Abstract: A photographic imaging system is disclosed comprised of a hardenable organic component containing ethylenic unsaturation sites and an initiator system for ethylenic addition. The initiator system is comprised of an electron acceptor activator, an electron donor activator, and, acting as a photosensitizer, a dye capable of absorbing imaging radiation. The dye has a reduction potential related to that of the electron acceptor activator and an oxidation potential related to that of the electron donor activator to permit each to release a free radical upon excitation of the photosensitizer by exposure to actinic radiation.