A Xe plasma flat lamp, which has been noticed as a new eco-friendly LCD (liquid crystal display) backlight, requires the improvement of the luminance and the luminous efficiency although it has several advantages. To improve the performance of a lamp, it is necessary to understand the effects of discharge variables on the luminous characteristics of the lamp. Since it is difficult to diagnose a lamp discharge experimentally, the numerical analysis can be used instead. In this study, the luminous characteristics of a planar type Xe plasma flat lamp were analyzed with the variation of an input voltage and a pulse frequency. The numerical analysis of a lamp discharge was then performed using a RCT (relaxation continuum) model and a LFA (local field approximation) model. The comparison with the experimental results showed that the RCT model is valid for the numerical analysis of the flat lamp. The numerical analysis also showed that the modifications of a high frequency component and a voltage falling rate in the input voltage waveform could improve the luminous characteristics of the lamp.