phototransistor
noun
pho·to·tran·sis·tor ˌfō-tō-tran-ˈzi-stər 
-tran(t)-ˈsi-
: a photoconductive semiconductor device used especially as a photodetector
Example Sentences
Recent Examples on the Web The capsule has tiny phototransistors that send the light information to a microprocessor, which broadcasts it wirelessly to a computer or smartphone. 
Sean Rossman, USA TODAY, 25 May 2018 Not much, but enough for a custom phototransistor to capture it and relay that information to a microprocessor—which sent the signal to an Android app developed by an undergraduate engineering student. Megan Molteni, WIRED, 24 May 2018
Sean Rossman, USA TODAY, 25 May 2018 Not much, but enough for a custom phototransistor to capture it and relay that information to a microprocessor—which sent the signal to an Android app developed by an undergraduate engineering student. Megan Molteni, WIRED, 24 May 2018 Word History
First Known Use
1950, in the meaning defined above