A novel low-cost method for assessing intra-urban variation in night time light and applications to public health.

Night time lighting (NTL) pollution is a public health concern given its known impact on a range of health outcomes. The daily cycle of the hue of natural ambient light shifting from relatively blue-white light at noon to relatively yellow-red light at sunset is important for human functioning. Disruptions of the circadian clock can result in melatonin suppression, sleep and mood disorders, and increased risks of cancer in adults. Current measures of intra-urban variation in NTL are based on costly in-person or coarse satellite image-based assessments. The central objective of the current study is to validate a novel low-cost measure of intra-urban NTL variation. Estimates of red, green and blue NTL intensity were derived from a cloud-free night time image of the city of Montreal, Canada, taken from the International Space Station (ISS). The new measures are shown to converge with in-person assessed NTL and to predict known child health-related outcomes. Specifically, the results suggest that ISS-assessed blue NTL is associated with feelings of safety and self-reported health. In conclusion, ISS-based measures of NTL, particularly of blue NTL, are valid indicators of intra-urban variation in NTL for applications in public health. Limitations of, and future directions for, the method are discussed.