Darkness map, sky brightness with cache lighting off

The map shows the sky brightness in North Holland in 2011-2012 with greenhouse lighting off. If there is no direct lighting nearby, the night sky determines the degree of darkness. The sky is illuminated by upward beaming light from a city or greenhouse from an area of ​​about 30 kilometers radius. In 2011 and 2012, the brightness of the sky at the point straight up (zenith) was measured at 225 locations in the province of Noord-Holland, as a measure of the 'darkness'. Previous measurements in Amsterdam and on the island of Texel have also been incorporated into this darkness map.