Fig. 2a–g.
Global distributions of natural and artificial light. a–c Modelled yearly levels of daylight, moonlight and twilight in total hours, respectively, following equations in Meeus (2008), d cloud cover [composite of 12 monthly cloud fraction images for 2012 (Stockli 2013)], e mean annual lightning flash rate [flashes km−2 year−1 for 2012; Lightning Imaging Sensor/Optical Transient Detector gridded lightning climatology data set (NASA 2012)], f fire [sum of 12 cloud-corrected fire pixel images for 2012; NASA Land Processes Distributed Active Archive Center (2013)], and g artificial nighttime lighting {represented as digital number in 2010 [US Defense Meteorological Satellite Program (DMSP)/Operational Linescan System (OLS) 2012]}