Source : Webster's Revised Unabridged Dictionary (1913)

Photochemistry \Pho`to*chem"is*try\, n. [Photo- + chemistry.]
   (Chem.)
   The branch of chemistry which relates to the effect of light
   in producing chemical changes, as in photography.

Source : WordNet®

photochemistry
     n : branch of chemistry that deals with the chemical action of
         light