We investigated the complex dielectric function of bromide perovskite single crystals (MAPbBr3, FAPbBr3 and CsPbBr3) by spectroscopic ellipsometry from 1 to 5 eV in the 183–423 K temperature range and under a dry nitrogen environment. The temperature dependence of all critical points provided a benchmark for the interband electronic transition energies in the three bromide perovskites for a wide spectral range. We found that the number of transitions in CsPbBr3 depends on the crystallographic phase, with the orthorhombic lattice showing an extra transition with respect to the tetragonal and the cubic phases. Through density functional theory calculations, we identified the changes in the electronic structure that accompany the tetragonal-to-orthorhombic transition, leading to splitting of the complex dielectric function along the a and b crystallographic directions. We thereon used a similar experimental …