@prefix skos: . skos:definition """A Sun photometer (also spelled Sunphotometer) is an instrument that measures the intensity of sunlight arriving directly from the Sun. Since it is designed to be pointed directly at the Sun, a Sun photometer measures only direct sunlight, not the diffuse light scattered from the sky, haze and clouds. Since haze blocks some direct sunlight, a Sun photometer is an ideal instrument for measuring haze. Scientists have used Sun photometers of various kinds for more than a century. The modern generation of hand held Sun photometers was pioneered in the late 1950's by Frederick Volz [1], who has made important discoveries about the effects of natural and volcanic haze on the environment. Although some Sun photometers respond to a wide range of colors or wavelengths of sunlight, most include special filters that admit only a very narrow band of wavelengths. These filters are expensive. They also have a limited life. While some filters may work well for a decade or more, others may last only a few years. Additional information available at "http://www.concord.org/haze/spwhat.html" [Summary provided by The Concord Consortium]"""@en ; skos:prefLabel "SUN PHOTOMETERS"@en ; skos:inScheme ; skos:broader ; a skos:Concept . skos:prefLabel "Photometers"@en ; a skos:Concept ; skos:narrower .