Controlled arc stream in high intensity discharge lamps

#The present invention relates to controlling the arc bowing normally encountered in arc discharge lamps. When a discharge lamp is operated with the arc tube in a position other than essentially vertical, and in particular when the arc tube and operating arc are in a horizontal or near horizontal position, the arc discharge does not remain along the central axis of the arc tube during continued operation, but bows upward within the arc tube due to convection. This arc bowing can and often does result in early lamp failure through excessive heating of a particular portion of the arc tube wall.

#It is well known that high-pressure mercury-vapor lamps operated at high power levels in a horizontal burning position tend to have a hot portion of the arc tube at the center top section thereof. Electromagnetic means have been used to deflect the arc discharge down into a more central portion within the arc tube by directing the magnetic field transverse to the arc current direction, wherein the interaction of the arc discharge current and magnetic field results in a downward force on the arc.

#U.S. Pat. No. 3,562,583, issued to Zollweg and Burnham on Feb. 9, 1971 describes a magnetically rotating, constricted arc discharge device having electromagnetic means to rotate a resultant magnetic flux generally transverse to the arc discharge to cause the arc discharge to rotate about the longitudinal axis of the arc tube and thereby avoid destructive arc bowing.

#For a better understanding of the invention, reference may be had to the exemplary embodiment shown in the accompanying drawing in which the sole FIGURE is a side elevational view of a discharge lamp constructed in accordance with the present invention, with parts of the outer envelope broken away.

#In the sole FIGURE there is shown the general arrangement of a high-pressure mercury-vapor discharge lamp in which refractory metal conductors in close proximity to the arc tube are used to stabilize the arc. The lamp, generally designated 10, includes an outer light transmitting envelope 12 which is sealed to a mogul base 14. Other types of bases such as a mogul bipost may also be used, as it should be noted that proper predetermined orientation of the refractory metal conductors is essential to proper operation. Mounted within the outer envelope 12, and spaced therefrom, is an arc tube 16. The arc tube 16 is mounted within the outer envelope 12 by a two-piece frame, comprising a base-end frame 18 and a dome-end frame 20. Sealed within the arc tube 16 and disposed at opposite ends thereof are a pair of main electrodes 22 and 24. The base-end main electrode 22 and the dome-end main electrode 24 are connected through the ends of the arc tube 16 by conventional ribbon seals 26. A starting electrode 28 is also connected through the arc tube adjacent to base-end main electrode 22 by means of a ribbon seal 26. In accordance with conventional practices, the arc tube 16 encloses a discharge-sustaining filling such as a charge of mercury 29 and a small charge of inert, ionizable starting gas such as 4 torrs of argon.

#A pair of lead-in conductors 30 extend through a conventional re-entrant stem press 32 connected to the mogul base 14, which in turn is connected to a conventional power source through a ballast 34 in a well known manner.

#A starting resistor 36 is connected between one of the lead-in conductors 30 and the starting electrode 28.