As the bandgap of CuInSe₂ is increased by alloying with Ga or S, the loss in efficiency due to the decrease of light generated current with increasing voltage becomes important. The standard technique of quantifying this loss is to analyze spectral response measurements made as a function of applied voltage. Instead, it is shown how to determine the voltage dependence of the light generated current by an analysis of the current-voltage (I-V) measurements made at two different light intensities. By adding an I-V measurement at a third light intensity one can also determine if the analysis technique is valid.