Morning

Ten minutes outside in the morning buys you the evening. Sleepiness turns up on its own at a decent hour, and the next morning is easier for it.

The body sets its clock by the light it sees early in the day. It is the strongest signal you have, it is waiting on the other side of the door every morning, and it is free.

Outdoor light is the part that does the work, and the difference between outside and inside is bigger than it looks.

Lux measures how much light lands on a surface. A well-lit kitchen gives you 300 to 500. A grey, drizzling morning on the other side of that kitchen window gives several thousand, and a bright one gives 100,000. Your eyes will not report the gap, because vision adjusts and the room feels bright enough. The clock reads it honestly, and 500 lux tells it dusk.

That first strong reading of the day sets when melatonin arrives in the evening, when you get hungry, and when your head is at its sharpest.

A week in a tent

A week of daylight is enough to move a whole group of people. Researchers measured them through an ordinary working week at home, lamps and screens and all, then sent them camping in the Rocky Mountains with sunlight, a fire and nothing else. Their clocks moved about 2 hours earlier, and the night owls moved the most. Nobody had been told to go to bed earlier. Living by daylight did it for them.

Outside, and early

Outdoors is where the light is. Glass takes most of it out, so a seat by a bright window is worth a few hundred lux while the pavement on the other side of that same glass is worth several thousand. One step past the door and you have all of it.

Early is the other half. Light in the first hour after waking pulls the clock earlier, which is what makes you sleepy at a decent hour that night. The afternoon walk is its own pleasure. The morning light is the one that sets the time.

How to get it

• 10 minutes outside in the first hour after waking, before the phone. The garden, the front step, the walk to the end of the street.
• 20 to 30 minutes when it is grey. Overcast still hands you thousands of lux, so winter mornings work. They just take a little longer.
• Hang it on something you already do. The coffee gets drunk outside, the dog goes out earlier, the last stop of the commute gets walked.
• Eat afterwards. Food is a second, weaker timekeeper, and it works best following the light.
• In midwinter, take the first daylight the day gives you. In New York in December the sun is barely up before half past seven, so the light is waiting on the way to work. Take it there.
• An open window is worth having when the morning will not allow anything else. Sit right in it, and give it longer.
• Keep the evening low and warm, and the bedroom properly dark. Morning light and night darkness are one instruction.

Give it a week or two and the evening starts arriving on its own. Sleepy at a reasonable hour, and waking that asks nothing of you.

Good hotels sell this back to us as breakfast on a terrace and a swim before anything else. It is the same light standing outside your door tomorrow morning.

You are winding the watch. The sun has kept time for everything alive since long before the first clock was ever carved, and it still sets yours each morning, for nothing at all.