Abstract: An irradiation device, especially for the cosmetic, diagnostic and therapeutic application of light, having an incoherent light source and a reflector that surrounds the light source and has a slit-like opening defining the direction of the radiation. Arranged in the beam path of the light source is a spectral dispersion element. In the output beam path of the spectral dispersion element, a fiber-optic cross-sectional transformer is disposed in such a way that its circular end is located opposite the spectral dispersion element. The fiber-optic cross-sectional transformer and the spectral dispersion element are movable relative to each other.