Photocurable compositions

A photocurable composition consisting of (a) one or more ethylenically unsaturated, photocurable compounds, (b) at least one photo-initiator of the formula I or II ##STR4## in which n is 1 or 2 and, if n is 1, Ar is unsubstituted phenyl or phenyl substituted by one or more of the radicals F, Cl, Br, C.sub.1 -C.sub.12 alkyl, -OAlk, phenyl, -Ophenyl, --SAlk, --SCH.sub.2 CH.sub.2 OH or -Sphenyl, or indanyl or tetrahydronaphthyl, and Alk is a lower alkyl radical having 1-4 C atoms, and if n is 2 Ar is C.sub.6 -C.sub.12 arylene or a group -phenylene-T-phenylene-, in which T is --O--, --S--, --CH.sub.2 -- or --CH.sub.2 CH.sub.2 --, X is one of the groups --NR.sup.4 R.sup.5, --OR.sup.6 or --OSiR.sup.7 (R.sup.8).sub.2, R.sup.1 is unsubstituted C.sub.1 -C.sub.8 alkyl or C.sub.1 -C.sub.8 alkyl substituted by --OH, OAlk, C.sub.2 -C.sub.8 acyloxy, --NR.sup.4 R.sup.5, --COOAlk or --CN, or C.sub.3 -C.sub.4 alkenyl, C.sub.5 -C.sub.6 cycloalkyl or C.sub.7 -C.sub.9 phenylalkyl, R.sup.2 has one of the meanings defined for R.sup.1 or together with R.sup.1 is C.sub.2 -C.sub.8 alkylene or C.sub.3 -C.sub.9 oxa- or aza-alkylene, R.sup.3 is a direct bond, C.sub.1 -C.sub.6 alkylene, C.sub.2 -C.sub.6 oxa-alkylene, C.sub.2 -C.sub.6 thia-, S-oxothia- or S-dioxothiaalkylene, phenylene, diphenylene or a group -phenylene-T-phenylene-, or together with the two substituents R.sup.2 and the two C atoms to which these substituents are bonded forms a cyclopentane, cyclohexane, endomethylenecyclohexane or cyclohexane ring, R.sup.4 is C.sub.1 -C.sub.12 alkyl or C.sub.2 -C.sub.4 alkyl which is substituted by --OH or OAlk, R.sup.5 is C.sub.1 -C.sub.12 alkyl or C.sub.2 -C.sub.4 alkyl which is substituted by OH or OAlk, or together with R.sup.4 is C.sub.4 -C.sub.5 alkylene, which can be interrupted by --O-- or --NR.sup.9 --, R.sup.6 is hydrogen, C.sub.1 -C.sub.12 alkyl, C.sub.1 -C.sub.8 alkyl substituted by Cl, Br, OH, OAlk, SAlk, C.sub.2 -C.sub.8 acyloxy, --COOAlk, --CONHAlk, --CON(Alk).sub.2 or CN, or C.sub.3 -C.sub.5 alkenyl, cyclohexyl, benzyl, unsubstituted phenyl or phenyl substituted by Cl or Alk, or 2-tetrahydropyranyl, R.sup.7 and R.sup.8 are identical or different and are C.sub.1 -C.sub.4 alkyl or phenyl and R.sup.9 is C.sub.1 -C.sub.4 alkyl, --CH.sub.2 CH.sub.2 CN or --CH.sub.2 CH.sub.2 COOAlk, and (c) at least one light stabiliser from the category of the polyalkylpiperidine derivatives.