Editing Photoelectric effect (section)

===Photomultipliers===
{{Main|Photomultiplier}}
[[File:Photomultiplier schema en.png|thumb|Photomultiplier|alt=]]
These are extremely light-sensitive vacuum tubes with a coated [[photocathode]] inside the envelope. The photo cathode contains combinations of materials such as cesium, rubidium, and antimony specially selected to provide a low work function, so when illuminated even by very low levels of light, the photocathode readily releases electrons. By means of a series of electrodes (dynodes) at ever-higher potentials, these electrons are accelerated and substantially increased in number through [[secondary emission]] to provide a readily detectable output current. Photomultipliers are still commonly used wherever low levels of light must be detected.<ref name="Ref_Timothy">Timothy, J. Gethyn (2010) in Huber, Martin C.E. (ed.) ''Observing Photons in Space'', ISSI Scientific Report 009, ESA Communications, pp. 365–408, {{ISBN|978-92-9221-938-3}}</ref>