Astronomers are always battling to detect the faint glow of distant objects. Telescopes are built with large mirrors and lenses to gather as much light as possible from a small point in the sky and are being made ever larger as astronomers hope to see ever fainter, more distant stars and galaxies. But even telescopes have difficulty detecting faint objects if the surrounding sky is bright. Even at night, the sky is never completely dark. Starlight and moonlight can brighten the night sky.
Artificial lighting can cause two problems.
Light that shines directly into an observer's eye or telescope is called glare, or light trespass. Most of the concern regarding light pollution, however, focuses on skyglow, the additional brightness that occurs as light escapes into the sky. Generally, light pollution countermeasures include the use of shielding known as full-cutoff lighting so that lamps don't light up the sky as well as the street. Proponents say that if the light is directed down where it's needed, lower- wattage bulbs could be used to brighten sidewalks and roadways. Because less power would be used, the cost would be less and gas and coal power plants would generate fewer pollutants.