An electric arc discharge lamp includes an elongated hollow tubular transparent envelope having a pair of opposite ends, a pair of electrode mounts respectively disposed in the ends of the tubular envelope, and a dosing capsule defining a hermetically sealed annular cavity containing a predetermined quantity of a dosing liquid therein. The dosing capsule has an inner edge defining an opening through the capsule for receiving a portion of one the electrode mounts therethrough such that the capsule is supported by the one electrode mount with the sealed annular cavity substantially surrounding the one electrode mount. The electrode mount includes a glass stem having inner and outer axially-displaced opposite ends, a pair of lead-in conductors extending through the glass stem and from the opposite ends of the glass stem, and an electrode supported between a pair of inner ends of the lead-in conductors adjacent to and spaced from the inner end of the glass stem. The capsule is supported about the glass stem of the electrode mount spaced from the inner and outer opposite ends thereof. The capsule is rupturable by directing heat energy through the envelope and into contact with a portion of the capsule so as to raise the temperature and cause a rupture of the capsule portion, resulting in release of the dosing liquid from the annular cavity of the capsule into the lamp envelope.