That is a fair question. This is what I find. [1] Ultraviolet B UV‑B 280–315 Ultraviolet C UV‑C 100–280 [1] https://en.wikipedia.org/wiki/Ultraviolet https:

That is a fair question. This is what I find. [1] Ultraviolet B UV‑B 280–315 Ultraviolet C UV‑C 100–280 [1] https://en.wikipedia.org/wiki/Ultraviolet https://en.wikipedia.org/wiki/Ultraviolet My read is "UVB" is the popular medicine way of saying UV is needed for the body to synthesize vitamin D. It was not considered necessary to point out part of the useful spectrum is in "UVC" territory.