Normalized SEDs of some of the sources considered by the photoionization models used by HCM-TEFF for both AGNs (solid lines) and star-forming regions (dashed lines), including individual massive stars from WM-Basic (Pauldrach et al. 2001) and planetary nebulae (Rauch 2003). The ionization potentials of the ions whose optical and IR emission lines are used in our calculations are indicated as vertical dotted lines.