Today's three-minute lesson

Phones, Screens and Bedtime Delay

Your phone can affect your sleep before you have even tried to fall asleep.

We often hear that screens are bad for sleep because of blue light.

Light does matter. Bright light in the evening can interfere with the natural rise in melatonin that helps your body prepare for sleep. Holding a bright screen close to your face may therefore make it harder for your brain to recognise that the day is ending.

But light is only part of the problem.

Phones are designed to hold your attention. Messages, videos, news, games and social media provide a continuous stream of stimulation with no obvious finishing point.

You may pick up your phone intending to check one thing and find that twenty or thirty minutes have passed.

This is known as bedtime delay.

Sometimes you are already tired enough to sleep, but continue scrolling, watching or replying instead of beginning the final part of your bedtime routine.

The phone has not necessarily prevented sleep.

It has prevented bedtime.

This distinction matters because no relaxation technique can replace time that has been taken away from sleep.

The content you consume can also influence how alert you feel.

A work email can return your mind to tomorrow's responsibilities. A news story can make you anxious. A conversation can become emotionally charged, while a short video can lead immediately into another one.

Even content that feels relaxing can keep you engaged for longer than you intended.

Yesterday, you looked at alcohol and the difference between feeling sleepy and experiencing good-quality sleep. A similar distinction is useful here.

Feeling tired while using your phone is not the same as allowing yourself to go to bed.

Night mode, reduced brightness and blue-light filters may make a screen less harsh, but they do not remove the messages, decisions and endless opportunities to continue.

The most useful change is therefore not simply adjusting the colour of the screen.

It is creating a clear point at which you stop using it.

Earlier this week, you introduced a 30-minute bedtime alarm. Let that alarm mark the end of phone use as well as the beginning of your final bedtime routine.

When the alarm sounds, place your phone somewhere you cannot reach from bed. If you use it as an alarm clock, put it across the room, turn on Do Not Disturb and leave the screen face down.

If possible, charge it outside the bedroom.

Decide in advance what will replace it during those final thirty minutes. You might read, listen to something without watching the screen, prepare for the following morning, stretch or simply allow the evening to become quieter.

The replacement does not need to be perfectly calming.

It only needs to have an ending.

Your task tonight is simple: when your 30-minute bedtime alarm sounds, finish what you are doing, put your phone away and do not pick it up again before bed.

The aim is not to prove that you can resist your phone.

It is to protect the bedtime you already chose.