Abstract: Photopolymerizable compositions comprising:(1) at least one vinyl monomr capable of undergoing free radical polymerization,(2) a visible light or ultraviolet light responsive photoinitiator system comprising:(a) a diaryliodonium salt,(b) a pigment, insoluble in the photopolymerizable composition, said pigment also serving as a sensitizer,(c) one or more electron donating compounds, and, optionally,(3) adjuvants.The three component photoinitiator system of this invention can increase, by several orders of magnitude, the rate of ultraviolet light or visible light photocuring of vinyl monomers.