Flagstaff Arizona Dark Sky Requirements

Flagstaff, Arizona is home to the Lowell Observatory as well as the US Naval Observatory Flagstaff Station, two of the largest and most well known astronomical observatories in the nation. These institutions contain high-powered telescopes and other equipment designed to observe celestial bodies, stars, and planets. As a result, many of the cities housing these observatories across the nation have dark sky requirements to reduce light pollution and keep the sky clear and visible for observers.

Shop 590nm Amber

Flagstaff has very specific requirements for any outdoor lighting installed within the city limits. Any outdoor lighting in the city must meet certain requirements including that it be between 585 and 595 nanometers, and that it also must be full cutoff.  The lighting in the photo to the right meets one of Flagstaff’s lighting requirements but not the other. Can you guess which one?

That’s right – it’s the right wavelength (590nm amber) but not full cutoff. The image of the gray  APTA sports light fixture to the right of this text with the bird spikes is both 590nm amber and full cutoff, as the light is angled parallel to the ground. Full cutoff fixtures prevent uplight and glare by design. This light fixture was used in another project by the ocean that needed both full cutoff fixtures as well as fixtures in 590nm amber.

Flagstaff AZ Requires Full Cutoff Light Fixtures with 590nm Amber LEDs

One of the big questions that our customer had for us was what the difference is between PC amber and 590nm amber, and if PC amber would work for his project. PC amber is strictly an LED term, and it was created to replace low pressure sodium lighting as it was phased out of production. PC amber is the name for a specific type of LED chip that emits light in a narrow spectrum as seen in the PC amber spectrum chart to the right. Some parts of the green spectrum and deep red spectrum are visible in this type of lighting.

It appears, however, to the human eye, as a warm amber glow, and it is nearly indistinguishable visibly from 590nm amber. 590nm amber appears on a spectral chart as an even narrower band of light at exactly 590nm. Comparing this to the PC amber spectral chart, we can see that PC amber emits light between roughly 513 and 700nm, which is much too broad to meet Flagstaff requirements.

After some discussion, the customer was made aware that they would need light fixtures in 590nm that were full cutoff in order to meet Flagstaff dark sky lighting requirements. They were recommended APTU wall pack fixtures as these are 590nm as well as full cutoff and available in a wide variety of optics, colors, and wattages.