An n-sheet, state-space model is employed for the assessment of insulator issues of relevance to the operation of alternating-current thin-film electroluminescent (ACTFEL) devices. The model presented herein has been refined by the inclusion of luminance, which is modeled as arising from impact excitation of luminescent impurities. Simulation demonstrates that ACTFEL devices which have large insulator capacitances and no space charge present in the phosphor are optimal in terms of providing maximum luminance and efficiency. A method for estimating the phosphor space charge density from a single transferred charge curve is presented. Simulation indicates that the use of a leaky insulator in an ACTFEL device can result in an increase in luminance, but a decrease in efficiency and that measured charge–voltage and internal charge–phosphor field curves are misleading when one or more of the constituent insulator or phosphor layers is leaky.