Abstract: A device for treating material by UV radiation has a UV radiating lamp with a reflector formed by a polished metal reflector having an outer surface of dull black chromium covered by layers of hafnium dioxide and silicon dioxide of which one is bonded to the black chromium surface.

Abstract: The invention concerns a method of producing optical elements, in particular filters, with interference layers comprising alternately slightly refractive and highly refractive dielectric layers deposited on a substrate S. The first layer 1 applied to the substrate is Al.sub.2 O.sub.3, constituting a slightly refractive layer, after which further layers 2 to n of ZnS and Al.sub.2 O.sub.3 are applied in an alternating sequence. The last layer n consists of Al.sub.2 O.sub.3. Such layers can be applied, at low temperatures, on flat substrates and, in particular, on sharply curved substrates. Production costs are reduced, and these layers possess the optical properties of known interference layers however resistance to external influences is greatly increased. In the case of mineral substrates, the coatings also offer considerable resistance to boiling.