UV transmittance, UV transmission or UVT is a measurement of the amount of ultraviolet light (commonly at 254 nm due to its germicidal effect) that passes through a water sample compared to the amount of light that passes through a pure water sample. The measurement is expressed as a percentage, % UVT.Thus ,the Ultraviolet transmittance tester was designed according to the The UV transmittance measurement. Measurement of UV Transmittance is important for ultraviolet (UV) disinfection of drinking water, wastewater and process water. Low-pressure UV disinfection systems disinfect water using monochromatic UV light at the 254 nm wavelength. The effectiveness of a UV disinfection system is determined by the dose that the system is able to deliver to the target microorganisms in the water. The effective UV dose is dependent primarily on the combined effects of the UV light intensity, the exposure time and the UVT. Ultraviolet transmittance tester includes the closest spectral cha