Why is the current from a photoelectric cell proportional to light intensity?

In the photoelectric effect, the current produced by a photoelectric cell is proportional to light intensity because light is composed of discrete particles called photons.12

According to the quantum theory of radiation, each photon carries a specific amount of energy determined by the light's frequency. When light strikes a material, each individual photon interacts with a single electron. Increasing the intensity of the light—while keeping the frequency constant—simply increases the total number of photons striking the surface per unit of time.123

Because each photon can eject one electron (provided its energy exceeds the work function of the material), a higher number of incident photons results in a greater number of emitted electrons. This increased flow of electrons is measured as a higher electric current. Conversely, the energy of the individual photoelectrons is determined by the frequency of the light, not its intensity, which is why intensity only affects the magnitude of the current rather than the kinetic energy of the electrons.132