Spectral energy density of the first light and CMBR at z = 8 (solid lines) and at z = 6 (dashed lines) when the ionization of hydrogen is ≈0.5 for models Ia and Ib. The vertical dotted lines show the thresholds of dissociation of molecules H⁻, HeH⁺, H, H₂, and HD (overlapped with H₂) and the ionization of HI, correspondingly. The dotted lines show these spectral energy densities at the current epoch. The spectral energy density of cosmic infrared background (dotted green line) is shown for comparison. In the models Ic and Id, the corresponding lines are lower by the ratios of dilution coefficients.