How bad is screen light in the evening for my sleep?

Blue light from screens activates special cells in your retina through a well-established biological mechanism. Those cells regulate your internal clock and send the signal to produce less sleep hormone. This mechanism is biologically well supported, but how large that effect turns out to be in everyday life varies from person to person.

A small study in medical students shows what can change when you reduce blue light exposure in the evening: self-reported sleep quality improved considerably, moving from a score associated with poor sleep to a score in the good range. That is a large effect, but the study is small and only measures what people report themselves. Take this as a positive signal, not as a hard guarantee.

For people with chronic sleep problems (insomnia) the picture is more nuanced. European sleep guidelines indicate that light management as a standalone treatment has not yet been studied enough to support strong recommendations. As part of a broader approach, such as sleep hygiene education combined with cognitive behavioural therapy, light awareness does feature as standard in the recommendations for adults and older people.

In people with dementia, light therapy as a sleep intervention showed no clear effect in multiple trials. That is a different situation from healthy people using screens in the evening, but it does show that light as a tool does not work equally well for everyone.

From a practical standpoint, it makes sense to spend less time looking at bright screens in the hour before going to bed, or to switch on a blue-light filter. There is no evidence that this is harmful, and the biological rationale is there. Large randomised studies in a broad population are still lacking, so the level of certainty is limited.