a junction transistor, whose base signal is generated by illumination of the base. The emitter current, and hence collector current, increases with the intensity of the light
phototransistor in American English
(ˌfoʊtoʊtrænˈzɪstər; ˌfoʊtoʊtrænˈsɪstər)
US
noun
Electronics
a device combining the function of a photodiode with the amplifying function of a transistor