Half-light radius as a function of mid-IR luminosity; blue stars/red diamonds denote type 1/2 AGNs; the error bar for NGC 4151 is not a statistical error but shows the range for r_1/2 from the upper limit (from single-dish observation) and lower limit from our modeling. The magenta and red lines show the innermost radius as derived empirically (Eq. 10) and the outermost radius for 300 K warm dust as given by the Barvainis formula. The half-light radii at 12 μm show a large scatter, but are about 20 times larger than at 2 μm. They are almost always a factor of three smaller than the Barvainis radius. The statistical errors of the MIDI size measurements are smaller than the symbols and therefore not shown. This plot makes use of the bolometric correction factors described in the text.