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

A few years ago a problem arose in Flagstaff, Arizona. 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. If the city went out and just swapped lumens for the cheapest LED products out there, the astronomers would have marched on city hall with pitchforks and (night-vision-preserving) torches. And that might have been the least of their concerns, as the Navy informed the city last year that “brightening of skies 10 percent over current conditions is not compatible with the [Naval Observatory’s] mission.”