Photocurable, addition polymerizable compositions contain an epoxy resin and a photoinitiator system containing (a) an epoxy resin, (b) a hydroxyl containing material and (c) a photoinitiator system comprising: (i) an iodonium salt; (ii) a visible light sensitizer; and (iii) an electron donor compound, wherein the photoinitiator system has a photoinduced potential of at least about 100 mV relative to a standard solution of 2.9.times.10.sup.-5 moles/g diphenyl iodonium hexafluoroantimonate and 1.5.times.10.sup.-5 moles/g camphorquinone in 2-butanone. The compositions cure on exposure to light in the visible spectrum and are useful in a variety of applications, including dental adhesives and composites.