Exposure to radiation of wavelengths shorter than those of visible light (γ, x-ray, or UV) either for medical purposes (cancer therapy, removal of skin blemishes), for destruction of bacteria in milk and other foodstuffs or for inducing polymerization of monomers or vulcanization of rubber. UV irradiation was formerly used to induce activation of vitamin D in milk and has been used for some time to sterilize the air in operating rooms, etc.