Bedtime mode in smartphones, tablets prevents disruption during sleep

London: Smartphones and tablets should have an automatic "bedtime mode" designed to reduce blue-light emissions at night so that the devices do not disrupt our sleep, experts suggest. Our body starts to produce the sleep hormone melatonin - which helps people to fall asleep - as it gets darker in the

evening, researchers said.

Wavelengths of light at the blue-green end of the visible

spectrum can disrupt the system. Paul Gringras, from Evelina Children's Hospital in London, analysed the light emitted by devices for the study, that found a clear trend for new devices to be bigger, brighter, have higher levels of contrast and emit more blue light.

"That is great for use in the day, but awful for use at night. There is converging data to say if you are in front of one of these devices at night-time it could prevent you falling asleep by an extra hour," Gringras told the 'BBC News'. Gringras said that smartphones should have settings to filter out the blue light that delays the body clock and keeps people awake later into the evening.

He said some sleep-aware apps had already been designed to reduce blue-green light emissions, and that a bedtime mode could automatically filter out the blue as software such as 'f.lux' already does. "It's not good enough to say do less and accept this is the world we live in, they're fun devices but we do need some protection on what they do at night-time," Gringras said.

The study was published in the journal Frontiers in Public Health.