Surface brightness of Fornax cluster dwarfs. Apparent r′-band magnitudes (m_r′) and mean effective SBs () of the FDSDC galaxies (black symbols) compared with the LSB extension galaxies described in this work (red symbols). The histograms on the x and y axes show the distributions of the magnitudes and SBs with the same colors as in the scatter plot. The blue and green contours show the 50% and 75% detection limits found using the artificial galaxies (Sect. 3.2), and the black and dashed gray lines show the a > 2 arcsec and SB selection limits, respectively. There are also galaxies with R_e < 2 arcsec as the selection was based on MTO detection a > 2 arcsec. For a comparison, we also show a sample of LG dwarfs and globular clusters (green squares clearly above these selection limits) from Brodie et al. (2011).