 Ultraviolet radiation

Ultraviolet radiation is electromagnetic radiation at shorter wavelengths than visible violet light and longer wavelengths than the neighboring X-ray band. Its photons have higher energies than visible photons because $E=h\nu =hc/\lambda$.

Its interaction with matter depends strongly on wavelength. A material that transmits visible light can absorb ultraviolet radiation, converting excitation into fluorescence, chemical change or heat. To measure transmission, compare the sample with a reference path at the same wavelength and account for the detector's spectral responsivity. Visible transparency is therefore an unreliable test of an ultraviolet window.