In order to attain the proper directional and spectral characteristics, a pyranometer's main components are: A pyranometer should have a so-called “directional response” (older documents mention “cosine response”) that is as close as possible to the ideal cosine characteristic. it should have full response when the solar radiation hits the sensor perpendicularly (normal to the surface, sun at zenith, 0 ° angle of incidence), zero response when the sun is at the horizon (90 ° angle of incidence, 90 ° zenith angle), and 50 % of full response at 60 ° angle of incidence. In an irradiance measurement by definition the response to “beam” radiation varies with the cosine of the angle of incidence i.e. By definition a pyranometer should cover that spectral range with a spectral selectivity that is as “flat” as possible. The solar radiation spectrum extends roughly from 285 to 3000 x 10⁻⁹ m. This quantity, expressed in W/m², is called “hemispherical” solar radiation. A pyranometer measures the solar radiation received by a plane surface from a 180 ° field of view angle.

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