actinism

from WordNet (r) 3.0 (2006)

actinism
    n 1: the property of radiation that enables it to produce
         photochemical effects

from The Collaborative International Dictionary of English v.0.48

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.
   [1913 Webster]