The effect of the primary light intensity (corresponding to the fundamental absorption edge) on the infrared quenching of photocapacitance (PHCAP IR quenching) in CdS : Cu evaporated films has been studied. Two methods, viz., the two‐beam and three‐beam methods, for PHCAP IR quenching on detecting deep Cu levels are developed. It has been found that PHCAP IR quenching depends on the primary light intensity, that is, the rates for capturing holes into Cu deep acceptor levels [Cu+levels and (Cu+Cu+) levels] vary as the primary light intensity changes. The experimental results are consistent with the calculations based on the three‐state model of Cu quantitatively. The photoionization cross sections and thermal emission rates of holes were also measured.