To measure the level of indoor light exposure at night in children and adolescents, identify demographic and behavioral characteristics of children and adolescents with high exposure level, and compare the differences in the level of light exposure at night based on subjective perception and objective measurement.A cross-sectional study was conducted in 875 children and adolescents aged 6-14 years in 18 schools in Beijing from November 2022 to March 2023. Objective measurement of light exposure at night was conducted by using TES136/TES1339R portable photometers, and questionnaires were used to assess subjective perception of light exposure level at night (none, dim, bright, very bright), sleep chronotype, types of light sources, and relevant behaviors. Participants were divided into high (>) and low (≤) exposure-groups based on thecutoff for objective measurement of light exposure, andtest was used to compare sociodemographic and behavioral characteristics between the two groups to identify factors associated with high exposure. Jonckheere-Terpstra test was used to assess the trend between subjective perception and objective measurement.The median (,) of objective light exposure level at night at recommended and actual sleep times were 4.31 (1.04, 10.80) lx and 1.36 (0.26, 4.91) lx, respectively. In most times, girls exhibited higher objective light exposure level compared with boys (all<0.05). The high-exposure group had higher proportions of girls, children and adolescents aged 10-14 years, children and adolescents with an evening chronotype, and those exposed to nightlights or illuminated decorative lights and television light in sleep (all<0.05). In addition, subjective perception of light exposure usually showed a significant positive association with objective light exposure level (allfor trend <0.05), although a mismatch in objective measurements was observed between the dim and bright categories at the recommended sleep time, the 1 hour before sleep and the 1 hour after sleep.Girls, children and adolescents aged 10-14 years, children with evening chronotype, and those exposed to nightlights, illuminated decorative lights, or television light in sleep had high level of light exposure at night. Subjective perception was consistent with objective measurement of light exposure at night levels, but some exposure misclassification remained, indicating that the validity of using subjective perception as a substitute for objective measurement of light exposure at night needs further evaluation. Objective: Methods: Results: Conclusions: P P P χ² Q Q P P P50 50 50 1 3
