A UV-Vis spectrophotometer is an instrument used to measure the absorbance or transmittance of a sample in the ultraviolet and visible wavelength range.

When light passes through a liquid sample, part of the light is absorbed by the substances in the solution, while the remaining light is transmitted. By comparing the intensity of incident light with transmitted light, the instrument can calculate absorbance and help determine the concentration of target compounds in the sample.

This measurement principle is based on the Beer-Lambert Law, which shows the relationship between absorbance, concentration, and optical path length. In practical laboratory work, this allows users to perform fast and reliable quantitative analysis once the proper test method has been established.