N-Vinylcarbazole is proposed as an additive for epoxy ring-opening polymerization ROP upon visible light exposure. This compound can convert hardly oxidizable radicals to carbon centered radicals by an addition process onto the N-vinylcarbazole double bond. The generated radicals can be further easily oxidized by an iodonium salt thereby leading to efficient initiating cations for the ROP of epoxides. Different visible light photoinitiating systems have been investigated: Type I photoinitiators (derived from phosphine oxides) and dye/iodonium salt couples. The underlying chemical mechanisms are investigated by electron spin resonance (ESR) experiments.