When light is absorbed by a substance it results in the excitement of an electron into a higher state. When the electron jumps back into the lower electronic state it emits the energy as electromagnetic waves. Fluorescence substances emit electromagnetic waves within the visible light spectrum, that is between 390 and 700 nanometers.

Fluorophores are used in many techniques such as fluoresecent microscopy, qPCR, flow cytometry and FACS

There are different ways of labelling a molecule fluorescently, including: - Fluorescent dyes - Immunofluorescence - Fluorescent tags