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.