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The Webfooted Astronomer - December 2001


Outdoor Lighting-The Dark Side of Light Pollution

By Greg Donohue

OUR annual banquet is less than two months away. Our guest speaker will be Dr. Phil Plait, a.k.a. “The Bad Astronomer,” so bring your family and friends to this fun and interesting event. (Oh, did we mention the door prizes?)

We held annual elections for SAS board positions. All of the current officers ran for re-election. The slate of officers passed with 25 yeas and 2 nays. It is worth noting that our by-laws contain two-year term limits, so none of these officers will be eligible for those same positions in 2003.

Club president Mary Ingersoll introduced the evening’s guest speaker, our very own Bruce Weertman. Bruce is the nephew of Ed Mitchell (Apollo 14). Partly in response to the Space Needle SkyBeam, Karl Schroeder started Dark Skies Northwest (DSNW) in 1998. DSNW is a local chapter of the International Dark-sky Association (IDA). Subsequently Bruce became chairperson. His presenation to SAS addressed outdoor lighting and light pollution. Bruce mentioned a book recently given to him by Professor Woody Sullivan, "Preserving the Astronomical Skies", a collection of articles about light pollution and radio noise pollution, published by the Astronomical Society of the Pacific.

Light pollution can be broken down into several components:

Glare: blinding light
Light trespass: unwanted light spilling from neighboring property
Clutter: so many lights and illuminated signs that it leads to confusion
Energy waste: estimated at some $2 billion annually
Urban sky glow: that drowns out the beautiful night sky

A recent analysis of sky glow (imaged by various satellites) produced a color-coded map showing light pollution as a percentage of natural sky brightness. This map gives a very graphic representation of the effects of light pollution. (A portion of the map showing the Northwest can be viewed at According to this analysis, there is no place in the entire state of Washington that does not suffer from at least some light pollution. The nearest truly dark skies are located in eastern Oregon. Table Mountain is surrounded by significant light pollution.

The IDA has adopted a “win-win” philosophy of cooperating with communities and governments, helping people see the value of the night sky, and the benefits of creating a pleasant, energy-efficient community. DSNW covers Washington, Oregon, Idaho, and Montana. Its mission is to be a focal point for information on local light pollution and lighting codes, and to promote the IDA goals of good outdoor lighting.

By far, the biggest contributor to light pollution is street lighting. Most streetlights are of the “cobra” type, of which there are two main varieties: flat-bottom/full-cutoff (which only shines downward), and rounded-bottom (which also radiates perhaps 30% of the light directly into the sky). IDA promotes the flat-bottom kind, since they only cause indirect sky-glow through reflection from the ground. The typical urban surface only reflects about 10% of the light it receives, so flat-bottom streetlights greatly reduce sky-glow. Bruce showed some photos of both kinds of streetlight side-by-side. Up close, the two lights appear nearly identical. But from only a block away, the full-cutoff light looks almost as if it were turned off or burned out. This demonstrated how full-cutoff lights eliminate glare. Lights with flat bottoms aimed toward the ground are full-cutoff lights.

Other sources of light pollution are unshielded security lights, globe lights, flood lights, and billboards lit from the bottom up. Unfortunately, businesses use lightning not only for security purposes, but also to compete with others for business. They have learned that the brighter their lights, the more customers they attract. Some examples of this can be seen at most gasoline service stations. Another unfortunate development is the growing popularity of up-lighting that shines directly into the sky to attract attention.

The good news is that better lighting codes are being adopted in a few locations around the Northwest, and there are more companies producing quality full-cutoff lights. Significant lighting ordinances have been enacted in Goldendale, Island County, Cle Elum and Redmond, as well as in Deschutes county, Oregon, and Ketchum Idaho. Five states-Connecticut, Maine, Texas, New Mexico, and Arizona-now have state lighting laws. Soft Lighting Systems ( specializes in good sports lighting that meets the needs of both the players and nearby residents. GlareBuster ( outdoor lights are good solutions for residential applications. A guide to “good neighbor” outdoor lighting is at

Light pollution is not only annoying, it can also be dangerous, and adversely affect health. Glare, light “halo-ing” (especially for older adults), and clutter can lead to hazardous night driving situations. Lack of dark skies at night has possible links to reduced sleep and diabetes, potential interference with our immune systems, and possibly even increased risk of breast cancer for women who work the night shift.

Bruce Weertman and DSNW have been working to improve outdoor lighting in our area, but they need our support. Only about 1 in 60 astronomy buffs are also members of the IDA. So, if you are not already a member, please join the effort to fight light pollution, restore the splendor of our Northwest night skies, and turn people to the “dark side.”

An important DSNW/IDA meeting will take place on Saturday, April 13, 2002, in Portland, Oregon, at the Haggart Observatory. Speakers throughout the day will address outdoor lighting and light pollution issues. Information about the event, hosted by the Rose City Astronomers, can be found by following the “Members and Meeting Times” link at the bottom of the DSNW home page. The DSNW Web site is at, and e-mail to will go to Bruce.

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