Abstract

We present the basics of light pollution for astronomers who have not explored the topic. The main sources of poor lighting (fixtures and techniques) are illustrated, along with proper methods for each situation. A list of suggested approaches to solving the problem is presented, along with references and links to further information sources. For educators, a PowerPoint presentation suitable for a class lecture, along with notes, will be provided on CDR or by download off the Internet.

Introduction

Light pollution is a serious and growing problem affecting all ground-based optical and infrared astronomy. Despite this, only about 5% of the membership of the AAS are also members of the International Dark Sky Association (IDA) (Crawford, 2002, private communication).

The main contributors to light pollution are roadway lighting, dusk-to-dawn "security" lights, parking lot lighting, billboard lighting, wall packs, and sports lighting.

Roadway Lighting
Roadway lighting is one of the largest sources of light pollution of the night sky. A typical bad fixture is the ubiquitous "Cobra Head":

These are easily replaced by a full cutoff (no light above the fixture's horizon) version, which has the side benefit of doing away with unwanted glare for drivers:

Dusk to Dawn Fixtures ("Security Lights")

Another example of poor lighting that causes light pollution is the dusk to dawn "security" light. These lights put much of their output above the horizon of the fixture, and glare badly:

These fixtures can easily be retrofitted with a reflecting "Dark Skies" cap which replaces the refracting lens normally found on these fixtures, which decreases both glare and light pollution dramatically:

These caps not only prevent any light from being emitted above the horizon of the fixture, they also make the lighting pattern from the fixture brighter everywhere else:

These sky caps are available from Hubble Lighting and GE Lighting, among others. An example GE cap is on display with the poster.

Parking Lot Lighting

Poor parking lot and car lot lighting also contributes to light pollution. Flood lights mounted at the corners of the property, while offering a cheap and easy solution, waste much of their light into the sky, and result in poor, glaring lighting:

A much better alternative is full cutoff "shoebox" fixtures, which emit little or no light above their horizon:

Wall Packs

Wall packs are almost never useful for the purpose they were intended to serve. They cause glare, blinding pedestrians and drivers, and waste much of their light up into the night sky:

Full cutoff wall packs do exist, and serve not only to reduce light pollution but also unwanted glare:

Billboard Lighting

Most billboards are lit from below, which again wastes most of their light up into the night sky:

Although some sign companies object because of more difficult maintenance and "hot spots", lighting from above is a much more sky friendly way to illuminate billboards:

Sports Lighting
This is another category of lighting that usually results in a large amount of light pollution and light trespass (see sky glow caused by stadium lighting on the far right of the newer Boone image, below). Sports lighting can be done correctly using cutoff fixtures like these units from Musco:

This results in sports field lighting in which the light is contained on the field, not wasted on the surrounding property and into the sky:

Conclusions

All the above named sources contribute to the overall light pollution problem. Contrast this image of Boone, NC, taken 35 years ago:

with this image of the same area taken 5 years ago:

It is clear from just these images of one small town in North Carolina that light pollution is a serious, growing problem. However, with proper fixtures and lighting design, current light pollution can be maintained, or even decreased.

Some Things You Can Do
Teach your students about the importance of dark skies by including a light pollution lecture in your astronomy course (we are handing out a PowerPoint presentation suitable for this, ask us for one!)

Look at your own lights–are they needed? Could you have it capped? Put it on a switch, timer or a motion sensor. Put in a lower wattage bulb.

Where do you eat out? Do the restaurants have glaring lights? If so, complain!

Are there some roadside lights that bother you as you try to drive? Complain!

Is there a street light that shines into your window at night? Call up the utility and ask for them to put a sky cap on it. Don't settle for simple spray painting of the fixture's lens!

Spend some time at www.darksky.org and become (more of) an expert! Join the IDA.

Write letters to your newspaper.

Teach your friends about good and bad lighting–point it out when you are out with them at night.

Make a difference! Start a project to get owners of "security" lights to have sky caps installed on them.

Work with your local governments to develop a local lighting ordinance based on the Model Lighting Ordinance being developed by the IDA

Resources

This is a very brief list of lighting resources. For a much more comprehensive list, visit www.darksky.org.

Organizations:

Illuminating Engineering Soc. of North America: www.iesna.org

International Dark-Sky Association: www.darksky.org

North Carolina IDA Chapter: www.ncdarksky.org

Lighting Design:

Lighting Forensics: www.lightingforensics.com

Clanton Associates: www.clantonassociates.com

Vendors:

GE Lighting: www.gelighting.com

Glare Buster Fixture: www.theglarebuster.com

Lumec-Schreder: www.lumecschreder.com

Musco Lighting: www.musco.com

Hubble Sky Caps: www.members.aol.com/outdoorltg/ola.html