Noun
phototransistor (plural phototransistors)
(electronics) Any semiconductor device whose electrical characteristics are light-sensitive.
A small notch on the right of the disk identifies that it is writable, detected by a mechanical switch or phototransistor above it; if it is not present, the disk is read-only. Source: Internet
Electronic symbol for a phototransistor A phototransistor is a light-sensitive transistor. Source: Internet