Pyranometer:

                                A perfection pyranometer is designed to respond to Radiation of all wavelengths and hence measures directly the total power in the incident diapason. It contains a thermophile whose sensitive face consists of indirect, blackened, hot junctions, exposed to the sun and cold junctions are fully shadowed. 

                               The temperature difference between the hot and cold junctions is the function of radiation falling on the sensitive face. The seeing element is covered by two concentric hemispherical glass polls to shield it from wind and rain. This also reduces the convection currents. A radiation guard girding the surface pate and coplanar with the seeing material, cuts direct solar radiation from hotting the bottom of the instrument. The instrument has a voltage affair of roughly 9 μV/ W/ m2 and has an affair impedance of 650 W. A perfection spectral pyranometer of Eppley laboratory.

The pyranometer, when handed with a shadow band (or suppressing slice) to help ray radiation from reaching the seeing element, measures the verbose radiation only.  Such an arrangement of shadow bandstand(model SBS). Numerous affordable instruments are also available for measuring light intensity, including instruments grounded on cadmium sulphide photocells and silicon photodiodes.  These instruments give good suggestion of relative intensity but their spectral response isn't direct and therefore can not be directly calibrated.