Nvis 590 Pyranometer is a device that measures solar irradiance from a hemispherical field of view incident on a flat surface. The SI units of irradiance is watt per square meter (W/m2). Traditionally pyranometers were mainly used for climatological research and weather monitoring purposes. However recent worldwide interest in solar energy has also lead to an increased interest in pyranometers.

To measure irradiance, it is required by definition that the response to “beam” radiation varies with the cosine of the angle of incidence. This ensures a full response when the solar radiation hits the sensor perpendicularly (normal to the surface).