Interesting article,
Why you should be worried about connected street lights
but I think this is relevant aspect,
"Retired astronomer Christian Luginbuhl at the Flagstaff Dark Skies Coalition published a research paper in 2014 which showed that if you switch from high-pressure sodium to white LED, the 'sky glow' will increase tremendously - even if you match the total number of lumens (the brightness thrown out) of light." ... ... ... Technology to the rescue
It doesn't have to be this way and, as usual, technology does have an answer. Even progressive Flagstaff needs to take advantage of LED's undoubted economic benefits, but unlike most towns it's not rushing in and buying the cheapest LED solution without first trying out night sky and eye-friendly alternatives already on the market.
The town is currently testing both narrow-band amber (NBA) and filtered white LED (FLED). NBA fixtures - recommended by the National Optical Astronomy Observatory - emit mostly yellow light, while FLED is a normal white LED fixture with a glass filter over the top that suppresses the shortwave blue light.
Together those technologies largely solve the problem of sky glow, while also achieving the same low electricity costs, but they're newer, so don't have economies of scale."