Example of different input spectra used in the CLOUDY calculations. The solid light-gray line represents the UVB SED of Khaire & Srianand (2019), and the dashed gray line the CMB, both at z = 5. The vertical black lines represent the ionization energies of C→C⁺ (dotted) and C⁺→C⁺⁺ (dashed). The colored lines represent the contribution to the SED due to young stars (Cerviño et al. 2002) at different normalizations, plus the contribution of the UVB. The units of the radiation field ϕ are M_⊙ year⁻¹ kpc⁻².