(EP25136-B)      Light-collecting system contains a coumarin deriv. of the formula (I) (in which T is O or NR4; R4 is H or opt. substd. ar(alk)yl or cycloalkyl; R1 is a C-bound 5- or 6-membered carbo- or heterocycle or an N-bound 5- or 6-membered heterocycle which is rotationally asymmetrical about the coumarin-N-heterocycle bond, these 5- and 6-membered rings have nonionic substits. and can be condensed with an opt. substd. benzene or naphthalene ring; X is -NR2R3 or -OR'2; R2 is H or opt. substd. (cyclo)alkyl or ar(alk)yl; R3 is R2, R6-(Y)n-CO- or R7-(Y)n-SO2-; R6 and R7 are opt. substd. (cyclo)alkyl or ar(alk)yl; Y is NH or O; n is O or 1; R2 and R3, when R3 is R2, together with the N atom can form a 5- or 6-membered heterocycle opt. contg. other heteroatoms and opt. with nonionic substits. and a condensed, opt. substd. benzene or naphthalene ring, or R2 and R3 together are a CHR8- gp.; R8 is opt. substd. (cyclo)alkyl or ar(alk)yl; and R'2 is opt. substd. (cyclo) alkyl, ar(alk)yl or alkenyl)..    (US4544496-A)      Light collecting system comprises an emission surface and an absorption surface in ratio 1:50-2000. It comprises a medium having greater optical density than its surroundings and at least one fluorescence centre which contains an energy converter(I).    (I) comprises a coumarin deriv. of formula shown and acrylic acid (deriv) homo- or co-polymer or polycarbonate. In the formula, R1 is a 5-6 membered carbocyclic or heterocyclic ring bonded via a C or N and opt. carrying nonionic substits. or being fused to a (substd) benzene or naphthalene ring. An N-bonded ring is asymmetrical to an axis placed through the coumarin/heterocyclic ring bond. X is NR2R3 or OR2'. R2 is H, (cyclo)alkyl, aralkyl or aryl and is opt. substd. R3 is as for R2 or R6(X1)nCO or R7(X1)nSO2. R6 and R7 are as for R2 but not H. X1 is NH or O. n is 0 or 1. Also NR2R3 may form a 5-6 membered ring opt. contg. a further hetero atom, opt. carrying nonionic substits and opt fused to a (substd) benzene or naphthalene ring; or R2R3 may form -CHR8-. R8 is (cyclo) alkyl, aryl, or aralkyl, all opt. substd. R2' is (cyclo)alkyl, aryl or aralkyl, all opt. substd. or alkenyl.    ADVANTAGE -   Cpds. (I) display good quantum yield, high intensification factor and excellent light fastness. (10pp)n    (US4764622-A)      Coumarin derivs. of formula (I) are new. In the formula, X is NR2R3 or OR2' whre where R2 is H or 1-4C alkyl; R3 is 1-4C alkysuphonyl or phenylsulphonyl; and R2' is 1-4C alkyl. Y is ONR5 or 5. R5 is 1-4C alkyl or phenyl. Ring A is opt. substd. by 1-4C alkyl, 1-4C alkoxy, halo, 1-4C alkylsulphonyl or sulphamoyl.    USE/ADVANTAGE -   As energy converters in light collecting systems. The derivs. exhibit good quantum yield, high intensification factor and excellent light fastness. (10pp)