In this paper, a new method for evaluation of low frequency voltage fluctuations, which cause light flicker, based on root-mean-square (RMS) computations of voltage waveforms, is presented. According to the IEC and IEEE standards, light flicker computation is achieved on the raw data of the voltage waveforms. However, in real world systems, since raw data storage is expensive and difficult, only RMS values of the voltage are stored for later analysis. The work presented in this paper, proposes a new method to compute light flicker directly from RMS values of the voltage, which are computed based on the IEC power quality standard, IEC 61000-4-30. Beginning from a low-frequency-modulated signal, analytical terms of the flicker frequency components are derived in terms of the RMS voltage waveforms. Then those flicker components are used to compute the flicker sensation values, based on the previously shown fact that flicker sensation is the result of additive effects of the squared flicker frequency components. The comparison of the results with those of the digital realization of the IEC flickermeter shows that the developed method reveals satisfactory estimations of flicker sensation values, obtained from RMS of the voltage waveforms. It can be mentioned that this method provides an accurate, simple, and fast solution for the flicker computation, where raw data of the voltage waveforms are not available, but RMS values are present. The method can be easily adopted by smart-grid applications, where fast and accurate flicker computation is required from RMS voltage waveforms, especially for generating control signals for the FACTS devices.