Sept. 27--BERLIN -- There are plenty of good reasons to power up a personal desktop or laptop computer in the evening -- writing emails, chatting on Facebook or making purchases over the internet, for instance.
But various studies indicate that people who stare at a PC's bright monitor shortly before going to bed probably sleep less soundly than they would otherwise because the light seriously disrupts their circadian rhythm.
Exposure to just 10 minutes of normal bathroom lighting is sufficient to affect the release of the sleep hormone melatonin, according to the Sleep Research & Clinical Chronobiology Team at Charite University Hospital in Berlin. Melatonin regulates people's natural wake-sleep cycle and makes them sleepy at nightfall.
Results of the research team's studies suggest that bright PC monitors also disturb the natural wake-sleep cycle. "They haven't proved it though," said Dieter Kunz, the team's director and head of the Department of Sleep Medicine at Charite's Psychiatric Clinic in St Hedwig's Hospital.
Ten years ago, a team of British and American researchers detected a photo-pigment in the human eye that signals to the body whether it is day or night, summer or winter. The photo-pigment is especially sensitive to blue light.
"The blue light more or less tells the body, 'It's daytime, be alert,'" Kunz said. Monitors have a mostly cold white light content and scientists suspect the photo-pigment may react similarly to it. So the longer people look into the bright light, the more alert they become -- and then sleep poorly.
Juergen Zulley, a researcher at the Sleep Disorders Centre at Regensburg University Hospital, also warned against working at a computer late in the evening. While any activity late in the day activates the human body, he said, "Working and playing games at the computer is especially bad for sleep because you're so concentrated and sit so close to the bright monitor."
Children in particular should not sit at a computer late in the evening.
What about staring at a television screen? "Television sets probably have less of a negative influence," Kunz said, noting that they were placed farther away from the viewer and their light source was not as bright as a PC monitor.
Zulley agreed that television viewing was less disruptive to sleep but said it would be better to read a book in the evening. "If I don't feel like doing that, I listen to quiet music instead. The main thing is for the body and mind to relax," he remarked, adding that an evening spent watching TV made a person restless and alert.
A lot of people have difficulty "switching off" in the evening. About half of the women in Germany and a quarter of the men sleep poorly, according to a survey.
Environmental stimuli from electronic devices are only one of the possible causes. Respondents cited job stress as well as personal and health concerns as the main reasons for their sleep problems.
Nearly two-thirds of the people surveyed said they would give up TV to get more sleep. Four in ten said they intended to stop surfing the internet or playing computer games. But few actually carry out these good intentions, a poll showed.
Those who cannot go without their computer in the evening should turn down the blue content if possible and dim the brightness somewhat, Kunz advised. "But nobody does that because, after all, you want to concentrate while working at the computer and the light helps the brain."
In addition electronic devices' standby lights and indicator lamps can be irritating in the dark and disturb sleep. "Sound scientific evidence is still lacking on this matter, though," noted Kunz.
Nevertheless, Kunz said he had the impression that the little lights affected the quality of sleep. "You can't predict it, however. It irritates some people but not others."
Sleep researcher Zulley recommends that people turn off all electronic devices in their bedroom -- "not because they disrupt sleep directly, but because you then can relax better, not to mention save electricity."
Kunz has some simple tips for people bothered by lights: turn off the devices, keep them out of the bedroom, tape over the lights or wear a sleep mask.
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