Artificial opals consist of close-packed arrangements of silica spheres in a face-centered cubic configuration. In recent years much attention has been paid to these structures as good candidates to 3D Photonic Crystals. Up to now, the analysis of diffraction effects in opals has been mostly focused on the first (111) Bragg peak, but the spectra present a rich variety of structures beyond that point .To reach a better insight of experimental results we have focused on simmetry properties of eigenstates within band structure.We found several bands that cannot match with an incident external plane wave along (111) direction.So a partial inhibition of light transport may take place at certain frequencies.This seems to be confirmed by transmission measurements.