9 OPTICAL AND OPTO-ELECTRONIC COMPONENTS IN THE FORM OF COATED SUBSTRATES, NAMELY OPTICAL FILTERS, AND IN THE FORM OF QUARTZ AND GLASS FIBERS AND LIGHT GUIDES AND LIGHT SEPARATORS MADE OF SUCH FIBERS, ALL OF THE FOREGOING FOR USE IN INDUSTRIAL APPLICATIONS AND NOT IN RELATION TO PHOTOGRAPHIC APPLICATIONS; OPTO-ELECTRONIC MEASURING APPARATUS FOR MEASURING THE FILL LEVEL OF CONTAINERS, INCLUDING FUEL TANKS