Many of us end the day looking at a phone, tablet or TV. You may have heard that screens and "blue light" harm sleep. The truth is more nuanced. In Part 5 of Sleep Science, we look at how light affects your body clock, what screens really do and what to know about melatonin.
Light and your body clock
As we saw in Part 1, light is the main signal that keeps your internal body clock in sync with day and night. Special cells in the eye are especially sensitive to short-wavelength light, often called blue light, which is abundant in daylight.
When it gets dark in the evening, the brain increases production of melatonin, a hormone that helps signal to the body that it is night. Bright light in the evening can suppress melatonin and shift your body clock later, making it harder to feel sleepy at your usual time.
Do screens disrupt sleep?
Screens emit some blue light, but research suggests the light from typical phones and tablets at normal brightness has a smaller effect than bright room lighting or daylight. Some studies have found modest delays in sleep from screen use in the evening, while others found small effects.
Many experts now think that what we do on screens can matter as much as the light itself:
- Stimulating content: exciting games, stressful news or work emails can make your mind more alert.
- Time displacement: "just one more episode" or endless scrolling can push bedtime later.
- Notifications: alerts during the night can wake you or break your sleep.
Practical tips
- Try a "screen curfew" 30 to 60 minutes before bed and switch to calmer activities.
- If you use devices in the evening, lower the brightness and use night mode or warmer display settings.
- Avoid work and emotionally charged content late at night.
- Turn on "Do Not Disturb" or keep your phone outside the bedroom.
- Use warm, dim lighting in the hour before bed.
- Get plenty of bright light during the day, especially in the morning, to strengthen your body clock.
Blue-light glasses
Glasses that filter blue light are widely marketed. Current research reviews have found limited and mixed evidence that they improve sleep for most people. Simple steps like dimming lights and reducing evening screen time are free and may help just as much.
Melatonin supplements
Melatonin is available as a supplement in some countries without a prescription, while in others it requires one. It is not a sedative like sleeping pills. Instead, it mainly acts as a timing signal for the body clock.
Research suggests melatonin may help in some situations, such as jet lag and certain body-clock disorders, but its effect on general insomnia is usually modest. Important points to know:
- Speak to a doctor or pharmacist before taking melatonin, especially if you are pregnant, breastfeeding, have a health condition or take other medicines.
- Do not give melatonin to children without medical advice.
- Products can vary in the amount of melatonin they actually contain, particularly where supplements are less regulated.
- Timing matters: taking it at the wrong time can shift your clock in the wrong direction.
Key takeaways
- Bright evening light can delay your body clock; daytime light strengthens it.
- Screens affect sleep through both light and stimulating content.
- A wind-down period with dim lights and fewer screens helps many people.
- Melatonin is a timing signal, not a cure-all; seek professional advice first.
In Part 6, we look at insomnia: why it happens and what helps.
Sleep Science: the full series
- Part 1: How Sleep Works
- Part 2: How Much Sleep You Need
- Part 3: Better Sleep Habits
- Part 4: Caffeine, Alcohol and Food
- Part 5: Screens, Light and Melatonin (you are here)
- Part 6: Insomnia
- Part 7: Snoring and Sleep Apnoea
- Part 8: Naps, Shift Work and Jet Lag
This article is for general information only and is not medical advice. If you have ongoing sleep problems, loud snoring, breathing pauses or daytime sleepiness, please speak to a doctor.
