Background: Exposure to light at night (LAN) can perturb the biological clock and affect sleep and health. Several epidemiological studies have evaluated LAN levels measured by satellites, but the validity of this measure as a proxy for personal LAN exposure is unclear. Also, outdoor light at night measured by satellites displays higher levels in urban environments, which means that this measure could potentially represent a proxy for other, likely urban, environmental exposures. Objectives: We evaluated correlations of satellite-assessed LAN with measured bedroom light levels, and explored correlations with other environmental exposures, in particular air pollution, green space and area-level socio-economic position. Methods: We compared satellite measurements with nighttime bedroom measurements in illuminance (Lux) in 251 children and additionally evaluated correlations to other urban exposures such as air pollution, area-level socio-economic position and surrounding green in 3021 children. Results: Satellite-measured LAN levels (nanoW/cm2/sr) were not correlated with bedroom-measured Lux (Spearman corr. coeff. -0.02). There was a weak correlation if parents reported influence of outdoor light on indoor light levels (rS=0.31). Satellite-measured LAN levels were correlated to air pollution (rS=0.76 with N02, rS=0.71 with PM10) surrounding green (rS=-0.68 for green space within 1km of the home), and weakly to area-level socio-economic position (rS=0.24). Conclusions: Our study results indicate that outdoor satellite-assessed LAN levels are not a good proxy for nighttime personal exposure in bedrooms, but rather a proxy for other urban exposures. Studies planning to evaluate potential risks from LAN should therefore consider modifying factors such as curtains and indoor lighting and perform indoor or personal measurements to validate their exposure proxies. Other environmental exposures should be accounted for in epidemiological investigations.
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