Shop Windows to the Universe

Check out the fun Earth science related bumper stickers in our online store! Express yourself!
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.

Last modified September 11, 2007 by Randy Russell.

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.

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Light Pollution

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

Aerosols: Tiny Particulates in the Air

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 air. These tiny particles are called aerosols or particulates....more

Air Pollution

Have you ever heard of air pollution? Air pollution is not new. 700 years ago, when people started burning large amounts of coal 700 years ago in London, England, they complained about the dust and soot...more

Gamma Ray Bursts - The Most Powerful Objects in the Universe?

Satellites in the 1960's looked for a type of light called Gamma Rays. They found bursts of Gamma Rays coming from outer space! They can't hurt you. They are stopped by the Earth's atmosphere. We have...more

Galaxies - Star Cities

When we look up at the night sky, we notice that there are many stars in our sky. Stars must like to live together in star cities - galaxies. Our city of stars is called the Milky Way, and it is home to...more

Neutron Stars

Neutron Stars form when really big stars die. When such a star runs out of fuel its center begins to collapse under gravity. When the center collapses the entire star collapses. The surface of the star...more

Spiral Galaxies

Spiral galaxies may remind you of a pinwheel that blows in the breeze. Like a pinwheel, a spiral galaxy is rotating, and it has spiral arms. Through a telescope or binoculars,a spiral galaxy may look...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA