The geometry of a High Intensity Discharge (HID) arc tube is controlled to improve lamp color control and temperature distribution. In some embodiments, conical sections located at the transition zones near the electrodes are included to provide funnel-like body-leg interface portions. The body-leg interface portions are shaped so as to advantageously control the temperature distribution along the internal surface of the discharge chamber wall so that it monotonically decreases resulting in a stable local cold spot location at the body-leg interface.