Predicted silicon ionic column densities as a function of gas density under the HM12 (a harder spectrum; open symbols with dashed–dotted curves) and HM05 (a softer spectrum; filled symbols with solid curves) ionizing spectra for the COS-Halos galaxy #225_38 at z = 0.27. The calculations are performed using the Cloudy software for ﹩\mathrm{log}\,N({\rm{H}}\,{\rm{I}})=15.8﹩ and solar metallicity. The predicted column densities will change proportionally with gas metallicity, but the overall trend remains. Under the HM12 ionizing radiation field, the abundance of Si III (triangles) is at least 0.5 dex smaller than expected from HM05. Consequently, for an observed ﹩N(\mathrm{Si}\,{\rm{III}})﹩, the required gas metallicity is higher under HM12 than under HM05.