This might be enough for photography, but the speed of light would probably push this above 1 millisecond for the area that needs to be dark for large telescope

This might be enough for photography, but the speed of light would probably push this above 1 millisecond for the area that needs to be dark for large telescopes. But engineering the light sources to be astronomy-friendly and nature-friendly in general seems like a good idea. Basically limit things to the red-orange part of the spectrum. It worked for sodium lights.