Screens at night: what we know and what else matters

Several pathways, and they don't carry the same weight

Researchers propose four pathways through which using screens in bed could worsen sleep,³ and a 2024 theoretical review concludes that the relationship is more complex than was thought.² The table summarizes what has been found in adults.

Light: measurable effects, almost always small

We summarize the most cited experiment, with four hours of a tablet at maximum brightness over five nights, in the weakest sleep rules. With more everyday exposures, the results have been more modest:

• Half an hour in bed, at home. In Norway, 16 students (average age 25) read for 30 minutes in bed, on a tablet or on paper, on different nights, with a recording of brain activity (polysomnography) at home. With the tablet more light reached them (about 58 lux versus 27), they were less sleepy when they turned off the light, and slow-wave activity, an indicator of sleep pressure, was delayed by about 30 minutes and was lower at the start of the night. But they didn't take longer to fall asleep, nor did the time spent in each sleep stage change.⁶
• Two hours, after a day with plenty of light. In Sweden, 14 people spent six and a half hours in bright light (about 569 lux) and then read from 9:00 to 11:00 p.m. on a tablet or on paper. Neither sleep, recorded with polysomnography, nor melatonin before sleep differed between the two. The authors suggest that daylight might cushion the effect of the screen and call for larger studies.⁷
• Which part of the light. In Switzerland, 72 healthy men aged 18 to 35 spent three and a half hours looking at an experimental screen, each at one of four brightness levels; the screen reduced, in a way not noticeable to the naked eye, the part of the light that acts most on the body clock. With less of that light they were sleepier and melatonin rose earlier, by about half an hour at three of the four levels; but only at the highest brightness did they clearly fall asleep sooner.⁸

A National Sleep Foundation expert panel, in a 2024 consensus, points out that the effects of light observed were usually small or came from laboratory designs not much like everyday use. As possible reasons why adults seem less sensitive than children and adolescents, it points to the adult eye (smaller pupils, a less transparent lens), daylight moderating the effect of light at night, or a lack of studies.¹ That daylight protects against light at night hasn't been demonstrated; we explain it in daylight and sleep routines.

What you do on the screen

The other usual suspect is content: a tense conversation or a gripping series could stir you up just when it's time to wind down. Two experiments from the University of Fribourg (Switzerland), in a sleep laboratory with healthy young people, don't fit the most alarmist view:

• Social media. 32 volunteers used social media for 30 minutes right before sleeping, with the effect of blue light excluded; on other nights they did muscle relaxation or nothing in particular. According to the study's abstract, social media didn't significantly increase arousal or substantially alter sleep, measured or self-reported; it only reduced one stage of light sleep. Relaxation, by contrast, shortened the time taken to fall asleep and improved sleep efficiency.⁹
• Suspense series. 50 young people (average age 23) watched three or four episodes in a row of a suspense series and, on another night, of a neutral one. The suspense increased stress, heart rate and cortisol before going to bed, but they fell asleep somewhat sooner, and neither the sleep stages nor awakenings changed. Heart rate stayed somewhat higher during the first two sleep cycles, and with episodes that ended on a cliffhanger there was a subtle change in brain activity during sleep.¹⁰

The authors of the social media study conclude that its most notable effect seems to be the extra time spent on it.⁹ And the 2024 panel didn't reach a consensus on content in adults, although it did for children and adolescents.¹

The time the screen takes away from the night

The simplest pathway is time: while you're still on the screen you're not sleeping, and since the time you get up is usually set by work or studies, the night gets shorter.⁹ This is what's called sleep displacement.³

A national survey of more than 45,000 Norwegian university students aged 18 to 28 found that, among those who used screens in bed, each additional hour of screen time after going to bed was associated with 59% higher odds of having insomnia symptoms, according to a questionnaire (odds are a way of expressing probability that these studies use; they're not equivalent to “59% more likely”), and with 24 minutes less self-reported sleep. The association was similar for social media and for other activities, and the authors read this as support for displaced time mattering more than content.³ But it's a cross-sectional study: it can't tell which comes first, and the authors themselves point out that people who sleep poorly may use the screen to pass the time or to help themselves fall asleep,³ a reverse direction that the 2024 theoretical review builds into its model.²

With adults of all ages, the picture is less clear. In a representative telephone survey of 1,342 adults in Canada, those who used screens at bedtime less than once a week and those who did so five nights or more a week reported the best overall sleep health.⁴ In another, of 844 adults in Flanders (Belgium), texting or calling with the light already off was associated with taking longer to fall asleep and with less efficient sleep.⁵

Night mode, filters and glasses: what has been tested

Is changing the color of the light enough? The two most direct studies we've found don't allow us to say so:

• The phone's night mode. In a trial with 167 students at a university in the United States, aged 18 to 24, randomly assigned for seven nights to using their phone in the hour before going to bed with night mode on, without it, or not using it, sleep estimated with a wrist sensor wasn't different among the three groups; nor between using the phone and not using it, so overall there was no effect for night mode to correct. In an exploratory analysis, among those who slept more than 6.8 hours on average, not using the phone gave the best sleep efficiency and the least time awake.¹¹
• Glasses that filter blue light. A 2023 Cochrane review brought together 17 trials with adults. On sleep, six trials with 148 participants from different populations gave contradictory results: three with improvements and three with no differences. With very low certainty, it concludes that it isn't known whether these glasses improve sleep more than ordinary lenses.¹²

In the laboratory, reducing the part of the light that acts most on the body clock did change melatonin and sleepiness,⁸ but that doesn't guarantee better sleep at home, and a phone's color setting isn't that experimental screen. Our reading: night mode hasn't been shown to improve adults' sleep, so it's best not to treat it as a solution.

What to try if you suspect your screens

According to the 2024 panel, strategies to reduce screen use at night have given mixed results, with many studies showing no effect, although those targeting interactive use at night tended to work; and most of the studies it reviewed were done with adolescents.¹ Of the trials with adults we've reviewed, the one closest to practical advice asked people to put their phone away before sleeping. In that pilot trial, carried out in China, 38 university students who slept poorly according to a questionnaire and usually used their phone for more than half an hour at bedtime were randomly split into two groups: one put the phone away 30 minutes before their usual bedtime for four weeks, with the phone locked or switched off and checks by the researchers; the other received no instructions.¹³

According to their diary, that group also slept somewhat longer (from 6.2 to 6.6 hours on average; the other, from 6.5 to 6.3) and improved on a sleep quality questionnaire.¹³

What follows is our suggestion, not the protocol of any study:

1. See what the screen takes from you. For a week, note what time you put it away and what time you turn off the light in a simple sleep diary. If it pushes back your bedtime while the time you get up doesn't move, you already have a clue.
2. Change just one thing. For example, the time you put your phone away, decided as a concrete plan: “if it's 11 p.m., the phone stays charging outside the bedroom.” That's an “if–then” plan.
3. Silence notifications at night. Interrupting sleep is one of the proposed pathways,³ although we haven't found studies with adults that measure it.
4. Give it a few weeks and don't rely only on your impression. How to do it, in a personal test in three steps.

If what keeps you on the screen is that you can't fall asleep, the screen may be more a consequence than the cause.² If difficulty sleeping lasts for weeks or affects your daily life, see a health professional: when it's worth doing so.