Actinism is the property of solar radiation that leads to the production of photochemical and photobiological effects. Actinism is derived from the Greek ακτίς, ακτῖνος (a ray or beam). The word actinism is found, for example, in the terminology of imaging technology (esp. photography), medicine (concerning sunburn), and chemistry (concerning containers that protect from photo-degradation), and the concept of actinism is applied, for example, in chemical photography and X-ray imaging.
Actinic chemicals include silver salts used in photography and other light sensitive chemicals.
The Collaborative International Dictionary
Actinism \Ac"tin*ism\, n. [Gr. ?, ? ray.] The property of radiant energy (found chiefly in solar or electric light) by which chemical changes are produced, as in photography.
n. (context chemistry physics English) That property of electromagnetic radiation that leads to the production of photochemical effects
n. the property of radiation that enables it to produce photochemical effects