Source : Webster's Revised Unabridged Dictionary (1913)

Actinometry \Ac`ti*nom"e*try\, n.
   1. The measurement of the force of solar radiation. --Maury.

   2. The measurement of the chemical or actinic energy of
      light. --Abney.

Source : WordNet®

actinometry
     n : measuring the intensity of electromagnetic radiation
         (especially of the sun's rays)