In this letter, we present a simplified evaluation method for light-biased photoconductance decay measurements. The measured effective lifetime is shown to be a differential quantity τeff,d, which may differ significantly from the actual effective lifetime τeff. However, the actual effective lifetime can be approximated by integrating τeff,d directly over the incident power density of the bias light. The quality of the approximation depends mainly on the surface recombination velocity and the wavelength of the used bias light. However, the inaccuracy remains well below 10% for most practical cases. © 1997 American Institute of Physics.