Light and sound in the bedroom

How much light does it take to change a night's sleep?

Less than most people picture as darkness. One night at 100 lux raised heart rate, and the average adult's melatonin halved near 25 lux.

Light is counted in lux. In a Northwestern laboratory study, young adults slept one night under 3 lux and one under ordinary room light at 100 lux. That single lit night raised nighttime heart rate and next-morning insulin resistance (Healio, 2022).

Evening light works on an even lower threshold. A study of 55 adults found the average person's melatonin cut in half at 24.60 lux, with people ranging from 6 to 350 lux (Phillips et al., 2019). Even 1 lux all night left 33 volunteers with more broken sleep, although their melatonin did not fall (IJERPH, 2020).

Children look at least as sensitive, so a child's room needs to be just as dark for sleep. In preschool-aged children, melatonin fell an average of 78 percent in response to light at 5 to 40 lux (University of Colorado Boulder, 2022).

How do you keep a bedroom dark with curtains or shades?

Blackout cloth blocks nearly all light. The glow comes in at the edges, so a bedroom gets dark by closing the gaps around curtains and shades.

A curtain lets light in over its rod, at its sides, at the center split and under its hem. Trade guidance says to hang the rod 4 to 6 inches above the frame and 6 to 12 inches past each side, with fabric 2 to 2.5 times the rod width (Curtarra, 2025). An inside-mounted shade leaves a gap of ⅛ to ½ inch at each side (Canisteo Blinds).

Of 24 seller pages Night Air read in September 2026, most rated the cloth alone, and 6 of the 10 shade pages warned that light gets past the edges. The full account of hanging, mounting and layering is in How do you keep a bedroom dark with curtains or shades?

Does white noise help you sleep, and how should you set it up?

Steady sound masks the peaks that wake a sleeper. The evidence is graded low, and the lowest level that hides the noise is the one to use.

White noise works by masking. In a small sleep-lab study, arousals rose from 13.3 per hour to 48.4 under recorded intensive care noise, and sat at 15.7 when white noise was added to the same recording (Sleep Medicine, 2005). A crossover trial found sleep onset 38 percent faster at 46 dB (Frontiers in Neurology, 2017).

The wider evidence is weaker. A 2021 review of 38 studies graded it low, and a 2026 lab trial found that pink noise cut dream sleep while foam earplugs worked better (SLEEP, 2026). Volume, placement and the sound being covered are set out in Does white noise help you sleep, and how should you set it up?

What noise level do health agencies publish for a bedroom at night?

WHO community guidance puts a bedroom at under 30 dB(A) at night. The peaks matter more than the average, since a single event can wake.

The World Health Organization's community noise guidance recommends less than 30 dB(A) in bedrooms at night (WHO). Outside the bedroom it sets a night target of under 40 dB(A). A quiet bedroom of the kind that guidance describes is quieter than most people's idea of quiet.

Averages hide what wakes people. A bus, a door or a voice is a short peak above the background, and the masking study above shows why a steadier background makes those peaks stand out less. That is the whole case for a fan or a sound machine.

Machines bring their own risk. All 14 infant sleep machines in one test passed 50 dBA at 30 cm at full volume, and three passed 85 dBA (ENTtoday, 2014). Distance from the bed and a modest setting do more for safety than any choice of sound.

Where do light and sound get into a bedroom?

Mostly through the window. Glass lets light pass and gaps let sound pass, and curtains do far more for the first than for the second.

The window is the weak point for both. Light comes through the glass and around whatever covers it. Sound comes through the glass too, and through every gap in the frame, the door and the vents.

Fabric helps with light far more than with sound. An acoustics supplier puts the realistic reduction from even heavy, well-sealed curtains at 1 to 5 decibels (Second Skin Audio, 2025). Stopping sound takes mass and a sealed edge, which a hanging curtain does not have.

Opening the window adds to both. Earlier work summarized in one study found that an open window lowers carbon dioxide while noise rises (PMC observational study). So a room that needs fresh air and quiet at once has a trade to make.

What do children's rooms and daytime sleepers need from a dark room?

Young children react to dim light at least as much as adults, and day sleepers face full sun. Both need closed edges, and a child needs no cords.

A child's room has two separate needs. The first is darkness, since preschool children's melatonin fell sharply under light most adults would call dim. The second is safety. Since December 2022, the Consumer Product Safety Commission has treated stock window coverings with hazardous operating cords as a substantial product hazard (Federal Register, 2022). A cordless lift, a wand or a motor avoids the question.

A daytime sleeper faces the brightest hours of the day. One night of sleep under 100 lux raised heart rate in a lab study (Mason et al., 2022), and a sunny window behind a single shade gives off far more than that at its edges. In Night Air's judgement, a shade and a curtain together are the setup to plan on from the start for day sleep.

How do light and sound connect to heat and fresh air?

The same window lets in sun heat, street noise and fresh air. Covering it or shutting it changes all three at once, so the topics overlap.

A closed curtain on a sunny afternoon keeps the bedroom cooler by bedtime. Closed drapes with white plastic backings can cut summer heat gain by about 33 percent (Consumer Reports, 2023). Night Air's bedroom temperature topic follows that heat through the night.

Shutting the window for quiet keeps the stale air in. The bedroom air topic sets out what a shut room does to carbon dioxide, and the ways to bring fresh air in without opening the glass.

A fan sits across all of these. It moves air across the skin on a warm night, and it also makes a steady sound that can mask street noise. That is why a fan turns up in Night Air's guides on heat and on sound alike, and why the room check asks about both.

What can a reader check at dawn and in the night?

Lie in bed at first light and look at the window edges. For sound, a phone reading at the hour the waking happens shows the peaks.

Light leaks are easiest to find from the pillow at dawn. Lie where the head rests and look at the top of the curtain, the sides of the shade and the floor. The brightest strip is the first one to close, and in most rooms it is the one above the rod or the shade roll.

Sound is easiest to find at the hour it wakes someone. A phone sound meter app gives a rough reading, good enough to tell a steady hum from a sharp peak. The peak is what a masking sound has to cover.

Night Air's room check starts from whether light or a sound is what wakes a sleeper. It points to the one check worth doing first.

What has Night Air published on this?

Common questions

How dark does a bedroom need to be?
Dark enough that the furniture is hard to make out. One night at 100 lux raised heart rate in a lab study, and the average adult's melatonin halved at about 25 lux.

Do blackout curtains block all light?
The cloth can block nearly all of it. Light still gets in around the edges, over the rod and under the hem, so the fitting decides how dark the room gets.

How quiet should a bedroom be at night?
WHO community guidance recommends less than 30 dB(A) in bedrooms at night, and under 40 dB(A) outside them.

Does white noise help sleep?
It can mask the peaks that wake people, and one trial found faster sleep onset at 46 dB. A review of 38 studies graded the evidence low.

Do curtains block noise?
Only a little. An acoustics supplier puts the realistic figure for heavy, well-sealed curtains at 1 to 5 decibels.

Sources

Night Air's reading for this piece, in the order it is cited, each with the question it helped answer.

Healio, 2022 (healio.com), helped answer “How much light does it take to change a night's sleep?”.
Phillips et al., 2019 (pmc.ncbi.nlm.nih.gov), helped answer “How much light does it take to change a night's sleep?”.
IJERPH, 2020 (pmc.ncbi.nlm.nih.gov), helped answer “How much light does it take to change a night's sleep?”.
University of Colorado Boulder, 2022 (colorado.edu), helped answer “How much light does it take to change a night's sleep?”.
Curtarra, 2025 (curtarra.com), helped answer “How do you keep a bedroom dark with curtains or shades?”.
Canisteo Blinds (canisteoblinds.com), helped answer “How do you keep a bedroom dark with curtains or shades?”.
Sleep Medicine, 2005 (utsouthwestern.elsevierpure.com), helped answer “Does white noise help you sleep, and how should you set it up?”.
Frontiers in Neurology, 2017 (ncbi.nlm.nih.gov), helped answer “Does white noise help you sleep, and how should you set it up?”.
SLEEP, 2026 (pmc.ncbi.nlm.nih.gov), helped answer “Does white noise help you sleep, and how should you set it up?”.
WHO (who.int), helped answer “What noise level do health agencies publish for a bedroom at night?”.
ENTtoday, 2014 (enttoday.org), helped answer “What noise level do health agencies publish for a bedroom at night?”.
Second Skin Audio, 2025 (secondskinaudio.com), helped answer “Where do light and sound get into a bedroom?”.
PMC observational study (pmc.ncbi.nlm.nih.gov), helped answer “Where do light and sound get into a bedroom?”.
Federal Register, 2022 (federalregister.gov), helped answer “What do children's rooms and daytime sleepers need from a dark room?”.
Mason et al., 2022 (pubmed.ncbi.nlm.nih.gov), helped answer “What do children's rooms and daytime sleepers need from a dark room?”.
Consumer Reports, 2023 (consumerreports.org), helped answer “How do light and sound connect to heat and fresh air?”.