The Collaborative International Dictionary of English v.0.48:
Actinometry \Ac`ti*nom"e*try\, n. 1. The measurement of the force of solar radiation. --Maury. [1913 Webster] 2. The measurement of the chemical or actinic energy of light. --Abney. [1913 Webster]WordNet (r) 3.0 (2006):
actinometry n 1: measuring the intensity of electromagnetic radiation (especially of the sun's rays)