A light-collecting system, which contains a coumarin derivative of the formula ##STR1## in which T denotes O or NR.sub.4,R.sub.4 represents hydrogen, optionally substituted aryl, cycloalkyl or aralkyl,R.sub.1 denotes a carbocyclic or heterocyclic 5 or 6 membered ring bonded via a C.atom, or a 5 or 6 membered heterocyclic ring which is bonded via a N atom and is rotationally asymmetrical to an axis placed through the coumarin/N-heterocyclic bond, the 5 or 6 membered rings may carry non-ionic substituents and for an optionally substituted benzene ring or naphthalene ring to be fused to the said rings;X signifies ##STR2## or --OR.sub.2 ', R.sub.2 represents hydrogen, alkyl, cycloalkyl, aralkyl or aryl, hydrocarbon radicals may be substituted, andR.sub.3, in addition to having the definitions given for R.sub.2, also signifies a radical of the formulaeR.sub.6 --(X).sub.n --CO-- or R.sub.7 --(X).sub.n --SO.sub.2 --R.sub.6 and R.sub.7 represent alkyl, cycloalkyl, aryl or aralkyl, the hydrocarbon radicals may be substituted,X represents NH or O andn represents O or 1, orR.sub.2 and R.sub.3 together with the N atom and optionally with the inclusion of further hetero-atoms form a 5 or 6 membered ring, this ring may carry non-ionic substituents and an optionally substituted benzene ring or naphthalene ring may be fused thereto, orR.sub.2 and R.sub.3 together form a di-unsaturated radical of the formula ##STR3## R.sub.8 represents optionally substituted alkyl, aryl, cycloalkyl or aralkyl, andR.sub.2 ' signifies optionally substituted alkyl, alkenyl, cycloalkyl, aryl or aralkyl,and their use in light-collecting systems.