An array of light-sensitive sensors utilizes bipolar phototransistors that are formed of multiple amorphous semiconductor layers, such as silicon. In the preferred embodiment, the bipolar transistors are open base devices. In this preferred embodiment, the holes that are generated by reception of incoming photons to a particular open base phototransistor provide current injection to the base region of the phototransistor. The collector region is preferably an intrinsic amorphous silicon layer. The phototransistors may be operated in either an integrating mode in which bipolar current is integrated or a static mode in which a light-responsive voltage is monitored.