Make the bedroom cool and dark

A cool, dark, quiet room removes the signals that keep the brain in "day" mode.

Why it works

Falling asleep requires a small drop in core body temperature, and a cool room helps the body shed heat to trigger it. Darkness matters because even modest light at night suppresses melatonin and lightens sleep. Removing heat, light, and noise lowers the arousal signals that compete with sleep onset and continuity.

How to do it

1. Keep the room on the cool side — many people sleep best somewhat below normal daytime comfort.
2. Block light with blackout curtains or an eye mask, and cover small device LEDs.
3. Reduce noise with earplugs or steady background sound if your environment is loud.

Evidence

The drop in core temperature at sleep onset is well established, and laboratory studies show light exposure before and during sleep suppresses melatonin and disrupts sleep. (observational)

Ideal temperature varies by person and bedding; the principle (cool enough to shed heat, dark enough to protect melatonin) is what holds.

Sources

• Cho et al. (2016), effects of light at night on sleep and melatonin, Chronobiology International

Common mistake

Leaving a TV, charging lights, or a bright clock visible — small light sources at night still nudge the clock and lighten sleep.