Fig. 1
(a) The nighttime image of Hong Kong taken from the International Space Station at 00:58, 20 January 2015. (b) The 2021 map of downtown Hong Kong, highlighting five CBDs in Kowloon and northern Hong Kong Island. Different symbols represent the locations of observation methods used in this study: a yellow star indicates the same position of the all-sky camera, SQM and spectrometer (at the Hong Kong Space Museum that participates in Earth Hour annually), a red triangle marks the wide-field camera (at the “Avenue of Stars”) and blue hexagons indicate the positions of the 360-degree cameras. Blue dots represent the buildings (green polygons) that were involved in Earth Hour 2021 and surveyed for this project. Light grey areas indicate unsurveyed regions in 2021. The regions surveyed with webcams outside the vicinity of Victoria Harbour are not shown here. The locations of lighting fixtures involved in Earth Hour from 2015 to 2024, as seen in the all-sky images (see Figs. 2, 3, 4), are labeled with letters. Some of the buildings in northern Hong Kong Island were also involved in Earth Hour 2013 (see Fig. 5). The map was created with arcgis 10.8 (http://www.esri.com/software/arcgis) using the road network data from OpenStreetMap.
