This letter proposes an index called the equivalent lamp index to characterize the harmonic attenuation effect of the compact fluorescent lamps (CFLs). The index can be used to facilitate the assessment of the collective harmonic impact of multiple CFLs. The proposed index is given in the form of a family of curves established by experimental studies. The implication of the results is that when N CFLs are installed in a house, the actual harmonic current injected by that house to the power system is equivalent to M lamps modeled as ideal current sources, where M is smaller than N.