Ultraviolet



Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, that is, in the range 10 nm to 400 nm.

Fluorescence
Many substances absorb visible and ultraviolet radiations an they have visible and ultraviolet spectra. Many minerals and gems fluoresce to various degree under ultraviolet light, or may fluoresce differently under short wave ultraviolet versus long wave ultraviolet.