1) Measure 2) Measurement 3) Measuring 4) Mensuration 
• (n.) The measurement of the force of solar radiation. • (n.) The measurement of the chemical or actinic energy of light.
Ac`ti·nom'e·try noun 1. The measurement of the force of solar radiation. Maury. 2. The measurement of the chemical or actinic energy of light. Abney. 
[n] - measuring the intensity of electromagnetic radiation (especially of the sun's rays)
The science of measurement of radiant energy, particularly that of the sun, in its thermal, chemical, and luminous aspects. See also: Actinometer, Sun.
noun measuring the intensity of electromagnetic radiation (especially of the sun`s rays)