Phototube

A vacuum electronic detector that converts incident light into an electrical signal by releasing electrons from a photosensitive surface and collecting them at an electrode.

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Photoelectric effect: The emission of electrons from matter after it absorbs electromagnetic radiation. It is the physical process that releases electrons from the phototube’s cathode.
Vacuum tube: An electronic device that controls electron flow through a vacuum between electrodes. A phototube is a light-sensitive vacuum tube with a photoemissive cathode.
Photodetector: A device that detects light and converts it into an electrical signal. Phototubes are one vacuum-based member of this broader detector family.
Photoconductivity: An increase or other change in a material’s electrical conductivity caused by light. Photoconductive detectors change resistance; phototubes instead emit electrons from a surface.
Photocathode: A photosensitive electrode that emits electrons when it absorbs light. Its material and surface determine how efficiently the phototube converts light into electrons.
Work function: The minimum energy needed to remove an electron from a material’s surface. It helps determine which photon wavelengths can release electrons from the photocathode.
Photocell: A light-sensitive electrical component whose output changes in response to illumination. Phototubes were widely used as photocells in light-controlled circuits and instruments.
Photovoltaic effect: The generation of voltage or electric current in a material exposed to light. Photovoltaic cells generate carriers within a solid rather than emitting electrons into a vacuum.
Anode: An electrode that collects electrons in a vacuum tube or other electrical device. A positive anode draws photoelectrons across the tube, producing the output current.
Electron: A negatively charged elementary particle that carries electric current in conductors and vacuum devices. Electrons emitted by the cathode form the phototube’s measurable signal.