As stated in the previous section, commercial spectrophotometers are not suitable for the characterization of complex transparent systems, because of geometrical and constructive limitations. For these reasons accurate measurements are not possible for samples characterized by complex geometry, high thickness or bulk scattering properties. A large diameter integrating sphere apparatus is needed to perform accurate measurements on such materials [14]. The schemes in Fig. 2 show the system configuration of the optical facility used for the characterization of the PC samples described