That question from the journalists had a major impact on my research career, and I’ve spent several years trying to understand the amount that different types of light sources radiate into the night environment.

That led to an EXTREMELY COOL research paper: https://doi.org/10.1177/1477153520958463

The city of Tucson, Arizona alternatively dimmed and brightened nearly their entire street light network (tens of thousands of lights!), in order to see how much light comes from the streetlights, and how much comes from other lights.

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First off, some background. In 2017, I published a paper that showed that most countries in the world are getting brighter at night in nighttime satellite observations: https://doi.org/10.1126/sciadv.1701528

A number of journalists who reported on that paper asked me “what is actually changing on the ground?” Are streetlights getting more numerous or brighter? Or is it because bike paths are getting lit up now? (seriously got that question from multiple journalists…) Or is some other kind of light changing?

I realized that not only did I not know the answer, but that no one even knows how much the different light types contribute to the brightness of the ground (as seen from space), or the brightness of the night sky (as seen from the ground).

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