Abstract: An illuminator apparatus has a light source and a liquid-core light guide comprising a tubular flexible sheath of a fluorocarbon polymer material which is filled with a lightguiding fluid such as glycol, a salt solution containing a chloride, fluoride or phosophate, phenylmethyl silicone oil (n.apprxeq.1.57), PCTFE oil, polychlorotrifluoroethylene oil (n=approx. 1.40) or also pure water. The tubular sheath is internally coated with a thin film of Teflon AF.RTM., the refractive index of which is lower than that of the sheath material.

Abstract: The specification describes an irradiation device, more particularly for use for causing the polymerization of fillings of resins in dentistry, using radiation in the UVA range which is transmitted from a radiation source via a light guide. The source of UVA radiation is a tungsten incandescent filament lamp with a color temperature of at least 3150.degree. K. and an electrical power of at least 15 Watts. For a defined solid angle, which is not less than 6 sterad, the radiation from the filament of the lamp is collected by an UV reflecting reflector and focussed at a focal point F.sub.1 lying outside the incandescent filament lamp. In the ray path between the filament of the lamp and the focal point F.sub.1 a dielectric thin film reflection filter is provided with a defined angle alpha of inclination .noteq. 0.degree. of the filter normal to the optic axis defined by the incandescent filament and the focal point F.sub.1.