Description of direct and diffuse parts of global radiation
Shortwave radiation (0.2 - 3.0μm) arising from a narrow solid angle (5° aperture) centered around the sun's disk impinging on a horizontal surface.
Shortwave radiation (0.2 - 3.0μm) arising from a narrow solid angle (5° aperture) centered around the sun's disk and impinging on a surface normal to the direction of the radiation.
Shortwave isotropic radiation (0.2 - 3.0μm) arising from the upper hemisphere reduced by the direct solar radiation from the sun's disk and its surroundings (5° aperture)