Self-consistent model of a positive column in the argon glow discharge has been developed, considering gas pressures higher than 10 Torr. There are two discharge modes at these conditions: diffuse and contracted one. Resonance radiation trapping, being a one of the most important mechanisms of species transport in non-equilibrium plasmas, is treated by solving the Holstein-Biberman equation using matrix method. High-resolution spatial measurements of the excited state densities in argon discharge are performed. Results of experiments are compared with data from the self-consistent model.