In fluorimetry, a photomultiplier tube is used to detect the emitted fluorescence. A photomultiplier tube or PMT is a type of vacuum phototube. It is a highly sensitive detector of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum.

A photomultiplier tube works by multiplying the current generated by incident light as much as 1000 million times. This makes it easier to detect individual photons when the incident flux of light is low.