Left: wavelength-integrated limb darkening curves for the 3D model of HD 209458 (black solid line), the mean 3D model (green solid line) and the 1D MARCS model (red solid line). Surface intensities between 2900 Å and 5700 Å were weighted with the sensitivity function of the HST STIS instrument and wavelength (see Appendix A). Right: relative deviation between the limb darkening predictions of the 1D MARCS model with respect to the 3D model.