Abstract: An irradiation apparatus for curing photopolymerizable dental fillings in situ comprises a lamp 10 for producing a convergent light beam with a convergence angle .alpha.E smaller than about 30.degree. with respect to the optical axis, and an optical wave guide 15 having an entrance surface 14 disposed in the light beam and an exit surface 16. The wave guide 15 is conical with a diameter decreasing from the entrance surface 14 to the exit surface 16 and has a refractive index of approximately .sqroot.2. At the exit surface 16, radiation of constant density and high intensity is produced within a substantially semi-spherical lobe, so that even such dental parts which are difficult to access can be irradiated and penetrated with high intensity radiation.