A photometer works by directing a beam of light through a sample and measuring the amount of light that either passes through (transmittance) or is absorbed (absorbance). The device usually consists of a light source, a sample holder, a filter or monochromator, a detector, and a readout system. The light source emits light at a specific wavelength, which is then filtered or split into its component wavelengths. The detector measures the light that exits the sample, and the readout system displays the results.
