Light pollution is excess or obtrusive light created by humans.
* Light pollution is a broad term that reflects to multiple problems, all of which are caused by inefficient, annoying or unnecessary use of artificial light
* Specific types of light pollution include light trespass, over-illumination, and sky glow.
* Light trespass occurs when unwanted light spills over beyond the boundary of the property on which a light is located to adjacent properties. Light trespass is often caused by high or poorly positioned lights. The result is bright night lighting on an area that would otherwise be dark.
* Over-illumination is the excessive use of light Specifically within the United States, over-illumination is responsible for approximately two million barrels of oil per day in energy wasted.
* Sky glow is the bright glow that can be seen over many cities and towns in the evening. It is caused by light traveling through and being scattered by particulates in the atmosphere. It is worse in heavily polluted areas and will always exist to some extent when the air quality is poor.
* About two thirds of the population of the world and 99% of people in the continental USA and Western Europe never see a truly dark starry sky from where they live because of light pollution.
* When a massive power outage stuck southern California in the 1990s, Los Angeles residents reportedly reported 911 to express alarm about strange clouds hovering overhead; they were seeing the Milky Way for the first time!
* Light pollution must be addressed by changing the habits of society, so that lighting is used more efficiently, with less waste and less creation of unwanted or unneeded illumination.
* If we all work together, future generations can regain some of the pleasures of seeing a star filled night sky.