Stacking rest-frame spectra of T/O-type sources with L_150 MHz < 10²³ W Hz⁻¹. The red T-type spectrum is the average of all round (q >  0.6) RLAGNs weighted by the possibility of each individual source being an intrinsic T-type. For clarity, the T-type stacking spectrum is shifted upwards. The blue O-type spectrum is derived in a similar way but using highly elongated (q <  0.4) RLAGNs and weighted by the possibility of each source being an intrinsic O-type. The grey shadows are the individual spectra of the sources used in the stacking. The emission lines needed for calculating the excitation index (Buttiglione et al. 2010) are marked in the figure.