Evening Smartphone Screen Time and Objective Sleep Quality in Undergraduate Students: An Actigraphy-Based Study

This study investigates evening smartphone screen exposure and objective sleep quality in college students within the context of behavioral sleep medicine and digital health psychology, an area of growing scientific importance given its implications for campus mental health programs and digital wellness interventions for college students. Using wrist actigraphy worn continuously for 14 nights with concurrent smartphone screen-time logging via device API, we examine blue-light-mediated melatonin suppression and cognitive arousal delaying sleep onset in 124 undergraduate students (aged 18-24) over a 14-night monitoring period drawn from natural dormitory and off-campus residential settings. Results indicate that each additional hour of smartphone use after 9 PM is associated with a 14.7-minute delay in objectively measured sleep onset and a 6.4% reduction in sleep efficiency (p = 0.004), with 14.7-minute sleep onset delay per hour as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to behavioral sleep medicine and digital health psychology and carry actionable implications for the design of programs and policies targeting campus mental health programs and digital wellness interventions for college students.