The term "light pollution" refers to that spill light which, due to its illuminance, its direction or its spectrum, causes interference in the context in question. Spill light and glare reduce the visual comfort and the desired content of information cannot be conveyed. The ecological consequences include the waste of energy and the negative effects on flora and fauna.

Graphic: Artificial Night Sky
Brightness in Europe

Credit: P. Cinzano, F. Falchi (University of Padova), C. D. Elvidge (NOAA National Geophysical Data Center, Boulder). Copyright Royal Astronomical Society. Reproduced from the Monthly Notices of the RAS by permission of Blackwell Science. www.lightpollution.it/d msp/