Light pollution impact on human health: Methodological insights and implications

Excessive exposure to nighttime lighting can disturb circadian rhythms, suppress melatonin production, hinder sleep, and strain the visual system. The impact of anthropogenic light at night (ALAN) on human health has been increasingly studied through observational, laboratory and field investigations. Despite the growing research, past reviews and studies often overlook a critical evaluation at the methods and quantification of the independent variable: lighting. This systematic review examines 76 research studies to assess the relationship between ALAN and health under five categories: sleep, mental and metabolic disorders, cancer, and other health impacts. While most studies reported a correlation with ALAN and negative health impacts, one-third reported null results for at least one health outcome. Laboratory investigations primarily involved rodent models, but exhibit deficiencies in controlling and reporting lighting conditions, such as lack of reporting spectral power distribution, light levels, or measurement conditions. Similarly, observational studies, often relying on self-reports or satellite data, face challenges in capturing accurate light exposure. Recommendations are provided to enhance study reliability, including comprehensive lighting characterization, relevant metric utilization, accurate measurement techniques, consideration of confounding factors and open science practices. Identifying dose-response relationships and thresholds for any adverse effect of ALAN requires utilizing more than two light levels (dim vs bright). While research supports ALAN's adverse health impact on humans, limitations in study design and reporting must be overcome to ensure findings are robust and research is replicable. Future studies should prioritize comprehensive reporting of lighting conditions and adherence to open science principles to foster transparency and collaboration.