Experimental evidence is presented that both the initial and light‐induced deep defects in high‐quality undoped a‐Si:H are generated by the same mechanism. A material in which it is easier to generate defects will therefore exhibit both more initial defects and a higher susceptibility to light‐induced degradation. These effects tend to balance each other in such a way as to make the absolute increase in the number of states added by a given light‐soak be about the same over a wide range of film quality. Thus the relative change in the number of states is greater for higher‐quality (lower initial defect‐density) material. Evidence is presented tohat the defect‐generating mechanism is related t strained bonds. Thus microstructural profiles with associated strain profiles can lead to profiles in both initial defect density and light‐induced susceptibility.