Energy produced by the invisible part of the electromagnetic spectrum with wavelengths of 100 to 400nm (nanometres).
Photographic emulsions are sensitive to visible light and also to other invisible radiations with wavelengths much shorter than 40nm, such as ultraviolet and X-rays.
Some wedge spectrograms show a fairly sharp cut-off in spectral sensitivity just below 350 nm. This is due to the ultraviolet absorption by the glass optical components in the exposing instrument.
In some cases, ultraviolet absorbers are coated in the supercoat on top of an emulsion in order to cut off the sensitivity at approximately 410nm.
Emulsions can also be sensitized to infrared radiation, with wavelengths slightly longer than 700nm.