Smartphones and tablets disrupt sleep, in part, because they emit what's known as "blue" light. This light is picked up by special cells behind our eyeballs, and it communicates to the brain that it's morning. (Red light, meanwhile, signals that it's time to go to sleep).
All of this blue light suppresses melatonin, a hormone that helps with sleep timing and circadian rhythms. At night, our melatonin levels are supposed to rise in anticipation of sleep. In 2013, scientists at Rensselaer Polytechnic Institute asked 13 people to use electronic tablets for two hours before bed. They found that those who used the tablets while wearing orange goggles, which filter blue light, had higher levels of melatonin than those who either used the tablets without goggles on or, as a control, with blue-light goggles on.
Percent Who Don't Sleep as Well Because of Technology
Where Do You Keep Your Phone While You Sleep?