A photoinitiator mixture comprising the components (a) a compound of the formula (I) wherein Ar and Ar2 independently of each other are or naphthyl which is unsubstituted or substituted one or more times by R1, R2, R3 or R&prime；； R1 and R3 in-dependently of each other are C1-C4alkyl, C1-C4alkoxy or halogen； R2 is hydrogen, C1-C4alkyl, halogen, C1-C4alkoxy or C2-C20alkoxy which is interrupted by one or more O； Q is C1-C4alkylene； R4 is methyl or ethyl； R&prime； and R&Prime； independently of each other are hydrogen or PG-Y-R&prime；&Prime；&mdash；X&mdash；； 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&prime；&Prime； is a direct bond, C1-C20alkylene or C2-C20alkylene which is interrupted by one or more O； (b) one or more compounds of the formula (II) wherein Ar1, Ar2 and Q are as defined above, and R5 is for example C3-C30alkyl which is unsubstituted or substituted and (c) optionally a compound of the formula (III) R5&mdash；OH &emsp；&emsp；(III), wherein R5 is as defined above； provides a liquid photointiator.
