US3445721A - Electric discharge lamp with the starting resistor impedance twice that of the lamp impedance - Google Patents

Description

1969 J. F. wAYMou'rH May 20,

ELECTRIC nxscmnem LAMP wnn THE STARTING RESISTOR IMPEDANCE TWICE THAT OF THE LAMP IMPEDANCE Filed July 1. 1966 Illnll rag-law FIGJ R H mm OE V N AJ W F N H O J Y B 3 G F Q I 8 2 L M- L a n 8 P L A 3 m B ROBERTS,CUSHMAN a GRQVER ATTORNEYS United States Patent ELECTRIC DISCHARGE LAMP WITH THE START- ING RESISTOR IMPEDANCE TWICE THAT OF THE LAMP IMPEDANCE John F. Waymouth, Marblehead, Mass., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed July 1, 1966, Ser. No. 562,361 Int. Cl. H01j 7/44; Hb 41/04 US. Cl. 315-60 '8 Claims ABSTRACT OF THE DISCLOSURE High pressure lamps, such as shown in United States Patent No. 3,262,012, comprise an outer transparent jacket and an inner arc tube envelope with two primary electron emitting electrodes between which an are discharge is established through the vaporized, ionized mercury fill in the inner envelope. The inner envelope of such lamps is commonly filled with mercury and inert gas under a few atmospheres of pressure. Recently the addition of iodine and certain metals to the mercury fill has been found to improve the spectral distribution of emission in the visible range greatly. However, in mercury, and particularly in mercury-iodine lamps, it is difiicult to strike an are between the two primary electrodes at low temperature. To aid starting, an auxiliary electrode has been placed closely adjacent one of the primary electrodes. Voltage applied between the auxiliary electrode and its adjacent primary electrode causes ionization in the small gap between them, providing electrons for acceleration and ionization in the main gap between the primary electrodes, and thereby causing ignition of the lamp. The auxiliary electrode is customarily connected to the primary electrode other than the electrode to which the auxiliary electrode is adjacent. In order to prevent this connection from short-circuiting the main gap, it is customary to include a resistor in the connection. To limit the flow of current to the auxiliary electrode when the lamp is operating and to minimize power dissipated in the resistor, resistances have previously been selected with a relatively high resistance, 40,000 ohms or greater. In fact, since it is known in the art that there is very little diife-rence in the main gap starting voltage with resistances between 20,000 and 100,000 ohms, the resistance has a value in the high end of this range, typically 70,000 ohms. But at low temperature the starting voltage applied to the primary electrodes still remain inadequate.

The object of the present invention is to increase reliability of starting at low temperatures and reduce the starting voltage necessary to strike the are between the primary electrodes.

According to the invention an alternating current electric discharge device comprises an envelope containing a gas fill and vaporizable, positively ionizable mate-rial, primary electrodes at each end of said envelope for supporting an arc discharge therebetween, lead in wires extending through the envelope to respective primary electrodes, an auxiliary electrode adjacent and insulated from one of said primary electrodes for providing ions to start said are discharge, connection means between the other of said primary electrodes and said auxiliary electrode, said connection means including elect-tic impedance means and normally closed thermostatic switch means in series with said impedance and responsive to heat from said arc discharge to open said connection, said impedance having a value between approximately twice and one hundred times the operating impedance of the device.

For the purpose of illustration a typical embodiment of the invention is shown in the accompanying drawing, in which:

FIG. 1 is an elevation of a high pressure lamp, partly broken away;

FIG. 2 is an enlarged detail of the lamp in section; and

FIG. 3 is a schematic drawing of the electrical circuit of the lamp.

As shown in the figures, a high pressure mercury lamp comprises an outer glass jacket 1. A quartz a-rc tube 3 is supported within the jacket 1 on a U-shaped conducting frame 4. Spring fingers 6 on the frame 4 engage the jacket 1 holding the frame and are tube in position. At its lower end the frame 4 is welded to a terminal wire 7. This terminal wire 7 and a like terminal wire 8 extend through a seal 9 to a lamp base 11. Collars 12 on the frame 4 engage shoulders at opposite ends of the arc tube 3.

At each end of the arc tube 3 primary operating electrodes 14 and 16 enter through seals. An auxiliary starting electrode 17 enters adjacent the lower main electrode 16. The upper main electrode 14 is connected by a nickel ribbon 18 to the frame 4, thence through the frame to terminal wire 7. The starting electrode 17 is connected through a resistance R1 and a thermostatic switch to the frame 4, thence to a terminal wire 7. The lower main electrode 16 is connected directly to the terminal wire 8.

As in lamps filled with mercury, iodine and a small amount of argon, the following starting and operating sequence occurs. At first alternating current supplied from lines A and C through a ballast B to the terminal wires encounters a very high impedance between electrodes 14 and 16, but a relatively low impedance through the resistance R1 and the space between the starting electrode 17 and lower primary electrode 1 6. Under some conditions a starting arc is then struck between these latter electrodes. Electrons from the starting are then initiate ionization of the mercury providing a very low impedance path between the two primary electrodes 14 and 16. A main arc is struck over this path, and during a starting period of four to seven minutes the temperature and pressure within the arc tube, and the impedance between the primary electrodes, increase to stabilized operating values.

-In series with the resistance R1 is a normally closed switch S1 comprising a bi-metallic element 18 carrying a contact 19 which connects with a contact 21 connected to resistor R1. The thermostatic switch is adjusted to open contacts 19 and 21 at a temperature approaching the normal operating temperature for operating the lamp of from 600 C. to 700 C. After the main arc is struck and the la'm'p warms up sufficiently to maintain the arc, the switch also closes a contact 22 on the bi metallic element 19 and an opposed contact on terminal wire 8 and connects the auxiliary electrode to its adjacent primary elect-rode, thus preventing the development of a potential difference between the two adjacent electrodes. The bi metallic switch S1 eliminates power loss in the resistor R1 once the arc discharge is established and prevents electrolysis of the auxiliary electrode 17.

I have found that, if the resistor R1 is selected with a value much smaller than the prior minimum of 20,000 ohms, a very significant reduction in the voltage necessary to start the main are between the primary electrodes is achieved. For example, in 1000 watt mercury-iodine lamps a reduction in starting voltage in the order of 15 percent at 20 F. is obtained. The selection of a resistance of such a low value is particularly useful in high pressure lamps of 750 watts and greater, and the value may range between 100 and 5000 ohms and still afford a substantial reduction of the required starting voltage with consequent reliability in starting particularly at low temperatures.

The resistance R1 should not be so low as to drop the voltage applied by the ballast across the lamp, and its low limit is approximately twice the operating impedance of the lamp. Also the resistance R1 should not be nearly so high as previously supposed, and for all high pressure lamps is far below the 20,000 to 100,000 range of prior lamps. More specifically the upper limit or resistance R1 is aproximately one hundred times the operating impedance of the lamp which is reflected in the ballast by a comparable impedance. In a 750 watt lamp having approximately 50 ohms impedance at 260 volts, a resistance between 100 ohms and 5000 ohms will produce the improved starting at low temperatures described'above.

While one desirable embodiment of the invention has herein been disclosed by way of example, it is to be understood that the invention is broadly inclusive of any and all modifications falling within the terms of the appended claims.

I claim:

1. An alternating current electric discharge device comprising an envelope containing a gas fill and vaporizable, positively ionizable material, primary electrodes at each end of said envelope for supporting an are discharge therebetween, lead in wires extending through the envelope to respective primary electrodes, an auxiliary electrode adjacent and insulated from one of said primary electrodes for providing ions to start said are discharge, connection means between the other of said primary electrodes and said auxiliary electrodes, said connection means including electric impedance means and normally closed thermostatic switch means in series with said impedance and responsive to heat from said arc discharge to open said connection, said impedance having a value between approximately twice and one hundred times the operating impedance of the device.

2. A device according to claim 1 where said impedance is substantially lower than 20,000 ohms.

3. A device according to claim 1 wherein said impedance is between 100 and 5000 ohms.

4. A high pressure are discharge lamp according to claim 1 wherein said envelope is enclosed in an outer jacket, said impedance and switch means being enclosed Within said outer jacket.

5. A lamp according to claim 4 wherein said gas fill is under pressure higher than atmospheric and said are consumes power in excess of 750* watts.

6. A lamp according to claim 5 wherein said impedance is substantially lower than 20,000 oh'ms.

7. A lamp according to claim 5 wherein said impedance is between 100 and 5000 ohms- 8. An alternating current electric discharge device comprising an envelope containing a gas fill and vaporizable, positively ionizable material, primary electrodes at each end of said envelope for supporting an arc discharge therebetween, lead in wires extending through the envelope to respective primary electrodes, an auxiliary electrode adjacent and insulated from one of said primary electrodes for providing ions to start said arc discharge, connection means between the other of said primary electrodes and said auxiliary electrode, said connection means including electric impedance means, said impedance having a value of approximately one hundred times the operating impedance of the device, or lower.

References Cited UNITED STATES PATENTS 2,315,286 3/1943 Hayes et al. 3l547 X 2,660,692 11/1953 St. Louis et al a- 315 3,226,597 12/1965 Green 31560 JAMES W. LAWRENCE, Primal Examiner.

C. R. CAMPBELL, Assistant Examiner.

US. Cl. X.R.

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