Most mild air pollution is not coming from streetlights

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Most light pollution isn't coming from streetlights

Light pollution is the arch enemy of astronomy and spoils both the enjoyment of the night sky and the professional study of our universe. For years we have assumed that street lights are the main cause of light pollution. However, a recent study showed that street lights account for no more than 20% of all pollution. If we are to solve this annoying astronomical problem, we have to think harder.

Street lights, car headlights, billboards, sports stadiums, shop displays and signs. The trappings of modern civilization make for safer (not to mention more fun) nighttime hours. But the abundance of modern civilization makes the night skies polluted. The more we turn on our lights at night, the less we can access the sky that our ancestors knew and loved.

In addition, professional astronomy is becoming increasingly difficult. The largest observatories of the last century are now threatened by the city lights, and astronomers are forced to build telescopes in some of the most remote and hostile environments on earth.

What to do? For decades it has been believed that street lights are the main cause of light pollution. After all, they are pretty much everywhere and lazily spray their light in all directions – including the sky.

However, new research in the October 2020 issue of Lighting Research & Technology magazine paints a very different picture.

With the Suomi National Polar-Orbiting Partnership (NPP) satellite, the research team took several night images of the city of Tucson, Arizona. Tucson recently upgraded its street lights to work smarter, allowing city officials to adjust their brightness as the night progresses.

In collaboration with the researchers, the city officials dimmed the street lights to just 30% of their maximum brightness and turned them all the way up in the following nights.

When comparing the light pollution in the satellite images, the researchers found that unfortunately not much has changed from night to night. Instead, only about 20% of the city's total brightness could be attributed to streetlights. These measurements were confirmed by a ground-based team who also took measurements during the experiment.

Smart street lights are certainly a smart, money-saving choice and reduce light pollution. However, we have to work even harder to preserve the night sky for generations to come.

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