In this diagram, which uses 3.6 Å resolution spectra, we compare the spectrum of an O7 dwarf (O7 V) star with an O7 supergiant (O7 If). A number of features are seen to be luminosity sensitive. First, the hydrogen lines (only H is shown here) are slightly weaker in the supergiant, whereas the He I lines are quite insensitive to luminosity differences. However, note that in the supergiant star, the N III 4634-42 feature actually goes into emission and the neighboring He II 4686 line decreases in strength (in O6 stars, it actually goes into emission in the supergiant). Note that the nearby He II 4542 line actually increases slightly in strength as we move toward higher luminosities.