How does absorbance detection work?

Spectrophotometers and absorbance plate readers measure how much light is absorbed by a sample. Microplate readers that are capable of detecting light in the ultraviolet (UV) range can be used to determine the concentration of nucleic acids (DNA and RNA) or protein directly, without the need for sample labeling. Light of a certain wavelength, dependent on the material being measured, is passed through a sample, and a detector on the other side of the microplate well measures how much of the original light was absorbed by the sample in the well.