Blue light gets the blame, but time on screens may cost more sleep

Key takeaways

• In a Boston hospital study published in 2015, 12 adults who read on an iPad for four hours before bed took nearly 10 minutes longer to fall asleep than when they read a printed book¹².
• In a 2021 Brigham Young University trial of 167 young adults, using a phone with Night Shift turned on did no better for sleep than using one with it off³.
• A 2023 Cochrane review found the research on blue-light-filtering glasses and sleep too weak and mixed to draw conclusions⁵.
• In a 2025 survey of 45,202 Norwegian students, each extra hour on screens after getting into bed went with 59% higher odds of insomnia symptoms and 24 minutes less sleep, whatever the activity⁶⁷.
• Only 24% of U.S. high school students got 8 or more hours of sleep on a typical school night in 2025, according to the CDC¹².

Twelve adults once checked into Brigham and Women’s Hospital in Boston for a two-week experiment on bedtime reading¹. Each evening they read for four hours, and then it was lights out at 10¹.

On five nights in a row, they read on an iPad, and on five other nights they read a printed book, in an order set at random¹.

After the iPad nights, they took nearly 10 minutes longer to fall asleep¹. Their bodies released less melatonin, the hormone that rises in the evening and helps signal night, and their body clocks shifted later². They also got less REM sleep and felt groggier the next morning¹.

That study was published in 2015 in the Proceedings of the National Academy of Sciences². A decade later, the picture looks more complicated. Newer studies suggest the glow matters less than what screens do to your evening: they keep you up, keep you engaged and eat into the hours you meant to sleep.

This article covers what the evidence shows about light, night modes, special glasses and phones in the bedroom, plus a plan you can start tonight.

In the lab, four hours of iPad reading delayed sleep

The Brigham study was careful and tightly controlled. Researchers drew blood every hour to track melatonin and recorded sleep with brain-wave sensors¹. The National Institutes of Health paid for it¹.

But notice the dose. People read on a tablet for four straight hours, five nights in a row, and compared it with a paper book¹. That’s a strong test of whether screen light can matter, not a test of a typical evening of mixed screen use.

Perspective helps. The blue light we get from screens and other artificial sources is roughly a thousandth of what daylight delivers, a 2023 Cochrane news release noted⁴. That doesn’t make screen light harmless at night, but it’s a reason to expect modest effects.

So the light effect is real, and in this study it cost about 10 minutes of sleep onset¹. The question is whether that’s the main problem with screens at night, and newer studies point elsewhere.

Night mode didn’t help sleep in a real-world trial

Most phones now offer a setting that warms the screen’s color at night, and Apple calls its version Night Shift.

In 2021, researchers at Brigham Young University tested it³. They randomly assigned 167 iPhone users aged 18 to 24 to one of three plans for a week: an hour of phone use before bed with Night Shift on, the same with Night Shift off, or no phone in the hour before bed³. Wrist sensors tracked their sleep³.

Across the whole group, the three plans made no difference, not even skipping the phone³. When the team looked only at people who slept more than about 6.8 hours, the no-phone group slept more efficiently and woke less during the night than the Night Shift group³.

The Night Shift users in that subgroup also woke more than people using phones with Night Shift off³. Don’t read too much into that. Those subgroup results were exploratory, an app glitch meant phone use couldn’t be confirmed for about 14% of people, and only 62% finished³.

The authors concluded that, for people getting enough sleep, skipping the phone beat using it with Night Shift. They suggested that what people do on their phones, such as mentally stimulating activities, may matter beyond the light³. The university funded the study, and the authors reported no conflicts³.

Blue-blocking glasses: the sleep evidence is thin

Glasses that filter blue light are sold for screen strain and sleep. In 2023, a Cochrane team led by Sumeer Singh and Laura Downie of the University of Melbourne reviewed 17 randomized trials⁴⁵.

For sleep, they found six small trials with 148 people in all⁵. Three reported better sleep scores with the glasses, and three found no difference⁵. The team rated that evidence very low in certainty and called the effects on sleep indeterminate⁵. None measured melatonin in the blood⁵.

Part of the issue is the lenses themselves. Typical blue-filtering lenses block only about 10% to 25% of blue light, the Cochrane release explained⁴. Side effects such as headaches were mild and showed up with ordinary lenses too⁴.

The researchers noted a gap between evidence and practice. In a 2018 Australian survey, 75% of the 372 optometrists who responded said they prescribed these lenses⁴. Downie said the findings don’t support prescribing them to the general public⁴.

If you already own a pair, they’re unlikely to hurt, but don’t count on them to fix your nights.

How long you stay on the screen may matter more than its glow

In 2025, researchers led by Gunnhild Johnsen Hjetland of the Norwegian Institute of Public Health published one of the largest looks yet at screens in bed⁶⁷. They surveyed 45,202 college students aged 18 to 28⁶.

Each extra hour of screen use after getting into bed went with 59% higher odds of insomnia symptoms and 24 minutes less sleep⁶. The study defined insomnia symptoms as trouble sleeping and daytime sleepiness at least three times a week for at least three months⁷.

The team expected social media to be worse than watching shows, gaming or browsing, but it wasn’t. The links with poor sleep looked similar across activities⁶⁷. Hjetland pointed to time displacement: minutes spent on a screen in bed are minutes not spent resting⁷.

This was a one-time survey, so it can’t show that screens cause poor sleep, and students who can’t sleep may reach for their phones⁷. It also didn’t measure sleep with devices⁷.

Other studies point to arousal, too. A mind kept busy by an absorbing game or a heated thread may be slow to settle. The Brigham Young team raised that idea³, and a 2020 trial found lower pre-sleep arousal when people stopped using their phones before bed⁸. Our read: time, content and light each likely play a part, with light the smallest.

“Just one more episode” has a name: bedtime procrastination

In 2014, a team of psychologists writing in Frontiers in Psychology gave the habit a name: bedtime procrastination, meaning going to bed later than you meant to when nothing outside you is stopping you¹⁰.

In their online survey of 177 adults, people who procrastinated more at bedtime tended to feel short of sleep and to sleep fewer hours, and the links were fairly strong¹⁰. About 84% said they felt they’d slept too little, or felt tired, at least one day a week¹⁰. The authors suspected that people today simply face far more distractions than a few decades ago, though they didn’t measure screen use¹⁰.

Willpower isn’t the whole story. In a 2018 study of 108 employees, University of Vienna researchers found that night owls put off bedtime more on workdays than early risers did¹¹. That suggests some “procrastination” is a mismatch between your body clock and your alarm. Lead researcher Jana Kühnel cautioned that the sample wasn’t representative¹¹.

There’s also “revenge bedtime procrastination,” a term said to have started in China. It means putting off bed on purpose, and Kühnel argues that “procrastination” doesn’t quite fit, since no dreaded task is being avoided¹¹. If that’s you, the fix may start with your schedule, not your phone.

The researchers who named the habit have suggested setting a concrete bedtime goal and taking a hard look at your evening routine¹¹. We found no trials testing those ideas.

Only 1 in 4 high schoolers gets 8 hours on school nights

The CDC tracks how many high schoolers get at least 8 hours of sleep on school nights. In its 2025 Youth Risk Behavior Survey, only 24% did, down from 27% in 2015¹².

It drops with age: 31% of ninth graders reached 8 hours, compared with 20% of 12th graders¹². The CDC notes that teens who keep screens in their bedrooms tend to sleep less, go to bed later and sleep worse, and it advises putting devices away at least an hour before bed¹².

Biology adds pressure. On the American Academy of Pediatrics (AAP) parenting site, pediatrician Anna Esparham explains that growth and body changes in the teen years can push the body clock later¹³. She advises putting all screens away at least an hour before bed and charging devices outside the bedroom overnight¹³.

In 2023, Surgeon General Vivek Murthy’s advisory on social media and youth mental health gave teens and parents similar advice, according to an Associated Press summary: limit phones, tablets and computers for at least an hour before bed and through the night¹⁴. It also urged families to agree on a family media plan¹⁴.

For younger children, our article on busy parents covers family routines. Our upcoming article on digital boundaries covers screen rules beyond bedtime.

Phones out of the bedroom: sensible, still being tested

One popular piece of advice is also the simplest: let your phone sleep somewhere else. How strong is the proof?

The main trial we found is small. In a 2020 pilot study published in PLOS ONE, 38 people were split at random⁸. Half were told to stop using their phones 30 minutes before bed for four weeks, while the other half got no instructions⁸.

The phone-free group reported falling asleep faster, sleeping longer and sleeping better⁸. They also felt less keyed up before bed, were in a better mood and did better on a memory test⁸. Sleep was self-reported in diaries and questionnaires, so the results need confirming⁸.

A bigger test is under way. At the University of Gothenburg in Sweden, researchers are recruiting 220 students aged 20 to 29 who report sleep problems, and the trial’s registry record lists December 2025 as the start of enrollment⁹. For 10 days, one group keeps phones out of the bedroom, on silent, with no screens from 30 minutes before bed⁹. Wrist sensors and sleep diaries will track results, with follow-ups at 3, 6 and 12 months, and the planned end date is June 2028⁹.

There’s a quiet lesson here for natural-health readers: the fixes with the most support aren’t products. They’re old habits: ending the day without a glowing rectangle and letting the evening be dark and quiet. You don’t need special glasses or an app to solve a problem caused by a gadget.

Your screen sunset plan and bedroom tech audit

This plan is our own, built from the studies above, and it hasn’t been tested as a package. Advice on timing varies. The publisher’s news release on the Norwegian study suggests stopping screens at least 30 to 60 minutes before sleep⁷. The CDC, the AAP and the Surgeon General advise at least an hour for teens¹²¹³¹⁴.

The screen sunset

When	What to do	Why
Early evening	Set a “go to bed” alarm for 60 minutes before lights out	Our suggestion; bedtime procrastination means missing the bedtime you intended10
60 minutes before bed (teens), 30 to 60 (adults)	Put phones, tablets and laptops away; turn off notifications	Official and research advice7121314
Same time	Plug the phone in outside the bedroom	AAP advice for teens13
If you do use a screen	Pick something with an end point, such as one episode, and turn off autoplay	Our suggestion; total time in bed on screens tracked with worse sleep6
Lights out	Use a basic alarm clock instead of your phone	Our suggestion

Night mode is fine for comfort, but don’t rely on it to protect sleep³.

The bedroom tech audit

Item	Ask yourself	Fix
Phone	Does it sleep within reach of your bed?	Charge it in the hall or kitchen13
TV or game console	Is it in the bedroom?	Move it if you can; screens in bedrooms track with shorter sleep in teens12
Tablet or laptop	Does work or streaming follow you into bed?	Keep the bed for sleep; set devices down before you lie down6
Smartwatch or speaker	Does it buzz or light up at night?	Turn on a do-not-disturb schedule7
Kids’ devices	Do they have a set “parking spot” overnight?	Write it into a family media plan14

What the evidence says, rated

Claim	What studies found	Evidence level
Screen light at night delays sleep	One tightly controlled 12-person study with four hours of reading a night: about 10 minutes later sleep, less melatonin12	Promising but early
Night mode protects sleep	No benefit in its one randomized trial, of 167 people3	Evidence says no, or unsafe (the claim failed its only test; no safety issue)
Blue-blocking glasses improve sleep	Six small, mixed trials; very low certainty5	Not enough evidence
More time on screens in bed goes with worse sleep	Clear links in a 45,202-student survey; can’t prove cause6	Promising but early
Stopping phone use 30 minutes before bed improves sleep	One 38-person pilot trial with self-reported sleep8	Promising but early
Phones out of the bedroom improve sleep	Observational links; a randomized trial is under way912	Not enough evidence

Questions readers ask

The bottom line

Screen light can nudge your body clock later, especially in long sessions. But in the studies that tested the popular fixes, night modes didn’t protect sleep and blue-blocking glasses showed no clear benefit. The bigger cost seems to be time: the minutes and hours that screens take from the night.

So the plan is simple and costs nothing. Set a bedtime and an alarm to remind you of it, put screens away 30 to 60 minutes before bed, or an hour for teens, and let your phone sleep outside the bedroom.

Related reading

• A warm shower and a to-do list do more for sleep than a nightcap
• Busy parents need a few anchors more than a perfect routine
• Sleep trackers count your hours well, but their sleep stages are rough guesses
• “FDA registered” isn’t “FDA approved”: a buyer’s map to wellness devices
• Health tracking has a helpful dose, and past it, checking feeds worry

Sources

1. Penn State News. “Light-emitting e-readers detrimentally shift circadian clock.” Pennsylvania State University, 2014. psu.edu
2. Chang A-M, Aeschbach D, Duffy JF, Czeisler CA. “Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness.” Proceedings of the National Academy of Sciences, 2015;112(4):1232-1237 (Penn State research record). pure.psu.edu
3. Duraccio KM, Zaugg KK, Blackburn RC, Jensen CD (Brigham Young University). “Does iPhone night shift mitigate negative effects of smartphone use on sleep outcomes in emerging adults?” Sleep Health, 2021. DOI 10.1016/j.sleh.2021.03.005 (journal page: doi.org; full text read via an author-manuscript copy at gwern.net)
4. Cochrane. “Blue-light filtering spectacles probably make no difference to eye strain, eye health or sleep.” News release, July 26, 2023. cochrane.org
5. Singh S, Keller PR, Busija L, McMillan P, Makrai E, Lawrenson JG, Hull CC, Downie LE. “Blue-light filtering spectacle lenses for visual performance, sleep, and macular health in adults.” Cochrane Database of Systematic Reviews, 2023, CD013244.pub2. cochranelibrary.com
6. Hjetland GJ, Skogen JC, Hysing M, Gradisar M, Sivertsen B. “How and when screens are used: comparing different screen activities and sleep in Norwegian university students.” Frontiers in Psychiatry, 2025;16. public-pages-files-2025.frontiersin.org
7. Frontiers. “Hours of screen use after bed increases insomnia risk.” Frontiers science news, March 31, 2025. frontiersin.org
8. He et al. “Effect of restricting bedtime mobile phone use on sleep, arousal, mood, and working memory: A randomized pilot trial.” PLOS ONE, 2020 (DOAJ record). pubmed.ncbi.nlm.nih.gov
9. ISRCTN Registry. “Does restrictive screen use before bedtime improve sleep in the long run? A randomised controlled trial among young adults with sleeping problems (SoS).” ISRCTN12324806, University of Gothenburg, accessed October 2026. isrctn.com
10. Kroese FM, De Ridder DTD, Evers C, Adriaanse MA. “Bedtime procrastination: introducing a new area of procrastination.” Frontiers in Psychology, 2014;5:611. frontiersin.org
11. Scientific American (from Spektrum der Wissenschaft). “It Goes by the Name ‘Bedtime Procrastination,’ and You Can Probably Guess What It Is.” Accessed October 2026. scientificamerican.com
12. Centers for Disease Control and Prevention. “Sleep” (Youth Health in Focus, Youth Risk Behavior Survey data). CDC, updated August 14, 2026. cdc.gov
13. Esparham A. “My teen is having trouble falling asleep at night. How can I help?” HealthyChildren.org, American Academy of Pediatrics, January 22, 2025. healthychildren.org
14. Associated Press. “8 tips for parents and teens on social media use — from the US surgeon general” (AP summary of the Surgeon General’s 2023 advisory, “Social Media and Youth Mental Health”). Via WVVA, May 23, 2023. wvva.com
15. MedlinePlus. “Sleep Disorders.” National Library of Medicine, updated December 4, 2025. medlineplus.gov