Results of an investigation of 23 planetary nebulae whose post-AGB central stars have been previously analyzed using direct spectroscopic non-LTE methods are presented. A comparison of spectroscopic effective temperatures with Zanstra and Stoy temperatures shows that most PN in the present sample are optically thin in the H-Ly continuum. A good correlation is found between spectroscopic T(eff) and nebular excitation class, for excitation classes not greater than 5. Corrected stellar surface gravities are used to redetermine stellar masses, luminosities, and distances, and bolometric corrections are calculated. A well-defined relation is found between nebular excitation classes not greater than 5 and bolometric corrections. The present central star luminosities are compared with those obtained under the assumption that the PN are completely optically thick. It is shown that most PN in the present sample are absorbing a rather small fraction of the central ionizing radiation. This fraction decreases as the central star becomes hotter.