Having trouble sleeping? Check for a glow, inches from the pillow.
Using a smartphone, tablet or laptop at bedtime may be staving off sleep, according to Harvard Medical School scientists, who have found specific wavelengths of light can suppress the slumber-inducing hormone melatonin in the brain.
"We have biologically shifted ourselves so we can't fall asleep earlier," said Charles A. Czeisler, a professor of sleep medicine at Harvard Medical School. "The amazing thing is that we are still trying to get up with the chickens."
The result is less sleep -- and less time for the body to recover. Routinely getting fewer than eight hours of sleep compromises alertness, reaction time, efficiency, productivity and mood, according to Australia's Sleep Health Foundation.
In the U.S. alone, revenue from clinics treating sleep disorders expanded 12 percent annually from 2008 to 2011, reaching $6 billion, according to IBISWorld. Drowsy drivers cause 1,550 fatalities annually, the National Department of Transportation estimates, and insomnia-related accidents in the workplace cost $31.1 billion annually, a study last year found.
"Sleep is in a battle for our time with work life, social life and family life," said David Hillman, a sleep specialist at the Sir Charles Gairdner Hospital in Perth, Western Australia, and the chairman of the Sleep Health Foundation. "For a lot of us, it comes off a poor fourth in that battle."
Regular sleep disturbances are associated with ailments including obesity, diabetes, heart disease and cancer, according to Hillman.
Modern technology isn't helping.
The National Sleep Foundation in Arlington, Va., commissioned a survey of 1,500 randomly selected adults in the U.S., Canada, Mexico, Germany, Britain and Japan to understand their bedroom environment and its effect on sleep for its inaugural 2013 International Bedroom Poll. The results, published in September, showed that more than half of respondents in the U.S., Canada and Britain, and two-thirds in Japan, used a computer, laptop or tablet in the hour before bed.
At least two-thirds of people in all countries surveyed watched TV in the hour before bed. Only about half said they get a good night's sleep on work nights.
"It's a massive issue, particularly when you talk about technology," said Sarah Loughran, a sleep researcher at the University of Wollongong, south of Sydney. "We're not just talking about mobile phones but iPads, TVs, laptops. A lot of these things are in the bedroom."
Smartphone manufacturers shipped 724 million of the units globally last year, compared with 151 million in 2008, according to data compiled by Bloomberg.
While the noisy ping of a nocturnal email or text message can interrupt sleep, staring at the gadgets' screen late at night may be more detrimental, according to researcher Czeisler, who is also head of sleep medicine at Boston's Brigham and Women's Hospital.
The timing of exposure to the light-dark cycle is the most powerful means by which the circadian clock, the body's biological time keeper, is synchronized to the 24-hour day, Czeisler's research found. He began studying the impact of the circadian rhythm on sleep in 1972 and has written about 200 scientific papers and review articles on the subject. He estimates that since the advent of electricity-powered light, people's internal sleep triggers have been pushed back six hours.
"It's our exposure to artificial light, particularly in the evening between the timing of sunset and when you normally go to bed, that's dramatically changed the timing of our endogenous circadian rhythms," Czeisler said in an interview.
After being awake 8 or 10 hours, people start to run out of steam, Czeisler says, prompting their internal clock to send out a surge of wakefulness that builds until melatonin is produced to suppress the circadian system and facilitate sleep. Light exposure in the evening delays the melatonin surge.
Two research groups in Britain and the U.S. published studies in 2001 showing that short wavelengths of light in the blue part of the spectrum are the most active in suppressing melatonin.
Energy-saving light-emitting diode lights, known as LED, are especially problematic, according to Czeisler. LED lights are used in flat-panel televisions, computer displays and smartphone screens and they are replacing less-efficient incandescent light bulbs worldwide.
Setting a technology curfew and using yellow-based lighting in the evening that can be dimmed and switched off completely by 10:30 p.m. will improve chances of a good night's sleep, he said.
"It may be that gradually lowering the light might be more powerful than just shutting them off all at once," Czeisler said. If computers can't be avoided at night, he recommends reducing the screen's blue wavelength light.
Michael Herf, creator of the Picasa online photo-sharing software bought by Google Inc. in 2004, has come up with an answer: a computer program that automatically alters the intensity and spectrum of light emitted by the display according to the time of day. The free software, called f.lux, has been downloaded 8 million times since Herf and his wife Lorna developed it in their Los Angeles home in 2008.
"We put it up just for some of our friends to try," Herf, 38, said in a telephone interview. "This one kind of took off."
The nighttime setting reduces exposure to the most alerting wavelengths of light by 70 to 90 percent by relying on other colors on the spectrum that interfere less with the circadian system, Herf said.
In theory, f.lux should make a difference, according to Czeisler. But it's no magic bullet.
There's another reason computers, phones and other technology can perturb sleep when used shortly before bed, says the University of Wollongong's Loughran. Engaging the brain with information that's exciting or provocative can trigger emotional and other hormonal responses, including the release of adrenaline.
"In evolutionary terms, as soon as you have something to which you have to respond, a little blip of adrenaline let's say, you're in a mode that might require a response," said Susan Greenfield, senior research fellow at England's Oxford University, whose interests include the impact of modern technologies on the brain. "You have to put yourself in an environment where you can feel relaxed and safe, where you can go back into your inner world just before you go to sleep."
The ideal bedroom has no distracting bright light or noise, Greenfield said.
Sleep specialist Russell Rosenberg, who was an adviser on the International Bedroom Poll, offers simple advice: "Relax, turn off the mobile phone and TV, and create a more pleasant bedtime routine."