Screen light has only a very minor direct impact on sleep (delaying sleep onset by about 10 minutes); the real issue is the cognitive arousal linked to the content. To address this, he suggests seeking light exposure in the morning and dimming ambient lighting three hours before bedtime.

noli's read

The findings regarding the limited direct impact of screens are based on a systematic review of the literature co-authored by Dr. Michael Gradisar in 2024, which establishes that a phone screen delays sleep onset by an average of only 9.9 minutes. This meta-analytic review confirms that mental arousal related to content and the delay of bedtime are the true disruptors of rest. Regarding the recommendation to dim lighting, experimental studies measuring melatonin under dim light conditions (the DLMO protocol) demonstrate that standard household lighting at the end of the day effectively delays the synchronization of the internal clock. Reducing ambient light intensity is therefore a validated practice for preparing the body for rest. Nevertheless, the strict three-hour rule is more of an expert practical recommendation, as the majority of research shows that a transition of one to two hours is already more than sufficient to observe benefits.

the sources

1. 1He X, Pan B, Ma N, et al. 2025
2. 2Santhi N, Thorne HC, van der Veen DR, et al. 2011
3. 3Brown TM et al. 2022
4. 4Blume C, Garbazza C, Spitschan M 2019