Darkness

Darkness is free, yet hardly any bedroom can provide it anymore. That is why the best hotels in the world have started charging for it.

The loss of true darkness at night is relatively recent. A street lamp went up outside. The charger, the clock and the smoke alarm all have a little light on them, because a light is cheap to add and looks like proof the thing is working. It became the new norm, to ignore the faint glow and go to sleep.

What one night of light does

Your body reads even a little light as a small emergency.

Researchers at Northwestern put healthy young adults to bed for two nights. The first night everyone slept in a properly dim room, under 3 lux. On the second night, half of them slept in a room lit to 100 lux, roughly an overhead light left on in a hallway, nothing anyone would call bright. Everyone stayed asleep and nobody reported being disturbed, so from the outside the night looked fine.

Inside the body it was a different night. Their heart rate ran higher throughout, and their nervous system stayed in its daytime setting. The ones who had slept in the dark handled a sugary drink better the next morning, and needed less insulin to do it. One night made that difference.

100 lux is less light than you need to read comfortably. A living room in the evening runs about that, and an office generally runs five times more. Nobody would call the room in that study bright, and one night in it was enough to change heart rate and blood sugar.

The cells that only report light

A set of cells at the back of your eye has one job: to report how much light there is. They are not for seeing. They tell the body what time it is, and they react most to blue light, which is what a standby lamp, a phone screen and a street lamp mostly give off.

They also work through closed eyelids. An eyelid is thin, and enough light gets through it to keep them reporting all night.

You can sleep straight through all of it and still get the light, which is what happened to everyone in the study. Make the room dark and the cells go quiet.

A thousand dollars a night

The best hotels already worked this out and put a price on it. There are now suites built around a good night's sleep, sold for over $1,000 a night, with darkened windows, filtered air and a very good bed.

Most of what you are paying for there is a room with the absence of: light, noise, fumes. At home, the darkness part of that costs only as much as a blackout setup.

How to make a bedroom genuinely dark

Here are things you can do, in the order that gives you the most darkness for the least effort.

• Kill the small lights first. Walk into the bedroom at night, stand still for a full minute until your eyes adjust, and count every glowing thing. Most people find between four and nine. Unplug what can be unplugged, and put a strip of black electrical tape over the rest. This is an easy and straightforward step.
• Close the seam. If you already have blackout curtains, they might be leaking down the middle, where the two panels meet, and around the edges. Overlap the panels and clip them shut, or move the rail wider and higher than the window so the fabric falls past it on every side. In short, make the curtains work.
• Deal with the door. A lit hallway throws a bright strip of light under the door. A rolled towel or a draught excluder ends it fast.
• Move the phone out of the room. The distraction and light that your phone gives off while you scroll in bed is only part of it. You kill two birds with one stone and remove the disturbance along with the source of electromagnetic fields from beside your bed. And you get to own a real alarm clock. Choose one without a permanently lit face.
• Deal with the street. Quality blackout curtains or external blinds are not entirely cheap. But if the lamps outside still light your room, this step is worth it. The curtains I would actually buy are in the blackout group of the Hearth directory. I would avoid the plastic-lined ones.
• A good sleep mask is the fallback. Not as good as a dark room, because light still reaches you at the edges, but far better than nothing and a great option in a hotel or on a train.

Get into bed, turn everything off, and wait ten minutes. Then hold your hand in front of your face. If you can see it, the room is not dark yet.

Give it two weeks

The first few nights in a properly dark room can feel oddly empty, the way a house does after the fridge stops humming. It passes. By the second week you might not want to look back: especially if you start waking a little before the alarm, and have an easier first hour.

Darkness is one of six principles I hold dear, and the rest of them are in The Hearth. The companion pieces, on the air in a closed room and the temperature of it, are showing you the foundations of a good night.