Schematic view of the relative location and size of the different regions of a quasar and illustration of the reverberation effect. R_S is the Schwarzschild radius of the central SMBH. The continuum light from the central accretion disk (red) is reverberated both in the BLR (green) and in the NLR (blue), which are much larger than the accretion disk and are therefore much less affected by microlensing (see Sect. 3.3).