The optical properties of InGaN quantum wells were studied using time-resolved cathodoluminescence (TRCL) spectroscopy. The rectangular excitation pulses with ultrafast on and off switching and with pulse lengths sufficiently long to ensure excitation into quasi-steady-state conditions were used to measure the onset and decay of the relaxation and recombination kinetics. It was found that both localization in potential fluctuations and quantum confined Stark effect (QCSE) due to fields have an effect on recombination. The results show that for L z = 6 nm the localization effects are dominant, whereas for L z = 8 nm field effects are dominant.