In many photoemission experiments the retarding voltage between the emitter and the collector is modulated to obtain an electron energy distribution curve. A technique is described in which the incident light beam is modulated as well, but at a much higher frequency. Problems arising from electronic and lamp noise and from stray shunt capacitance are reduced. If the light is modulated by varying its polarization, as in an experiment to study ``surface'' photoemission, the effects of reverse photoemission can also be reduced.