https://www.alleghenyfront.org/wp-content/uploads/2021/09/AF102221_KH_DarkSky.mp3 Kara Holsopple: Pittsburgh’s ordinance is not as simple as turning off the lights. What are the mechanics of this in terms of technology and practices?
Diane Turnshek: So these values-centered ordinances that the International Dark Sky Association put out in January, and then revised in July, make sense to anybody. They are in plain language, and they explain how the light has to be shielded on top, so there’s no light that goes up into space. Their recommendation for street lights is 2200 Kelvin, and that’s not an actual temperature. That’s the nomenclature that lighting engineers use to describe the color. They have to be only as bright as you need them and have no backlight, and dimmable is preferred, because then if something happens in the area, you can brighten it for an accident and then return them back to their levels afterward.
Holsopple: You mentioned the color of the lights. Can you say a little bit more about that?
Turnshek: So [the city of Pittsburgh is] changing 35000 streetlights that were high-pressure sodium . They’re now going to be LEDs. Plus, there were almost 5,000 lights that were changed to LEDs 10 years ago that were done incorrectly. They’re at 5000 degrees Kelvin.
Any light that has a lot of blue in it is way too hot for nighttime. In a lot of cities, people say it’s like living in a prison yard. The color also is important because blue light scatters more than red light. That’s why the sky is blue. It also matters because blue light affects the nocturnal environment more. We know that you’re not supposed to have blue light on your screens late at night, or you won’t get to sleep all night. That’s a hormone called melatonin, and the blue light inhibits the production of that. You need melatonin to get a good solid night’s sleep.
Plants and animals are really affected by light at night. This artificial light at night tricks them into thinking the seasons are different because their biology tells them that the length of day indicates what time of year it is. If you extend that with artificial light, they get really confused. Trees drop their leaves at the wrong time or leaf out too early. It’s a problem for a lot of things that we don’t even know yet.
Map of light pollution in Pennsylvania is the by Pa. Outdoor Lighting Council. Blue is the darkest area, followed by green, yellow, orange, red, and white. White is described as “stars are weak and washed out, and reduced to a few hundred. The sky is bright and discolored everywhere. Most people don’t look up.” Image provided by Diane Turnshek
Holsopple: What are some of the other benefits of darker skies?
Turnshek: We’re wasting $3 billion a year in the U.S. alone, just sending light up to space for no reason, because we didn’t realize we were doing it or nobody thought about it. I would really like to see a cultural shift where people value darkness. Darkness in and of itself is a beautiful thing.
People tend to be scared of the dark and that’s built into us. Evolution teaches you that there could be scary wild animals in the dark. Well, they are not here, not now. We all have cell phones with flashlights on them, so you don’t really have to be scared of the dark.
Holsopple: How much light is too much light?
Turnshek: The International Dark Sky Association says just light what you need, when you need, how much you need. But there’s the rub. How much do you need? People feel differently about that. The standards are set by organizations of lighting engineers who work on these for decades, and they go on the books, done by committee. The fact that they are lighting engineers, you know, they sell light. That is what they do. They light things.
You’re coming from a position where astronomers are like, dark is beautiful. Lighting engineers think light is beautiful and most people think light is beautiful. It means celebration. It means progress and joy and beauty.
But I think we need to appreciate that if it’s not necessary, you’re wasting the electricity. Is this a big change that’s going to happen with Pittsburgh’s dark sky ordinances? The city light bill and the city excess light are not the majority of the light. It’s businesses and people. The city wants to lead by example.
The Pittsburgh region as seen from the International Space Station. Image: NASA
Holsopple: What are the biggest sources of light pollution?
Turnshek: Tucson has wonderful lighting ordinances, and they got satellite photos as they turned the street lights up and down and off and on, just to answer that question: Do streetlights produce the most amount of light pollution? That came out at about 20 percent. But Tucson already has so many ordinances that are not really representative of other cities. I would say the streetlights probably are like half the light that we see because even if they’re shielded, they’ll bounce off the roadway.
I think if you’re talking about light pollution in general, all over the world, centers of population obviously contribute the most. Then there are weird things like fracking — they light those all up — oil rigs, marijuana greenhouses. So it’s different from cities, but there are a lot of things like Amazon warehouse hubs — to the Moon they can see them.
Holsopple: How can people apply dark sky principles to their own homes and workplaces?
Turnshek: That’s a great question. Everybody can be part of this. If you have a globe light that’s just like a ball and light is going everywhere, change that fixture. If you are putting in new lights, make sure that they’re pointed where you intend them to be, not on your neighbor’s property.
The idea is to use dimmers, timers, motion sensors, and lower temperature lights. If you have a motion sensor, that’s so much safer than those lights — they call them security lights, but I call them insecurity lights, because just blasting light does not make you safer. I mean, 7-Elevens and gas stations get robbed all the time when they’re lit up.
So I would like to see people be a little more careful with the way they spread light around. But of course, I’m an astronomer. So yeah, I think what we should do is be very careful about our lights so we can see the Milky Way.
I want more people to see the Milky Way right from where they live. When you first see it, it looks like clouds, but it’s 400 billion stars, so it’s all that light together. You can’t pick out individual stars. It just looks like a milky spill in the night sky. We should all be able to see it wherever we are.
Diane Turnshek is an astronomer and special faculty in Carnegie Mellon University’s Department of Physics.
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