Abstract: To prevent attack on electrodes (4, 5) within a discharge vessel (2) by an ionizable metal halide fill, due to spurious or free oxygen arising within the lamp during operation thereof, which oxygen combines with the metal of the electrodes, and is then dissociated in the arc and re-deposited at the hottest part of the electrode, an oxygen removing getter material is introduced into the discharge vessel. Spurious oxygen arises due to emission of oxygen from the glass wall of the discharge vessel, typically quartz glass, and unavoidable contaminants of the fill substance. The getter material is, preferably, phosphorus, boron or aluminum, a halide of the foregoing, a tungsten boron compound, a tin phosphorus compound, or scandium or a rare earth. If the getter is a halide, iodine, bromine or chloride are suitable. The getter may be introduced in quantities of between 0.05 to 0.6%, depending on the getter substances and the fill composition.