Relation between the faint end slope α of the luminosity function and the characteristic luminosity of individual galaxies with more than 20 H II regions brighter than L(Hα)≥10³⁷ erg s⁻¹. Different colours are used for galaxies belonging to different cluster substructures: cyan for cluster A and LVC, 16.5 Mpc; magenta for cluster B, 15.8 Mpc; green for W′ cloud, 23 Mpc; and red for W and M clouds, 32 Mpc. The Hα luminosities of individual H II regions are corrected for dust attenuation and [N II] contamination as described in Sect. 3.2.