Photoelectric conversion device and light detection system

A photoelectric conversion device comprising:

• a plurality of pixels each including a photoelectric conversion unit configured to output a photon detection signal according to incidence of a photon, a counting unit configured to hold a count value obtained by counting the photon detection signal in a predetermined number of bits, and a switching unit configured to switch information output from the counting unit to first information including information of an upper bit or second information including information of the upper bit and another bit among the predetermined number of bits held by the counting unit;
• a detection unit configured to extract a detection pixel that outputs the second information from among the plurality of pixels based on the first information;
• and
• a region control unit configured to control the switching unit of each pixel based on a detection result from the detection unit,
• wherein the region control unit causes the counting unit of the detection pixel and an adjacent pixel adjacent to the detection pixel to output the second information.