Screens before bed: how much do they really hurt?

What light does

Light in the blue part of the spectrum reaching the eye in the evening delays the release of melatonin, the hormone that signals night to the body. Phone screens do this, but they are dim compared with daylight, so the delay is usually modest, in the order of 10 to 30 minutes.

What content does

A tense series, work email or a social feed activates attention and emotion. That arousal often delays sleep more than the light itself. The same phone used to read a calm book has far less effect.

Practical rules that work

• Dim the room lights an hour before bed, not just the screen.
• Keep charging outside the bedroom so night wake-ups do not turn into scrolling.
• If you must use a screen late, choose passive, low-stakes content.
• Get bright daylight in the morning: it anchors the clock more powerfully than any evening restriction.

Night mode filters

They reduce blue light slightly and do no harm, but studies show only a small effect on falling asleep. Treat them as a bonus, not a solution.