Abstract: To optimize operating conditions with respect to overall size of a high-psure discharge lamp having a metal halide fill, the wall thickness (d) in millimeters is selected in accordance with a theoretical optimum relationship of d=1.5+0.1.times..cuberoot.P, in which P is the power rating of the lamp, in watts. The optimal theoretical thickness should not vary by more than .DELTA.d=.+-.0.2.times..sup.d, in millimeters, from the theoretical optimal value, with lower power ratings permitting a thinner wall thickness than higher power ratings. Optimizing the wall thickness improves the color rendition index and the light distribution of the emitted light, as well as decreasing the devitrification of the quartz glass of the discharge vessel.