Screens before bed: what really keeps you awake

If you use a laptop or a phone in the hour before bed and then lie awake, the screen is the obvious suspect. For most people, though, the light from it plays a smaller part than its reputation suggests. What usually does more harm is what you are doing on the screen, and how much later it keeps you up.

So the changes that help are less about filters and more about timing: dim things down in the evening, stop the engaging stuff a little earlier, and keep the phone out of reach of the bed. Here is what the research does and does not say, and how to put it into practice.

What light at night does to your body clock

Your body runs on a roughly 24-hour clock, and light is the main thing that sets it. In the evening, as the light fades, your brain starts releasing melatonin, a hormone that tells the rest of the body that night is coming. Bright light in the evening can hold that back and nudge the whole clock later, so you feel sleepy later and find it harder to get up in the morning. Light toward the blue end of the spectrum has the strongest effect.

Screens give off blue-rich light, which is where the worry comes from. The question is how much. A phone or laptop at normal evening brightness is far dimmer than daylight, and often dimmer than the ceiling lights in the same room.

The best-known study on this, a lab experiment at Brigham and Women's Hospital in Boston published in 2014, had people read on a light-emitting tablet for several hours each evening, several nights in a row, and compared that with reading a printed book. On the tablet nights they took a little longer to fall asleep, their melatonin rose later, and they felt less alert the next morning. The effects were real but modest, and the setup was more intense than most people's evenings. Studies of more everyday screen use have tended to find that the light on its own makes a smaller difference.

The bigger problem: what is on the screen

Light is only one of the things a screen brings to bed. Two others are probably more important.

The content keeps you switched on. A work email, a tense group chat, the news, a game with one more level, a show that ends on a cliffhanger: all of these keep your mind busy at exactly the time it is meant to be slowing down. Even pleasant things can do it. Feeds and autoplay are designed so that there is never a natural point to stop.

The time comes out of your sleep. If you would have been asleep by 11 and the last episode ends at 12:15, that is more than an hour of sleep gone, whatever color the screen was. A number of sleep researchers now argue that this plain loss of time explains more of the link between screens and poor sleep than the light does.

This tends to happen most on the evenings after long days, and there is a reason. Wanting some time that is yours, and taking it from sleep because that is the only place left, has a name: revenge bedtime procrastination.

What actually helps

None of this means screens have to go off at 9 PM. It means the priorities are a little different from the usual advice.

Stop the engaging stuff earlier

The most useful single change is to give anything that hooks you an end point, and to put it 30 to 60 minutes before you want to be asleep. Work email and messages first: close them, and if something is nagging at you, write tomorrow's first task on a note so your mind can let go of it. Then anything with no natural end. A film has an ending. A feed does not.

Dim the room, not only the screen

If light matters, it is the total light that counts. In the last hour, switch the ceiling lights off and use a lamp. Turn the screen down as well, using the brightness keys or Control Center.

Night Shift, which warms the colors on the screen after dark, lives in System Settings > Displays, behind the Night Shift button in recent versions of macOS. You can schedule it from sunset to sunrise or set your own hours. It is easier on the eyes in a dim room. Whether it improves sleep is less clear: the few studies that have tested night modes have not found much effect on sleep on their own. Use it for comfort, and do the other things as well. The Night Shift guide covers the settings in more detail.

Pick calmer screen time

If you do want a screen in the last hour, choose things that are familiar, finite and low stakes: an episode of a show you have seen before, a long article, a recipe for the weekend. Avoid anything you have to reply to. The aim is something you can stop without a fight.

Charge your phone outside the bedroom

This is one of the changes sleep experts suggest most often, and for good reason. A phone by the bed is a screen within reach at the moments you are least able to resist it: when you can't get to sleep, when you wake at 3 AM, and first thing in the morning. Put the charger in the kitchen or the hall. If the phone is your alarm, a plain alarm clock does the job and removes the excuse.

If the phone has to stay in the room, put it across the room, face down, with a Sleep Focus on so that it stays quiet.

When the last screen is your Mac

For a lot of people who work at a computer, the last screen of the day is not the phone. It is the Mac, with one more thing to finish. That is the hardest screen time to stop, because it feels like it counts. Closing the lid at a set time, and treating that as the end of the day, does more than any filter.

This is where Notchpals can help. Its Sleep characters, Boo, Snooze, Bramble and Bitsy, work from the bedtime you set in Settings, and if Sleep is one of the areas you pick, one of them joins your crew. In the hour before bedtime, that character comes down from the notch to suggest you start winding down.

BrambleBedtime soon... I'm starting to curl up. You could start slowing down too.

Keep going past your bedtime and you get one more visit. If you have already closed the lid or left the desk, there is none, since the Sleep moments only come while you are using the Mac. If you are somehow still there between 1 and 4:30 AM, a separate Very late moment checks on you. The screen itself gets a turn too: Blip, the Eyes character every crew starts with, can drop by late in the evening (any time from 9 PM to midnight, once) to suggest dimming the screen, which is the brightness advice above arriving on cue. Nothing gets locked. It is a nudge from the top of the screen at about the right moment, which is often all it takes to make you notice the time.

When it is more than screens

Screens are one factor in sleep, and usually not the main one. Stress, caffeine late in the day, a bedtime that moves around, a warm room and alcohol all play their part, and keeping a regular bedtime often helps more than anything you do with a screen.

If you have trouble falling or staying asleep most nights for weeks, or you feel exhausted however long you sleep, talk to a doctor. Putting the phone away is good advice, but it is not a treatment for a sleep problem. For everyone else, the short version is simple: dim the lights, stop the things that hook you a little earlier, and let the phone sleep somewhere else.