An arc discharge metal halide lamp having a discharge chamber having visible light permeable walls bounding a discharge region supported electrodes in a discharge region spaced apart by a distance L.sub.e with an average interior diameter equal to D so they have a selected ratio. Ionizable materials are provided in this chamber involving a noble gas, one or more halides, and mercury in an amount sufficiently small so as to result in a relatively low maximum voltage drop between the electrodes during lamp operation.