How to fix your sleep schedule with light timing

If you fall asleep later than you'd like, or your hours keep changing, you can use light to move your body clock. Going from a 1:30 a.m. bedtime to 11:30 p.m. takes about two weeks if you do it in small steps.

How light changes when you feel sleepy

Your body clock sets itself by the light that reaches your eyes. Bright light in the morning, after you wake, tends to shift your clock earlier, so you feel sleepy earlier and wake earlier. Bright light in the late evening does the reverse, keeping your clock running later ¹². Keeping the evening dim lets melatonin rise at its normal time.

How to wake up and fall asleep earlier

Without light to reset it, most people's body clock runs a little later each day ³, so moving earlier is harder than moving later.

How fast to change your wake time

Move your wake time 15 to 30 minutes earlier, hold it for two or three days, then take the next step. The first day or two after each change can feel rough. Burgess and colleagues had volunteers move sleep an hour earlier each day for three days. The group given repeated sessions of bright morning light shifted further than the group kept in dim light ⁴. You won't get that much light at home, so move in smaller steps than they did.

Move your bedtime earlier by the same amount as the alarm, but if you are not sleepy at the new time, stay up in dim light until you are. You usually start feeling sleepy earlier within a few days of each change. Going to bed before you're sleepy tends to mean lying awake, because the hour or two before your usual bedtime is often when you feel most awake ⁵.

How much sleep you still need

Adults generally need at least seven hours of sleep on a regular basis ⁶. Count back from your new wake time. Your planned bedtime should leave room for seven hours of sleep plus however long it takes you to fall asleep. If it doesn't, move the alarm more slowly instead of forcing yourself to bed earlier.

Get bright light in the morning and less at night

• Morning: get outside within the first hour after your new wake time. If it's still dark, the morning sunlight guide explains what to do until the sun is up.
• Evening: for the last three hours before your target bedtime, keep the lights low and warm and turn screen brightness down. Ordinary room light before bed delays melatonin and cuts it short ⁷, and bright tablet reading at night pushed sleep timing later in a lab study ⁸. A 2022 expert panel recommends keeping light very dim for those three hours ⁹. Turning off the overhead lights and using one or two low, warm lamps gets you much closer to that.
• Night: keep the bedroom dark.

Example schedules for moving earlier

In each example you keep the same times for two or three days before moving again, and you get at least seven and a half hours in bed.

Example 1: you sleep from 1:30 a.m. to 9:30 a.m. and need to be up at 7:30 a.m. Moving 20 minutes every two days takes about two weeks.

Example 2: you start a new job in two weeks and need to get up an hour earlier. You sleep from midnight to 7:30 a.m. now and need a 6:30 a.m. alarm, so you move 15 minutes every two or three days.

Example 3: it's winter and still dark at your new wake time. You sleep from 12:45 a.m. to 8:45 a.m., want to wake at 7 a.m., and sunrise is around 8 a.m. You move 25 to 30 minutes at a time. From day 7 the alarm goes off before sunrise, so turn on your brightest lights first and go outside once it's light.

What to do if waking earlier leaves you exhausted

Sometimes the alarm moves earlier but you still can't fall asleep until your old time. You lose sleep with each change and get more tired as the week goes on.

If that is happening, stop moving the alarm and stay at your current times for a few extra days. Keep the wake time where it is, including weekends, and get more light in the morning. Get outside within half an hour of the alarm, or as soon as it's light, and stay out 10 to 30 minutes, closer to 30 minutes if it's cloudy. Start dimming the house earlier in the evening. Move the alarm again once you are getting sleepy at the new bedtime.

A short nap can help on the hard days. Keep it to around 10 to 20 minutes and before mid-afternoon. After a night of short sleep, a 10-minute afternoon nap improved alertness in one study without the grogginess of longer ones ¹⁰. Keep caffeine to the morning and early afternoon so it doesn't keep you up later.

If you are sleepy enough that driving feels unsafe, don't drive, and slow the plan down.

How to shift your sleep later

Sometimes you want to go to bed and wake up later, for example before several late nights in a row, a trip west across time zones, or a run of late shifts. To stay on a later schedule, get bright light in the evening. In the morning, keep the lights low and wear sunglasses outside for the first couple of hours after you wake. This is the usual approach for westward travel ¹¹. When you want to go back to your normal times, start getting light in the morning again.

Using light if you work shifts

Light can help you stay alert during a shift and sleep afterward, by moving your body clock toward your working hours ¹².

• When you need to be alert, get into brighter light. Around the time you want to sleep, keep light low.
• On the way home after a night shift, wear dark sunglasses and avoid bright light so it's easier to fall asleep when you get in.
• Make the bedroom fully dark during the day so daylight doesn't wake you up early.
• Keep sleep and wake times as steady as your roster allows, and expect your body to take a few days to adjust after each change. Night-shift workers who adjusted only partly still had better alertness and mood in a lab simulation ¹².

Why your sleep schedule moves later again

Sleeping in two or three hours on weekends shifts your clock later, and the alarm on Monday feels hard again. Skipping morning light for a few days does the same. Keep the wake time within about an hour across the whole week.