For the light sampling, a 2-in. Ulbricht sphere from StellarSphere IC2 with a 180◦ field of view and wavelength range of 200–1700 nm is used. This Ulbricht sphere, with a flat side as the input aperture and a field of view blocking baffle between the input aperture and the fiber optic cable exiting to the spectrometer, yields a near perfect cosine response for the whole wavelength range. The use of an Ulbricht sphere provides the best suited probe of the luminous flux. It measures the spectral irradiance hitting the PV cell surface area at different incident angles, when mounted in the same incidence plane as the PV cell. It probes a near perfect sampled light beam and transfers it to the spectrometer using the fiber optic cable. An overview of the Ulbricht sphere interior can be seen in Fig. 3.