For most people, yes: sleeping with the light on is worse than sleeping in the dark. It makes sleep lighter and more easily broken, it can nudge your body clock, and a growing body of research links light during sleep to effects beyond sleep itself. None of this means a night light will harm you. It means that darkness is the default your body expects, and every step away from it costs a little.
If you need some light for safety, or you simply cannot sleep in the pitch dark, there is a sensible middle ground, and it is easy to reach.
What the research says
Three things are reasonably well established.
Light during sleep makes sleep shallower. Your eyelids are not opaque, and light reaching the eye at night keeps the brain slightly more alert, so you spend less time in the deeper stages and wake more easily. This is the effect people notice: a lit room feels less restful even when the hours look the same.
Light at night nudges the body clock. Light is the main signal your clock uses to set itself, and light in the middle of the night, especially towards morning, can shift the clock or suppress melatonin. A dim bulb has a much smaller effect than a bright one, and warm-coloured light less effect than cool or blue-white light.
Light during sleep may affect more than sleep. In a 2022 study by Mason and colleagues, published in the journal PNAS, healthy young adults who slept one night under moderate room light of around 100 lux had higher heart rates through the night and were less sensitive to insulin the next morning than those who slept in dim light. Larger observational studies have linked bedroom light to weight gain and to depression in older adults. These studies show associations and short-term changes, not proof of long-term harm, and the effects at the level of a dim night light are likely to be small. But the direction is consistent.
In short: Dark is best. Dim, warm and low is nearly as good. Bright, cool and overhead is the thing to avoid.
The practical middle ground
If you need to see your way in the night, use a low-level light rather than a lamp: a plug-in night light near the floor, a motion-sensor light in the hall or bathroom, or a bedside lamp on its dimmest setting. Light that comes from below and does not reach your eyes directly does the job with a fraction of the exposure.
Choose warm over cool. A warm, amber or red-toned bulb of a few lumens is enough to navigate by and has the least effect on the body clock. Avoid anything blue-white. Our guide to bedroom lighting for sleep goes into bulbs, lamps and placement.
Point it away from the bed. A light behind furniture or in an adjoining room is better than one you can see from the pillow.
Turn off the television. A screen is a bright, flickering, cool-toned light source aimed straight at your face, and falling asleep to it is the worst version of sleeping with the light on. If you need sound to drift off, use sound without the picture.
If you get up in the night, keep the lights as low as you can manage. Blasting the bathroom light at 3am makes it harder to drift off again, which is one of the small things covered in our guide to waking in the middle of the night.
If you can't sleep in the dark
Some people find complete darkness unsettling, and that is a real preference rather than a failing. A dim night light is a perfectly reasonable compromise; the gain from going fully dark is smaller than the cost of lying awake anxious. Children who are afraid of the dark are in the same position, and a warm, dim night light is the usual advice.
It can be worth asking why the dark is difficult, though. For some it is a fear that fades with gradual dimming over a few weeks. For others it is that silence and dark leave nothing to focus on except thoughts, in which case steady sound, or a short relaxation routine, may do the job that the light was doing.
If the light is not yours to control
Street lights, a partner who reads, a landing light for a child, a security light next door: for all of these, the room-level fixes are curtains, blinds and a lamp with a dimmer, covered in our guide to making your bedroom darker. The personal-level fix is a mask, which we look at in does a sleep mask actually help you sleep. For anyone sharing a room with someone on a different schedule, a mask is often the most realistic answer.
If the light is not yours to switch off
A contoured mask blocks light without pressing on the eyes, which matters if you wear it all night.
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Contoured (3D) sleep mask
Example: Manta Sleep Mask
A contoured mask has raised eye cups so the fabric does not press on your eyelids, which many people find more comfortable and which allows the eyes to move freely in REM sleep. Manta's version is marketed with adjustable eye cups and a wide, flat strap designed to reduce light leaks.
- Best for
- Side sleepers and anyone who dislikes pressure on the eyes
- Key feature
- Moulded eye cups that sit around, not on, the eyes
- Why it may help
- The main failure of a cheap flat mask is light leaking in around the nose. A contoured design with an adjustable strap closes that gap for more face shapes.
- Worth knowing
- Bulkier than a flat mask, so less convenient for travel.
Where to go next
Tonight, switch off anything overhead and anything with a screen, and if you need light, make it dim, warm and low. If that is not enough, the next step is either the window or a mask. For more short answers to common questions, see our sleep questions.
Sources and further reading
- Sleep Foundation: Light and sleep
- CDC: About sleep
- NHS Every Mind Matters: How to fall asleep faster and sleep better
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Written and reviewed by the Quiet Mind Sleep editorial team in line with our editorial policy. Spotted an error? Let us know.
