*/** equal contributions

Introduction: Evening blue light exposure has been associated with delayed and insufficient sleep, but causal directions and daytime consequences in everyday life remain to be determined. We investigated the relationship between electronic screen use and daytime symptoms of insufficient sleep in secondary school students, using a multi-design approach.

Methods: We first performed a large-scale targeted population-based cross-sectional study in 15468 secondary school students (age 12-17 y) to establish the association of screen use with daytime symptoms of insufficient sleep. The observed associations were verified in a complementary case-control study, in which we monitored real-life sleep timing during a week in 30 infrequent and 25 frequent screen users. Finally, in a randomized controlled trial with a crossover design, the 25 frequent screen users underwent two 1-week interventions: wearing blue-light-blocking glasses in the evening, or abstaining from screen use in the evening. Main outcomes were: 1) daytime symptoms of insufficient sleep evaluated using the Sleep Reduction Screening Questionnaire (SRSQ), 2) actigraphic features of sleep timing and duration: sleep onset time, wake-up time, mid-sleep time, and total sleep time.

Results: The cross-sectional study showed more daytime symptoms of insufficient sleep with increasing screen use. The case-control study confirmed increased daytime symptoms of sleep deficiency in frequent screen users without group differences in actigraphic estimates of sleep timing and duration. The randomized controlled intervention study showed that both wearing blue-light-blocking glasses and screen use abstinence in the evening advanced sleep onset and ameliorated daytime symptoms of insufficient sleep. Average evening salivary melatonin concentrations  were higher when wearing blue-light-blocking glasses, but not when abstaining from screen use.

Conclusion: Limiting evening exposure to blue light from electronic screens benefits sleep and daytime functioning.