The comparison of the calculated departure coefficients b_n with principal quantum number n using the Case B model (blue), the EPA model (red), and the current model with full radiative transfer (black). The dashed and dash-dotted lines respectively indicate the values at the locations 0.05R (center) and 0.95R (boundary) distant from the central massive star in the spherical H II region. R is the radius of a spherical H II region. The electron temperature and density of the H II region are 10000 K and 10⁷ cm^–3. The results for EM = 2 × 10¹¹ cm^–6 pc and EM = 6 × 10¹¹ cm^–6 pc are shown in the top and middle panels, respectively. The differences between b_n in the center and the boundary of H II regions of the corresponding EMs are plotted in the bottom panel.