Abstract: A photopolymerizable composition includes a water-insoluble olefinic compound that is polymerizable with free-radical initiators, an oil-soluble phenothiazine dye that is soluble in water-immiscible organic solvents, and a reducing agent operable to react with the dye to form reactive free radicals only when the dye is in an excited state induced by exposure to light. The reducing agent and the dye are reacted together under the influence of light, and particularly red light. The resulting reactive free radicals cause the olefinic compound to polymerize to a polymer that is substantially unaffected by the presence of moisture.