Abstract: A high pressure metal (sodium) vapor lamp comprises an outer vitreous envelope and an inner ceramic arc tube supported within it. The arc tube contains vaporizable metal in excess of the quantity vaporized in operation and the heat balance determines a cold spot whereat excess metal collects. The temperature of the cold spot determines the metal vapor pressure and the voltage drop across the lamp which must lie between specified limits. A thermal link is provided to a metal member such as the exhaust tube the heat loss from which influences significantly the temperature of the cold spot. In completed lamps measuring too low in voltage, such thermal link may be partly severed without breaking open the outer envelope in order to raise the voltage. One convenient way utilizes an auxiliary wire which is cut by aiming a laser beam at it.

Abstract: Jacketed high pressure sodium vapor lamps of conventional construction operated on sonic frequency pulses with short duty cycles in order to raise the color temperature produce excessive acoustic noise. The noise level is reduced by using non-magnetostrictive material for the inleads extending from the base into the outer envelope and including the portions embedded in the press of the stem, and for the frame parts that support the arc tube within the outer envelope.