... and blacklight isn't black! It's invisible (to human eyes).
You don't see black light? I do. I think most people do. It's just dim.
Blacklight = ultraviolet light = shorter wavelength (10-400 nm) than visible light (400 - 700 nm)
Blacklight isn't actually ultraviolet. You can't see UV, but you can see blacklight. At least everyone I know can. It's right on the edge of being UV, hence why it is a deep purple rather than invisible. But it's still visible. They just always call it UV to make it sound cooler than it is. Not that it isn't cool, but I can certainly see it. That's why lots of places light with it, even when not triggering the effect that people want, it's still enough to see by.
The violet glow of a black light is not the UV light itself, but visible light that escapes being filtered out by the filter material in the glass envelope.
It depends on what you refer to as "black light".
If you define a blacklight to be the device itself that emits UV light, then yes, you are seeing the visible light that escapes as mentioned above.
And FFS, to finally readdress my original point, the light isn't black.