“Using photometric and spectroscopic sensors, we observed up to 50% night sky darkening during Earth Hour from 2011 to 2024 in Hong Kong, primarily as a result of a small but critical number of lights-out instances in central business districts, as evidenced by crowd-sourced photography records. The emission reductions mostly occurred in the 445–500, 500–540, and 615–650 nm spectral ranges---corresponding to peak emissions from LED billboard screens--- and in the 585–595 nm range, associated with metal halide floodlights used for facades and billboards. Our study identifies these sources as major contributors to urban light pollution.”
(Note: not yet peer reviewed, but the authors are legit.)
www.researchsquare.comUrban night sky is drastically lit up by a few decorative buildings: Natural experiments from Earth HourLight pollution, an underappreciated environmental issue, has gained attention in recent years. While controlling light pollution requires sustained efforts, Earth Hour offers a unique natural experimental setting to assess temporary lights-out measures. Using photometric and spectroscopic senso...
