Do Screens Before Bed Really Hurt Your Sleep? What the Research Shows

Yes, but the effect of the light itself is smaller than many people think. In a 2014 Harvard sleep lab study, people who read on an iPad for 4 hours before bed took about 10 minutes longer to fall asleep, had less REM sleep and felt sleepier the next morning than when they read a printed book. What you do on the screen, and how long it keeps you up, often matters more.

The e-reader experiment

Anne-Marie Chang and colleagues at Brigham and Women’s Hospital in Boston studied 12 healthy young adults over two weeks in a sleep lab. For five evenings, participants read for 4 hours before bed on an iPad, and for five evenings they read a printed book. The order was randomised.

Compared with reading a printed book, after reading on an iPad people:

• took nearly 10 minutes longer to fall asleep
• had lower evening melatonin levels
• had less REM sleep
• had a later body clock
• felt sleepier and took longer to wake up properly the next morning

The study was small and the conditions were extreme, with 4 hours of reading at full brightness, but it shows that evening light from screens can shift the body clock.

Light, or what’s on the screen?

Screens affect sleep in at least three ways:

• Light: bright, blue-rich light in the evening tells your body clock it’s still daytime and suppresses melatonin.
• Stimulation: messages, news, social media and games keep your brain alert and can raise stress.
• Displacement: “one more episode” or “five more minutes” of scrolling pushes bedtime later and cuts sleep short.

Night mode and blue-light filters reduce some of the blue light, but they don’t solve the second and third problems.

What helps

• Set a screens-off time at least 30 minutes before bed, as the AASM suggests. An hour is better if you struggle to fall asleep.
• Charge your phone outside the bedroom, and use a separate alarm clock.
• Turn the brightness down and use night mode in the evening.
• Swap the last screen session for a paper book, music, a podcast or stretching.
• Get bright light in the morning, which helps balance out evening light and keeps your body clock on time.
• Set a regular bedtime with the sleep calculator, and stick to it even if the episode isn’t finished.

Teenagers and screens

Teenagers’ body clocks already shift later during puberty, so late-night screen use can push their sleep even later. Keeping devices out of the bedroom at night is one of the most common recommendations from pediatric sleep experts. Read more in how much sleep do teenagers need?

Sources

• Chang AM et al. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences, 2015 (published online December 2014). Summary: Medical News Today
• AASM Sleep Education: Healthy sleep habits
• National Institute of Neurological Disorders and Stroke: Brain basics: understanding sleep

Frequently asked questions

Does night mode help you sleep?

It reduces blue light a little, but it doesn’t stop screens from keeping you alert or delaying bedtime.

Is watching TV before bed bad?

TV is usually further away and less bright than a phone, but late-night viewing can still delay bedtime. Set a cut-off time.

How long before bed should I stop using my phone?

At least 30 minutes, according to the American Academy of Sleep Medicine.