More devices like the iPhone, iPad and Kindle emit a blue light that causes our sleep to be restless and disrupted, according to a new study. Led by Dr Paul Gringras at the Department of Children’s Sleep Medicine, Evelina London, the study found that manufacturers have started making bigger, brighter, bluer screens in an effort to increase the efficiency of our screens during daytime. As an unwanted byproduct, this light is affecting our sleep and productivity. Kindle, for instance, didn't backlight its screen in older models, but the new version tested - the Kindle Paperwhite first generation - does. The study, reported first by the BBC, said that this type of light is likely to cause the most disruption to sleep, as it most effectively suppresses melatonin, a hormone that reminds us to sleep every night; the light also increases alertness. In fact, using our devices before bedtime could even affect our performance during the day, because exposure to this blue light changes our body's natural rhythms. Devices like the iPhone have started enlarging screens and increasing brightness resulting in disrupted sleep Photo: Getty "The development of light-emitting devices means that for many people, a 'book at bedtime' is now often an 'e-book,'" the paper pointed out. Reading a traditional paper book by the light of your bedside lamp doesn't affect your sleep, because bulbs emit a yellow-red light. "In comparison, the same book read in electronic format will provide a very different light signal with biological effects," the researchers said. Both adults and children can avoid these negative effects by keeping our digital devices outside of the bedroom, which is easier said than done. For Android devices, apps like F.lux can adjust a computer display’s colour according to its location and time of day, which may be more helpful on a daily basis. Ultimately, though, the push to adjust screen lighting has to come from manufacturers. "All hardware devices [should have] an automatic “bedtime mode” that shifts blue and green light emissions to yellow and red as well as reduces backlight/light intensity," Gringras and the team write. "We hope that as technology improves, 'brighter' will not always be synonymous with 'better'."