# Screens, blue light and sleep: how much does your phone matter?

Source: https://sleepfacts.uk/sleep-better/screens-and-blue-light/
Author: Tess Marlow · Updated 2026-11-04

**Short answer:** Bright light in the evening, including from screens, holds back melatonin and shifts the body clock later. In a lab study, reading on a bright tablet for four hours a night delayed sleep and the body clock compared with a printed book. In everyday life the light effect of a phone is smaller; what you do on it, and how long it keeps you up, probably matters more.

**Evidence grade:** Weak evidence. Small or short studies, surveys, or results that are mixed.

## Why does evening light matter?

Your [body clock](/how-sleep-works/body-clock/) uses light to tell the time. Light-sensitive cells in the eye, most responsive to blue light, signal the brain's master clock. Bright light in the evening holds back melatonin, the hormone that tells your body it is night, and pushes the clock later, so you feel sleepy later.

Screens give off blue-rich light. So do LED room lights and daylight, which is far brighter than any screen.

## What did the tablet study find?

The most cited study was run at Harvard. Twelve young adults lived in a sleep lab for two weeks. For five evenings they read on a light-emitting tablet for four hours before bed, and for five evenings they read a printed book in dim light.

After the tablet, compared with the book, they:

- took longer to fall asleep,
- felt less sleepy in the evening,
- released less melatonin, with its rise delayed,
- had a later body clock,
- had less REM sleep, and
- felt less alert the next morning.

It was a careful study, but small, and four hours of bright tablet reading at close range is more light than most people get from a phone. The differences were measurable but not dramatic.

## So is my phone ruining my sleep?

Probably less through its light than through what it does to your evening:

- **Time.** Scrolling, games and streaming push bedtime later without you noticing.
- **Arousal.** Work email, news and arguments wind you up rather than down.
- **Interruptions.** Notifications in the night wake you.

That's why we grade the evidence for the light itself as weak: the lab effect is real, but studies in everyday settings find smaller and less consistent effects. The overall advice still makes sense.

## What helps?

- Stop using screens for the last 30 to 60 minutes before bed if you can. The NHS advises not using devices right before bed.
- If you do use them, turn the brightness right down and hold them further from your face.
- Keep the phone out of reach of the bed, or at least on silent with notifications off.
- Dim the room lights in the evening too, and use warm-coloured bulbs in the bedroom.
- Get bright daylight in the morning, which makes your clock less sensitive to evening light.

## Frequently asked questions

### Does night mode help you sleep?

It reduces blue light, which should lessen the effect on melatonin a little, but studies of night mode settings have not found clear improvements in sleep. Turning the brightness down and putting the phone away earlier probably helps more.

### Do blue-light-blocking glasses work?

The evidence is weak and mixed. A Cochrane review found no clear benefit for eye strain or sleep from blue-light-filtering lenses in the general population. Dimming lights and screens does a similar job for free.

### Is watching TV in bed bad for sleep?

A TV across the room gives off far less light at your eyes than a phone held close. The bigger problems are staying up later than you meant to, and, for people with insomnia, the bed becoming a place for being awake.

## References

1. [Chang AM et al. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. PNAS, 2015.](https://pubmed.ncbi.nlm.nih.gov/25535358/)
2. [NHS. Insomnia: how you can treat insomnia yourself.](https://www.nhs.uk/conditions/insomnia/)
3. [Czeisler CA et al. Stability, precision, and near-24-hour period of the human circadian pacemaker. Science, 1999.](https://pubmed.ncbi.nlm.nih.gov/10381883/)
4. [Singh S et al. Blue-light filtering spectacle lenses for visual performance, sleep, and macular health in adults. Cochrane Database of Systematic Reviews, 2023.](https://pubmed.ncbi.nlm.nih.gov/37593770/)