Your bed window is the hour tonight when sleep should come most easily, as your body clock sees it. Your wake window is the hour your sleep need after it, when waking should feel easiest. With a bed window of 22:45 to 23:45 and a sleep need of 8 hours, for example, your wake window is 06:45 to 07:45. Both are on the Sleep page.
What your bed window is
Your body clock runs your evening to a timetable:
- Melatonin starts rising. Research suggests your body starts releasing melatonin, the hormone that signals night, roughly 2 hours before your usual bedtime: about 6 hours before the middle of your usual night.
- The forbidden zone. The hours just before and around that point are some of the hardest to fall asleep in, because your body clock is still pushing for wakefulness. It's why an early night can fail even when you're tired.
- The sleep gate. Then sleepiness rises quite suddenly, around your usual bedtime. Researchers call this the sleep gate.
Your bed window is the hour around the sleep gate: past the point where your body clock holds you awake, and early enough to make the most of the night.
How NOYU works it out
NOYU places your bed window from the times you've woken up and fallen asleep over your last two weeks, with your most recent nights counting most, once it has a week of nights. The middle of your usual day awake times your body clock, as a well-tested model of alertness does (Hursh et al. 2004), and your window follows from it.
- It's an estimate. Research suggests sleep times place melatonin within about an hour for most people. Only a lab test measures it exactly.
- It doesn't depend on your sleep need. Your need sets your wake window and Tonight's Asleep by, not when your body clock is ready.
- It moves the way your body clock does. One late night or late morning moves it a little. A lasting change, such as a new early alarm, moves it over a week or so, the pace research suggests your body clock adjusts at.
- After a break, such as a week without your watch, it comes back once NOYU has 5 nights from your last two weeks.
Why windows differ from person to person
- Early and late sleepers. Your window follows your usual sleep times. Asleep at 22:00 and up at 06:00, it sits earlier in the evening; asleep at 01:00 and up at 09:00, later. Neither is wrong.
- Weekend lie-ins. Your window sits later on Sunday evening after a weekend of late nights and lie-ins, then drifts back through the week. That's your body clock too: in one study of older teenagers, melatonin started about 45 minutes later after a typical weekend. It's part of why Sunday nights and Monday mornings feel hard.
- Night owls. Research suggests the gap between melatonin and sleep varies more in people who sleep late, so if your window feels off, that may be why.
- Short and long sleepers. Your window comes from when you sleep, not how much you need. If you need more sleep, aim for its start. If you need less, its end is fine.
- After travel. Your body clock catches up with a new time zone at roughly an hour a day, more slowly after flying east, and NOYU keeps your window on your body's time. So after flying west it shows earlier on the local clock for the first evenings, after flying east later, and it moves towards local time as your new nights come in.
- When the clocks change. The same on a smaller scale: when the clocks go back, your window shows about an hour earlier on the first evening, then settles over the week as your body catches up.
What moves your window
- Morning daylight moves it earlier. 10 to 15 minutes outside soon after waking is the simplest way. Morning light can remind you.
- A steady wake time, weekends included, keeps it steady. In one study, waking 3 hours later for two weeks moved melatonin more than 2 hours later.
- Dim evenings protect it. Research suggests ordinary room light in the evening holds melatonin back. Wind down and Screens away can remind you.
- Caffeine late in the day works against it. Last coffee reminds you 8 hours before your bed window.
- Naps don't move it, but a long or late one takes the edge off your sleepiness, so your window is harder to use. Short and early is best.
All of them are under Reminders in the Sleep page's menu.
Your nights on the Sleep page draws both windows behind your nights, so you can see which nights fell inside them.
Tonight
In the evening, from 4 hours before your bedtime, Tonight leads the Sleep page:
- Wind down in: how long until it's time to start winding down.
- Bed window: tonight's hour.
- Asleep by: the time to aim to be asleep.
- Up at: the time to get up.
When NOYU suggests an earlier night
NOYU aims for the time inside your bed window that gets you your sleep need before your usual wake time: nearer its start if you need more sleep, nearer its end if you need less. If your usual bedtime (your usual on the Sleep page) is later than that, NOYU suggests going to sleep up to 15 minutes earlier than usual, keeping your wake time the same. As your nights move earlier, your usual moves with them, and NOYU keeps stepping, 15 minutes at a time, until you're there. Small steps are easier to keep than one big change. It never steps you to before your window, because before it sleep is hard to come by, and it never suggests a later night than your usual.
NOYU doesn't suggest a step on a night after a hard session late in the day. When you've been slow to fall asleep lately, it doesn't step either, because morning daylight helps more.
Reminders
Wind down reminds you 40 minutes before tonight's bedtime by default, and moves when your bedtime does. Tap Remind me on Tonight to set it. For it and the others, such as Screens away, Morning light and Last coffee, choose Reminders from the Sleep page's menu.
Regular bedtime or Bed window
They're two different streaks:
Regular bedtime: asleep within 15 minutes of your usual time, the middle of your last 14 nights. Bed window: asleep inside the hour your body clock sets. Best of all is both: the same time every night, inside your window.
To work on your window, try the Get to bed in your bed window experiment, or ask NOYU in the chat.
