Ultraviolet light occupies the spectral range of 4,000 to 1,200 angstroms, which is from just below visible light to soft X-rays. Ultraviolet radiation at about the center of the range has been found to kill or deactivate many pathogens. Chemistry UV treatment is unique in its mode of action in that it does not necessarily kill the target organism, instead the radiation alters cell DNA so that the organism is sterilized. This serves to inactivate the pathogen so that it cannot proliferate and cause disease. Bacteria are the easiest group to treat and differ the least in amount of radiation required.
Viruses are most resistant and variable.
In channel submerged systems consisting of lamps mounted on racks that can be lowered into the flow channel. Each lamp is inserted into a transparent tube and sealed to protect it from exposure to the water. For this type of system, water level variations should be kept to a minimum to avoid short circuiting. Enclosed submerged lamp systems much like the other submerged system except that the lamps are fixed in place. This arrangement allows for the possible use of new high intensity lamps for enhanced treatment capabilities.