Smartphones, tablets and e-readers should have an automatic "bedtime mode" that stops them disrupting people's sleep, a study revealed.
Researchers from Evelina London Children's Hospital sleep medicine department, King's College London and the University of Surrey, measured short-wavelength blue light devices like tablets (iPad Air), e-readers (Kindle Paperwhite first generation) and smartphones (iPhone 5s) emit when displaying text or a game.
According to earlier research, short-wavelength blue light may disrupt the production of melatonin, a hormone that helps us sleep.
The new study confirmed that the three devices do produce short-wavelength blue light, with text producing slightly more intense light levels than the popular Angry Birds game, BBC reported.
It also found special orange safety glasses filter out some of the blue light, and a sleep app for children -- called Kids Sleep Dr -- produces less blue light.
"Since this type of light is likely to cause the most disruption to sleep as it most effectively suppresses melatonin and increases alertness, there needs to be the recognition that at night-time 'brighter and bluer' is not synonymous with 'better'," the researchers were quoted as saying.
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They suggested future software designs are better optimised when night-time use is anticipated, saying devices could have an automatic "bedtime mode" that shifts blue and green light emissions to yellow and red, as well as reduce backlight and light intensity.
The researchers also said that Harvard Medical School suggests avoiding blue light two to three hours before going to bed, while the National Sleep Foundation suggests turning all electronic devices off at least an hour before bed.
Parents can remove devices from the bedrooms of young children or turn them off before they go to bed, the researchers suggest.
The study only tested widely used tablet, smartphone and e-reader devices for short wavelength blue light and its findings did not measure people's sleep duration and quality when they did or did not use these devices before sleep.
The research findings have been published online in the peer-reviewed medical journal Frontiers in Public Health.