Global trends in population exposure to outdoor artificial light at night and future projections

Exposure to artificial light at night (ALAN) is a form of environmental change, and is associated with disease in epidemiological studies. The population exposure to ALAN from outdoor sources can increase due to changes in emissions or migration from rural to urban areas. We examine changes in population exposure by merging two satellite datasets into a single time series, and project the future impacts of migration and growth using Shared Socioeconomic Pathways scenarios(SSPs). We found that the population exposed to light emissions increased from 4.3 billion in 2000 to 6.3 billion in 2020, with 88% of this growth coming in areas with medium to high light emissions, which are mainly distributed in suburban and urban regions. Regarding the exposure to high light emissions, which is predominantly distributed in urban areas, 73% of the increase can be attributed to population growth and migration. In the case of exposure to medium light emissions (mainly suburban areas), the increase in radiance plays a more pronounced role (63%). By 2050, nearly 70% of this growth will take place in medium to high light emission areas. Preparation for potential increased disease burden and actions to reduce light growth are therefore advisable.