During the initial discharge phase of a shadow mask display panel (SM-PDP), the time evolution of the number of electrons and electron temperature were investigated by simulation. Their dependence on the Xe concentration, dielectric layer and rise time of the driving voltage were analyzed, respectively. The results, indicating the temporal variation of both the number of electrons and the electron temperature, are of great importance in understanding the discharge process and characteristics of PDPs and can be used as guide lines to achieve higher luminous efficacy in the SM-PDP. A dielectric layer thickness of 30 mu m and a dielectric constant of 10 or less, together with a reduction of the voltage rise time below 250 ns are found to be optimum for high efficacy. (c) 2012 Elsevier B.V. All rights reserved.