What’s really worrying is that, according to a study published in September 2015, the amount of caffeine in a double espresso has less of an effect on sleep schedule than bright light exposure at night!
While most of us wouldn’t bring a double espresso to bed, we happily bring our phones.
The light exposure can actually push back sleep time twice as long as coffee does, thanks to its ability to suppress melatonin, the hormone that helps with sleep timing.
When Harvard researchers looked at the effect of 6.5 hours of exposure to blue light, and to green light, they found that the blue light suppressed melatonin for twice as long as the green did.
The blue also shifted sleep schedules by three hours, compared to an hour and a half for the green light.