ABSTRACT
Ultraviolet (UV) radiation is the portion of the electromagnetic spectrum that extends from the lower wavelengthlimitofhumanvision(usuallyde©nedas380-400nm)towavelengthsasshortasabout 10nm,whereitoverlapsthex-rayregion.Inthenaturalenvironment,theshortestwavelengthofsunlightthatcanberoutinelymeasuredattheearth’ssurfaceisabout290nm,largelyduetotheabsorption propertiesofozoneandotheratmosphericgases.So,theonlyenvironmentallyrelevantUVregionis from290to380nm.However,arti©cialUVsourcessuchascertainÀuorescentlamps,mercuryand xenonarcs,andlasersarereadilyavailableandextendthepossibilityofexposureofbiologicalspecimenstoUVdowntowavelengthsofabout190nm.Below190nm,air(oxygen)andwaterbeginto absorbUVheavily,makingitdi¿culttoexposebiologicalsamplesexceptunderextremeconditions (e.g.,inavacuum).Hence,UVphotobiologyisconcernedmainlywiththee¨ectsonbiologicalprocesses due to exposure to photons in the wavelength range of 190-380nm.1
