Abstract
<title>Abstract</title> <p> The association between adolescents’ screen time, and mood are central to ongoing scientific inquiry and heated public debate, yet the mechanistic effect of sleep in their dynamic interplay remains insufficiently understood. In the current study, 196 adolescents (M <sub>age</sub> =15.63, SD = 0.83) were followed for 17 consecutive days during which they reported daily measures of sleep and screen time, and momentary mood six times a day. Dynamic structural equation models were used to examine the within-person associations. Associations between screen time and mood were concurrent, while sleep and mood showed bidirectional within-person associations. A mediating role of sleep duration was found: a one-hour increase in social screen time compared to usual predicted a 5-minute longer subsequent sleep duration, which preceded higher energetic mood the following day. Together, these findings point to a dynamic regulatory process in which sleep functions as a mechanism through which adolescents recover from periods of increased social screen use. </p>