Acoustic resonance operation of xenon-metal halide lamps on unidirectional current

The method of operating a miniature high pressure metal vapor discharge lamp of a kind comprising:

• a vitreous envelope defining a discharge space having a volume not exceeding approximately 1 cubic centimeter,
• a cathode and an anode sealed into the envelope and defining a horizontal arc gap,
• and a fill comprising mercury, metal halide, and xenon gas in a quantity exerting a partial pressure of at least 25% of the total vapor pressure during continuous operation;
• which method comprises:
• initiating ionization across the gap by high voltage pulses,
• forcing a unidirectional current across the gap at a high level during a starting phase in order to warm up the lamp and reducing said current to a lower level during the run phase,
• and imposing a high frequency ripple on said current at a modulation depth which is a lower percentage during the starting phase than during the run phase.

In combination a miniature high pressure metal vapor discharge lamp of a kind comprising:

• a vitreous envelope defining a discharge space having a volume not exceeding approximately 1 cubic centimeter,
• a cathode and an anode sealed into the envelope and defining a horizontal arc gap,
• and a fill comprising mercury, metal halides including sodium, and xenon gas in a quantity exerting a partial pressure of at least 25% of the total vapor pressure during continuous operation;
• and a source of unidirectional current having a high frequency ripple imposed thereon for operating said lamp, said ripple providing modulation of power to the lamp in frequency bands in which acoustic resonance excites arc-straightening modes,
• and means providing a horizontal magnetic field at said gap transverse to current flow in order to supplement the acoustic modes in straightening and controlling the arc.

An integrated compact discharge headlamp and ballast assembly comprising:

• a vitreous arctube lamp having a volume less than 1 cubic centimeter, a cathode and an anode sealed therein defining an arc gap in the range of 2 to 5 mm, and a fill comprising xenon in a quantity exerting a partial pressure of at least 25% of the total vapor pressure in operation,
• a headlamp reflector within which said arctube is horizontally mounted on a fore and aft axis with the gap located near the focal point,
• starting means supplying high voltage pulses to ionize the gap and initiate current flow in the lamp,
• circuit means supplying unidirectional current to said lamp, said current having a high frequency ripple component imposed thereon for exciting arc-straightening acoustic resonance modes in said lamp,
• and timing and control means providing a higher current through said lamp during a start warm-up phase than during the run phase and increasing the modulation depth of the ripple as the current is decreased,
• said starting means, circuit means and timing and control means being combined and contained in a portion of the headlamp and ballast assembly.