Light pollution
Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.

The International Dark-Sky Association
International Dark-Sky Association
The International Dark-Sky Association is a U.S.-based non-profit organization incorporated in 1988 by founders Dr. David Crawford, a professional astronomer, and Dr. Timothy Hunter, a medical doctor/amateur astronomer...

 (IDA) defines light pollution as:
This approach confuses the cause and the result, however. Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

 is the adding-of/added light itself, in analogy to added sound, carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, etc. Adverse consequences are multiple; some of them may be not known yet.