Assessing and mapping taxon-specific effects of ecological light pollution for environmental impact analysis

Predicting the adverse effects of light at night is necessary to ensure compliance with laws and regulations that protect species. Using two case studies, we developed a method to map the impacts of roadway lighting on two endangered species using software widely available and used in lighting engineering and conservation planning. We calculated vertical and horizontal illuminance at each site and converted the values based on the spectral sensitivity of the species and the spectral composition of the lamps. We mapped illumination in equivalent moonlight illuminance (lux), meaning the illumination is as bright as the same amount of moonlight would appear to the organism, once the spectral sensitivity of the organism is considered, proposing a threshold for adverse impacts at 0.01 and 0.1 moonlight equivalent illuminance. Finally, we compared as-built lamps to lamps with other spectral compositions and calculated illumination that would result from use of commercially available shields. Although this workflow was feasible, improvements in software and characterization of species spectral responses is needed. Nevertheless, spectral tuning reduced the impact area for both species (8–19% and 21–25%). Shielding reduced the impact area for one case study by focusing light more closely on the roadways, but for the other site the available shields increased high-angle forward light emissions. The results demonstrate an approach to calculate the effects of new lights and to analyze benefits of spectral tuning, shielding, or reduction in light intensity that could be further refined through both basic ecological research and software development. • Study on light impact on endangered species using real-world projects. • Developed maps to assess roadway lighting impacts on species. • Converted illuminance to moonlight equivalent lux and defined impact thresholds at 0.01 lx and 0.1 lx. • Spectral tuning and shielding reduce the impact on sensitive species. • Effective mitigation requires detailed consideration of lighting equipment and species information.