NEW YORK - The blue glow from televisions and other screens suppresses natural mechanisms that help us fall asleep at night, but blocking just the blue wavelength may restore normal night time sleepiness, according to a new study.
Teen boys who used computers and other digital devices while wearing the glasses every evening for a week felt markedly more relaxed and sleepy at bedtime than when they just wore clear glasses, Swiss researchers found.
"LED screens are widely-used in smart phones, tablets, computer monitors and TVs," said study co-author Vivien Bromundt of the Centre for Chronobiology at the Psychiatric Hospital of the University of Basel.
"The effect of screen light on the circadian physiology is particularly high in devices which are used in close distance to our eyes," Bromundt told Reuters Health by e-mail.
"Looking at these screens in the evening can keep teenagers awake since it involves light exposure, particularly in the blue-wavelength range to which the biological clock and its associated arousal promotion has its greatest sensitivity."
Looking at computer screens in bed has been linked to insomnia and to difficulty waking up in the morning in previous studies. Light impacts circadian rhythms and sleep-wake cycles, the authors note.
Teenagers already have a pronounced preference for staying up late, the study team writes in the Journal of Adolescent Health. But having to wake up early for school builds up a chronic sleep debt that affects teens' mood and focus.
Light-emitting diode (LED) screens give off short-wavelength light, which has been shown to block a natural evening rise in the hormone melatonin that promotes sleepiness. Exposure to this blue light keeps the brain alert and "activated" when it should be slowing down to shift into sleep mode, the researchers say.
For the new study, they used orange-tinted "blue-blocker" glasses that filter out short wavelengths of light in the blue portion of the visible spectrum.
The researchers recruited 13 healthy boys between ages 15 and 17 and for one week, the teens kept to their regular sleep schedule at home but did not go out in the evenings or have caffeine drinks.
They wore blue-blocker glasses from 6pm until bedtime each evening, while keeping diaries of how long they wore the glasses and how much time they spent with LED and non-LED screens as well as a sleep-wake log.
At the end of the week, the participants spent one overnight in the laboratory, sitting for two hours in dim light, darkness for half an hour and then three hours in front of a backlit LED computer screen wearing the blue blocker glasses. They completed cognitive tests and provided saliva samples.
Then the participants went to sleep for eight hours, and performed the same cognitive tests and saliva samples upon waking in the lab again.
All participants went through the weeklong study protocol twice, once wearing blue-blocker glasses and once wearing clear glasses for comparison.