Calculation of the resonance level 6**3P, Hg atom population in the ac discharge in a mixture of mercury vapors with argon is carried out on the basis of a theoretical model of the positive discharge column. The main processes resulting in an increase in the density of mercury atoms in the state of resonance and, consequently, in an increase in light emission of the elevated frequency ac discharge plasma are explained. It is shown that high energy levels of Hg atoms play an important role in increasing the plasma radiation efficiency of the ac discharge with respect to the dc discharge.