The light output is actually most intense on the cathode side, dropping off exponentially in a conical shape towards the anode in a pure Xenon lamp. While in a Xenon-Mercury lamp the highest light output is at each electrode with exponential fall of in a conical shape towards the center of the arc gap.JD said:Yes, in an HMI lamp, I stand corrected, the metal vapor in the gas arc does produce most of the light. In xenon lamps, the light output is off of the positive electrode, or anode. (see alignment diagram. Picture credit, PTI Photon Technology International) The exception to this would be the common flash tube.