Light-collecting system using coumarin derivatives as energy converters

In a light-collecting system comprising an emission surface and an absorption surface wherein the ratio of the emission surface to the absorption surface is 1:50-2,000, said light-collecting system comprising a medium which has a greater optical density than its surrounding and which has at least one center capable of fluorescence wherein said center contains an energy converter, the improvement wherein said energy converter comprises a coumarin derivative of the formula ##STR76## in which T denotes O, in which

• R.sub.1 denotes a carbocyclic or heterocyclic 5-membered or 6-membered ring bonded via a C atom, or a 5-membered or 6-membered heterocyclic ring which is bonded via a N atom and is asymmetrical to an axis placed through the coumarin/N-heterocyclic bond, it being possible for the said 5-membered or 6-membered rings to carry non-ionic substituents and for an optionally substituted benzene ring or an optionally substituted naphthalene ring to be fused to the said rings;
• X signifies ##STR77## or --OR.sub.2 ', in which R.sub.2 represents hydrogen, alkyl, cycloalkyl, aralkyl or aryl, it being possible for the said hydrocarbon radicals to be substituted, and R.sub.3, in addition to having the definitions given for R.sub.2, also signfies a radical of the formulae
• R.sub.6 --(X.sub.1).sub.n --CO--
• or
• R.sub.7 --(X.sub.1).sub.n --SO.sub.2 --
• in which
• R.sub.6 and R.sub.7 represent alkyl, cycloalkyl, aryl or aralkyl, it being possible for the said hydrocarbon radicals to be substituted,
• X.sub.1 represents NH or O and
• n represents 0 or 1, or
• R.sub.2 and R.sub.3 together with the N atom and optionally with the inclusion of further hetero-atoms form a 5-membered or 6-membered ring, it being possible for this ring to carry non-ionic substituents and for an optionally substituted benzene ring or an optionally substituted naphthalene ring to be fused thereto, or R.sub.2 and R.sub.3 together form a di-unsaturated radical of the formula ##STR78## in which R.sub.8 represents optionally substituted alkyl, optionally substituted aryl, optionally substituted cycloalkyl or optionally substituted aralkyl, and
• R.sub.2 ' signifies optionally substituted alkyl, alkenyl, optionally substituted cycloalkyl, optionally substituted aryl or optionally substituted aralkyl and a homopolymer or copolymer of acrylic acid or its derivatives or a polycarbonate.