FAQs
UV254, also known as the Spectral Absorption Coefficient (SAC), is a water quality test parameter which utilizes light at the UV 254nm wavelength to be able to detect organic matter in water and wastewater. This is due to the fact that most organic compounds absorb light at the UV 254nm wavelength. Unlike other organic test parameters, UV254 has a bias towards reactive or aromatic organic matter which has double bonded ring structures and is typically the most problematic form of organics in water. UV254 is typically represented as a calculation of UV absorbance (UVA) or UV transmittance (UVT). UVT is a relative measurement. It is essentially a measure of how much light passes through a water sample compared with how much light passes through a pure water sample. The sample water measurement is actually divided by the pure water measurement and then converted to a percentage. Therefore, any unit of measure of the light itself is cancelled in the division. An example of a UVT measurement would be 96.4% UVT. Pure water (DI water) will read 100% UVT, and completely opaque water will read 0% UVT. Typically UVT is only used to refer to the transmittance of light at the 254nm wavelength since its application is usually for UV disinfection system dosing. 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.
