Last month, the American Medical Association issued a policy recognizing “that exposure to excessive light at night, including extended use of various electronic media, can disrupt sleep or exacerbate sleep disorders, especially in children and adolescents.”
Any light at night can be disruptive, researchers say, but in recent years studies have zeroed in on the particularly potent “blue light” emitted abundantly from the energy-efficient screens of smartphones and computers as well as many energy-saving fluorescent bulbs.
Because blue light is especially prominent in daylight, our bodies associate it with daytime, which may be why exposure to blue light can make us more alert and improve our response times. It also has been shown to suppress melatonin, a hormone that helps regulate sleep and is not produced during the day.
In May 2011, Swiss researchers at the University of Basel reported that subjects who spent time at night in front of an LED computer screen, as opposed to a screen emitting a variety of colors but little blue light, experienced “a significant suppression of the evening rise in endogenous melatonin and … sleepiness.”
Over the last decade, neuroscientists have discovered novel light-sensitive cells in the eye that detect light. These cells are separate from those we use for vision and contain a photopigment called melanopsin that is particularly sensitive to blue light. Scientists think this light-detecting mechanism, which regulates our sense of night and day and time of year, evolved before the ability to see.
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