The dark side of keeping the lights on

Light pollution is the excessive and obtrusive light produced by humans at night. This light is from artificial sources, mainly electricity from houses, offices, streetlamps, billboards or car headlights. There are two main types of light pollution: point source, that is light directly from a source, and skyglow, the combined and accumulated effect of point source lighting that spreads through the atmosphere. This is the slight glow one can see on the horizon if looking towards a city from a rural area. Almost a quarter of global land area is now under light polluted skies. And 80% of the world's population now lives under such light polluted skies, meaning a third of humanity can no longer see the Milky Way.