For Mme. Chloé Legris – link in French only – (IDA Québec and Sherbrooke-Innopole) and the Mont Mégant AstroLAB – light pollution can be defined as any modification of the natural light environment, especially that which causes some sort of nuisance.
Mr. Jan Hollan (Czech physics and astronomy teacher – link to one of his works) is citing Mr. Pierantonio Cinzano (one of the biggest scientific personality studying the light pollution – link to his maps of artificial night sky brightness and another link to his site on the light pollution) which is defining the light pollution as being the alteration of light levels in the outdoor/indoor environment (from those present naturally) due to man-made sources of light. The word “indoor” was added by IDA Quebec because Mr. Hollan is introducing the definition of the indoor light pollution – see the second link for Mr. Hollan.
In papers and presentations Mr. Mihai R. Pecingina (IDA Québec and Groupe SMi) presents his definition: light pollution is the introduction of artificial light (which became a contaminant) into a naturally dark environment that causes instability, disorder, harm or discomfort.
Everything could be expressed even shorter as International Dark-Sky Association does in its glossary: any adverse effect of manmade light.
That amount of lighting that, by waste or bad design, does not contribute in any way positively to human nightime activities. ZéNuno Sampaio
You can choose your preferred one or send us your definition!