Screens before bed

Is screen time before bed bad for sleep?

Somewhat, in the laboratory, at a high dose. The best-known study came from researchers at Brigham and Women’s Hospital in Boston in 2015. Participants read for four hours before a fixed 10 p.m. bedtime, on five evenings from a light-emitting tablet and on five from printed books. On the tablet evenings they took longer to fall asleep, felt less sleepy beforehand, released less melatonin — the hormone that rises as the body’s night begins — and had later body clocks, less REM sleep and less alertness the next morning (Chang and colleagues, 2015).

The effect on falling asleep was modest. As the same laboratory summed it up three years later, it took about 10 minutes longer on average after the tablet (Chinoy and colleagues, 2018). The dose was large: four hours of reading on a lit screen, five evenings running.

Context changes it, too. In a later study, 14 people spent six and a half hours of the day in bright light and then read a novel for two hours, on a tablet one evening and in print another, about a week apart. Their sleep and their melatonin before sleep did not differ (Rångtell and colleagues, 2016). It was small, but it fits a wider pattern: daylight seems to blunt what evening light does, which is one more reason to get outside in the morning (light is the clock).

Is blue light from screens the problem?

It is part of it. Colour is only one of the things that matter: light’s effect on the body clock grows with how bright it is, how long it lasts and how late it comes, as well as with how much short-wavelength, blue-rich light it contains — which is what LED screens emit (Chinoy and colleagues, 2018).

By those measures, the screen is often not the biggest light in the room. The tablet in the 2015 study gave 30 to 50 lux at the eye (Chinoy and colleagues, 2018). In a study of 116 young adults, ordinary room lighting of under 200 lux, in the eight hours before bed, delayed the evening rise of melatonin in almost everyone and shortened the body’s melatonin night by about 90 minutes, compared with dim light (Gooley and colleagues, 2011). Dimming the room can do more than dimming the phone.

Does Night Shift or night mode help you sleep?

Not measurably, in the trial that tested it. In 2021, 167 iPhone users aged 18 to 24, recruited at a university, were randomly assigned to spend the hour before bed, for a week, on their phone with Night Shift on, on their phone with it off, or off the phone altogether. Their sleep was measured with wrist-worn accelerometers. There were no differences between the three groups. Only in an exploratory look at people who usually slept more than 6.8 hours did the no-phone group come out ahead, with more of the night asleep and less time awake after first falling asleep (Duraccio and colleagues, 2021).

So the filter did not make the difference; for some people, putting the phone down did. Keep night mode if you like it, but on this evidence it is not the fix it is presented as.

Do blue-light glasses help you sleep?

No one can say yet. A 2023 Cochrane review gathered 17 randomised trials of blue-light-filtering lenses in adults. On sleep, six trials with 148 participants between them disagreed — three found better sleep scores and three found no difference — in very different groups of people, and the reviewers rated the evidence as very low certainty: they did not know whether the glasses help sleep at all (Singh and colleagues, 2023). The same review found the glasses may not reduce eye strain from computer use, either.

Side effects were reported only occasionally — headaches, discomfort and lower mood among them. Wear the glasses if you like them; just do not count on them, or take them as permission to keep scrolling.

If not the light, what is it about screens?

Mostly the time they take, and partly what is on them. When the Boston group repeated its study with fewer rules — nine adults, anything they liked on the tablet, and bedtime their own choice — people went to bed about half an hour later on tablet evenings than on evenings with printed reading, fell asleep later, and were sleepier the next morning. They also felt less sleepy in the evening, which the authors think is part of why they stayed up. What the researchers could not tell is whether the light, or the more engaging things a tablet offers, caused the later bedtimes (Chinoy and colleagues, 2018).

What is on the screen matters, though less than people assume. In a 2023 sleep-laboratory study, 50 healthy young adults each watched three or four episodes of a suspenseful series before bed one night and a neutral series another; in one group, the suspenseful run ended on a cliffhanger. The suspense raised stress, heart rate and cortisol, most of all with the cliffhanger — and yet people fell asleep faster after it than after the neutral series, with no change in the structure of their sleep or in how often they woke. Their heart rate stayed higher through the first two sleep cycles, and only the cliffhanger left a trace in sleep itself, a lower EEG measure of sleep quality, which the authors suggest may be the mind still working on an unfinished story (Baselgia and colleagues, 2023).

In the laboratory, though, the researchers decided how many episodes people watched. At home, the series decides.

In the largest of these studies, time beat type. In a 2022 survey of 45,202 Norwegian students aged 18 to 28, each extra hour of screen use after getting into bed went with higher odds of insomnia symptoms and 24 minutes less sleep, and the link was the same whether the hour went on social media or on anything else. The authors read that as displacement: the screen takes time that sleep would otherwise have had. It is a survey, so the arrow can point both ways — some people reach for a screen because they cannot sleep (Hjetland and colleagues, 2025).

Put together: the light of a screen nudges the body clock, what is on it can wake you up a little, and the most consistent cost is time, because a screen in hand keeps you up. We found no study of autoplay itself (searched Europe PMC, October 2026), but it is easy to see where it fits: a programme that starts the next episode for you is a decision about bedtime you did not make.

If a screen is how you fall asleep, falling asleep with the TV on is about that habit. If scrolling is how you keep the day’s thoughts at bay, racing thoughts at night is about those.

How can you use a phone before bed without losing sleep?

Without giving it up, mostly by deciding things before you start:

• Choose the stopping point first. One episode, one chapter, a set time — decided before you start, because a lit screen makes you feel less sleepy in the evening, and the bill arrives the next morning (Chinoy and colleagues, 2018).
• Pick things that end. A finished episode is a natural place to stop; a feed is not. Turning off autoplay is common sense rather than a finding, but it removes the decision you did not make.
• Dim the room as well as the screen. Lamps instead of ceiling lights for the last hours of the evening.
• Get daylight in the morning. It sets the clock and may blunt what the evening’s light does to it.
• Charge the phone out of reach. Brief waking in the night is normal (waking at 3 a.m. is normal); a bright screen at that hour is an invitation to start the day.
• Keep night mode if you like it, but do not count on it.
• If you need something to fall asleep to, make it sound rather than pictures, with the screen face down, and something without a plot to follow.

Where screens fit among caffeine, light, a warm shower and the rest of an evening is in a bedtime routine for adults. And if sleep has been poor on most nights for months, the phone is unlikely to be the whole story — when a routine is not enough says where to turn.