Spectral energy distribution of the radiation field λJ_λ for R = 11 kpc and for z = 0,8,22 kpc (from top to bottom). Red lines represent the radiation field obtained with the TRADING model, black lines represent the model described in this paper and the green line represents the galactic radiation field in the solar vicinity obtained by Mathis et al. (1983) rescaled to have the same G₀ that we obtain in our model at (R [kpc], z [kpc]) = (11,0).