The present invention relates to an irradiation device having a radiation source and a filter which is arranged in the optical path and has two transparent filter disks which are substantially arranged in parallel with each other and which are held with their surrounding edges in a frame made of a material of good heat conduction, the filter disks and the frame defining a closed cavity which has provided therein a medium which selectively influences the radiation spectrum. In order to improve an irradiation device such that a degassing of the medium is prevented during heating and the filter disks do not deform as the pressure increases, provision is made for the cavity to be in the form of a pressure chamber, so that during operation of the irradiation device overpressure prevails in the cavity, and for the filter disks to be made of glass ceramic or mineral glass, wherein the filter disk which is arranged closer to the radiation source is in the form of a safety device such that it is more susceptible to breaking than the filter disk which is further away from the radiation source.