Screens and blue light

The light from your phone matters less than you've heard. What you do on it, and how late it keeps you up, matters more. Dim the room, and put the phone down when you're sleepy.

• Evidence: Some
• Medium effort
• Free
• Works: tonight

Why it matters

Screens can affect sleep in three separate ways, and they’re often lumped together [7]:

• Light. Light in the evening, especially blue-rich light, suppresses melatonin and pushes your body clock later [1].
• Content. A tense game, work email or an argument online keeps your mind busy.
• Displacement. One more episode or ten more minutes of scrolling pushes bedtime back.

Light: real, but usually modest

In the much-quoted 2015 e-reader study, twelve young adults read on a light-emitting e-reader or a printed book for about 4 hours before bed, for 5 evenings each. With the e-reader, they took about 10 minutes longer to fall asleep (26 vs 16 minutes), had about 12 minutes less REM, their evening melatonin was suppressed by about 55%, and their melatonin rise came more than 1.5 hours later. Total sleep did not differ [1]. A clear effect, under conditions more extreme than most evenings.

Shorter use shows smaller effects. In 16 teenagers, an hour on a bright tablet before bed made no significant difference to time to fall asleep or deep and REM sleep, compared with a dim screen [3]. A trial in 72 men found that the effect of screen light grows with its “melanopic” strength, the part of light that affects the body clock [2]. Screens tuned to be low in melanopic light, while looking the same, led to falling asleep faster than high-melanopic screens.

Your room lighting matters too. Experts recommend keeping evening light below 10 lux melanopic at eye level from at least 3 hours before bed [8]. So dim the room, not just the screen.

Content and lost time: probably bigger

In a survey of 45,202 Norwegian students aged 18 to 28, each extra hour of screen use after getting into bed was linked to 24 minutes less sleep and 59% higher odds of insomnia symptoms. The link was the same for social media and other activities [5]. A systematic review of 42 studies in 16- to 25-year-olds also linked screen use, especially phones at night, to shorter sleep, later bedtimes and poorer sleep quality [6]. These are associations: poor sleepers may also reach for their phone to pass the time awake [7].

How to do it

1. Set a “screens down” time about 30 to 60 minutes before bed, and make it the time you stop, not start, winding down. If that’s not realistic, at least stop once you notice you’re sleepy.
2. Choose calm content late at night. Familiar shows beat work email or competitive games.
3. Dim the room as well as the screen. Use warm, low lamps in the last few hours [8], and turn screen brightness down.
4. Keep the phone out of reach in bed so a wake-up at 3 a.m. doesn’t become 30 minutes of scrolling.
5. Use night mode if you like, but don’t count on it. In 167 young adults, phone use with Night Shift on gave no better sleep than phone use with it off [4].

Common mistakes

• Buying blue-light glasses to fix sleep. A Cochrane review of 17 trials found the evidence for better sleep was very uncertain: of six trials, three found better sleep scores and three found no difference [9].
• Dimming the phone under bright ceiling lights. Room light counts too [8].
• Blaming the light and ignoring the clock. If you’re up until 1 a.m. watching videos, the problem is mainly the lost hour [5].

Effect on your sleep score

• Time to fall asleep: about 10 minutes longer after hours of bright e-reader use [1]; no clear change after an hour on a tablet [3].
• Timing: bright evening screens can push your body clock later [1].
• Total sleep: in the lab, total sleep was fixed by the schedule [1]; in real life, late screen use is linked to shorter sleep [5][6].
• Efficiency and wake-ups: no phone at all beat Night Shift for efficiency and wake-ups in a subgroup sleeping over 6.8 hours, measured with wrist trackers [4]. That was an exploratory finding.
• HRV and resting heart rate: we found no study measuring these for screen use in healthy adults with wearables.

How confident: moderate that light affects the body clock; low on how much normal phone use changes your scores.

Evidence

Rated Some. Controlled studies show screen light can delay the body clock and slow sleep onset, in a dose-dependent way [1][2], but the effects at ordinary brightness and duration are small [3]. Large surveys link late screen use to shorter sleep [5][6], though they can’t show cause. A 2024 review argues the link runs both ways and that light is only one of several mechanisms [7].

Limits: the lab studies were small, in young adults, and sometimes men only [1][2][3]. The survey data are mostly from students [5][6]. Blue-light glasses trials were small and at high risk of bias [9].

General information for healthy adults, not medical advice. If you have a sleep problem that lasts, read when to see a doctor. Sources checked 4 October 2026. Spot a mistake? Tell us.