Almost all sleep advice concerns the bed, and almost none of it concerns the air, light and sound of the room around it, which is where a sleeper spends every one of those eight hours.
Where to start
What does a bedroom do to a sleeper overnight?
A closed bedroom changes across a night: the air cools or warms, humidity and carbon dioxide build, and light and sound arrive on their own schedule.
Outdoor air keeps cooling toward a low near dawn, a shut room holds the moisture and carbon dioxide of everyone breathing in it, and street light and early sun reach the bed whether anyone is awake or not. None of this is visible from the pillow, and most of it can be checked with an inexpensive meter.
This publication collects what published research, health agencies and building science say about those conditions, and what that means for a person trying to sleep.
Which conditions are worth checking at home?
Five: air temperature at the pillow, relative humidity, carbon dioxide in a shut room, light at the pillow, and the noise events that wake people.
The overnight curve rather than the thermostat setting, and the ranges health services publish.
What a closed door does across eight hours, where condensation starts, and the band agencies advise.
How carbon dioxide builds in a shut bedroom and what ventilation research says about it.
Light at the pillow before dawn, and the noise peaks that wake a sleeper.
How does this site reach its figures?
By reading published studies and agency guidance, and by counting what sources state. No instrument has been run in any room for this site.
Every figure is linked to the page it came from, in the sentence that uses it, so any number can be checked against its source. Where a common claim about bedroom air turns out to be unsupported, the page says so in the sentence that carries the claim. The method page sets out the rules.
Latest guide
Dust mites need 70% humidity, so what does that mean for your bedroom?
The 70% figure comes from lab studies of how house dust mites keep water in their bodies. People often repeat it as if mites switch on at 70% and off below it. The research describes a slope, not a switch, and that slope runs thro