These images illustrate three types of light pollution: light trespass, over illumination, and sky glow.
Click on image for full size
Images courtesy of Kevin Wigell (light trespass), Joe "Rocket" Roberts (over illumination), and Charliebrown7034 via Wikipedia (sky glow).
Types of Light Pollution
Light pollution is the unwanted illumination of the night sky created by human activity. Light pollution is a broad term that refers to multiple problems, all of which are caused by inefficient, annoying, or arguably unnecessary use of artificial light. Specific types of light pollution include light trespass, over-illumination, and sky glow.
As its name implies, 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.
In recent decades, there has been an increase in exterior lighting for safety reasons or security needs. Combined with the increased exterior lighting from sporting events and commercial activities, light trespass has become a significant problem in many parts of the world. Certainly it is important to have adequate light for safety and security, however, when misapplied, additional problems are created.
Over illumination is the use of light well beyond that required for a specific activity. Many places, both indoors and out, have lights on when no people are present. In many cases, this goes beyond the need for security lighting. Think of office buildings that have lights on all night even though the buildings are virtually empty.
Sky glow is the bright ‘glow’ seen over many cities and towns in the evening. It is the result of the many electric lighting fixtures that shed light above urban areas. It is caused by light traveling through the atmosphere being refracted or scattered by water droplets or particles (aerosols) such as dust, pollen, bacteria, spores, salt from sea spray, mineral particles lifted from deserts and waste products from industry. It is therefore worse in heavily polluted areas, and will always exist to some extent when the air quality is poor.
Shop Windows to the Universe Science Store!
The Summer 2010 issue of The Earth Scientist
, available in our online store
, includes articles on rivers and snow, classroom planetariums, satellites and oceanography, hands-on astronomy, and global warming.
You might also be interested in:
What is light pollution? Simply put, light pollution is the unwanted illumination of the night sky created by human activity. Light pollution is sometimes said to be an undesirable byproduct of our industrialized...more
When you look up at the sky, you are looking at more than just air. There are also billions of tiny bits of solid and liquid floating in the atmosphere. Those tiny floating particles are called aerosols...more
What do smog, acid rain, carbon monoxide, fossil fuel exhausts, and tropospheric ozone have in common? They are all examples of air pollution. Air pollution is not new. As far back as the 13 th century,...more
In the 1960's, the United States launched some satellites to look for very high energy light, called Gamma Rays. Gamma Rays are produced whenever a nuclear bomb explodes. The satellites found many bursts...more
During the early 1900's, which is not very long ago, astronomers were unaware that there were other galaxies outside our own Milky Way Galaxy. When they saw a small fuzzy patch in the sky through their...more
Neutron Stars are the end point of a massive star's life. When a really massive star runs out of nuclear fuel in its core the core begins to collapse under gravity. When the core collapses the entire star...more
Spiral galaxies may remind you of a pinwheel. They are rotating disks of mostly hydrogen gas, dust and stars. Through a telescope or binoculars, the bright nucleus of the galaxy may be visible but the...more