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?