Illustrations: Alexis Jamet

Elemental Light Week

Does Blue Light From Screens Really Ruin Sleep?

A recipe for managing the light in your life, at night and during the day

Published in
11 min readFeb 13, 2020


This story is a part of Elemental Light Week, a five-day series on what light does for your body, brain, and well-being.

DDreaded short-wavelength “blue” light from smartphones and other screens is supposedly creating a generation of sleepless zombies, spurring the creation of “night mode” apps that tamp down cold blue light and infuse smartphone screens with warmer yellows and reds. But as with zombies, some things appear different in the scientific light of day.

Studies reveal that light at night, especially blue light, can negatively affect sleep duration and quality. But some scientists say light from smartphones, tablets, computers, and TVs before bedtime is just one ingredient — and quite possibly a relatively minor one — in the recipe of environmental and behavioral monsters that keep people up at night.

The common recommendation to turn off screens two to three hours before bedtime remains good advice for kids and for anyone who struggles to fall asleep. But it fails to take into account the way humans are messing with their biological clocks by spending entire days indoors, in relatively dim lighting, leaving a body with no clue when it’s time to go to sleep.

Get outdoors or sit by a window for at least two hours a day, and you probably don’t have to worry about what you look at in the home at night,” says Mark Rea, PhD, a professor of architecture and cognitive sciences at Rensselaer Polytechnic Institute’s Lighting Research Center. “Your ability to sleep at night [will improve] and your sleepiness during the day will be much dissipated if you follow that simple recipe.”

Not every scientist agrees entirely with that bold statement. But in multiple interviews and reviews of the scientific literature on the topic, it’s clear that screens at night are not as evil as we’ve been led to believe.

Setting the body’s clock

Humans, like all creatures and even plants, have an internal biological clock attuned to the cycle of night and day. Our circadian rhythm, as it’s…



Robert Roy Britt

Editor of Aha! and Wise & Well on Medium + the Writer's Guide at Author of Make Sleep Your Superpower: