Aha. And that article also explains why. In terms of lumens per watt, it appears that the amber LEDs are actually about 40% less efficient than the low pressure sodium lights they would be replacing.

True. That said, LED lighting has a directionality advantage as well. So it turns out you need less of them to get the same basic coverage as the sodium lamps. Here’s an account of how Tucson, with its many observatories, managed to keep within budget using standard, high-efficiency blue LED fixtures:

“If you absolutely must use white LEDs, you could do what Tucson has done,” Hall said. “They... switched out their whole high-pressure sodium system to 3,000 degree white but reduced their lumen budget for street lighting from 480 million to, like, 170 million [lumens] or something. And you need to do that. For every white LED lumen, you're increasing your skyglow by a factor of about three, but they cut the lumen budget by about a factor of three. So overall, they managed to wash out the skyglow because they’ve got a lot of observatories down there.”

> high-efficiency blue LED fixtures

The extra blue is probably screwing up the circadian rhythms of humans and animals:

* https://www.health.harvard.edu/staying-healthy/blue-light-ha...

* https://www.npr.org/sections/thetwo-way/2016/06/21/482936520...

Lumens per watt is the curse of bureaucratic/industrial mandated lighting. Problem is people hate lighting with low CRI, people also hate dim blue light. But you can't put a number on hate like you can lumens per watt.

Efficiency regulations for residential fluorescent lighting delayed adoption by probably 25 years. Because regulations mandated lamps with terrible CRI.