Taking into account the effects of the dispersion of radiation on the central region of self-reversed atomic lines emitted from high-pressure strongly absorbing plasmas, the temperatures in a high-intensity discharge lamp are determined from the self-reversed lines of mercury. The diagnostic method is based on the determination of the inhomogeneity parameter using the one-parameter approximation for the relative source function. It was shown that the presence of the dispersion does not affect the diagnostic method. On the contrary, it was found that the intensity at the central line minimum is several times higher than that obtained solving the conventional radiative transfer equation, whereas the respective optical depth is several times lower. The changes in the minimum intensity and the optical depth are determined by comparing the experimental results with those obtained by numerical simulation of the studied discharge.