Light Pollution and Sleep: How Light at Night Affects Your Body (and What to Do)

Look around your bedroom tonight after you switch off the lamp. There's probably a glow from the streetlight through the curtains, a little blue light on the TV, the green dot on a charger, the phone screen that lights up every time a notification arrives. It doesn't seem like much. But your body notices more than you might think.

For most of human history, nights were properly dark. Now, artificial light at night is everywhere. Studies of satellite data have found that most people in the U.S. and Europe live under skies so lit up that the Milky Way is hidden. That glow doesn't just hide the stars. It can mess with the internal clock that tells your body when to sleep and when to wake.

How light controls your body clock

Inside your brain sits a tiny area called the suprachiasmatic nucleus, your master clock. It uses light signals from your eyes to keep your body on a roughly 24-hour schedule, called your circadian rhythm. This rhythm affects:

• When you feel sleepy and alert
• Hormone release, including melatonin and cortisol
• Body temperature
• Digestion and metabolism
• Mood

Your eyes contain special light-sensitive cells that are especially responsive to blue-wavelength light, the kind that's plentiful in daylight. Bright light in the morning tells your brain, "It's day, be alert." As light fades in the evening, your body starts releasing melatonin, a hormone that helps prepare you for sleep.

Artificial light at night, especially bright or blue-rich light, can delay or suppress melatonin release and shift your body clock later. That can make it harder to fall asleep and lower your sleep quality.

How light at night affects sleep and health

Harder to fall asleep

Exposure to bright light in the evening, including from screens and overhead lights, can delay melatonin and make you feel more alert at bedtime.

Lighter, more broken sleep

Even dim light while you sleep may affect your body. A 2022 study from Northwestern University found that sleeping with moderate light for one night raised participants' heart rate and increased insulin resistance the next morning compared with sleeping in dim light. That was a small study, but it suggests light at night may affect more than just sleep.

Links to longer-term health

Large observational studies have linked exposure to light at night with higher risks of weight gain, obesity, depression and other health concerns. These studies can't prove that light causes these problems, but they add to a growing body of evidence that darkness at night matters for health.

Shift workers and night owls

People who work night shifts are exposed to light when their bodies expect darkness, which may be one reason shift work is linked to sleep problems and other health issues.

Sources of light pollution in your home

Light at night comes from both inside and outside:

Outdoor light pollution

• Streetlights
• Neighbors' security lights
• Car headlights
• Light from shops, signs and billboards

Indoor light at night

• Overhead lights left on late in the evening
• Phones, tablets, laptops and TVs
• Standby lights on chargers, routers and electronics
• Hallway or bathroom lights shining under the door
• Bright alarm clock displays

How to make your bedroom darker

Block outdoor light

• Use blackout curtains or blinds
• Add a curtain liner to existing curtains
• Close gaps around blinds with blackout tape or curtain extensions
• Consider window film for small or awkward windows

Cover small light sources

• Put tape or stickers over standby lights on electronics
• Turn alarm clock displays away from your bed or dim them
• Unplug or switch off devices you don't need overnight

Try a sleep mask

A comfortable sleep mask is a simple, cheap way to block light, especially when traveling or if you share a room with someone who stays up later.

Use dim, warm nightlights

If you need a nightlight for safety, choose a dim, warm-colored one placed low to the ground, rather than a bright white light.

Circadian-friendly lighting at home

You don't need to sit in the dark every evening. A few lighting changes can help your body clock stay on track.

Bright light in the morning

Get outside within an hour or two of waking if you can. Even on a cloudy day, outdoor light is much brighter than indoor light. Open your curtains as soon as you get up, and sit near a window for breakfast. This is also one of the best tools for fighting the winter blues and seasonal affective disorder.

Dimmer, warmer light in the evening

• Switch from overhead lights to lamps after dinner
• Use warm-white bulbs (often labeled around 2,700K or lower) in bedrooms and living rooms
• Consider dimmable bulbs or smart bulbs that shift to warmer tones in the evening

Limit screens before bed

Screens give off light that can affect melatonin, and what you're doing on them, like scrolling news or answering emails, also keeps your brain alert. Try:

• Turning screens off 30 to 60 minutes before bed
• Using night mode or warm-light settings in the evening
• Turning brightness down
• Charging your phone outside the bedroom

Our guides to digital detox and how to stop overthinking at night can help you build a calmer wind-down routine.

Do blue light glasses help?

The evidence is mixed. Some small studies suggest blue-blocking glasses in the evening may help some people, but reviews haven't found strong, consistent benefits. Cutting screen time and dimming lights is likely to make more difference.

Light pollution and the wider environment

Light pollution affects more than human sleep. Artificial lights at night can disorient migrating birds, confuse sea turtle hatchlings and disrupt insects, including pollinators. Some communities are adopting "dark sky" lighting rules with shielded, downward-facing and warmer outdoor lights.

You can help at home:

• Use outdoor lights only when needed, with timers or motion sensors
• Choose shielded fixtures that point light down, not up or sideways
• Pick warmer outdoor bulbs
• Turn off decorative outdoor lights late at night

Get your daylight, too

Darkness at night is only half the story. Getting enough natural light during the day helps strengthen your circadian rhythm so your body knows the difference between day and night. Time outdoors also comes with its own benefits, which we explore in our guides to forest bathing and awe walks.

A light plan for your whole day

The easiest way to think about light is as a daily schedule. Your body clock likes a clear contrast: bright days and dark nights.

Morning (first two hours after waking)

• Open curtains right away
• Get outside for 10 to 20 minutes if you can, even on cloudy days
• Eat breakfast near a window

Daytime

• Work near natural light when possible
• Take short breaks outside. Our microbreaks at work guide has ideas.
• Keep indoor spaces well lit while you're active

Evening (two to three hours before bed)

• Switch from overhead lights to lamps
• Use warmer, dimmer bulbs
• Turn on night mode on screens and lower brightness

Bedtime and overnight

• Make the bedroom as dark as possible
• Use a dim, warm nightlight low to the floor if needed
• Keep phones face down or out of the room

If you work nights or have an early schedule

Shift workers and people with unusual schedules face extra challenges because they often need to sleep while it's light outside. A few strategies can help:

• Use blackout curtains and a sleep mask for daytime sleep
• Wear sunglasses on the way home after a night shift to reduce bright morning light before sleep
• Keep a consistent sleep schedule, even on days off, as much as you can
• Use bright light during your shift to help you stay alert
• Talk to a doctor if you're struggling, since shift work sleep problems are common and treatable

Our guide to how much sleep adults need explains why getting enough sleep matters, whatever time of day you get it.

Frequently asked questions

Does light at night affect sleep?

Yes. Bright or blue-rich light in the evening can delay melatonin release and shift your body clock, making it harder to fall asleep and potentially lowering sleep quality.

Should I sleep in complete darkness?

A dark bedroom is generally best for sleep. Research suggests that even moderate light during sleep may affect heart rate and metabolism. If you need light for safety, use a dim, warm nightlight placed low.

Do blackout curtains help you sleep?

Blackout curtains can help by blocking streetlights and early morning light, especially if you live in a bright urban area or sleep during the day.

Is it bad to sleep with the TV on?

A TV gives off light and noise that can disrupt sleep. If you use it to fall asleep, set a sleep timer so it turns off.

What color light is best before bed?

Dim, warm light, like amber or warm white, is better in the evening than bright, cool or blue-rich light.

Your environment shapes your sleep. See how your environmental and physical wellness are doing with our free wellness wheel quiz.