A half adder circuit built entirely from photon-coupled fluorescent proteins is presented. The design utilizes the principles of fluorescence and stimulated emission depletion (STED), a process that precisely controls the fluorescent state by de-exciting fluorophores with a secondary light source. This single-process mechanism is expected to achieve significantly faster response times compared to traditional photoswitchable fluorescent protein systems, paving the way for enhanced computing speeds. The circuit is composed of three distinct types of photon-coupled fluorescent proteins and its operational viability was demonstrated through simulation. The simulation results confirm that the circuit’s operation aligns with the truth table of a half adder, and its response time is on the order of a few nanoseconds.