The decay of photoconductivity from the steady state is widely utilized to characterize semiconductor materials such as hydrogenated amorphous silicon and its related alloys. We propose an efficient and low-cost light-emitting diode (LED) pulse generator with variable duty cycle and intensity to be used in measurements of photoconductivity response time. It is crucial to switch on/off the light swiftly. The circuit developed allows measurements of decay times ranging down to a few hundred nanoseconds. The LED pulse generator was successfully tested in measurements of the temperature dependence of the response time for an a-Si:H film and an a-Si1-xCx:H film.