The subject of the present research is a quantitative study of opportunity to obtain a photoplasma in a low pressure mixture of alkali metal vapor and noble gas by concentrated solar (or gas lamp) irradiation. The ground, resonance and high-excitation levels, and atomic and molecular ions of an alkali metal were considered. The proposed self-consistent model along with plasma-chemical reactions and radiation transfer accounted for charge transport processes and ambipolar diffusion, unlike previous studies (LIBORS project and others). Spatial uniformity of resonance excitation rate in the all plasma volume was assumed. An iterative method to determine the main parameters of photoplasma was proposed and tested on the example of a mixture of Na vapor and Ar gas for pressures pNa = 0.02 and pAr = 1 Torr in a cylindrical cell of radius R = 0.005 m and length L = 0.01 m in the range of resonance radiation flux density Fλ0 = 4×(1–103) Wm−2 nm–1 inside the gas cell. The minimal value of resonance excitation rate, which is necessary to create a plasma in the considered gas cell, was evaluated as 1.1 × 1022 m−3 s−1. According to our rough estimation, to provide this rate, the minimal value of Fλ0 of an external source should be 40 Wm–2 nm–1. This can be implemented by the concentration coefficient of solar irradiation about 30. The model and obtained results can be used for the calculation of plasma parameters in different mixtures of an alkali metal vapor and a noble gas induced by a nonlaser irradiation source (concentrated solar or gas lamp irradiation) and designing of photovoltaic converters on their base