Light exposure differs by sex in the US, with females receiving less bright light.

Light is the primary entraining cue for the circadian system and has other, non-circadian, effects on health. Sex differences in light exposure patterns could drive sex differences in health outcomes. Real-world light exposure (measured with wrist-worn ActiGraph GT3X+) was investigated in the 2011-2014 U.S.-based National Health and Nutrition Examination Survey (NHANES) with metrics reflecting duration in and timing of exposure at different light levels. Sex differences were tested using two-sample t-tests and linear regression models. Occupational and physical activity-related factors were also explored as contributing factors using linear regression models adjusted for age, season, and race/ethnicity. 11,314 NHANES participants (age range: 3-80+, 52.2% females) were included in the analysis. The results show males spending approximately 52% more time in bright light than females, with this sex difference beginning in childhood. While further research is needed, these findings may be due to sex differences in indoor vs. outdoor activities.