Low pressure sodium is useful for safety (you don't need color vision to see the shadow of an attacker, a fallen branch, shiny reflective shards of a glass bottle, or a pothole), efficient (Lumen/W), and extremely tame for star-observing (look through a narrow-band filter to block the two very thin very close spectral lines (so close you need decent instruments to see that its not just a single one)). The downside is that you don't get color vision, because the light is so close to monochromatic that you might as well think of it as truly monochromatic for human vision purposes.

Ok, but that's where I'm confused. You don't need to see everything in full colour and detail to be safe. You need to be able to make out shapes, movements and shadows.

A few years ago I lived in a neighbourhood where all the street lights had a dark yellow tint, very warm coloured. They weren't all that bright either. I could see a person a block away with ease.

Again, that was far from ideal to read a book, but why would I do that out on the streets at night?