NOVELTY - Color converter comprises at least one polymer and at least one organic fluorescent dye that comprises at least one structural unit which is benzo(de)benzo(4,5)imidazo(2,1-a)isoquinolin-7-one (I), where the structural unit is optionally substituted by at least one identical or different substituents and at least one CH group of six-membered ring of the benzimidazole is replaced by nitrogen.    USE - The color converter is useful: in illumination device; for conversion of light produced by LED (claimed), mercury lamps, organic LED or UV-LED; as light collection system in photovoltaics and in fluorescence conversion solar cells; for conversion of blue light to white light or green-yellow; and in remote phosphor structure.    ADVANTAGE - The color converter: exhibits good color reproduction and produces pleasant light; does not require any materials comprising rare earths, which have to be mined and provided in a costly and inconvenient manner; and exhibits high quantum yield, long lifetime and high photostability.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) producing the color converter, comprising dissolving at least one polymer and the organic fluorescent dye in a solvent and removing the solvent or the extrusion of the organic fluorescent dye with the polymer;    (2) illumination device comprising at least one LED and at least one color converter;    (3) a polymer mixture comprising the polymer and the organic fluorescent dye, comprising at least one structural unit which is substituted benzo(de)benzo(4,5)imidazo(2,1-a)isoquinolin-7-one compounds of formula (II), where at least one CH group of the six-membered ring of the benzimidazole is replaced by nitrogen; and    (4) the organic fluorescent dye.    n = 0-(10-p);    p = number of CH units that are replaced by N in the six-membered ring of the benzimidazole;    X1-R = phenyl, naphthyl, anthranyl, phenanthrenyl, pyrenyl, benzopyrenyl, fluorenyl, indanyl, indenyl, tetralinyl, phenoxy, thiophenoxy, tolyl, ethylphenyl, ortho/meta/para xylyl, mesityl or 4-ethoxyphenyl (all optionally substituted by at least one 1-30C alkyl (whose carbon chain comprise -O-, -S-, -NR1-, -CO-, -CR1=CR1- and/or -CO- and is optionally substituted by at least one 1-12C-alkoxy, OH, halo, CN and/or aryl (all optionally substituted by at least one 1-18C-alkyl and/or 1-6C-alkoxy)), 3-8C-cycloalkyl (whose carbon skeleton comprise -C-, -S-, -NR1-, -CR1=CR1- and/or -CO- and which is optionally substituted by at least one 1-18C-alkyl, 1-12C-alkoxy and/or 1-6C-alkylthio), aryl or heteroaryl (optionally fused to form 5-7-membered ring (whose carbon skeleton optionally comprise -C-, -S-, -NR1-, -N=CR1-, -CR1=CR1-, -CO-, -SO- and/or -SO2- and the ring system is optionally substituted by at least one 1-18C-alkyl, 1-12C-alkoxy, -C=CR1-, -CR1=CR1-, OH, halo, CN, -NR2R3, -NR2COR3, -CONR2R3, -SO2NR2R3, -COOR2 and/or -SO3R2)), -U1-aryl (optionally substituted by at least one radical for aryl), 1-12C-alkoxy, 1-6C-alkylthio, -C=CR1, -CR1=CR12, OH, mercapto, halo, CN, nitro, -NR2R3, -NR2COR3, -CONR2R3, -SO2NR2R3, -COOR2 or -SO3R2;    R1-R3 = 1-18C alkyl (whose carbon chain optionally comprise -O-, -S-, -CO-, -SO- and/or -SO2- and optionally substituted by at least one 1-12C alkoxy, 1-6C alkylthio, OH, mercapto, halo, CN, nitro and/or -COOR1), aryl or heteroaryl (optionally fused to form 5-7-membered rings whose carbon skeleton optionally comprise -O-, -S-, -CO- and/or - SO2-, and overall ring system is optionally substituted by at least one 1-12C-alkyl and/or the above radicals for alkyl) or H; and    U1 = -O-, -S-, -NR1-, -CO-, -SO- or -SO2-.