Use of specific photoinitiators in a photopolymerization process using combined led light wavelengths

A photopolymerizing process of a photopolymerizable composition comprising a photoinitiator of formula (I)

• wherein
• R1 and R2, each independently, in any occurrence, are C1-C4 alkyl;
• and
• either
• R3 is H;
• R4 is selected from C1-C6-alkoxy, hydroxy-C1-C4-alkoxy, linear or branched C1-C12-alkyl, unsubstituted phenoxy, unsubstituted benzyl, unsubstituted phenyl, and group of formula (a) or (b):
• wherein
• Y is selected from —O—, —CH2-, —CHOH—, —CH(alk)-, and —C(alk)2-, wherein alk is a C1-C4 alkyl;
• R5, R6 and R7, each independently, are C1-C4-alkyl;
• and
• The wavy line indicates the link to the phenyl group of formula (I);
• or
• R3 and R4, together with the two carbon atoms to which they are linked, form a group of formula (c):
• wherein
• R8 and R9, each independently, are H or C1-C4 alkyl;
• and
• the stars indicate the positions of R3 and R4 in formula (I);
• wherein said photopolymerizing process is carried out by means of at least two different LED light wavelengths, at least one being equal or lower than 300 nm and at least one being higher than 300 nm, provided that the at least two LED light wavelengths are separated by at least 10 nm,
• and wherein said photopolymerizable composition does not comprise any liquid crystals.