US2538561A - High-pressure mercury vapor lamp - Google Patents

Description

Jan. 16, 1951 v. J. FRANCIS ET AL HIGH-PRESSURE MERCURY VAPOR LAMP Filed April 23, 1946 FIG.

IN V'ENTO Rs:

VICTOR J. FRANCIS, EglAN H. NELSON,

BY WWW HEiR ATTORNEY overcomes the difficulty of excessive heating in high-power lamps.

The lifeof a lamp of the type above described, employing a single anode, depends on the watts dissipated per unit volume of the discharge column terminating on the anode. For lamps having cylindrical anodes, in order to secure a life of at least ten hours, which is a reasonable life in certain applications of high power lamps, the maximum permissible dissipation may be expressed as:

where W denotes the watts per cu. mm. of the I discharge column and D represents the diameter of the anode in mm. The above expressed relation prevails where the anode is of tungsten and its length is 'such that an increase in length will not appreciably reduce the temperature of its termination surface, where the diameter of the discharge column is measured by the points having a brightness equal to one-half of the maximum brightness on the axis of the discharge column, and lastly where the axis of the discharge column is substantially coincident with the axis of the cylindrical anode.

In employing lamps constructed in accordance with our invention, it is desirable to consider the possible obstruction of the light from one discharge column by an anode in which it does not terminate. Where a concentrating reflector, such as a parabolic mirror, is employed with lamps having the above described features, one suitable arrangement is to position the cathode so. that its termination surface lies on the axis .of the reflector and is nearer to it than any of the termination surfaces of the anodes, the termination surfaces of the latter being symmetrically distributed around the axis. Alternatively, in order to reduce obscuration, the termination surface of the cathode may be placed off the axis and be nearer to the reflector than the termination surfaces of any of the anodes. In which instance, the termination surface of the cathode may then be nearer to some anodes than others. 'By the adjustment or selection of appropriate values of stabilizing resistors in series with the different anodes, the power can be distributed among the anodes so that the dissipation per cu. mm. of the discharge column is the same for all columns. 7

For a better understanding of our invention reference may be had to the following descripdrawing and its scope will be pointed out in the appended claims. Fig. 1 diagrammatically illustrates an embodiment of our invention as applied to a multiple anode, single cathode high pressure mercury vapor lamp wherein a reflector is positioned so that'its axis is substantially coincident tion taken in connection with the accompanying with the axis of the discharge established between the. electrodes. Fig. Z'diagrammaticaIly illustrates a modification of the embodiment of the invention shown in Fig. 1 wherein the cathode seal structure is positioned at the side or bottom of the envelope so that it does not obscure the light path from the arc discharge to the reflector. Fig. 3 is a transverse view showing one possible arrangement of the multiple-anode structure and includes a heat reflector such as a tungsten disc which is symmetrically placed within the cluster of anodes.

Referring now more particularly to 'Fig. 1, our invention is'there illustrated as applied to an gelectric discharge device, such as a high-pressure mercury vapor lamp, comprising an enclosing envelope 2 provided with suitable seal structures, described hereinafter. We provide, within the envelope, an ionizable medium such as mercury vapor, a single cathode 2 preferably constructed in cylindrical form as illustrated and having a tapered end providing snare-supporting or terminationsurface 3 which supports the arc discharge, or more specifically the plurality of arc discharge columns established between the cathode 2 and a plurality of anodes 4-! l inclusive. The anodes 4-H inclusive may be arranged in a cluster symmetrically placed about the axis of the electrodes or the axis of the discharge path of the lamp, as shown in detail in Fig. 3.

The envelope 1 may be constructed of quartz and may have an external diameter of approximately mm. with walls about 3.5 mm. thick. The cathode 2 is preferably constructed of a tungsten block substantially 25 mm. long and 12 mm. in diameter. Of course, any suitable starting arrangement or starting electrode of the conventional type (not illustrated) may be employed for initiating the establishment of the arc discharge between the main or principal electrodes comprising the cathode 2 and the plurality of anodes. The cathode 2 may be supported by a suitable inner lead-in conductor I2 such as a tungsten rod, having a. diameter of 6 mm., and is connected to an exterior energizing circuit such as a direct current circuit (not-shown) through an outer lead l3 constituting a terminal for the lamp. Conductor or rod I2 is of course embedded ina suitable sealing structure such as' a vitreous seal M which in turn is positioned within a. suitable neck or tubing l5 constituting a part of the envelope i.

In like manner the anodes 4-! I, inclusive, may be constructed of tungsten cylinders. We have found that in one modification of our invention the anodes may be constructed of tungsten cylinders having a diameter of 8 mm. and being about 26 mm. long, each supported on. 2 mm. tungsten rods iii. The tungsten rods it are connected to an exterior energizing circuit through a multiple strip seal H which supports eight individual strips l8, all of which are embeddedwithin the seal and the latter being'sealed to the neck or tube i9 constituting a part of the enclosing envelope l'. External lead conductors are. connected to the strips I8 and may comprise the anode terminals. For the dimensions above set forth, we havefound thateach strip l8, and its associated anode, may conduct 20 amperes without sacrificingthe desired lamp life. 7 i

As shown in Fig. 3 the anodes are arranged so that their axes are parallel to one'another and parallel to the principal axis of the main electrodes of the lamp, Furthermore, the anodes 4-! l are positioned so that their termination surfaces lie in a plane transverse to the axis of the main electrodes and are symmetrically arranged around this axis in a ring-shaped cluster. In this form of our invention all of the anodes are equidistant from the cathode 2, and each has an uninterrupted view of the termination surface 3 of the cathode 2.

Where it is desired to employ a concentrating reflector, such as a parabolic mirror 26, the latter may be positioned so that its axis is substantially coincident with the axis of the 'main electrodes of the lamp and so that thecenter of the light intensity produced by the arc discharge coincides One suitable arest-tan termination surface 3of the cathode lies onth'e axis of the mirror 2s,- and is nearer to it thanany other termination surfaces'of the anodes; the latter termination surfaces being symmetrically distributed around the axis.

. In view of the above given dimensions'and-"in accordance with the general principles of our'invention described herein it will be'appreciated that the distance'between the terminations of'the discharge, that is the distances between'the'terminating surfaceof cathode '2 and the terminatingsurfaces of the plurality of anodes which is 1pm., is'less than the distances of the termina- 'tionv surfaces from the inside of the envelope I. .The embodiment of our inventionshown-inFig.

T1 is peculiarly adaptable for operation "on"direct current wherein the plurality o-fjexterior'lead' in conductors 2i may be connected to a direct current circuit (not shown) through a plurality of stabilizing lstances, not shown in Fig. 1 but illustrated gen-.rally in Fig. 2. These stabilizing stantial part within the envelope, these resistances may be suitably constructed of a wire such as tungsten or molybenum wound on a refractory insulating core such as zirconia, and the wire and the core may act as a support for the anode with which these elements are associated.

In operation, a source of unidirectional potential is applied to the terminals of the lamp and upon initiation of an arc discharge, by auxiliary starting means, the anodes d-l l inclusive conduct current simultaneously establishing arc discharge columns between their terminating surfaces and terminating surface 3 of cathode 2 thereby establishing, by virtue of their combined eifect, a high power light source of great intensity. K

A decided advantage of mercury vapor lamps of the high pressure type constructed in accordance with our invention is evidenced by considering the fact that if the discharge column dissipating kilowatts, having'a length of 20 mm. and a voltage drop of 156 volts were terminated in a single anode, the discharge would take the form of a cylinder about 11 mm. in diameter, measured between points of one-half maximum brightness which would be about 109;") 0 candles per square centimeter. The volume of such a discharge column would thus be about 260 cu. mm. and the energy dissipation would be 12.5 watts per cu. mm. of discharge. The minimum diameter of a cylindrical anode, as constructed in accordance with the above described relationship, for a life of ten hours, would therefore be 1.8 times 12.5 or 22 mm. Such an anode would be larger than we have been able to obtain.

Fig. 2 diagrammatically illustrates a further embodiment of our invention as applied to a highpressure mercury vapor lamp which is similar to the arrangement shown in Fig. 1 and correspond-- ing elements have been assigned like reference numerals:

6 In theiarrang'ement of Fig: 2 -tl1e cathode seal 22 through "which" thie -cathode lead l2 passes is positioned atthe-side of the envelope so 'that'the seal structure does not obscure and does not he in the path of the reflector'ormirror axis; Inthis arrangementthe cathode seal 22 and-the cooperating neck or tube of the envelope I extend from-a side-of the envelope and lie in a plane -'sub'stantially-"perpendicular to th'e' axis of the principal electrodes and perpendicular to the axis-"of the'reflector. This arrangement offers a further advantage in that'thecondensed mercury withinthe envelopel 'will tendto collect there when the'lampis not in'operaticn, and the heat developed atthe cathode willaccelerate the=evaporation'of the mercury upon subsequentoperanon. 'two'ofwhich have been illustrated, may-bacon- -Individual-stabili2ling resistances 23, only nected to the outer lead conductors 2| inter- -mediate' these leads and the source of direct current (not shown) Wherethe *anQdes A-H are arranged ina ring "aboutthe'axis of the reflector or the axis of the main'electrcdes, it may be desirabletouse a reflectingdisc 241, (shown in-Fig. 3) and, prefe'rably constructed of tungsten, with its center on the "axis of the main electrodes and its plane perpendicular to the axis andwithin or a-short distance behind-'the'ring'of termination surfaces of the anodes, in order' to' preve'nt loss of- 'power by radiation of the discharge itself through this ring. The use of the disc 2 i'is optional and when it is desired to employ such a disc we'have found that it is preferable to'p'o'sitio'n it about half way along the length of the anodes-44 i In *anothersuitable-arrangement of the-lamp and a're'flector, the-anodes are so disposed that their termination surfaces-lie inor substantially in a common plane and are distributed around a line which is perpendicular to the axis of the re-- fiector and which passes through the termination surface of the cathode. In this case the distance between the termination surface of the cathode and the termination surface of one of the anodes that is nearer to the reflector may be longer than the distance between the termination surface of the cathode and the termination surface of one of-the anodes that is farther from the reflector, in order that light from the discharge to the said farther anode may reach the reflector more easily through the gap between the cathode and the said nearer anode.

If the anodes are thus distributed around a line lying in a plane which is perpendicular to the axis of the reflector, the seal through which the anode lead or leads pass and the seal through which the cathode lead passes may both lie along the said line. But there may be an advantage in arranging for the cathode lead to issue from the envelope in a direction approximately perpendicular to the said line; for in this arrangement the anodes are likely to be supported on a lead or leads sealed into the bottom of the envelope, and, if the cathode seal were at the top, it would be heated by convection currents.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a high-pressure direct-current mercury vapor electric discharge lamp designed for a power consumption of at least about 10 kw. and. comprising a plurality of simultaneously conducting anodes associated with a single cathode, the cathode being arranged with its termination surface upon one side of a plane transverse to the axis of the discharge paths between the cathode and the anodes, and the anodes being arranged with their termination surfaces in a confined cluster on the opposite side of said plane and so arranged that each has an uninterrupted view of the termination surface of the cathode, and a concentrating reflector positioned so that the termination surface of said cathode lies on the axis of the reflector and is nearer to it than any of the termination surfaces of said anodes.

2. In a high-pressure direct-current mercury vapor electric discharge lamp designed for a power consumption of at least about 10 kw., the combination comprising a plurality of anodes associated with a single cathode, the cathode being arranged with its termination surface upon one side of a plane transverse to the discharge path between the cathode and the anodes and the anodes being arranged with their termination surfaces in a cluster on the opposite side of said plane and so disposed that each has an uninterrupted view of the termination surface of the cathode, and an enclosing envelope structure including a multiple seal for lead conductors supporting said anodes and a seal for supporting the'lead conductors and said cathode, said last mentioned lead issuing from the envelope in a direction approximately perpendicular to the axis of the electric discharges established between said cathode and said anodes.

'3. In combination, a high-pressure direct-current mercury vapor lamp designed for a power consumption of at least about 10 kw., comprising an enclosing envelope, a single cathode having a termination surface for supporting an arc discharge, a plurality of cylindrical anodes associated with said cathode and each having a termination surface constituted by the end face of the cylinder, said termination surfaces lying in a plane substantially parallel to the termination surface of said cathode and bein symmetrically positioned about the dischargeaxis, and a multiple-strip seal for lead-in conductors supporting said anodes. I

.4. A high-pressure direct-current electric discharge lamp designed 'for a power consumption of at least about 10 kw. and comprising an envelope enclosing an atmosphere of an ionizable medium, a single cathode having a termination surface upon one side of a plane transverse to the electric discharge path, a plurality of anodes disposed with their axes parallel to each other and arranged in a confined cluster about the axis of said discharge path on the opposite side of said plane, and a reflecting disc disposed substantially perpendicular to said axis of the discharge path and within the said cluster of anodes.

' VICTOR J. FRANCIS.

EVAN I-I. NELSON.

REFERENCES CITED UNITED STATES PATENTS Great Britain Sept. 14, 1944

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