The luminous efficiency of the plasma display panel, is investigated in terms of the xenon mole fraction. A theoretical model of the luminous efficiency in a mixed gas is developed, based on the energy balance equation. The luminous efficiency eta is expressed as eta=kchiexp(-epsilon*/T-b), where chi is the gas mixture ratio, T-b is the electron breakdown temperature and epsilon* is the xenon excitation energy in eV As an example, the luminous efficiency in neon gas mixed with xenon is investigated. It is shown that the luminous efficiency eta increases monotonically as the xenon mole fraction increases from zero to unity. A preliminary experiment is carried out for neon gas mixed with a small percentage of xenon. The theoretical results agree reasonably well with experimental data. However, the efficiency enhancement dampens significantly when the xenon mole fraction is considerably large. (C) 2004 Published by Elsevier B.V.