What is UVT?
UV transmittance at 254 nm (which is the wavelength of light that UV lamps operate at) is a measure of the fraction of incident light transmitted through the water column. The UV transmittance is the ratio of the light entering the water to that exiting the water. The UVT is usually reported for a pathlength of 1 cm. As UV absorbance increases, the UV transmittance decreases (USEPA UVDGM 2003). UVT is measured using a spectrophotometer. High levels of color &/or tannins will cause a decrease in the UVT level.
