Measuring and Mitigating Light Pollution
Published on Oct 6, 2007 at 10:58 am.
2 Comments.
Filed under politics, skywatching.
Light pollution is the bane of astronomers world wide. Now, we all know that outdoor lighting is sometimes needed at night. But, outdoor lighting is almost always over done. At night, there are plenty of reasons to have lights on outside. Streetlights improve traffic safety. Sporting events are played at night using artificial lights. Parking lots are lit to assist people to safely get to and from their cars at night. Security lights are believed to deter crime (though, in reality, nowhere near as much as most people think that they do). Some businesses, such as car dealers, need lights for their customers at night. And, other businesses need lights to bring in patrons. But, the vast majority of this outdoor lighting is done incorrectly. The light is needed in certain places for various activities. But, do street lights really need to light up far more than the street? Does a car dealer’s lights need to light up adjacent properties. Does one person’s security light need to light up a whole neighborhood street? Lights on the playing field allow athletes to play sports at night, but do those same lights need to light up the city for blocks in all directions? A lot of light is shining all over the place where it was not orginally intended. When light shines where it is not wanted, this is light trespass. But, all the stray light is generically called light pollution. This stray light scatters across the sky, making the sky too bright to see dim stars and other celestial objects.
Naturally, astronomers hate light pollution. But, organizations like the International Dark Sky Association have been working for a number of years to bring other issues of light pollution to people’s attention. Excessive light does not always provide security. In fact, it turns out that criminals like light, too, in order to conduct their crimes. Nocturnal birds and animals are adversely affected by light pollution. Humans already have a massive environmental footprint, but for some reason, environmentalists seem slow to realize the negative impact of light pollution. And, there are plenty of economic issues. Electricity to make light costs money. The more stray light, the more it costs to operate the lights. It takes energy to make light. Most electric energy here in the US is produced by burning fossil fuels, thus producing greenhouse gasses. Again, there’s that environmental impact.
Now, I am not saying that we shouldn’t have outdoor lighting. Rather, we should have reasonable outdoor lighting. Stray light does no one any good. You still pay for the electricity for light that goes other than where you want it to go. But, if you made sure that all of the light went where you wanted it to go, then you’d have less light pollution, less cost, and brighter light where you wanted it. Light intensity is the power of the light divided by the area. So, the less area that the light spreads over, the greater the intensity. A 60W bulb with a reflector directing all of its light in a desired direction can light up an object much brighter than a 200W bulb that has light shining in all directions, and it does so for less than 1/3 of the cost of electricity. And, since it is not shining in all directions, there is less light going where it isn’t wanted, and thus less light pollution, and it costs less.
There are plenty of resources for people wanting to learn more about light pollution. An inexpensive nice book is Mizon’s Light Pollution: Responses and Remedies. This book has a lot of common sense information about light pollution. For those concerned with the environmental impact of light pollution, see Rich and Longcore’s Ecological Consequences of Artificial Night Lighting. And for the person really serious about this, such as a lighting engineer or someone working for a company or city that wants specifics of illumination, etc, then there’s the Light Pollution Handbook by Narisada and Schreuder. This book is more expensive, but it is written more for the professional. This handbook has a lot more detailed information about the effects of light pollution on the economy and environment. It also contains guidelines for municipalities and lighting ordinances. If you intend to talk to someone in authority about light pollution, it helps to arm yourself with a lot of information. Most people who don’t know any better just assume that more light is better light. You need data to show otherwise and to back up what you say, not just your word and good looks. If light pollution is addressed at the local level, in every community, then there will be some improvement.
But, to effectively combat light pollution on a global scale, we need to have a measure as to how bad it really is. I read about the Great World Wide Star Count light pollution project over at Tony’s Astronomy Buff blog, and I thought that it would be good for me to post about it here, too. The Great World Wide Star Count is a project by the University Corporation for Atmospheric Research, which operates an education web site called Windows to the Universe. The project aims to collect data on the severity of light pollution around the world. The time honored way of determining how dark (or bright) skies are is to determine the limiting magnitude of the sky. By knowing the magnitudes of stars in a given constellation, you can determine the dimmest star in that constellation. If you use the same constellation every time, then you can compare your results on one night to those on another night to determine observing conditions. The constellation that I’ve seen used most often for this is Ursa Minor, but for this project they are using Cygnus for northern hemisphere observers and Sagittarius for southern hemisphere observers. You go to their star chart download page and download the appropriate star chart. Then, you go out sometime in the first two weeks of October and observe your constellation, determining the dimmest star that you can see. If you happen to be in more than one place during that time, then presumably you can do this at each site. To participate in this project, read their web page. You report your observations online. It is important for people to do this, because the more people who participate, then the more data we have on how bad light pollution really is. So, go give it a shot!
-Astroprof
A Ler…-- Rastos de Luz on October 8, 2007 at 4:43 pm: 1
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