It is a transistor which amplifies current induced by photoconductivity.

An optoelectronic device that conducts current when exposed to light. Produces more current and is much more sensitive to light than the photodiode.

a bipolar transistor used as a photodetector

transistor with a window on the top face to allow light to fall on the active surface. Also available as a Darlington photo-transistor to produce a very sensitve light detecting device.

A transistor whose collector current is controlled by the light intensity at its optical input (base).

A phototransistor is a photojunction device in which current flow is directly proportional to the amount of incident light. Phototransistors are well-matched spectrally to infrared LEDs.