UV-Vis absorption spectroscopy is the measurement of the attenuation of a beam of light after it passes through a sample or after reflection from a sample surface.
The Lambda 35 operates on the principle of UV/Visible spectroscopy, where it measures the intensity of light before and after it passes through a sample. The difference in intensity is used to calculate the absorbance, which can be related to the concentration of the analyte in the sample using the Beer-Lambert law