Editing Plate reader (section)

===Fluorescence polarization===
Fluorescence polarization measurement is also very close to FI detection. The difference is that the optical system includes polarizing filters on the light path: the samples in the microplate are excited using polarized light (instead of non-polarized light in FI and TRF modes). Depending on the mobility of the fluorescent molecules found in the wells, the light emitted will either be polarized or not. For example, large molecules (e.g. proteins) in solution, which rotate relatively slowly because of their size, will emit polarized light when excited with polarized light. On the other hand, the fast rotation of smaller molecules will result in a depolarization of the signal. The emission system of the plate reader uses polarizing filters to analyze the polarity of the emitted light. A low level of polarization indicates that small fluorescent molecules move freely in the sample. A high level of polarization indicates that fluorescent is attached to a larger molecular complex. As a result, one of the basic applications of FP detection is molecular binding assays, since they allow to detect if a small fluorescent molecule binds (or not) to a larger, non-fluorescent molecule: binding results in a slower rotation speed of the fluorescent molecule, and in an increase in the polarization of the signal.{{citation needed|date=May 2020}}