In water treatment applications, UV light provides rapid, effective inactivation of microorganisms through a physical process. When microorganisms are exposed to wavelengths of UV light, they are instantaneously rendered incapable of reproducing. Microorganisms are inactivated by UV light as a result of damage to nucleic acids. The high energy associated with short wavelength UV energy, primarily at 254 nm, is absorbed by cellular RNA and DNA. This absorption of UV energy forms new bonds between adjacent nucleotides, creating double bonds or dimers. Dimerization of adjacent molecules, particularly thymine, is the most common photochemical damage. Formation of numerous thymine dimers in the DNA of microorganisms prevents replication.