A photopolymerizable composition comprising: at least one monomeric or oligomeric ethylenically unsaturated photopolymerizable compound, and at least one liquid photoinitiator mixture comprising the components: (a) a compound of the formula wherein Ar 1 and Ar 2 independently of each other are or naphthyl which is unsubstituted or substituted one or more times by R 1, R 2, R 3 or R'; R 1 and R 3 independently of each other are C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen; R 2 is hydrogen, C 1 -C 4 alkyl, halogen, C 1 -C 4 alkoxy or C 2 -C 20 alkoxy which is interrupted by one or more O; Q is C 1 -C 4 alkylene; R 4 is methyl or ethyl; R' and R" independently of each other are hydrogen or PG-Y-R"'-X-; PG is a polymerizable group or methyl or ethyl; Y is a direct bond, O or S; X is a direct bond, O or S; R'" is a direct bond, C 1 -C 20 alkylene or C 2 -C 20 alkylene which is interrupted by one or more O; (b) one or more compounds of the formula wherein Ar 1, Ar 2 and Q are as defined above, and R 5 is C 3 -C 30 alkyl which is unsubstituted or substituted by one or more of the groups selected from OH and or R 5 is C 2 -C 28 alkyl which is interrupted by one or more O or C 3 -C 8 cycloalkylene and wherein said C 2 -C 28 alkyl interrupted by one or more O or C 3 -C 8 cycloalkylene is unsubstituted or substituted by one or more of the groups selected from OH and and (c) optionally a compound of the formula wherein R 5 is as defined above. at least one monomeric or oligomeric ethylenically unsaturated photopolymerizable compound, and at least one liquid photoinitiator mixture comprising the components: (a) a compound of the formula wherein Ar 1 and Ar 2 independently of each other are or naphthyl which is unsubstituted or substituted one or more times by R 1, R 2, R 3 or R'; R 1 and R 3 independently of each other are C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen; R 2 is hydrogen, C 1 -C 4 alkyl, halogen, C 1 -C 4 alkoxy or C 2 -C 20 alkoxy which is interrupted by one or more O; Q is C 1 -C 4 alkylene; R 4 is methyl or ethyl; R' and R" independently of each other are hydrogen or PG-Y-R"'-X-; PG is a polymerizable group or methyl or ethyl; Y is a direct bond, O or S; X is a direct bond, O or S; R'" is a direct bond, C 1 -C 20 alkylene or C 2 -C 20 alkylene which is interrupted by one or more O; (b) one or more compounds of the formula wherein Ar 1, Ar 2 and Q are as defined above, and R 5 is C 3 -C 30 alkyl which is unsubstituted or substituted by one or more of the groups selected from OH and or R 5 is C 2 -C 28 alkyl which is interrupted by one or more O or C 3 -C 8 cycloalkylene and wherein said C 2 -C 28 alkyl interrupted by one or more O or C 3 -C 8 cycloalkylene is unsubstituted or substituted by one or more of the groups selected from OH and and (c) optionally a compound of the formula wherein R 5 is as defined above. (a) a compound of the formula wherein Ar 1 and Ar 2 independently of each other are or naphthyl which is unsubstituted or substituted one or more times by R 1, R 2, R 3 or R'; R 1 and R 3 independently of each other are C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen; R 2 is hydrogen, C 1 -C 4 alkyl, halogen, C 1 -C 4 alkoxy or C 2 -C 20 alkoxy which is interrupted by one or more O; Q is C 1 -C 4 alkylene; R 4 is methyl or ethyl; R' and R" independently of each other are hydrogen or PG-Y-R"'-X-; PG is a polymerizable group or methyl or ethyl; Y is a direct bond, O or S; X is a direct bond, O or S; R'" is a direct bond, C 1 -C 20 alkylene or C 2 -C 20 alkylene which is interrupted by one or more O; Ar 1 and Ar 2 independently of each other are or naphthyl which is unsubstituted or substituted one or more times by R 1, R 2, R 3 or R'; R 1 and R 3 independently of each other are C 1 -C 4 alkyl, C 1 -C 4 alkoxy or halogen; R 2 is hydrogen, C 1 -C 4 alkyl, halogen, C 1 -C 4 alkoxy or C 2 -C 20 alkoxy which is interrupted by one or more O; Q is C 1 -C 4 alkylene; R 4 is methyl or ethyl; R' and R" independently of each other are hydrogen or PG-Y-R"'-X-; PG is a polymerizable group or methyl or ethyl; Y is a direct bond, O or S; X is a direct bond, O or S; R'" is a direct bond, C 1 -C 20 alkylene or C 2 -C 20 alkylene which is interrupted by one or more O; (b) one or more compounds of the formula wherein Ar 1, Ar 2 and Q are as defined above, and R 5 is C 3 -C 30 alkyl which is unsubstituted or substituted by one or more of the groups selected from OH and or R 5 is C 2 -C 28 alkyl which is interrupted by one or more O or C 3 -C 8 cycloalkylene and wherein said C 2 -C 28 alkyl interrupted by one or more O or C 3 -C 8 cycloalkylene is unsubstituted or substituted by one or more of the groups selected from OH and and Ar 1, Ar 2 and Q are as defined above, and R 5 is C 3 -C 30 alkyl which is unsubstituted or substituted by one or more of the groups selected from OH and or R 5 is C 2 -C 28 alkyl which is interrupted by one or more O or C 3 -C 8 cycloalkylene and wherein said C 2 -C 28 alkyl interrupted by one or more O or C 3 -C 8 cycloalkylene is unsubstituted or substituted by one or more of the groups selected from OH and and (c) optionally a compound of the formula wherein R 5 is as defined above.