Wiktionary
n. Any device used to detect electromagnetic radiation
Wikipedia
Photosensors or photodetectors are sensors of light or other electromagnetic energy. A photo detector converts light signals that hit the junction into voltage or current. The connection uses an illumination window with an anti-reflect coating to absorb the light photons. This results in creation of electron-hole pairs in the depletion region. Photodiodes and photo transistors are few examples of photo detectors. Solar cells are also similar to photo detectors as they absorb light and turn it into energy.
Usage examples of "photodetector".
Their identical protective rims kept them too far apart-their photodetectors a millimeter beyond the plane of focus of each others signal lasers.
I have photodetectors so I can measure the light that's reflecting off that thing, and the light it emits, at a variety of energies.