Comparison of methods to compute ﹩{U}_{\mathrm{MW}}﹩, the UV background field in units of the locally observed field according to Draine (1978). Based on the Faucher-Giguère et al. (2009) model, we compare the flux at 1000 Å (dark blue solid line) and the flux in the LW band (dark blue dashed line). The results are almost indistinguishable because the Faucher-Giguère et al. (2009) and Draine (1978) spectra resemble each other in shape in the relevant energy range. Both methods predict a low ﹩{U}_{\mathrm{MW}}\approx {10}^{-3}﹩ at z = 0. For comparison, we also show ﹩{U}_{\mathrm{MW}}﹩ assuming the Haardt & Madau (2012) and Puchwein et al. (2018) UV background models (light blue and pink lines).