A model based on an equilibrium between light-induced creation and light-induced recovery of defects has been applied to defect creation kinetics on a wide variety of hydrogenated amorphous silicon films. A tentative approach to determine the structural properties responsible for the instability of the films show that there is a good correlation between stability and dilute-phase SiH bond concentrations for samples deposited from helium or hydrogen dilution of silane and a large scatter in films deposited from pure silane.