In a filter fluorometer, a light source emits light of an excitation wavelength that is relevant to the compound to be measured. Filter fluorometers produce specific excitation and emission wavelengths by using optical filters. The filter blocks other wavelengths but transmits wavelengths relevant to the compound. The light passes through the sample to be measured, and a certain wavelength is absorbed while a longer wavelength is emitted. The emitted light is measured by a detector. By changing the optical filter, different substances can be measured.