Does my bedroom need to be completely dark to sleep well?

How to get your bedroom dark enough

1. Block light from outside. Blackout curtains or a blind cut streetlights and early dawn, the two biggest sources of unwanted light in most bedrooms.
2. Kill the little glows. Cover or move standby LEDs, chargers, and clock displays; a surprising amount of disruptive light comes from these small sources.
3. Get screens out of the bed. A phone or tablet is a bright light source held close to your eyes, so charge it across the room rather than on the pillow.
4. Use a sleep mask as a shortcut. If you cannot darken the room, such as in a hotel or with a partner who reads, a mask gives your eyes darkness instantly.
5. Dim the hour before bed. Darkness matters before sleep too; lower the lights in the evening so melatonin can start rising on schedule.
6. Keep night lighting dim and warm. If you need light for a bathroom trip, use a low, warm-toned night light rather than switching on bright overhead bulbs.

Why darkness matters for sleep

Light is the master signal for your circadian clock. Special cells in the retina detect brightness and tell the brain whether it is day or night; light exposure in the evening and overnight suppresses melatonin, the hormone that promotes sleep, and can shift your clock later. This is why a dark bedroom helps you both fall asleep and stay asleep, and why light leaking in at dawn can wake you before you are ready.

The effect is not only about falling asleep. A controlled study published in PNAS found that sleeping for a single night in a moderately lit room, rather than a dim one, raised participants' overnight heart rate and worsened their insulin resistance the next morning, suggesting even modest light during sleep activates the body in unhelpful ways. You do not need a pitch-black bunker to benefit, but the evidence points consistently in one direction: darker is better, so reducing light is worth the effort.

Common mistakes

• Leaving the TV or a bright night light on all night out of habit.
• Charging a phone on the pillow where its screen and notifications light your face.
• Ignoring small standby LEDs and clock displays that add up to meaningful light.
• Having no way to block dawn light, so you wake far earlier in summer.