Wiktionary
phototube
n. A gas-filled electron tube that has a photosensitive cathode
Wikipedia
Phototube
A phototube or photoelectric cell is a type of gas-filled or vacuum tube that is sensitive to light. Such a tube is more correctly called a 'photoemissive cell' to distinguish it from photovoltaic or photoconductive cells. Phototubes were previously more widely used but are now replaced in many applications by solid state photodetectors. The photomultiplier tube is one of the most sensitive light detectors, and is still widely used in physics research.
Usage examples of "phototube".
Light from the tritiated stilbene is strongest in regions of the spectrum where the eye is least sensitive, but where phototubes are most sensitive.