An arc discharge metal halide lamp for use in selected lighting fixtures having a discharge chamber with light permeable walls of a selected shape bounding a discharge region of a selected volume through which walls a pair of electrodes are supported with ionizable materials being provided in the discharge region of the discharge chamber comprising at least one member selected from a group consisting of halides of cerium, dysprosium, holmium, lithium, sodium, praseodymium, thallium and thulium, and further comprising a halide of calcium in a selected fraction of that weight total of all halides present in the discharge chamber with this selection depending also on the addition or not of a halide of aluminum. Others of the foregoing halides that are present are provided in amounts with certain limits.