Plasma display panel emission measurements are correlated with panel efficacy trends, and directions for the improvement of the discharge efficiency are derived. An increase of the ratio of the phosphor emission in the visible to the Xe emission in the infrared indicates an increased Xe excitation efficiency. Also, the time dependence and the spatial distribution of the Xe emission are important discharge characteristics. Experiments reveal that a high panel efficacy is obtained, especially for design and driving conditions that govern a fast and spatially distributed discharge development. A high sustain voltage V>200 V causes a "high efficiency discharge mode." It is proposed that in this mode, the cathode sheath is not, or is incompletely, formed during the rise of the discharge current. Then the electric field in the discharge cell is dominated not by the space charges, but by the externally applied voltage. The effective discharge field is lowered, resulting in a lower effective electron temperature and more efficient Xe-excitation. Under the fast discharge buildup conditions also the electron-heating efficiency increases due to a decrease of the ion heating losses in the cathode sheath. A high sustain voltage combines well with a high Xe content gas mixture, that further increases the discharge efficiency. Changes in the phosphor to Xe- and Ne-emission ratio show that for higher Xe content, a lower electron temperature accounts for a more efficient Xe excitation. Further, the use of a TiO/sub 2/-layer underneath the phosphor causes an increase of the ratio of the phosphor emission in the visible to the Xe emission in the infrared, i.e., an increased Xe excitation efficiency. As a result, a high efficacy of 5 lm/W and a high luminance of 5000 cd/m/sup 2/ have been realized in a 4-in color plasma display test panel design with a 50% Xe in Ne gas mixture, a TiO/sub 2/-layer underneath the phosphor, and a high sustain voltage 260-290 V.