Light‐induced creation of defects and their annealing process were studied by ESR, photoconductivity and photoluminescence measurements for a‐Si1−xNx:H and a‐Si1−xCx:H films besides a‐Si:H films with various spin densities and H contents. The results show that the degradation of the photoconductivity and the photoluminescence is mainly attributed to creation of dangling bonds due to bond breaking.