Comparison between the Hα-based T_eff scale and the photometric T_eff scales obtained by applying the calibrated relations of Alonso et al. (1996, 1999) and Casagrande et al. (2010)+ Ramírez & Meléndez (2005), to colour indices V−I. The y-axis shows ΔT_eff = T_eff(Hα) −T_eff(photometry) for the calibrations. For stars with temperatures below 4950 K, the excitation temperatures are shown. The corresponding error bars are overplotted in grey. Horizontal error bars correspond to the fitting uncertainty, vertical error bars represent the uncertainty in the photometric temperatures as given by the spread in colour around the fiducial, added in quadrature with the uncertainty in the spectroscopic temperatures as given by the fitting error.