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, and subjective perception was consistent with objective measurement of light exposure at night levels overall but some exposure misclassification remained.
Key Findings
Results
The median objective indoor light exposure at night during recommended sleep time was 4.31 lx, and during actual sleep time was 1.36 lx.
Study included 875 children and adolescents aged 6-14 years in 18 schools in Beijing, measured from November 2022 to March 2023.
Objective measurement used TES136/TES1339R portable photometers.
Median (Q1, Q3) at recommended sleep time: 4.31 (1.04, 10.80) lx.
Median (Q1, Q3) at actual sleep time: 1.36 (0.26, 4.91) lx.
High exposure group was defined as >P50 (above median) of objective light measurement.
Results
Girls exhibited significantly higher objective light exposure levels at night compared to boys across most time periods.
Sex differences in objective light exposure were statistically significant at most measured time points (all P<0.05).
Girls were also more represented in the high-exposure group compared to boys.
The cross-sectional study design did not allow causal inference about reasons for this sex difference.
Results
The high night-light exposure group had significantly higher proportions of girls, children aged 10-14 years, evening chronotype individuals, and those exposed to nightlights, illuminated decorative lights, or television light during sleep.
All comparisons between high (>P50) and low (≤P50) exposure groups were statistically significant (all P<0.05).
Chi-square tests were used to compare sociodemographic and behavioral characteristics between the two groups.
Specific light sources associated with high exposure included nightlights, illuminated decorative lights, and television light during sleep.
Evening chronotype was identified as a behavioral characteristic associated with high night-light exposure.
Results
Subjective perception of night light exposure showed a significant positive association with objectively measured light exposure levels across all time periods.
Jonckheere-Terpstra trend tests were used to assess the relationship between subjective perception categories (none, dim, bright, very bright) and objective measurements.
All trend tests were statistically significant (all P for trend <0.05).
Subjective categories included: no light, dim, bright, and very bright.
Overall trend between subjective and objective measures was consistent.
Results
Exposure misclassification was observed between the 'dim' and 'bright' subjective categories at the recommended sleep time, 1 hour before sleep, and 1 hour after sleep.
Despite the overall positive trend, objective measurements overlapped between the 'dim' and 'bright' subjective perception categories at specific time points.
Misclassification was identified at the recommended sleep time, the 1 hour before sleep, and the 1 hour after sleep.
This finding suggests that subjective perception cannot fully substitute for objective measurement of night light exposure.
The authors concluded that 'the validity of using subjective perception as a substitute for objective measurement of light exposure at night needs further evaluation.'
What This Means
This research examined how much artificial light children and adolescents aged 6 to 14 years are exposed to indoors at night in Beijing, China. Using portable light meters, researchers measured light levels in participants' bedrooms during sleep and the hours around sleep time. They found that the typical light level during recommended sleep hours was about 4.31 lux (a relatively low but non-zero light level), and about 1.36 lux during actual sleep time. Certain groups of children tended to have higher nighttime light exposure, including girls, older children (ages 10-14), those with an evening (night-owl) chronotype, and those who slept with nightlights, decorative lights, or television on in the room.
The study also compared how well children's own sense of how bright their room was at night matched what was actually measured. Overall, children who reported brighter rooms did tend to have objectively higher light levels, suggesting their perceptions were generally accurate. However, there were some important errors in classification: children who said their room was 'dim' and those who said it was 'bright' sometimes had similar actual light levels, particularly around the time they were supposed to be sleeping. This means self-reported light exposure cannot perfectly replace direct measurement.
This research suggests that nighttime light exposure in children's bedrooms is common and varies by age, sex, sleep habits, and the types of light sources present. Because light at night can affect sleep quality and biological rhythms, these findings may help identify which children are at greatest risk for sleep-related issues linked to nighttime light. The results also highlight the limitations of relying solely on children's or parents' perceptions when assessing bedroom light environments in research or health assessments.
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Dang J, Shi D, Liu Y, Cai S, Li J, Huang T, et al.. (2026). [Identification of high indoor light exposure at night and comparison between subjective and objective exposure level in children and adolescents].. Zhonghua liu xing bing xue za zhi = Zhonghua liuxingbingxue zazhi. https://doi.org/10.3760/cma.j.cn112338-20251031-00780