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  4. The ideal bedroom: cool, dark and quiet

Cool, dark and quiet

Short answer

The ideal bedroom supports your biology on three fronts: cool, around eighteen degrees, so your core temperature can drop; completely dark, so your melatonin rises undisturbed; and quiet, to prevent micro-awakenings. Clean air and humidity between forty and sixty per cent complete it.

~18 °C
Ideal room temperature
0 lux
Aim for complete darkness
40 – 60%
Optimal humidity

Cool

Your core temperature has to drop by roughly 1.2 degrees for you to fall asleep. A cool room gets that drop going. Sleeping too warm suppresses deep sleep and REM; a bed that breathes and bedding that carries moisture away strengthen the effect.

Dark

Even faint light suppresses melatonin and disturbs the circadian rhythm. Aim for complete darkness: blackout curtains, no standby lights, and if need be a sleep mask as a last resort.

This is the cheapest improvement most bedrooms can undergo, and at the same time the most often skipped. Sit up in your own bedroom one night and count how many little lights you can see burning.

Quiet and clean

It isn't the volume of a sound that wakes you, but its sudden change. A constant background sound reduces that contrast and prevents micro-awakenings you won't even remember the next morning, but will feel.

Finally, air the room daily. A closed bedroom builds up carbon dioxide levels overnight that demonstrably worsen sleep.

Sources

  1. Okamoto-Mizuno & Mizuno (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology.
  2. Cho et al. (2016). Let there be no light: the effect of dim light at night on sleep. Sleep Medicine.
  3. Basner et al. (2014). Auditory and non-auditory effects of noise on health. The Lancet.

Frequently asked questions

Does a sleep mask really help?

It does if complete blackout isn't achievable. It is a stopgap rather than an ideal: a dark room is more pleasant than something on your face. But it is demonstrably better than light.

Which matters more: dark or cool?

Dark, because light acts directly on your hormone balance and not only on your comfort. Coolness is a solid second. Fortunately you don't have to choose — both are cheap to fix.