Ultraviolet (UV) light is a range of light within the electromagnetic spectrum that is invisible to the human eye. UV light has shorter wavelengths and higher frequencies than visible light, and these properties are dependent on the type of UV light that is being emitted. There are three types of UV light: UV-A, UV-B, and UV-C. The sun naturally emits UV-A and UV-B light, which are responsible for sunburns and cellular damage. UV-C light is absorbed by the Earth’s atmosphere, so we are not exposed to it.
In 1877 an accidental discovery was made when Downes and Blunt noticed the effect of light on microorganisms when exposing test tubes containing microorganisms to sunlight. As they noticed that sunlight prevented the microorganisms' growth , Blunt and Downes demonstrated that bacteria growth depended on intensity, exposure time, and wavelength of the light.
Because of the high energy, short wavelength properties of the UV-C range, organic material, including microorganisms, strongly absorb this wavelength. Once absorbed, this energy causes damage to the organism’s cellular properties, disabling its abilities to reproduce. Specifically, UV-C energy can cause DNA lesions within the cells that directly damage the structure of the DNA backbone and the connection between two strands of DNA. UV light induces the production of reactive oxygen species (ROS) which cause stress and damage to many cellular components.