Ok, so the name for this stuff really IS that straightforward, at least in British English.

From that Wiki site:
"Streetlamps are designed to illuminate the surrounding area at night, serving not only as a deterrent to criminals but more importantly to allow people to see where they're going."

I guess they had to clarify that

Oh, and "mongo"?!? Love the name. Does anybody know where it came from?

Thanks, everyone!