Comprehensive Assessment of Real-Life 24-h Light Exposure Pattern in Children and Young Adults: Intensity, Timing and Rhythm.

Increased urban living has changed our daily patterns of light exposure, with lower light levels during the day and higher levels at night. However, few studies have documented the light exposure pattern in school-aged children and free-living young adults. To characterise the 24-h light exposure pattern in children and young adults, and to explore the difference between the two age groups, this study measured daily light exposure pattern, including intensity, timing, rhythm, via wearable light sensors for at least 5 consecutive days among 831 children aged 7-11 years and 344 young adults over 18 years recruited from China. The median intensity of light exposure during daytime was more than 1000 lx in children, but significantly lower for young adults (191.62 lx [98.76, 338.57]; p < 0.001). Children were exposed to higher levels of light exposure during the entire nighttime and sleep time compared to young adults. In addition, children showed more robust light exposure rhythm, with higher interdaily stability (IS) and lower intradaily variability (IV) (IS: 0.90 [0.85, 0.94]; IV: 0.59 [0.51, 0.68]) than young adults (IS: 0.71 [0.62, 0.78]; IV: 0.85 [0.70, 0.99]; all p < 0.001). The median intensity of daylight and nightlight was higher on weekdays both in children and young adults. In this cross-sectional study, children and young adults were exposed to light exposure patterns diverging from recommendation. Our findings suggest that interventions enhancing daylight and avoiding nightlight need to be implemented, especially for young adults.