Wideband interharmonic voltage distortions generated by active front ends (AFEs) may cause visible flicker in modern LED lamps. While the flicker impact of spectral components at individual interharmonic frequencies or producing standard modulated waveform (sinusoidal and rectangular) is well understood, the superposition behavior of multiple simultaneously occurring interharmonic components (wideband interharmonic spectra), as typically present in AFE emission spectra, has not yet been sufficiently studied and validated experimentally. This paper investigates the flicker emission of LED lamps caused by a wideband interharmonic voltage distortion derived from the simulated waveform of an AFE. The flicker impact of the full interharmonic spectrum, individual interharmonic subgroups, and single interharmonic components is measured using a light-based flickermeter. Based on these measurements, the superposition behavior is quantified by means of geometric summation estimating the corresponding summation exponents. The results show that the summation exponent mainly lies in the range of 2 to 3, which is consistent with the commonly assumed summation exponent of independent flicker sources. Furthermore, the findings indicate that a coordination framework based on interharmonic subgroups applying an energy-equivalent aggregation of multiple spectral components is reasonable to appropriately capture the flicker effect of simultaneously occurring wideband interharmonic components of this origin.