There are no lights that are actually black. The term "black light" is a misnomer.
Understanding "Black Lights"
The phrase "black light" is a common marketing term for ultraviolet (UV) light bulbs. These bulbs emit ultraviolet light, which is invisible to the human eye. However, they cause certain materials to fluoresce, appearing to glow in the dark. This effect is what gives the impression of a "black" light, but the light itself is not actually black. Black light is just a marketing term for UV emitting light bulbs.
Why the Confusion?
The confusion arises because these lights appear to be producing light from nothing. The light emitted by the bulb is outside of the visible spectrum; what we perceive is the fluorescence from objects illuminated by the UV light, not the UV light itself.
