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 bott

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.