Full cut-off fixtures. These fixtures contain and direct all their light downward. They control the light output with a reflector inside the fixture rather than by a refractor dropped below the fixture, as noted above. No light reaches above or even near the horizontal, so glare is minimized. The fixtures can contain most any kind of lamp but usually are seen with high-pressure sodium or metal halide lamps, both reasonably energy efficient.
These fixtures are easy to recognize because you can't see any glass hanging below the fixture, and you can't see the lamp unless you are relatively close to the fixture and looking directly up at it. They can look like the cobra head fixtures but without the dropped refractor, or they can look like boxes or small opaque cylinders on top of the lighting pole. These fixtures can also be used as wall mounted "wall packs," and they have little or no glare and an excellent distribution of the light output, just as they do when used for street lighting.
Motion sensor lights. These lights are not on all the time from dusk to dawn, but only when their infrared sensor detects motion of people, large animals, or other objects. They then turn on for a few minutes, and go off later when they do not detect any more motion. They don't waste light or energy nor do they create adverse sky glow when well installed to control the light output. Since they come on when a potential burglar approaches, they tend to scare criminals away. They also serve to light walkways or such for the homeowner. They can contain any kind of light that comes on "instantly," but not all lamps do this. Even an energy inefficient incandescent lamp is OK with this type of lighting, as they are so seldom on that little or no energy is wasted.
Timer-controlled lighting. There are many applications where lighting is not needed all night, and this can save a great deal of energy. Some examples are advertising lighting, parking lot lighting, signs of all sorts, decorative lighting, and many others. In some applications, lighting that is still needed can be dimmed when the need for the lighting decreases. Visibility can still remain excellent.
Glare-free lighting. Glare never helps visibility. The eye can see remarkably well even at very low lighting levels in the absence of glare.
Recognizing the heroes. Photo of a low-pressure sodium fixture.
Energy-efficient lamps. Naturally, these can help save energy when used in place of energy-inefficient lamps. Here is a list of lamps in order of decreasing energy efficiency: low-pressure sodium, high-pressure sodium, metal halide, and compact fluorescent. Use them whenever possible. Explore your city and your neighborhood, and make a list of the lighting heroes and the villains. Take photographs if you can. Help publicize the heroes. Help others understand the value of heroes and the villainy of villains. Good nighttime lighting has great value.
Light Pollution and the U.S. National Science Education Standards
The only good thing about light pollution is that it makes an excellent topic for teaching and learning about science and technology and their relationships to society. And science educators now know that teaching is most effective when an inquiry-based approach is taken. This usually means "hands-on activities," and there are lots of those in the light pollution field. Effective teaching also requires that topics be introduced to students at an age when they can appreciate the concepts and issues involved. As students progress from grades K through 12, the U.S. National Science Education Standards (NSES) gradually introduce them to the scientific, technological, and societal issues with which light pollution connects so well.
The NSES were developed over many years by thousands of teachers, scientists, and other experts across the country. The Standards address not only content issues but exemplary teaching practices, effective professional development, criteria for assessing and analyzing students' attainments, the nature and design of the school and district science program, and the resources and other supports needed.
The content standards include topics to be addressed in the physical, biological, Earth, and space sciences. They also include unifying processes, science as inquiry, science and technology, personal and social perspectives, and the nature and history of science. The study of light pollution touches on virtually every one of these topics. In particular, activities and projects on light pollution relate to two important themes in the content standards. In "science as inquiry," students ask a question, plan and conduct an investigation, employ tools and equipment to extend their senses, use data to construct an explanation or interpretation, and then communicate their results. In the "nature and history of science" thread, an underlying principle is that science is a human endeavor. What better example than the use and misuse of light!
Returning the heavens. In the photograph to the left, few stars in Orion are visible from Flagstaff, AZ, because of sky glow from low-pressure sodium lamps, but astronomers can easily work around this monochromatic problem by placing a sodium filter in their telescope. In the image to the right, see the return of Orion's stars by the use of such a filter.
At the grade K-4 level in the physical science stream, students are introduced to light. In the biological science stream, they are introduced to the concept of the environment. In the Earth and space science stream, the sky becomes part of the environment. But there may be changes in the environment: "changes... can be natural or influenced by humans. Some changes are good, some are bad, and some are neither... Pollution is a change in the environment that can influence the... activities of... humans." Students learn to recognize that science and technology produce local challenges; the effects may be good or bad.
At the grade 5-8 level, the science and technology stream deals with the development, implementation, and evaluation of technological designs and products (lighting!). The social perspectives include environmental degradation and the concept of risks and benefits; students must think critically about the positive and negative aspects of technological activity. Again, light pollution is an example which can be understood at a very basic level.
At the grade 9-12 level, in the physical science stream, light and spectra are introduced. Astronomy topics center on the origin and evolution of the universe - questions which inspire so many people (including astronomers) to look at the sky and lament the gradual disappearance of its beauty. The topics in the science and technology stream - technological design and the complex nature of science and technology, their motivations and interactions - are tailor-made to be illustrated through a study of light pollution. And the social perspectives include natural resource consumption, environmental quality, and the role of science and technology in local, national, and global challenges.
[Note: All illustrations are from the ASP slide set "Light Pollution: Problems and Solutions."]
David Crawford is a professional astronomer and executive director of the International Dark-Sky Association. He was the 1997 winner of the Van Biesbroeck Award for his leadership in the battle against light pollution. His email address is firstname.lastname@example.org.
Margarita Metaxa is a physicist and astronomer, and a teacher at the Arsakeio School of Athens, which is associated with the National Observatory of Athens. She is active in astronomy education through projects with the Greek Ministry of Education, Universities, and Schools. Her email address is email@example.com.
John Percy is a professor of astronomy at the University of Toronto, and is the current President of the Astronomical Society of the Pacific. His email address is firstname.lastname@example.org.
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