A new ramped-square sustain waveform is proposed to improve both the luminance and the luminous efficiency of an alternate current plasma display panel (ac PDP). The luminous characteristics such as the luminance and luminous efficiency have been measured with a square-voltage and a ramp-voltage (or voltage slope) of the proposed sustain pulse. With an increase in the square-voltage of a ramped-square sustain waveform, the luminance increases but the luminous efficiency decreases. On the other hand, with an increase in the ramp-voltage of a ramped-square sustain waveform, both the luminance and the luminous efficiency increase. When compared with the conventional square sustain waveform, an improved luminance of 22% and luminous efficiency of 36% are simultaneously obtained based on the proper adjustment of the square-voltage and ramp-voltage of the ramped-square sustain waveform in a 4-inch ac PDP test panel at a frequency of 62 kHz.