flinders University in Australia. While he’s not ruling out the notion that blue light can repel sleep, Gradisar says it’s more likely that devices “indirectly” repel sleep by keeping people active and alert during times when they’d normally be winding down for bed.
Not all devices are created equal. “Interactive devices” — namely smartphones, computers, and video games — “are more likely to be associated with people having difficulty falling asleep,” says Gradisar, citing a large-scale sleep study he co-authored, based on nationwide data collected by the National Sleep Foundation. On the other hand, he says there is “almost a zero relationship” between watching TV and sleep. “This could be because TV is a passive device,” Gradiser says. “There’s no real interaction with what’s happening on the screen.”
Other researchers agree. “Almost everything we do on phones and tablets is stimulating, especially social media, texting, email, and online shopping,” says Jean Twenge, a professor of psychology at San Diego State University and author of iGen, a book that examines the relationship between adolescents and technology.
Twenge says social media and other smartphone activities tend to spur rumination — or problems with turning off our thoughts. “It’s too easy to keep thinking about your friend’s text, the frustrating work email, or the comments on your Facebook post,” she says. Stressing about the news you just read or whether you made the right choice while shopping online can also keep your brain churning. “None of this is conducive to settling down for sleep at night,” Twenge adds.
It’s hard to find a sleep expert who doesn’t recommend banishing all mobile devices from the bedroom.
Twenge’s research reveals that, among adolescents, device use and time spent on social media are both associated with poor sleep. These same trends pop up in Gradisar’s work; compared to adults, young people are more likely to go to bed with their phones and more likely to experience insufficient sleep.
For lots of Americans, middle-of-the-night device alerts are a common source of sleep disruption. Gradisar and his colleagues found that, among people who use their cellphone just before bed, 57 percent leave their ringers on, and one in 10 Americans reports being awakened by buzzes or alerts at least a few nights a week.
Assuming you’re looking for solutions to this problem, the answer is obvious (though maybe not easy): Stay away from screens during the hour before bed. “Use of electronic screens prior to bedtime is probably the biggest problem we see,” says Judith Owens, MD, director of sleep medicine at Boston Children’s Hospital. In fact, it’s hard to find a sleep expert who doesn’t recommend banishing all mobile devices from the bedroom. (“You don’t need an $800 alarm clock” is a common refrain.) One exception to this rule: Some e-readers — assuming you’re using them to read books, not to surf or shop — should be safe, since they’re similar to reading a book.
It would be nice if blue light alone were to blame for device-related sleep woes. But your friend’s comment on your Instagram feed or that infuriating email from your boss is likely just as much, if not more, to blame.