Positive column of classic fluorescent discharge lamps has been extensively studied in the past years. In this paper, we use a collisional radiative model to study the low-pressure positive column of discharge lamps filled with only pure gases: neon, argon, or xenon. We show the electron temperature, the electron density, and the electric field. By adding the atomic to molecular ions conversion, we extend the pressure range from 1 to 50 torr. Finally, we show evolution of the molecular ions densities in the rare gases' positive column.Index Terms-Argon, collisional radiative model, low and middle pressure, molecular ions, neon, positive column, xenon.