SOCORRO, N.M., March 22, 2001 -- A campus-wide outdoor lighting improvement project at New Mexico Tech promises to deliver improved safety and security and lower electrical bills at the university, as well as darker nighttime skies above it.

The quaint, but inefficient, "carriage house" lamp posts which have graced the New Mexico Tech campus for decades are rapidly being replaced by taller, energy efficient lights which are designed to cast their light downward, thereby minimizing the amount of light which is directed or scattered upward into the night sky.

The lights currently being installed along the sidewalks which line the main quad of the campus use high-pressure sodium (HPS) lamps, which produce light by passing an electric arc through a tube filled with sodium vapor.

Other recently installed lights illuminating Tech's newer parking lots also include low-pressure sodium (LPS) lamps, which, in addition to being less pressurized than their HPS counterparts, consume even less energy and further lower operating costs.

The newer, pressurized sodium vapor lamps are also more "astronomy friendly" than the older mercury vapor lamps which were, and, in some cases, still are, commonly used for outdoor lighting applications such as street lighting, yard security, and business exterior lighting fixtures.

"Mercury vapor lighting essentially casts a white light," explains Jon Spargo, a local amateur astronomer, "a white light which contains various spectral line elements. Unfortunately, astronomical observation often involves picking up many of those same spectral lines. So, mercury vapor lighting is essentially poison for astronomers--poison with a capital 'P.'"

Mercury vapor lamps also are relatively long-lived in comparison to incandescent lamps--the ubiquitous "light bulbs" which are most familiar to homeowners. However, this long lifespan becomes a disadvantage as mercury vapor lamps fade to lower and lower outputs over years of usage, but still end up consuming the same amount of power they did when they were new.

In fact, the inherent problems with mercury vapor lamps garnered them special mention in New Mexico's "Night Sky Protection Act"--legislation enacted two years ago to regulate outdoor night lighting fixtures in order to preserve and enhance the state's dark skies.

As of January 1, 2000, state law has prohibited the sale or installation of any new mercury vapor outdoor lighting fixtures throughout New Mexico.

"The high-pressure sodium lights, which are the next most common form of outdoor lighting, in comparison are better for astronomy, particularly if they're shielded," Spargo maintains.
"Most of the new street lights which have been installed around Socorro, as well as New Mexico Tech, are of this variety. They're almost monochromatic, with one significant spectral line of sodium, but that can be easily filtered or screened out of your observations."

Sodium vapor lamps, however, tend to cast a pale yellowish- tinged light that, while highly visible to humans, remains nearly monochromatic, or produces light at nearly a single wavelength.

The characteristic pale yellow light, in turn, makes it difficult to determine colors under sodium vapor lamps.

"Cars in parking lots which have sodium vapor lights appear black or gray; you can't differentiate the true colors," Spargo relates. "So, in places like Tucson, where outdoor lighting ordinances are strict because of all the observatories in the area, exceptions are often made for car dealerships to use metal halide lights, which essentially give off a white light which allows for truer colors. However, even those lights must be shielded to prevent direct or scattered light reaching the sky."

New Mexico's Night Sky Protection Act also requires that all outdoor lighting fixtures installed after January 1, 2000, be shielded in such a manner that light rays emitted by the fixture radiate only below the horizontal plane of the fixture.

"For astronomers, high-pressure sodium lights are okay for street lights," Spargo says, "provided that they are fully shielded. If you use them on wall packs, shield them, so that no stray light goes up. After all, if the purpose is safety and security, then you want to able see what's underneath the light and not be blinded by it so you can't see anything."

The real winner in a lighting comparison test, however, Spargo says, would have to be low-pressure sodium vapor lamps, which provide a diffuse light in an energy efficient manner, while at the same time preserving New Mexico's famous dark-sky environment for both backyard astronomers and research astrophysicists.

"This becomes even more important since New Mexico Tech will be establishing a $40 million observatory," Spargo notes, referring to the planned Magdalena Ridge Observatory (MRO). "We
need to keep our dark skies."

To further emphasize the importance of maintaining New Mexico's famous dark nighttime skies around Socorro, Spargo points out that recently published scientific data ranks the 10,600-foot-high ridge atop the nearby Magdalena Mountains as the best undeveloped astronomical observation site in North America, with its best viewing nights rivaling the best viewing nights on the taller and more famous Mauna Kea summit in Hawaii.

"Once you get the infrastructure in place," Spargo adds, "it's my opinion that Socorro is going to become the astronomical center of the U.S.A. Move over, Tucson! This place is going to be Mecca for astronomers. But, in order to keep it Mecca, we also desperately need to get a handle on the outdoor lighting that's allowed in the area."

Dr. Dan Klinglesmith III, a research associate and adjunct faculty member with New Mexico Tech's physics department who is directly involved with the MRO project, is also a staunch advocate of working to preserve the state's dark skies.

"It's really in the best interest of everybody involved -- citizens, astronomers, city and county governments -- to get the correct types of outdoor lighting installed," Klinglesmith says. "When you do it correctly, everyone wins: you can increase security, save money, and keep the astronomers happy all at the same time. And, keeping the astronomers happy is bound to invigorate the economy in Socorro . . . maybe not tomorrow, but certainly ten years from now, which is about the time it takes to develop major astronomy projects.

"One of the major benefits of living in Socorro for me is that I can look out of the windows of my bedroom, while lying in my bed, and see the Milky Way," Klinglesmith relates. "I spent my adult life in the Washington, D.C. area, where you can barely see the stars, so you can imagine what a sense of awe this gives me."

Both Spargo and Klinglesmith say they hope that the Night Sky Protection Act and the more stringent city ordinance governing outdoor lighting, which was passed by the Socorro City Council several years prior to the state legislation, will ensure dark skies for years to come.

"However, the laws won't mean much if they aren't enforced," cautions Spargo.

"We'd like to see Tech at the forefront in setting a good example of how to correctly set up outdoor lighting," Klinglesmith says, "and also setting a good example by demonstrating that you can put up good lighting and still save money in the long run."

"There's no question that the outdoor lighting on the Tech campus is better now than in the past," Spargo says, "but it can become even better. . . . The night sky is a resource that we can't afford to lose."

 


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