A metal halide discharge lamp comprises a lamp body and a chamber formed within the body. A pair of electrodes extends into the chamber and have electrode tips spaced apart from one another. A discharge medium composition is sealed within the chamber that generates a plasma, which generates visible light. The composition comprises a rare gas, a first metal halide that produces a luminous flux and zinc iodide that generates a desired lamp operating voltage. The composition may also comprise zinc, sealed in the chamber, in elemental form that is not derived from the first metal halide or the zinc iodide. The zinc iodide halide serves as a substitute for mercury for purposes of generating desired lamp operating voltage; and, the excess pure zinc attracts or reacts with iodine atoms thereby making available electrons and the first metal halide for generation of a luminous flux.