Many of today's industrial processes use light as a tool in order to carry out production processes effectively. UV-cured printing inks are used to print packaging, for example, whilst UV-cured adhesives are used in medical and automotive spheres. The radiation sources used in these cases share the common feature of having to use large-area reflectors to direct the UV light into the working plane effectively. To this end, use is made of reflectors which on the one hand, specifically reflect the desired UV light to a high degree, and on the other, are able to withstand the harsh conditions of industrial use. Optimized dielectric coatings fulfil both these requirements and thus facilitate optimum process conditions.