The interaction of a two-level atomic ensemble with a quantized single mode electromagnetic field in the presence of
optical collisions is theoretically investigated. The main accent is made on achieving thermal equilibrium for coupled
atom-light states (in particular dressed states). We propose a model of atomic dressed state thermalization that accounts
for the evolution of the pseudo-spin Bloch vector components and characterize the essential role of the spontaneous
emission rate in the thermalization process. Our model shows that the time of thermalization of the coupled atom-light
states strictly depends on the ratio of the detuning and the resonant Rabi frequency. The predicted time of thermalization
is in the nanosecond domain and about ten times shorter than the natural lifetime of rubidium D-lines.