Convection and diffusion in the discharge region of a metal–halide lamp are studied using a computer model built with the plasma-modeling package Plasimo. A model lamp containing mercury and sodium iodide is studied. Recently, the underlying program architecture in Plasimo has been overhauled to allow nonrectangular computational domains. We used this new feature to model the effects of the electrodes protruding into the plasma. The effects of the total lamp pressure on the degree of segregation of the light-emitting species are examined and compared to the earlier model with flat electrodes. Significant differences are observed, justifying the use of the more complete approach.