Light Pollution: A Short Definition
Since the invention of electric lighting a century ago, light pollution has become a problem in cities worldwide . Broadly speaking, light pollution is excess sky light created by human activities that interferes with astronomical observations and affects the environment.
As of today, many people, besides astronomers, from environmentalists to architects, realise the impact light pollution that has on people and the environment. The most affected people are astronomers, as light pollution has drastically reduced their efforts to study the night sky.
Interestingly, several studies have shown that light pollution also affects the environment and the people. It also contributes to global warming and carbon dioxide emissions.
Causes of Light Pollution
Light pollution is caused by both emission and reflection sources. Emission sources are poorly designed lighting fixtures that fail to direct all their light output downwards. They are by far the most common and include billboards and streetlights. Reflection sources are reflective surfaces that cause illumination to reflect off clouds and produce sky glow in urban areas. These would include the different surfaces of ground. For example, tar, cement and concrete.
These are a but a few of the suggested lighting fixtures as part of a Lighting Law in Bradford, Connecticut, USA, from Bob Crelin’s article in the Night Sky magazine: Backyard Astronomy for Everyone, Oct 2004, Pg 60: My Defense of the Dark Skies by Bob Crelin. Also see Pg 54 Licking Light Pollution by J. Kelly Beatty.