An experimental study of the in-plane optical conductivity of (Pbx,Bi2−x)(LaySr2−y)CuO6 (Bi2201) is presented for a broad doping and temperature range. The in-plane conductivity is analyzed within a strong coupling formalism. We address the interrelationship between the optical conductivity, the single particle self-energy and the electron–boson spectral function. We find that the frequency and temperature dependence can be well described within this formalism. We present a universal description of optical, angle resolved photoemission spectroscopy (ARPES) and tunneling spectra. The full frequency and temperature dependence of the optical spectra and single particle self-energy is shown to result from an electron–boson spectral function, which shows a strong doping dependence and weak temperature dependence.