Seeking true darkness

On those nights when we’re not shrouded in fog, the Coastside has the most spectacular sky in the Bay Area. We still get a ton of spillover on the horizon from San Francisco and elsewhere, but one of our least appreciated natural features is our starry nights.

A couple of weeks ago, the New Yorker published an excellent article on the effects of light pollution and how to mitigate it. It turns out that a great deal of light pollution is unnecessary or even counterproductive, and we can save money and improve visibility while using less artificial llight. For example, some schools have reduced vandalism by turning off their lights at night.

The mall’s large parking lot was fully illuminated—as we walked from the car to the restaurant, I had no trouble reading notes that I had scribbled in my notebook—but it was free of what dark-sky advocates call "glare bombs": fixtures that cast much of their light sideways, into the eyes of passersby, or upward, into the sky. Tucson’s code limits the brightness of exterior fixtures and requires most of them to be of a type usually known as "full cutoff" or "fully shielded," meaning that they cast no light above the horizontal plane and employ a light source that cannot be seen by someone standing to the side. These are not necessarily more difficult or expensive to manufacture than traditional lights, and they typically cost less to operate. Calgary, Alberta, recently cut its electricity expenditures by more than two million dollars a year, by switching to full-cutoff, reduced-wattage street lights.

Diminishing the level of nighttime lighting can actually increase visibility. In recent years, the California Department of Transportation has greatly reduced its use of continuous lighting on its highways, and has increased its use of reflectors and other passive guides, which concentrate luminance where drivers need it rather than dispersing it over broad areas. (Passive guides also save money, since they don’t require electricity.) F.A.A.-regulated airport runways, though they don’t use reflectors, are lit in a somewhat similar fashion, with rows of guidance lights rather than with high-powered floodlights covering broad expanses of macadam. This makes the runways easier for pilots to pick out at night, because the key to visibility, on runways as well as on roads, is contrast.

It’s hard to imagine that just 100 years ago, most of the United States had night skies that were as dark and starry as those observed by Galileo with his primitive telescope, or our ancient ancestors for that matter.

As our population continues to grow, what can we do today to improve how we experience the Coastside at night now and in the future?