English▸ adjective (of electromagnetic radiation) having a wavelength shorter than that of the violet end of the visible spectrum but longer than that of X-rays.
▪ (of equipment or techniques) using or concerned with this radiation:
an ultraviolet telescope.
▸ noun the ultraviolet part of the spectrum; ultraviolet radiation.
Ultraviolet radiation spans wavelengths from about 10 nm to 400 nm and is an important component of sunlight although the ozone layer prevents much of it from reaching the earth's surface. While ultraviolet is necessary for the production of vitamin D2 in the skin, excessive exposure can be harmful, causing skin cancer and genetic mutation.