A standard biology textbook would likely explain that vision in dim light is enabled by rods — sensitive light detectors that are only capable of producing black and white vision. (sciencedaily.com)
But they can also be used the other way around and serve as light detectors. (sciencedaily.com)
The concept was to equip telescopes with extremely sensitive electronic light detectors that could record the slight dip in brightness that occurs when a planet passes in front of a star. (discovermagazine.com)