Question: How can light be black?
I assume that you are referring to the light emitted by a black light. The light is not black in color. In fact, there is no such thing as “black light.” The color black is produced when all visible light striking a material is absorbed. This means that no light is reflected back to your eyes.
Black Light refers to a special instrument that emits mostly invisible ultraviolet A radiation (UVA) with some bluish visible light.
Ultraviolet Light and Visible Light are both a form of radiation, for information, see ELECTROMAGNETIC RADIATION