The general name for any instrument used to measure the intensity of radiant energy, particularly that of the sun. Actinometers may be classified, accordingly to the quantities that they measure, in the following manner: 1) pyrheliometer, which measures the intensity of direct solar radiation; 2) pyranometer, which measures global radiation (the combined intensity of direct solar radiation and diffuse sky radiation); and 3) pyrgeometer, which measures the effective terrestrial radiation. See actinometry, bolometer, dosimeter, photometer, radiometer; compare sunshine recorder.