Evolution of the mean radiation field, or equally, of the dust mass weighted luminosity, with redshift of main sequence galaxies. The red and blue circles correspond to the ⟨ U ⟩ values of D49 and M28 as derived from the DL07 models. The grey and black squares correspond to the average ⟨ U ⟩ values of MS galaxies as derived from the stacking analysis of Béthermin et al. (2015) and Magdis et al. (2012b) respectively. The open black square corresponds to the mean value of the local Herschel Reference Sample by Ciesla et al. (2014). The solid and dashed pink lines represent the evolutionary trends expected for a broken and universal FMR, respectively, while the dotted line depicts the best fit to the data.