The precise treatment of weakly coupled systems in the HQM might be slightly different than the way we introduced here since we used the collective coupling strength as the value to be inserted in the expression for the permittivity. In fact, we presumed that the emitters were coherently coupled to the plasmonic cavity. Outside of the strong coupling limit, coherence becomes weaker and consequently, the value for Ω that is to be used might be a bit lower than the collective coupling strength. The nanopar-ticle systems that we presented here are all strongly coupled. Single particle spectra of bare nanorods indicated a plasmon linewidth in the realm of 150 meV. Hence, even the largest particles verge on the strong coupling regime.