HR diagram of CSPNs in NGC 300. The evolutionary tracks are H-rich post-AGB models by Miller Bertolami (2016). The luminosities are lower limits, assuming a maximum [O III]λ5007 conversion efficiency of 11%. For measurements within the error of log T_eff > 4.98, lower limit effective temperatures are assumed. The ratio [N II]λ6584/Hα is the indicator of optical thickness, with a value less of than 0.3 likely indicating optically thinness. Type I PNe are classified with [N II]λ6584/Hα > 1.0.