Flicker effect caused by voltage harmonies modulation is discussed. Simple functions are used to show that harmonic components, despite satisfying the specific harmonic limits, may produce flicker due to combined amplitude modulation (AM). Computer simulations, based on the International Electro-technicaI Commission (IEC) methodology, are numerically validated and then applied to calculate the instantaneous flicker sensation, resulting from different combinations of harmonies modulation. The results are also confirmed in laboratory tests using a flickermeter to measure the flicker levels obtained by synthesizing the same type of signals on a programmable function generator.182387392