ultraviolet (UV) rays [L, ultra, beyond; OFr, violette + L, radius] , electromagnetic radiations found just beyond the violet edge of the visible spectrum, with wavelengths extending to the beginning of x-rays. The wavelengths range from 390 to 290 nm for near-UV rays to 290 to 20 nm for far-UV wavelengths. Ultraviolet radiation in the region of 260 nm can cause photochemical reactions in deoxyribonucleic molecules, causing mutations and destroying microorganisms, including bacteria and viruses.
