Sleep and screens: what the research says

“Screens before bed” is one of the most regular health searches, peaking every back-to-school season. Ready-made answers abound, from total bans to miracle filters. The research is more nuanced. Here is what is agreed today, what remains debated, and what you can apply without complicating your life.

What is firmly established first: light, especially in the evening, delays the release of melatonin, the hormone that signals night to the body. Intensity and distance matter a great deal: a phone held twenty centimetres from the eyes has more effect than a lamp across the room. “Night” modes, which warm the screen’s tint, reduce part of that effect but do not cancel it.

What probably matters more, and is often overlooked: content. A news feed, a competitive game or an argument in a chat keep attention and arousal high long after you put the device down. Studies that separate passive use — reading, calm video — from interactive use generally find the latter weighs more on falling asleep, for the same exposure time.

A third factor: bedtime itself. Screens do not only disturb sleep, they shorten it by pushing back the moment you go to bed — one more episode, one more round. Over a week, that accumulated debt often explains tiredness better than the physiological effect of light.

For teenagers the question has a biological dimension too: their internal clock is naturally shifted later, while school start times stay fixed. Night-time notifications then interrupt sleep that is already too short. For that reason several health bodies recommend keeping the phone out of the bedroom, which works better than any software setting.

The practical rules that come up most often are simple: stop interactive use thirty to sixty minutes before bed, lower brightness and move the screen further away, mute notifications overnight, keep regular wake-up times including at weekends, and get daylight in the morning — that last point resets the internal clock far more effectively than any evening filter.

A word on blue-light glasses: the available evidence does not show a clear benefit for sleep quality. Before spending money, it pays more to work on bedtime, on the content you consume and on a consistent wake-up time.

Finally, if trouble falling asleep or night-time waking persists for several weeks despite these adjustments, it is worth talking to a health professional. Sleep disorders have many causes — apnoea, pain, anxiety, medication side effects, shift work — and screens are only one of them, sometimes the most visible but rarely the only one.