In my Phoenix neighborhood the LED streetlights have a yellowish color. Yet the skyglow continues to get brighter but has a definite white blue tone. I think it is commercial lighting.
The comparison between normal and reduced illumination are indicating that street lights has minimal effect, basically they are not really polluting much.
I believe the study highlights the importance of needing to mitigate all sources of light pollution.
In 2017 the small City of Goldendale, Washington (population 3400) converted all of their HPS fully shielded streetlights to fully shielded 3000 K LED, and there has been absolutely no decrease in night sky brightness. If anything there is an obvious increase in sky glow that I have noted from my rural location a few km away, and it has been significant:
The "light domes" of Yakima and Goldendale, Washington. Left - July 2017 an aurora display creates the red-purple glow along the horizon. Right - July 2020 air glow creates the faint green glow along the horizon. Mike McKeag
The pictures above were taken by Oregon IDA State Coordinator Michael McKeag prior (July 2017) to and after (July 2020) the September 2017 Goldendale 3000 K LED streetlight conversion. They were taken from close to the same location on Dalles Mountain Road looking north north-east. They do not indicate a decrease in the amount of light pollution from Goldendale with the conversion to 3000 K LED streetlights. If anything, the relative brightness of the "light dome" from Goldendale (enacted but unenforced lighting codes) now exceeds that coming over the Simcoe Mountains from Yakima, Washington 75 miles (120 km) to the north. Yakima replaced almost all HPS streetlights with 5000 K LED street lights in 2014, and has no lighting codes at all. Also note the obvious change in the color temperature of the Goldendale light pollution. These images seem to confirm that 3000 K LED street lighting worsens skyglow by a factor of two compared to HPS - and without at least 60% dimming - generally is more damaging to the night sky than previously installed HPS street lighting.
Flagstaff Dark Skies Coalition
Edited by BYoesle, 18 November 2020 - 02:02 PM.