How Flagstaff, Arizona, switched to LEDs without giving astronomers a headache

Enlarge / A couple of different types of dark-sky-friendly LED streetlights. (credit: Scott K. Johnson)

"I feel like we're protecting the last tree, in a way." That's what Flagstaff, Arizona, city council member Austin Aslan said at a recent meeting. The subject of that earnest statement might surprise you: it was streetlights. To be more specific, he was talking about a careful effort to prevent streetlights from washing out the stars in the night sky.

Flagstaff became the first city to earn a designation from the International Dark Sky Association in 2001. That came as a result of its long history of hosting astronomy research at local Lowell Observatory, as well as facilities operated by the US Navy. The city has an official ordinance governing the use of outdoor lighting-public and private.

Lighting issues

A few years ago, though, a problem arose. The type of dark-sky-friendly streetlight that the city had been using was going extinct, largely as a casualty of low demand. In fact, as of this summer, there are none left to buy. Meanwhile, the age of the LED streetlight has arrived with a catch: limited night-sky-friendly LED options.

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