Ultraviolet radiation emitted by UV light bulbs inactivates bacteria by inhibiting DNA replication when the bacteria absorbs the light. The damaged DNA cannot repair itself, causing it to die.
UV irradiation is a popular way of disinfecting water because it is particularly effective against protozoa such as Cryptosporidium spp. The ultraviolet radiation reduces the ability of water-dissolved organic matter to grow bacteria.
UV radiation is also used in air-exchange systems, such as those used for cooling and filtering indoor air, and to sterilize open surfaces, especially in hospital rooms and operating rooms. Using ultraviolet light to control bacterial growth reduces the need for chemical disinfectants.