US3331982A

US3331982A - High pressure electric discharge device having a fill including vanadium

Info

Publication number: US3331982A
Application number: US405087A
Authority: US
Inventors: John F Waymouth; Koury Frederic
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1964-10-20
Filing date: 1964-10-20
Publication date: 1967-07-18
Anticipated expiration: 1984-07-18
Also published as: GB1067923A; DE1260023B

Description

Y 1957 J. F. WAYMOUTH ETAL 3,331,982

HvlGH PRESSURE ELECTRIC DISCHARGE DEVICE HAVIN A FILL INCLUDING VANADIUM Filed Oct. 20, 1964 FILL INCLUDES MERCURY HALOGEN VANADIUM JOHN F WAYMOUTH FREDERIC KOURY INVENTOR 3 AT ORNEY United States Fatent C) 3,331,982 HIGH PRESSURE ELECTRIC DISCHARGE DEVICE HAVING A FILL INCLUDING VANADIUM John F. Waymouth, Marblehead, and Frederic Koury,

Lexington, Mass, assignors to Sylvania Electric Products Inc., a corporation of Delaware Filed Oct. 20, 1964, Ser. No. 405,087 9 Claims. (Cl. 313-225) This invention relates to high pressure electric discharge devices and particularly to the production of white light from such devices.

High pressure electric discharge devices are well known to the art, however, white light with high red rendition has not been obtained from their practical commercial applications. Most commercial high pressure electric discharge devices contain mercury vapor and the discharge produced is only the typical mercury discharge consisting of discrete, separate wavelengths, generally called lines. Almost all of the radation is contained in the blue region together wth a line in the green and a line in the yellow. Hence when a conventional high-pressure mercury discharge device illuminates a red object, particularly one reflecting light only in the range of 6000 to 6800 A., the object appears black.

Attempts have been made by the art to obviate this problem and among the suggested modifications have been the inclusion in the mercury arc stream of various metallic elements which emit radiation at wavelengths different than mercury emission, so that lamps having such inclusions will produce radiations resulting from a combination of mercury lines together with lines of the metallic additions. Typical of the inclusions have been the addition of zinc, cadmium or sodium metals. Although such additions did add other lines to the spectrum and improve the color rendition, still only a series of separate and discrete lines were generally present. Little, if any, color selectivity was provided.

Another suggested modification was the color-improved mercury vapor lamps wherein the inner surface of the outer bulbous envelopes was coated with fluorescent phosphors which converted some of the invisible ultraviolet arc radiation into visible light of a red-orange color. Although the mixture of the red-orange together with the blue-green of the mercury produced some change in color, there was a loss of efficiency in the lamp because the phosphor absorbed some of the visible radiation from the arc. Furthermore, phosphors coating failed to solve the real problem which is the lack of the desired light emission in the radiation of the discharge itself.

We have discovered that light of color other than the bluish hue can be obtained from a high pressure electric discharge if certain materials are used as fills in the arc tube. Such fills are the conventional mercury together with a halogen, preferably iodine and except fluorine, either as the elements, the corresponding compounds or mixtures thereof. Included in this fill is vanadium added either as the element or the corresponding halide, iodides being preferred or mixtures of the element and the iodide compound. Through this combination, certain new and unexpected results occur. A beautiful orchid color emission is produced. Notably, certain ratios of iodine atoms to mercury atoms must be maintained, elsewise maximum light emission will not be realized.

The radiation which is produced from are tubes using fills including vanadium is a spectrum containing all colors and many spectral lines, the spacing between the lines averaging less than about A. The emission has a broad base continuous spectrum when measured on an instrument of moderate resolution with a large number of broad peaks, particularly in the red, 6000 to 6400 A., region. Because of the presence of mercury, the typical mercury lines at 4048, 4348, 5461, 5770 and 5790 A. will be superimposed upon the spectrum. Included also is a number of peaks in the red and green regions which accounts for the orchid emission. Of course, the emission spectrum of any color modifying metals or other additions will be present when such metals are added. For example, thallium can be added for increased green emission and sodium for increased yellow.

As we have indicated, the quantities of iodine and mercury must be closely controlled to attain maximum efiiciency. We prefer to use a ratio of iodine atoms to mercury atoms of about 0.5, although it is possible to use ratios between 0.025 to 0.85; the preferred range of ratios being between 0.025 and 0.65. Irrespective of whether the mercury is added as the metal or the corresponding iodide, its quantity should be sufiicient to allow complete vaporization at normal operating temperatures of the arc tube and to form a restricted arc in the arc tube.

Accordingly, the primary object of this invention is the production of a continuous spectrum with high red rendition from high pressure electric discharge devices.

A feature of this invention is the incorporation of mercury, either as the metal or as the iodide, together with controlled quantities of vanadium, also either as metal or as the iodide.

Many other objects, features and advantages of the present invention will become manifest to those conversant with the art upon making reference to the detailed' description which follows and the accompanying sheet of drawings in which preferred embodiments of a high pressure electric discharge device which emits a continuous spectrum are shown and described and wherein the principles of the present invention are incorporated by way of illustrative examples.

Of these drawings:

FIGURE 1 is a spectral energy distribution graph illustrating the emission spectrum of vanadium-containing lamp.

FIGURE 2 is an elevational view partially in cross section of a high pressure electric discharge device illustrating the positioning of an electric discharge are tube disposed within an outer bulbous envelope.

According to our invention we have discovered that arc tubes having a filling of a combination of certain materials can produce an orchid colored light having a continuous spectrum without the necessity of a correctional phosphor; the lamps having an efiiciency of to lumens per watt and red rendition of 6 to 8%. In particular, when mercury and iodine, either as the individual elements or as the corresponding compounds, are added to the arc tube in very specific atomic ratios together with specific quantities of vanadium, can be obtained. By a continuum we mean an almost complete forest of spectral lines in the emission spectrum, appearing generally less than 5 A. apart and containing superimposed upon this forest, the typical mercury lines at 4048, 4348, 5461, 5770 and 5790 A.

In lamps containing iodine and metals other than mercury, the arc tends to be somewhat restricted. These problems have been remedied through the addition of sodium atoms. Such atoms can be easily excited at the relatively low temperatures existing at the perimeters of the arc tube, that is nearer the wall. Hence the arc becomes more diffuse. The operating voltage is reduced because the energy can be dissipated through a wide area throughout the entire arc tube rather than in a narrow zone between the electrodes. In our lamp containing vanadium, this sodium can be eliminated. Sodium additions, however, can make valuable contributions to the color of the discharge and hence, may be included for this reason.

Referring to FIGURE 2, an elevational View of a high pressure electric discharge device is shown. For clarity of presentation, the outer bulbous envelope and the base of the lamp are shown in phantom lines surrounding the are tube harness and the arc tube. The device, such as shown in the drawing, comprises an outer vitreous envelope or jacket 2 of generally tubular form having a central bulbous portion 3. The jacket is provided at its end with a reentrant stem having a press seal through which extend relatively stiff lead-in wires 6 and 7 connected at their outer ends to the electrical contacts of the usual screw type base 8 and at their inner ends to the 'arc tube and the harness.

The are tube is generally made of quartz although other types of glass may be used such as alumina glass or Vycor,

the latter being a glass of substantially pure silica. Sealed in the arc tube 12 at the opposite ends thereof are main discharge electrodes'13 and 14 which are supported on.

lead-in wires 4 and 5, respectively. Each main electrode comprises'a core portion which may be prepared of a suitable metal such as for example molybdenum or tungsten. The prolongations of these lead-in wires 4 and can be surrounded by molybdenum or tungsten wire helixes. If desired and necessary, asmallsliver of a metal of loW work function, such as thorium, which in this case should be less than about 0.5 mg, can be disposed between the heliX and the core in each of the electrodes to reduce cathode drop. In some caseswhere it may be disadvantageous to add the spectrum of thorium, thoriated-tungsten wire (containing about 2 to 4% thorium by weight) can be used or, of course, the thorium can be eliminated entirely.

An auxiliary starting probe or electrode 18, generally prepared of tantalum or tungsten is provided at the base end of the arc tube 12 adjacent the main electrode 14 and comprises an inwardly projecting end of another lead-in wire.

Each of the current lead-in wires described, have their ends welded to intermediate foil sections of molybdenum which are hermetically sealed within the pinched sealed portions of the arc tube. The foil sections are very thin, for exampleapproximately 0.0008 inch thick and go into tension without or scaling off when the heated arc tube cools. Relatively

short molybdenum wires

23, 24 and 35 are welded in the outer ends of the foil and serve to convey current to the various electrodes inside the arc tube 12.

Metal strips

45 and 46 are welded onto the lead-in

wires

23 and 24 respectively. A resistor 26 is welded to foil stripv 45 which in turn is welded to the arc tube harness. The resistor may have a value of for example, 40,000 ohms and serves to limit current to auxiliary electrode 18 during normal starting of the lamp. Metal foil strip 46 is welded at one end to a piece of molybdenum foil sealed in the arc tube 12 which in turn is welded to

main electrode

13 and 14. Metal foil strip 47 is welded-to one end of leadin 35 and at the other end to the harness. The pinched or flattened end portions of the arc tube 12 form a seal which can be of any desired width and can be made by flattening or compressing the ends of the arc'tube 12 while they are heated.

A U-shaped internal wire supporting assembly or are tube harness serves to maintain the position of the arc tube 12 substantially coaxially within the envelope 2. To support the arc tube 12 within the envelope stiff lead-in wire 6 is welded to the base 53 of the harness. Because stiff lead-in wires 6 and 7 are connected to opposite sides of a power line, they .must be insulated from each other, together with all members associated with each of them.

Clamps

56 and 57 hold the arc tube 12 at the end portions and are fixedly attached to legs 54 of the harness. A rod 57 bridges the free end of the U-shaped support wire 54 and is fixedly attached thereto for imparting stability to the structure. The free ends of theU-shaped wire 54 are also provided with a pair of metal springs 60, 'frictionally engaging the. upper tubular portion of the lamp envelope 2. A heat shield 61 is disposed beneath the arc tube 12 and above the resistor 26 to protect the resistor from any excessive heat generated during lamp operation.

The are tube 12 is provided with. a filling of mercury which reaches a pressure in the order of one half to several atmospheres during normal lamp operation at temperatures of 450 to 700 C. We have found that through the addition of iodine and/ or certain mercury iodides to the mercury fill, the quantity of the latter can bereduced. Arc lengthis measured as the distance between opposing tips of the

main electrodes

13 and 14. Although the amount of mercury added can be varied widely as we have indicated, we prefer to add approximately 2.5 l0- to 4.1 10" gram atoms of mercury per centimeter of arc length. However, substantial light emission can beobtained at filling pressures less than the above stated limits. Furthermore, the continuum formation with the orchid color appears to be substantially independent of the amount of mercury metal added and hence the quantity of the latter can be reduced while lamp operation is still attained. As is conventional in the art, a quantity of rare gas such as helium, argon, neon, krypton or xenon at a pressure of about 25 millimeters of mercury is added to facilitate starting.

As we have indicated previously iodine must be added to the arc tube together with the vanadium to attain the formation of the continuum. About 0.5 atom of iodine should be added for every atom of mercury irrespective of whether it is added as the element or the corresponding mercury compound; although this ratio may be varied in reasonable tolerances between 0.025 to 0.65 atom of iodide per atom of mercury. The tolerance range is necessary since it is difficult, if not impossible, to produce lamps in production lines wherein the ratio of mercury to iodine is exactly 0.5. Within such tolerances, reasonable continuum formation is still evidenced. Itis quite important, to use materials which are as anhydrous as possible in thearc tube, since the incorporation of water tendsto make the discharge hard to start.

We have found that about 5.2 10-' to 1.6X 10- gram atoms per centimeter of arc length of vanadium should be added to the arc tube to attain emission such as shown in FIGURE 1. Below the lower limit, the emission will not be apparent because insufficient quantities. of metal are present and above the upper limit, the metals will condense upon the arc tube and blacken it. The spectral energy distribution of the lamp as shown in FIGUREI is for a lamp containing vanadium and iodine. The emission is an orchid or violet with string blue and red. In the spectrum,

the predominent lines are due to vanadium and a strong line at 5980 A. is because of sodium contamination. Evaluation of the spectrograms shows many more lines in the vanadium spectrum than are evident in the figure, however, this is due to broad slits of the instrument on which the spectrum is recorded. Hence for practical description, the spectrum is a continuum which is stronger in the red and blue regions than in the green.

As we have stated, it is sometimes desirable to add 5.25 10-' to 6.8 10- gram atoms of sodium, lithium,

potassium, rubidium and/or cesium per centimeter of arc length for color correction. Moreover, without such metals, the are sometimes tends to be slightly unstable, a bit restricted and the voltage drop is sometimes too high to operate the lamp on conventional ballasts. But when more than the stated upper limit is used, the metal will condense upon the arc tube and blacken it. The metal may be either as the metal or the corresponding iodide the latter being substituted for the metal on a mole for mole basis.

Of course, as discussed previously, the addition of the sodium adds the characteristic sodium spectrum to the emission and increases the brightness of the lamp somewhat and for that reason alone, it may be advantageous.

The fabrication of theenvelope, sealing techniques and positioning of the electrodes in the high pressure electric discharge device according to our invention takes place in a manner quite similar to that known to the art with conventional mercury lamps. And further, the mercury may be added to the arc tube by techniques well known to the art. To prepare the arc tube, we pump down an envelope having a pair of electrodes disposed at either end thereof, and spaced about 7 cm. from each other, through an exhaust tubulation extending from the surface of the envelope and disposed in communication with the interior thereof. The envelope is then electrically baked and filled with argon to flush out residual impurities, it is quite important to eliminate or substantially eliminate hydrogen from the arc tube. Hydrogen is known to effect the starting of mercury lamps adversely, but its effect appears to be greater in the lamps prepared according to our invention. The diificulty with hydrogen appears to be due to the formation of hydrogen iodide which has a much higher vapor pressure than any other iodide present. We believe that for every atom of hydrogen, that there is an extra atom of iodine in the vapor state. Presence of the iodine in the vapor state increases the voltage which must be applied to the lamps for starting. Hence, not only must hydrogen be substantially eliminated from the gases in the filling of the tube, but each and every part going into making up the arc tube must be free of residual hydrogen impurities. For example, the electrodes can be baked at 600 to 800 C. for a few hours before their use to eliminate hydrogen which might occur due to precessing. Furthermore, care should be exercised when sealing the electrodes into the arc tube to prevent hydrogen-containing, combustion gases from seeping in or becoming absorbed upon the surface.

The pump and fill procedure above described is usually repeated three to four times and then an arc is struck between the electrodes while there is a filling of argon gas. This operation of the arc removes any residual impurities from the electrodes and these contaminants can then be easily drawn from the system when the argon filling is pumped out. We then drop through the exhaust tube approximately 42 mg. of mercury, 7.4 mg. grams of mercuric iodide, 2.5 mg. of vanadium, 1.6 mg. thallium iodide and 6.5 mg. sodium iodide to an envelope having an arc length of approximately 6.4 centimeters. The are tube is then filled to atmospheric pressure with argon gas which is slowly leaked out until a pressure of about 23 millimeters of mercury is obtained. Subsequently, the exhaust tubulation is tipped off and the envelope is sealed. Testing of the lamp indicates that while light is present, the emission of the lamp being in the order of 68 lumens per watt and having a 7% red rendition.

It is apparent that modifications and changes may be made within the scope of the instant invention. For example, up to 50% of scandium or thorium may be substituted on an atom for atom basis for the vanadium atoms in order to modify the emission color and enhance the efiiciency of the lamp and still obtain the continuous spectrum. It is our intention, however, to be limited only by the scope of the appended claims.

As our invention we claim:

1. A high pressure electric discharge device comprising: an arc tube having sealed ends and electrodes disposed in said ends; means to convey electrical energy to each of said electrodes, whereby an arc can form therebetween; mercury and vanadium atoms disposed in said are tube, said mercury being in suflicient quantities to be completely vaporized at normal operating temperatures of said are tube and to form a restricted arc therein; atoms of at least one halogen selected from the group consisting of iodine,

chlorine, bromine disposed in said are tube, said halogen and said mercury being present therein at an atomic ratio of halogen to mercury between 0.025 and 0.65 said vanadium atoms being present in the vapor state, when said device is operating, in sufiicient quantities to contribute to the spectrum of the arc.

2. The device according to claim 1 wherein iodine is the halogen.

3. The device according to claim 1 wherein up to 5 0% of the vanadium is substituted by atoms of a metal selected from the group consisting of scandium and thorium on an atom for atom basis.

4. A high pressure electric discharge device comprising: an arc tube having sealed ends and electrodes disposed in said ends, means to convey electrical energy to each of said electrodes, whereby an arc can form therebetween; mercury and vanadium atoms disposed in said arc tube, said mercury being in suflicient quantities to be completely vaporized at normal operating temperatures of said are tube and to form a restricted arc therein; atoms of at least one halogen selected from the group consisting of iodine, chlorine, bromine disposed in said are tube, said halogen and said mercury being present therein at an atomic ratio of halogen to mercury between 0.025 and 0.65; the atoms of vanadium being present in quantities in the range of 5.2 10- to 1.6 10+ gram atoms per centimeter of arc length.

5. The device according to claim 4 wherein iodine is the halogen.

6. The device according to claim 4 wherein up to 50% of the vanadium is substituted by atoms of a metal selected from the group consisting of scandium and thorium on an atom for atom basis.

7. A high pressure electric discharge device comprising: an arc tube having electrodes sealed at either end thereof; means to convey current to each of said electrodes whereby an arc can form therebetween; a vaporizable fill of iodine, mercury and vanadium atoms, said iodine and mercury respectively being present in an atomic ratio between 0.025 and 0.65, said mercury being present in sufiicient quantities to be completely vaporized at normal operating temperatures of said arc tube and to form a restricted arc therein; the atoms of vanadium being present in the arc stream in sufficient quantities to produce a continuous spectrum.

8. The device according to claim 5 wherein 5.25 10+ to 6.8 10 gram atoms of an alkali metal are added per centimeter of arc length.

9. The device according to claim 7 wherein said vanadium is present in quantities in the range of 5.2 10+ to 1.6 l()+ gram atoms per centimeter of arc length.

References Cited UNITED STATES PATENTS 3,022,437 2/1962 Cooper 313-222 X 3,234,421 2/1966 Reiling 313-229 X 3,243,625 3/1966 Levine 313-92 FOREIGN PATENTS 1,177,248 9/1964 Germany.

JAMES W. LAWRENCE, Primary Examiner. STANLEY D. SCHLOSSER, Examiner.

Claims

1. A HIGH PRESSURE ELECTRIC DISCHARGE DEVICE COMPRISING: AN ARC TUBE HAVING SEALED ENDS AND ELECTRODES DISPOSED IN SAID ENDS; MEANS TO CONVEY ELECTRICAL ENERGY TO EACH OF SAID ELECTRODES, WHEREBY AN ARC CAN FORM THEREBETWEEN; MERCURY AND VANADIUM ATOMS DISPOSED IN SAID ARC TUBE, SAID MERCURY BEING IN SUFFICIENT QUANTITIES TO BE COMPLETELY VAPORIZED AT NORMAL OPERATING TEMPERATURES OF SAID ARC TUBE AND TO FORM A RESTRICTED ARC THEREIN; ATOMS OF AT LEAST ONE HALOGEN SELECTED FROM THE GROUP CONSISTING OF IODINE, CHLORINE, BROMINE DISPOSED IN SAID ARC TUBE, SAID HALOGEN AND SAID MERCURY BEING PRESENT THEREIN AT AN ATOMIC RATIO OF HALOGEN TO MERCURY BETWEEN 0.025 AND 0.65 SAID VANADIUM ATOMS BEING PRESENT IN THE VAPOR STATE, WHEN SAID DEVICE IS OPERATING, IN SUFFICIENT QUANTITIES TO CONTRIBUTE TO THE SPECTRUM OF THE ARC.