UV light output at 254 nanometres is known as UVC light (germicidal region). UVC light has the ability to inactivate all known microorganisms, bacteria, pathogens, virus and moulds, including chemically resistant organisms, such as Cryptosporidium and Giardia. UV dose is measured in mJ/cm2. Systems are typically sized in two ways: –
1. To provide a minimum level of UV intensity. This sizing ensures that the UV intensity at the furthest location from the UV lamp (UVC light source) is the minimum dose the system will provide. This UV dose is known as a wall dose.
2. An average dose takes into account the wall dose (furthest distance from the UV lamp) and the area immediately in front of the UV lamp where the UV output is greatest. The sizing method calculates an average dose for the system.