It was reported that the discharge characteristics of an AC plasma display panel (PDP) with a single sustainer, which is sustained by the successive application of bipolar pulses, are different from those with a conventional driver. The luminous efficacy of an AC PDP with a single sustainer increases with increased sustain voltage, whereas the conventional PDP shows the opposite trend, resulting from the dependence of the luminous efficacy on the polarity of the sustain pulse. In this study, the IR emission efficiency was analyzed to determine the dependence on the polarities of the sustain pulses. The IR emission efficiency showed dependence on the amplitude of the sustain pulse with opposite polarities, which provided a motive to optimize the sustain pulse amplitude in each polarity of the sustain pulse. The luminous efficacy in an AC PDP with a single sustainer increased with increasing positive-going pulse amplitude, and decreased as the negative-going pulse amplitude increased. The optimal sustain can be obtained under the condition where the positive-going pulse amplitude is high and the negative-going pulse amplitude is low. As a result, a 5% higher luminous efficacy can be achieved when the maximum positive and minimum negative sustain voltages are used than when equal positive and minimum negative sustain voltages are used.