Submarines use red lights for the same reason that they make great night lights (and were used in old photography dark rooms): human night vision isn't disrupted by red light so red lights can be kept minimally dim and be more than enough to see by.

Admittedly for submarines light pollution can be life-or-death (because you don't want an enemy submarine to spot you) and it's a little less critical in cities already full of light pollution at all hours.