Image Credit: Gemma Lighting
Believe it or not, the photo above shows what will soon be a major quandary for astronomers, both professional and amateur. Take a look at the streetlights in the foreground. They're a nice white color; you can see the colored paint on the pavement, and the lights seem reasonably bright. Then look in the background, and you'll see the orange glow of low-pressure sodium streetlights. If you've lived somewhere with the low-pressure sodium lights (like Tucson or San Jose), you know that it is impossible to see colors (other than light, dark and orange; even red cars look black under those lamps) and their glow is a little garish.
For many years, astronomers have been pushing for low-pressure sodium lamps. Because all of their light comes out in a single color, we can design filters that block that specific color of light. This allows astronomical observatories like Lick Observatory, just outside of San Jose, to keep operating within the blinding glow of lights from a large metropolitan area. Cities have been willing to use the low-pressure sodium lights not just because of astronomy, but because they are less expensive than most streetlights, and because they use less electricity than other types of streetlights. So, low-pressure sodium is economically friendly, too. Astronomers and astronomy-related groups like the International Dark-Sky Association have pushed hard on this economic end because, frankly, money talks.
But now we face a problem. The white lights in the picture above are LEDs, or light-emitting diodes. LED streetlamps are starting to become available. The LED lamps use less than half the electricity of low-pressure sodium lamps, they last five times longer than low-pressure sodium lights, and they are certainly prettier than low-pressure sodium lamps. But, because they emit light across the entire rainbow, they are not friendly for astronomers.
The economic arguments that proved so persuasive in getting low-pressure sodium lights installed are now going to be a primary argument against keeping those astronomy-friendly lights, and if we astronomers try and argue against money and energy-saving lights, we are going to lose both our dark skies and our credibility.
The city of San Jose, California, home to the aforementioned Lick Observatory, is going to install LED lights, and most people are quite happy that the ugly yellow lights are going away. Is this the end for astronomy at Lick?
Not necessarily. It is possible to make white-looking LEDs out of a collection of red, green and blue LEDs; this light can still be filtered out, though not as completely as the low-pressure sodium lamps (the last I heard, San Jose was considering these types of LEDs). Further, these lights can be more easily controlled, including having variable brightness. And, if people are happier with the colors of the lights, they might be more likely to follow other dark-sky related solutions, like shielding.
As I've written before, humans inherently distrust the dark. But excessive and poorly-designed lights not only hide the stars from astronomers; they are wasteful, environmentally unfriendly, and even a human health hazard! Dark Skies Awareness is therefore a cornerstone project of the International Year of Astronomy 2009.
But, in my opinion, professional astronomers and astronomy enthusiasts need to be careful in talking about dark skies. The old arguments of saving money and energy won't go as far as they used to; the LED lights show that human ingenuity can alleviate that problem without sacrificing light. And it is hard, though not impossible, to get most people to see that something as innately comforting as outdoor lighting can be harmful, especially for our own health.
I think that many types of lighting ordinances, especially in regard to light design and shielding, are still quite attainable goals. But I worry, perhaps too much, that LED outdoor lighting is going to remove that highly-successful economics argument from the dark skies sales pitch, and I worry that if we try and fight against LED lighting, we will come out on the losing end.
If you've never seen a truly dark sky from a site dozens of miles from the nearest town, it's hard to describe what you are missing. The sky is not black but glows ever so faintly. There are so many stars that familiar constellations like Orion and the Big Dipper are nearly impossible to find. The Milky Way is a bright glowing band stretching across the entire sky. And shooting stars are actually quite common. The experience is far less frightening than the murky shadows cast in the alleys of our cities. It's worth the trip to find those dark skies, and it's worth the political effort to try and bring those skies as close to people's homes as we can.