For the irradiance, symbol G is used, although it could have been also Gb to point out that only high irradiance levels are accepted in the test sequence, leading to a low diffuse fraction. No correction for nonstationary conditions is made, so very stable inlet and radiation conditions are needed for each test point.
Furthermore, it is assumed that the solar radiation incidence is nearly normal, so that incidence angle effects can be neglected. Finally, the test conditions stipulate that the wind speed shall be in the range 2 to 4 m/s, so that wind speed effects can also be neglected.