A method for prolonging the life span of a planar light source generating apparatus is provided. The planar light source generating apparatus forms an emitting layer not only on a plurality of cathodes but on a plurality of gates as well. Moreover, an anode of the planar light source generating apparatus is electrically connected to a current sensor for reading out a maximum current density when the planar light source generating apparatus operates. To operate the planar light source generating apparatus, a DC square voltage is applied to the cathodes (or gates) while the gates (or the cathodes) are electrically connected to a ground. Once the current density detected by the current sensor drops to a definite ratio of the maximum value, the external voltage supplying the aforementioned cathodes and the gates are switched. Thus, the life span of the planar light source generating apparatus is prolonged.