The disclosure relates to an EUV microlithography projection exposure apparatus having an exposure light source for producing radiation in a first spectral range from 5 nm-15 nm, and a heat light source for producing radiation in a second spectral range from 1-50 μm. The apparatus also includes an optical system having a first group of mirrors for guiding radiation from the first spectral range along a light path such that each mirror in the first group can have a first associated intensity distribution applied to it in the first spectral range during operation of the exposure light source. The heat light source is arranged such that at least one mirror in the first group can have a second associated intensity distribution in the second spectral range applied to it during operation of the heat light source. The first intensity distribution differs from the second intensity distribution essentially by a position-independent factor.