Do Screens Before Bed Harm Sleep? What to Change in the Last Hour
- A 2024 review in Sleep Medicine Reviews found that screen light and stimulating content delay sleep by no more than about ten minutes, while using devices past bedtime reduces sleep by roughly an hour.
- In a Norwegian survey of 45,202 students, each extra hour of screen use after going to bed was linked to 24 minutes less sleep and 59% higher odds of insomnia symptoms. The study could not show which caused which.
- A 2021 trial of 167 young adults found no difference in sleep between people using an iPhone with Night Shift on, with Night Shift off, or not using a phone before bed at all.
- The NHS says most adults need 7 to 9 hours of sleep, and the CDC reports that 30.5% of US adults got less than 7 hours in 2024.
- Insomnia that has lasted three months or more, or that affects daily life, is a reason to see a GP or doctor. A phone curfew is no substitute for that appointment.
It is 11.40pm. You went to bed at 10.30pm, and the seventy minutes in between went on a group chat, two news stories you did not need and a video of a man restoring a rusty axe.
The alarm is set for 6.30am. You have just turned an eight-hour night into one of six hours and fifty minutes, and no amount of amber screen tint was going to change that sum.
That small piece of arithmetic is where the research on screens and sleep has ended up. This guide sets out what the evidence supports, where the popular version overstates it, and what to change in the last hour and a half of the day.
What do screens before bed do to sleep?
Researchers describe three routes. Light from the screen could delay the body clock. The content could leave you alert or upset. And the device could simply push bedtime later, which sleep scientists call displacement. For years the first route got nearly all the headlines.
A 2024 review in Sleep Medicine Reviews went back through the better-designed experiments. It came to a different ranking.
Its authors concluded that using a bright screen instead of a dim one, or stimulating content instead of neutral, does not seem to change the time it takes to fall asleep by more than about ten minutes. Using technology past the intended bedtime, on the other hand, meaningfully reduced sleep, by around an hour.
| Route | What the evidence says | What to do about it |
|---|---|---|
| Displacement (the screen pushes sleep later) | The largest effect in experiments: about an hour of lost sleep when devices are used past bedtime | Set a lights-out time and keep the phone out of reach of the bed |
| Content and arousal | Small in adult experiments, ten minutes at most. A US expert panel agreed that pre-bed content impairs sleep in children and teenagers | Keep work email, news and arguments out of the last hour. Familiar, low-stakes viewing is less of a concern |
| Screen light | Small. Measurable in the lab under heavy exposure, hard to detect in normal use | Dim the screen and the room. Do not rely on night mode to do the job |
| Night-time interruptions | Less studied, but a phone that buzzes at 2am wakes you whatever colour the screen is | Flight mode, Do Not Disturb, or another room |
Survey data points the same way. A 2025 study of 45,202 Norwegian university students found that each additional hour of screen time after going to bed was associated with 59% higher odds of insomnia symptoms and 24 minutes less sleep.
It made no difference whether the hour went on social media or something else. The authors are clear that the data are cross-sectional, so poor sleepers may be reaching for phones because they are awake, as well as the other way round.
The habit itself is close to universal. In a 2025 survey for the American Academy of Sleep Medicine, half of 2,007 US adults said they use a screen in bed every day, and 38% said reading news on a phone or tablet before bed made their sleep worse.
Is blue light the problem, and does night mode help?
The blue light story rests largely on one well-known experiment. In a 2015 study at Brigham and Women's Hospital in Boston, 12 adults read on an iPad for four hours before bed, from 6pm to 10pm, for five nights running, then did the same with a printed book.
On the iPad nights they took nearly ten minutes longer to fall asleep, had less REM sleep and felt groggier the next morning. Those are real effects. They also came from twelve people in a sleep lab, under a dose of screen light that few of us manage on a weeknight.
When researchers at Brigham Young University tested the feature that phone makers built in response, it did not hold up. Their 2021 study in Sleep Health assigned 167 adults aged 18 to 24 to use an iPhone with Night Shift on, to use it with Night Shift off, or to avoid the phone before bed.
Across the whole sample there were no differences in how long people slept, how well, or how quickly they dropped off. Only among those already getting about seven hours did the no-phone group sleep slightly better.
A National Sleep Foundation expert panel reviewed the field in 2024. It reached consensus that screen use in general, and the content of screens before bed, impair sleep in children and adolescents, and that behavioural strategies can reduce the harm. Adults and pre-bed light do not appear in its list of agreed conclusions.
Official advice has not quite caught up. The NHS insomnia page still gives blue light as the reason to avoid devices before bed.
The instruction is sound even if the explanation is dated: the phone you are not holding cannot keep you up. Leave night mode on if you like the look of it, and do not expect it to buy you any sleep.
How much sleep are you aiming for?
The NHS says adults need 7 to 9 hours on average. The CDC recommends 7 or more hours for adults aged 18 to 60 and 8 to 10 for teenagers.
Plenty of people miss that. The CDC's National Center for Health Statistics found that 30.5% of US adults slept less than 7 hours in 2024, and 15.4% had trouble falling asleep most days or every day.
On switching off, the official guidance differs only in degree. The CDC and the American Academy of Sleep Medicine both say to turn off electronic devices at least 30 minutes before bedtime, and the AASM's longer advice says 30 to 60 minutes. The NHS Every Mind Matters pages suggest an hour. Pick whichever you will keep to.
To find your own lights-out time, work backwards. Take the time your alarm goes off, subtract the hours you need, then subtract another 15 to 20 minutes for falling asleep.
For a 6.30am alarm and eight hours, that is lights out at about 10.15pm. Run the opening example across five weeknights and the seventy minutes of scrolling adds up to nearly six hours of lost sleep by Friday.
What should the last 90 minutes look like?
This plan puts the effort where the evidence is strongest: protecting the bedtime itself. The example uses a 10.30pm lights-out, so shift the times to suit your own alarm.
| Time | What to do | Why |
|---|---|---|
| 9.00pm (90 minutes before) | Finish anything that needs a decision or a reply: work email, tomorrow's logistics, the group chat. Set the alarm now | Clears the content most likely to keep your mind running |
| 9.30pm (60 minutes) | Main lights down, lamps on. Television is fine if it is something you can switch off at the end of an episode. Turn autoplay off | Dimmer rooms and a natural stopping point |
| 10.00pm (30 minutes) | Phone on Do Not Disturb and onto its charger outside the bedroom. Wash, teeth, clothes out for tomorrow | Matches CDC and AASM advice, and removes the device before you are in bed |
| 10.15pm (15 minutes) | In bed with a book, a magazine, the radio or an audiobook on a sleep timer. If worries arrive, write tomorrow's list on paper | The NHS suggests a written to-do list for people who worry in bed |
| 10.30pm | Lights out | This is the step that protects the hours |
You do not have to adopt the whole table. If you change one row, make it the 10pm one.
People who use a phone for a sleep story, white noise or a meditation track need not give that up: the 2024 review's authors suggest less engaging activities and flight mode as a realistic middle course. Start the audio, put the phone face down across the room and leave it there.
This plan will not suit everyone. Shift workers, parents of young babies and anyone on call have constraints that a tidy table ignores. Keep the principle that fits, which is usually a set gap between the last scroll and sleep, whatever the clock says.
Should the phone leave the bedroom?
If late scrolling is your problem, yes. It is the only change that does not depend on a decision made when you are tired.
Gallup's 2022 survey of US smartphone owners found that 72% keep the phone near them while they sleep and 64% check it as soon as they wake. The AASM advice is blunt: place phones in another room when going to bed.
Replace the alarm first
The alarm is the reason most phones are on the bedside table, so deal with that before anything else. A basic battery alarm clock will do.
Choose one with a dim or unlit face and no ticking. Put the charger in the hall, the kitchen or the landing the same day the clock arrives, and the phone has no reason to come upstairs.
If you need to be reachable
Parents of teenagers out late, carers and people on call can keep the ringer on and the phone outside the bedroom door. On an iPhone or Android phone, Do Not Disturb can be set to let calls from chosen contacts through while holding everything else until morning.
If the bedroom is the only room
In a studio or a shared house, distance still works at a smaller scale. Charge the phone on the far side of the room, on a shelf you have to stand up to reach. Most late-night scrolling does not survive having to get out from under a duvet.
What if you wake at 3am and reach for it?
The NHS and the AASM agree. If you are still awake after about 20 minutes, get up, sit somewhere comfortable in low light and do something quiet, such as reading. Go back to bed when you feel sleepy. The AASM adds that it is especially important not to get on electronics at this point.
A phone in another room makes that easier to follow. Checking the time on it is how a 3am wake-up becomes a 4am one: the clock tells you how little sleep is left, and the lock screen offers something to read about it.
When is it insomnia, and who can help?
See a GP or doctor if any of this applies
In the UK, the NHS advises seeing a GP if changing your sleep habits has not helped, if you have had trouble sleeping for months, or if it is affecting your daily life. It classes insomnia lasting three months or longer as long-term. A GP may offer cognitive behavioural therapy (CBT).
NICE recommends the digital CBT programme Sleepio as a cost-saving option in primary care. It is available free across Scotland, and in England access depends on where you live, so ask your practice. NHS 111 can advise if you are unsure where to start.
In the US, speak to your doctor or primary care provider. The American College of Physicians recommends cognitive behavioural therapy for insomnia (CBT-I) as the first-line treatment for adults with chronic insomnia, ahead of sleeping tablets. Ask for a referral or a recommended digital programme.
Low mood or anxiety most days alongside poor sleep is also worth raising. If you feel unable to keep yourself safe, call 999 in the UK or 911 in the US. Samaritans are on 116 123 in the UK, and the 988 Suicide & Crisis Lifeline takes calls and texts in the US.
Sleep habits are the foundation of CBT-I, but they are not the whole of it. If you have done everything in this article for a month and still lie awake, that tells you something useful, and the next step is a professional.
Questions readers ask
Do blue light glasses help you sleep?
The studies covered here did not test them. This article makes no claim either way.
What can be said is that the best recent review puts the whole effect of screen light on falling asleep at around ten minutes or less, which leaves little for any filter to remove. Time spent on the device past bedtime costs far more, and glasses do nothing about that.
Is reading on a Kindle or e-reader before bed a problem?
The 2015 lab study used a backlit tablet at four hours a night and found roughly ten minutes' delay in falling asleep. A basic e-ink reader without a light emitted none in that study.
If a dimmed e-reader gets you to lights-out on time and a phone does not, it is the better choice. A book has no feed to refresh.
Is watching television in the evening as bad as scrolling?
Probably not, for a practical reason. An episode ends, and a feed does not. The content guidance still applies: something familiar is a safer bet than the news or a thriller at 10pm. Turn off autoplay so that the end of the episode is a real stopping point.
How long before a phone curfew makes a difference to sleep?
If the change wins you back an hour in bed, you gain that hour on the first night. Whether you feel better depends on how short of sleep you were. Give it a fortnight before you judge, and keep the lights-out time the same at weekends while you test it.
Should teenagers have phones in their bedrooms overnight?
The evidence of harm is stronger for children and teenagers than for adults. The National Sleep Foundation panel reached consensus that screen use impairs sleep health in both groups, and teenagers need 8 to 10 hours. A family rule that every phone, adults' included, charges in the kitchen overnight is easier to enforce than one aimed only at the teenager.
Sources
- Bauducco S, et al. A bidirectional model of sleep and technology use: a theoretical review of how much, for whom, and which mechanisms. Sleep Medicine Reviews. 2024.
- Hjetland et al. How and when screens are used: comparing different screen activities and sleep in Norwegian university students. Frontiers in Psychiatry. 31 March 2025.
- Chang AM, Aeschbach D, Duffy JF, Czeisler CA. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. PNAS. 2015;112(4):1232–1237.
- Duraccio KM, et al. (Brigham Young University and Cincinnati Children's Hospital Medical Center). Does iPhone night shift mitigate negative effects of smartphone use on sleep outcomes in emerging adults? Sleep Health. 2021.
- Hartstein LE, Mathew GM, Reichenberger DA, et al. The impact of screen use on sleep health across the lifespan: a National Sleep Foundation consensus statement. Sleep Health. 2024;10(4):373–384.
- NHS. Insomnia; How to fall asleep faster and sleep better.
- Centers for Disease Control and Prevention. About sleep; National Center for Health Statistics. Short sleep duration and sleep difficulties among adults: United States, 2024. Data Brief 559, April 2026.
- American Academy of Sleep Medicine. Healthy sleep habits; Americans are "doomscrolling" at bedtime. Survey of 2,007 US adults, 5 to 13 June 2025.
- Gallup. Americans have close but wary bond with their smartphone. June 2022.
- NICE. Sleepio to treat insomnia and insomnia symptoms (MTG70). American College of Physicians. ACP recommends cognitive behavioral therapy as initial treatment for chronic insomnia. 3 May 2016.
© The Reset Edit™ 2026 — Modern Tools + Lifestyle Essentials for Sustainable, Reset Living. All rights reserved.