Cascade Highlands Neighborhood Association

Where Did the Milky Way Go?

A Primer on Light Pollution

Do you remember in your childhood the wonder of looking into the night sky and gazing at the Milky Way, the stars, and the many constellations? Have you noticed that the Milky Way and many of the stars are no longer visible from your own backyard?

Certainly air pollution has contributed to the loss in night sky visibility, but the major cause in most urban areas is a symptom of light pollution called "sky glow." Some of the sky glow is a natural result of urbanization, from the lights we use to improve the safety of our streets, the security in our neighborhoods and commercial areas, and the aesthetic appearance of our properties at night. But much of the sky glow comes from poorly designed lighting that is excessive, and fixtures that direct light upward. It is by illuminating the haze in our sky that sky glow reduces the visual contrast between dark sky and faint stars, making fainter objects in the sky invisible.

There are other forms of light pollution, too -- glare, light trespass, and overlighting.

Glare is produced when a very bright light hits you in the eyes, such as the high beams of oncoming traffic that can blind you at night. Like those oncoming vehicle headlights, the glare from outside lighting that is not adequately diffused or shielded can blind you to dangers in the shadows hidden by that glare.

Light trespass occurs when light is directed where it is not wanted. One example would be the street and yard lights that flood your bedroom at night, making it difficult to sleep.

Overlighting includes excessive lighting, light leakage, and lighting in places where, or at times when, it is not needed. There are few places where nightime lighting to daylight levels is really needed, and there are many instances in our area where lower lighting levels would suffice. Light leakage is simply light going where it isn't needed; where it is unwanted, it can become a light trespass.

Obviously, these forms of light pollution can contribute to sky glow, but there are other effects as well. Glare or harsh lighting is generally considered ugly, and can create safety and security hazards. Light trespass and overlighting both result in energy waste, additional energy costs, and the adverse environmental effects of producing that additional energy. Some of these adverse environmental consequences include the carbon monoxide emissions of our coal, oil and gas-fired generating plants, which contribute to global warming; and tradeoffs between hydropower generation and the habitat needed for spawning fish populations.

What can you do to help? Quite alot, actually:
- Use outdoor lighting fixtures that direct the light downward, and confine that light to the area that needs lighting
- Use lower-wattage and lower-output light bulbs wherever possible
- Use timers and/or motion detectors to limit the time periods that outdoor lights are active
- Contact your local officials and legislators to voice your opinions on this subject!

More Information Sources on Light Pollution

International Dark Sky Organization -
Dark Skies Northwest (part of the International Dark-Sky Organization) -
Oregon Dark Skies (Rose City Astronomers) -
New England Light Pollution Advisory Group -
Light Pollution Awareness Community -
Illuminating Engineering Society of North America -
LiteLynx List: Light Pollution Ordinances
Wikipedia on Light Pollution –
SkyTonight - Dissecting Light Pollution –
NOAA on Skyglow/Light Pollution –
...and you can search or for additional information on Light Pollution!

Posted by dcw on 05/19/2007
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