We study the concentration of the defects created by the light from the measurement of the Fermi state displacement deduced from the conductivity variation with the temperature for samples of hydrogenated amorphous silicon (a-Si:H) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD). This study demonstrated that the value of the activation energy of the samples in the case of As-depos. indicate that the samples before the warm-up (as are upon receipt of these samples from the laboratory) partially exposed to light during the process of transportation and storage. Been explained the effect of light on this samples that it was returning to cut weak silicon bonds and then the creation of new dangling bonds. We also found that the samples containing less hydrogen are the most affected by the light which indicates the important role of hydrogen in the satisfaction of defects. Also found that samples which contain germanium by less dopant are most affected by light.