How to make a bedroom dark for sleeping

Stand in your bedroom at night with the lights off and wait five minutes for your eyes to adjust. You will be able to see. Most people can read the time, make out the furniture, and identify half a dozen small glowing points they had stopped noticing years ago.

How dark a bedroom actually needs to be

The 2022 consensus recommendations published in PLOS Biology suggest keeping light at the eye under about 1 melanopic lux during sleep, a maximum of 10 in the three hours before bed, and at least 250 during the day.

One lux is genuinely dark - considerably darker than most people’s idea of a dark room. Harvard Health notes that even dim light around 8 lux, roughly twice a night light and less than most table lamps, has measurable circadian effects, and that blue light suppresses melatonin about twice as long as green light of comparable brightness.

Try this tonight, for free, in this order

1. Do the walk-around. Lights off, five minutes to adjust, then find every glowing thing: router, TV standby, charger, smoke alarm, thermostat, clock, monitor, extension lead. There will be more than you expect. Most can be turned around, unplugged, moved out of the room, or covered with a small piece of electrical tape.
2. Block the gap above the curtain rail. The strip of light above a rail is the single brightest leak in most bedrooms and almost nobody addresses it. A pelmet, a board, or hanging the curtain from the ceiling instead of the frame all work.
3. Seal the gap under the door. Hallway light under a bedroom door is brighter than it looks, and a draft excluder handles both that and some of the noise.
4. Overlap the window, do not match it. A curtain the same width as the window leaves a vertical line down each edge. Several inches of overlap on each side fixes it. Blinds fitted inside the recess are the worst configuration available, because light escapes around all four edges by design.
5. Move the phone out of arm’s reach. A screen checked at 3am is the brightest thing that will happen to your eyes all night.
6. Turn the clock to face the wall. Two benefits: less light, and you stop doing arithmetic about how little sleep you are going to get.

The gear that finishes it

A sleep mask - cheapest, and the only thing that handles the whole room

Curtains deal with the window. They do nothing about a charging indicator, a partner’s phone, or a hallway light. A mask blocks light from every direction, costs about as much as lunch, travels, and works tonight.

The three failure modes are all fit problems with known fixes: light leaking at the nose, pressure on the eyelids, and bulk if you sleep on your side. The full mask guide covers which shape solves which, and side sleepers have their own shortlist.

Blackout curtains - for a permanent fix to window light

Worth it if the window is genuinely the problem and you want something that cannot slip off at 4am. Fit them wider and longer than the window, and deal with the top gap - otherwise you will have spent a lot of money and still have a bright line. Mask versus curtains, compared properly.

If you sleep during the day, you need both

Daylight is orders of magnitude brighter than anything at night and arrives from every direction. The night shift guide and the night-shift mask roundup cover that properly.

The other end of the same problem

Darkness at night is half of it. The same PLOS Biology recommendations put a daytime minimum of 250 melanopic lux at the eye, and a modern indoor life supplies far less than that. Getting proper light in the morning is the other half of keeping your body clock anchored - which is the entire argument for sunrise alarm clocks, and also an argument for going outside, which is free.

Light is one of four variables that decide whether a bedroom works at all. How to set up your bedroom for sleep covers the other three and how to tell which one is yours.