Spectral-level assessment of light pollution from urban façade lighting

Abstract

Façade lighting makes cities brighter at night and causes ecological impacts, as more wavelengths associated with species spectral sensitivity are emitted in light spectra. To assess the resulting ground-level light pollution and explore ecological lighting strategies, this study collected hyperspectral data of 74 lighting facades in Shanghai, China and analyzed lighting features related to ecological impacts. Spectral-level assessment shows that multi-spectral lighting causes higher luminance, more variable colours, and stronger eco-impacts, e.g., on human circadian rhythms, human photopic vision and plant photosynthesis than uniform-colour lighting. High ecological impacts are associated with narrow spectra of saturated blue and red colours, and cannot be effectively reduced by luminance control. A colour gamut mapping strategy is thus proposed to reduce the eco-impacts through colour restriction. This study quantitatively assesses the light pollution from façade lighting and reveals the associations between different lighting indicators and ecological impacts. The colour gamut mapping strategy provides a trade-off between visual effects and eco-impacts, which helps to balance the needs of urban development and environment. The findings provide guidance to lighting manufacturers, designers and policy makers on eco-lighting design and its integration into sustainable lighting masterplans.