Photo-ionisation rate (top) and photo-heating rate (bottom), for a redshift dependent uniform Haardt & Madau (2012) UVB spectrum (left) and an aging SSP with M_cl = 10⁶ M_⊙ at a distance of 100 pc (right). The blue line shows the ionisation and heating rate for the common PWC approximation of the radiation field in combination with a constant σ_eff. The red line corresponds to our new PWPL approximation for the radiation field in combination with the power-law photo-ionisation cross-section (Eq. 6).