A high intensity discharge lamp comprises at least an arc-tube containing two electrodes, chemical compounds and a fill gas. In a double-ended arc tube, an electrode lead assembly is sealed in each end portion of the arc tube. The electrode lead assembly typically comprises a tungsten electrode, a molybdenum foil, and an outer molybdenum lead. The fill gas can comprise one or more gases. To initiate operation of the lamp, the fill gas is ionized to facilitate the conduction of electricity between the electrodes. HID lamps generally include a discharge device comprising a discharge vessel containing a pair of internal spaced discharge electrodes, and a small quantity of vaporizable and ionizable material referred to as the fill material. The arc tube comprises a generally tubular body of light transmissive material such as quartz or ceramic material which forms a hermetically sealed light emitting chamber containing the lamp fill material and an inert fill gas. The fill material is a sodium mercury amalgam, and it may also contain other materials such as metal halides. The arc tubes employed in HID lamps are hollow tubes of alumina, quartz or hard glass shaped in various sizes with cupped or conical ends filled with gas at several different pressures, depending on the operating state of the lamp. Generally, there are several types of arc tube bodies for HID lamps. One type of arc tube body is a "cylindrical" body formed from quartz tubing having the diameter of the generally cylindrical arc tube chamber in which the chamber is formed by pinch-sealing the end portions of the tubing. Another type of arc tube body is a "formed" body which is formed from quartz tubing of a much smaller diameter in which a bulbous light emitting chamber is formed by expansion under internal pressure between two end portions having the much smaller diameter of the tubing. A metal halide lamp includes an arc tube made of quartz glass and a pair of electrodes spaced apart with a predetermined distance in the arc tube, and mercury and a metal halide are enclosed as luminous materials in the arc tube. The arc tube of the metal halide lamp contains metal halides which are mixtures of some metals such as sodium and scandium with halogen such as iodine, high pressure xenon serving as a starting gas, and mercury. The arc tube is sealed with electrode sealing portions at both ends, and the pair of electrodes are connected to respective external lead wires via metal foils hermetically sealed in the electrode sealing portions. The external lead wires are electrically connected to an operating circuit of the lamp. The operating circuit includes a ballast for restricting current flow to less than a predetermined amount during operation and means for applying a high-voltage pulse voltage. High intensity discharge (HID) lamps are typically coupled to an electronic ballast which provides an alternating current (AC) signal to the lamps. The electronic ballast is one of the most cost sensitive products of power electronics. Its cost is a major factor constraining market penetration of electronic ballasts for HID lamps. The ballast supplies the requisite open circuit voltage to start and maintain an arc in the discharge tube as well as limiting the current through the discharge tube. The use of a high frequency electronic ballast can reduce the size and the weight of the ballast and improve the system efficacy. This feature is especially attractive for low wattage HID lamps because the overall lighting system is expected to be of small size.

High intensity discharge lamps are energized by an electric current to create a metallic vapor and the current through the lamp causes high intensity illumination. An HID lamp is ignited through application of a high voltage pulse, nominally of several thousand volts, across the electrodes of the lamp. The high voltage pulses are produced by pulsed ignition circuits. Generally, high intensity discharge (HID) lamps require a higher starting voltage than is necessary for starting well-known fluorescent lamps. The starting voltage must provide a sufficiently higher electric field, such that, in the presence of an avalanche-initiating electron, breakdown will occur. A voltage necessary to cause the insulation breakdown is called "breakdown voltage", and the breakdown voltage is generally a high voltage of several hundreds times higher than the lamp voltage during steady-state operation. A ballast circuit is used to provide a high voltage to initiate an arc in the arc tube and supply power to maintain the arc. By regulating the power supplied to the lamp, the arc tube temperature can be controlled. Typically the ballast must supply the high voltage pulse for a duration of approximately 10 microseconds. The efficiency of an electronic ballast in supplying power to an HID lamp largely depends on its power factor rating. Power factor is a function of the degree to which the load current and voltage are in time phase with each other. The greater the degree to which the load current leads or lags the voltage, the lower is the power factor rating and the less efficient the ballast. The HID lamps operate at a completely different principle from conventional light bulbs. Electrical discharge, created by a predetermined current, between electrodes of the HID lamps causes the filler materials in the discharge tube to emit light. The light is generated directly by an arc discharge. An open circuit voltage is applied to the electrodes and to the starting probe causing the gap between the probe ano one of the electrodes to break down and emit electrons which are accelerated by the field between the lamp electrodes initiating a desired discharge between lamp electrodes. High intensity discharge lamps do not illuminate instantaneously, but require time for the lamp to ignite. HID lamps normally require a short period in which to warm up and build up pressure within the lamp, during which time the light output therefrom is limited. When the fill material within the discharge vessel has been partially vaporized the internal pressure within the discharge vessel increases to greater than one atmosphere. This pressure increase will result in a higher voltage being required in order to initiate a discharge than in the case of the lamp being started at a lower internal pressure. As a consequence, if power is momentarily interrupted the lamp will have to cool somewhat and the internal pressure of the discharge vessel will have to decrease before discharge can be reestablished. The overall life and efficiency of a high intensity discharge lamp are affected by the starting sequence as are the values and tolerances of the components required to effect this starting sequence.