This invention relates to dimmable metal halide lamps using ceramic arc tubes for the application of energy saving, mood control, and constant light output over the life of the lamp. Under dimmed conditions, as low as 50% of rated wattage, the color temperature (CCT) can remain substantially the same and be perceived by the viewer as a constant color light source. Furthermore, the invention improves the color rendering index (CRI) and the efficacy of the lamp under dimmed operation. Such improvements are provided by placing a metal shield on an end of the arc tube, whereby the emissivity of the shield is lower than the emissivity of the ceramic in the arc tube, whereby cold spot temperature in the lamp is increased, even under dimmed conditions.