Ultraviolet transmission or UV transmittance (UVT) is a water quality measurement. The method works by measuring the amount of UV light, typically at 254 nm, that is able to pass through a water sample of a given path length. It is defined as the ratio of the intensity of light after passing through a water sample (l) to the intensity of light at the source (l0), expressed as a percentage:
UVT will be different for different path lengths. Because the UVT varies with path length and the concentration of matter, the UVT is usually expressed with the assumption that a 1 cm path length is used so that the UVT provides a measure of matter in the water independent of path length.
When light passes through the water sample, any substances present will absorb or scatter the light. Therefore, a sample with a high concentration of substances will have a low UVT and a sample with a low concentration of substances will have a high UVT. A pure water sample, such as deionized (DI) water, will have a UVT of 100%. The below image further illustrates the relationship between water quality and UVT.
APPLICATIONS FOR UV TRANSMITTANCE (UVT)
UVT is an important measurement for the UV disinfection process. UV disinfection is a treatment process where UV light is used to inactivate pathogenic microorganisms in water or wastewater. Understanding water quality conditions and the capacity of UV light able to penetrate the water via UVT enables the system to determine the UV dose or lamp output settings require for proper disinfection of the water. UVT is also useful prior to the installation of a UV disinfection system to determine the expected UVT water quality range for design purposes.
UVT instruments come in a variety of forms for the different application requirements including portable test meters, bypass cabinet analyzers and submersible probes. To learn more about Real Tech’s UVT solutions, visit our products page.