US2724790A - Arc lamp - Google Patents

Description

Nov. 22, 1955 e. EMBSHOFF ETAL ARC LAMP 2 Sheets-Sheet 1 Filed Dec. 20, 1951 a k w INVENTORS G gorge F Embsho Georgie Sperti,

ATTORNEKs Nov. 22, 1955 2,724,790

G. F. EMBSHOFF ET AL ARC LAMP Filed Dec. 20. 1951 2 Sheets-Sheet 2 1217411 111 QO16 1-l1612 Fab. 6. '7

INVENTORS George E Embshofifi George Sperilz) BY W,Wm

ATTORNEYS United States Patent ARC LAMP George F. Embshoif and George Sperti, Cincinnati, Ohio, assignors to The Institutum Divi Thomae Foundation, Cincinnati, Ohio, :1 nonprofit corporation of Ohio Application December 20, 1951, Serial No. 262,521

2 Claims. (Cl. 315115) This invention relates to are lamps of the type in which an arc discharge is established between spaced electrodes in an ionizable medium such as mercury vapor or other gas or vapor. This application-is a continuationin-part of our prior application Serial No. 173,824, filed July 14, 1950, now Patent No. 2,613,328.

As disclosed in the aforesaid prior application, the present invention can be used advantageously in lamps of the type sold to the general public for household use as sun lamps and including a mercury are as a source of ultraviolet radiation, with or without an accompanying source of infrared radiation. By way of example, it will be described hereinafter with particular reference to such a lamp, but it is to be understood that the invention is not restricted to this application.

The usual method of providing ultraviolet radiation in sun lamps is to operate a mercury vapor arc in series with a suitable ballast resistance, which may be designed to provide infrared radiation if desired. Such lamps are illustrated for example by prior U. S. Patent No. 2,369,987 and also by the copending application of George F. Embshoif, Serial No. 52,363, filed October 1, 1948, now Patent No. 2,625,670. The desirable and beneficial ultraviolet wave lengths are those longer than about 2800 Angstroms, whereas shorter wave lengths may have harmful effects. Since the spectrum of the mercury arc emits substantial amounts of energy at these undesirable shorter wave lengths, the usual practice in sun lamps is to enclose the arc in glass which filters out most if not all of the radiation below about 2800 Angstroms. On the other hand, as the operating temperature and vapor pressure in the arc increase, the power consumed and the energy emitted by the are both increase and also the proportionate ultraviolet energy output in the region of the desirable longer wave lengths mentioned above increases with respect to the shorter wave lengths. Hence for sun lamp purposes, it is desirable to operate the are at relatively high vapor pressure, and accordingly to utilize the heat developed by the ballast resistance to increase the operating temperature of the are and with it the vapor pressure as rapidly as possible. Forexample, these effects are facilitated when one or more elongated ballast resistors are arranged parallel with and closely adjacent to a tubular arc'burner, whereby heat losses are minimized 'and the ballast heat is distributed more or less uniformly throughout the length of the are as disclosed in the aforesaid copending applications. Of course, the ballast resistance may also be used as a source of infrared radiation if desired.

As the operating temperature and vapor pressure and the power consumption of the arc increase, however, the glass walls of the burner tube are exposed to considerable heat and care must be taken that they do not reach a temperature at which the glass softens and the tube is damaged or destroyed. The danger of overheating is increased as the mercury vapor pressure increases, and the arc changes from a diifusedglow to a concentrated stream,

because of the frequent tendency of such concentrated 2,724,790 Patented Nov. 22, 1955 are streams to follow a bowed or curved path between the electrodes and thus to approach closely to or even to touch the glass wall of the tube. This tendency is increased by uneven heat distribution, since the arc tends to pass through the hotter zones. In a sun lamp of the type described above, for example, it usually but not necessarily tends to pass closest to that side of the tube which is adjacent the ballast resistance. Similar problems are encountered with various other types of arcs, as will be understood by those skilled in the art.

The chief object of the present invention is to overcome the above mentioned tendency and to confine the concentrated arc stream more or less closely to a substantially straight path between the electrodes and spaced from the tube wall.

Other objects will appear hereinafter as the description of the invention proceeds.

Several embodiments of the invention have been illustrated in the accompanying drawings, but it is to be expressly understood that such drawings are for purposes of illustration only and are not to-be taken as a definition of the limits of the invention, reference being had to the appended claims forthis purpose.

In the drawings,

Fig. 1 is a section through a typical arc burner tube embodying the invention;

Fig. 2 shows a somewhat difierent form of the invention;

Fig. 3 is a wiring diagram illustrating the use of the tube of Fig. 1 in a sun lamp of the type described above;

Fig. 4 shows another form of the invention;

Fig. 5 is a section on the line 55 of Fig. 4;

Figs. 6 and 7 illustrate additional embodiments of the invention; and

Figs. 8 and 9 show still another embodiment, Fig. 9 being an end view of Fig. 8.

The are lamp or burner may be of any suitable type and, as shown by way of example in Fig. 1, is an ultraviolet generator of the same general type as those disclosed in the prior patent and copending applications mentioned above. Referring to this figure, the glass wall 11 of the burner is substantially tubular in shape and is suitably closed and sealed at each end as by means of stems or presses 12 of the usual type. This bulb contains a quantity of vaporizable and ionizable material such as mercury, and is usually filled with argon or other suitable rare gas at a low pressure. Preferably the quantity of mercury employed is limited so as to prevent the development of unduly high mercury vapor pressures when the lamp is in operation. Mounted in the press 12 at one end of the lamp is a wire or conductor 13 leading to an arc electrode 14. A similar wire or conductor 15 is mounted in the press 12 at the opposite end of the lamp and leads to an arc electrode 16. Filaments 17 and 18, which are preferably coated with or otherwise embody a suitable electron-emissive substance, are connected at one end to the leads 13 and 15 respectively and at the other end to wires or conductors 19 and 20 respectively which lead out through the presses 12.

When an arc is formed between the electrodes 14 and 16 as hereinafter described, and as the mercury vapor pressure increases and the arc becomes concentrated, the path of the are often tends to bow or curve instead of following a straight axial path between the electrodes and thus to approach closely to the glass wall 11. In order to avoid possible softening of the glass due to such bowing, arc centering means are provided between the two electrodes 14 and 16. These means may take any of the various forms described hereinafter, or their equivalents, and may be mounted in any suitable manner. The centering means is not part of the lamp circuit, being electrically disconnected therefrom, and its function is only to prevent the arc stream from approaching too closely to the wall of the tube.

As shown in Figs. 1 and 2, the centering means comprises one or more loosely wound flat spirals 21 of suitable refractory metal wire such as molybdenum, the spirals being electrically disconnected from the electrodes and filaments mentioned above and being supported in the bulb in any suitable manner as by attachment to the tubular wall 11 (see Fig. 2) or to the presses 12 (see Figs. 1 and 4).

Fig. 3 is a wiring diagram of a typical operating circuit for a sun lamp including an ultraviolet burner of the type described above. The lamp is energized by supply lines 22 and 23. The line 22 leads to one end of a ballast resistor 24 the other end of which is connected by a wire 25 with the adjacent end of a second resistor 26, and the other end of the resistor 26 is connected by a conductor 27 with the lead-in-Wire 13 and the electrode 14. At the opposite end of the lamp, the electrode 16 and its lead-in-wire 15 are connected by a wire 28 with the line conductor 23. Reference to Fig. 3 shows that in the normal operation of the lamp, the current flows through a series operating circuit comprising conductor 22, resistor 24, wire 25, resistor 26, wires 27 and 13, electrodes 14 and 16, wires 15 and 2S, and line conductor 23.

The are may be started either automatically or manually. In the form shown, the starting circuit includes the filament lead-in conductor 19 which is connected to a wire 29! leading to one terminal of a manual starting switch indicated generally at 39, the other terminal of this switch being connected by a wire 31 with the filament lead-in conductor 20. The starting switch 30 is of any suitable type which normally remains open but can be held closed long enough to start the operation of the lamp. The starting current passes from line conductor 22 through resistor 24, wire 25 and resistor 26, wires 27 and 13, filament 17, wires 1% and 2%, switch 30, wires 31 and 2t filament 18, wires 15 and 28 and supply line 23. As the filaments become hot, electronic emission therefrom will result in ionization of the atmosphere in the arc bulb. After a brief initial period, the starting switch 343 is released and opens to break the starting circuit described above and the main are then strikes between the electrodes 14, 16 through the ionized atmosphere, the current then flowing through the series operating circuit mentioned above.

As the arc burns and its temperature and vapor pressure increase, the are becomes concentrated in an intensely luminous stream between the electrodes. In the absence of arc centering means such as shown in Figs. 1 and 2 or as described hereinafter, this stream often is deflected out of a straight path between the electrodes and close to or in contact with the wall of the tube, especially if one side becomes hotter than the rest of the bulb for any reason such as heat from the ballast resistors 24 and 26. Such deflection may result in overheating and softening of the glass wall and eventual destruction of the burner. The location of the wire spiral or spirals 21 along the arc path prevents such deflection of the arc stream and protects the tube wall against overheating.

In cases such as described above, Where one side of the tube is usually hotter than the others and deflection of the are stream usually occurs toward that side only, it may be sufflcient to provide arc centering or deflecting means on that side of the tube only.

Figs. 4- and show a modified form of arc deflector that can be used in such cases. The tubular glass bulb 11 is provided as before with are electrodes 14, 16 and starting filaments 17, 18, only one end of the tube being shown. The are centering means takes the form of one or more are deflecting grids located between the electrodes on the hot side of the tube (e. g., the side next the ballast resistance unit). In the form shown, this grid comprises a length of molybdeum or other suitable wire bent into generally triangular shape in a plane perpendicular to the tube axis as shown at 32. Of course, shapes other than triangular can be employed if desired. The location of the grid prevents the are from melting the glass wall of the tube at high output.

The grid or grids 32 can be mounted in any suitable manner, either on the tube wall or on the presses 12. In the form shown, the shank 33 of the molybdenum wire extends parallel to the axis of the tube and close to one side thereof and is welded at its end to a wire 34 which is mounted in the press 12 at the end of the lamp. Preferably both wires 33 and 34 are enclosed in insulating tubes 35 and 36 respectively which may suitably be made of glass. Without such protection, the arc may sometimes strike to and run down the wires 33 and 34 and melt the grid support, even though the wires are not electrically connected in the lamp circuit, particularly because the activating material from the starting filament may sputter onto the grid support wires.

Arc centering means as shown in Figs. 1 and 2 surround or substantially surround the arc path, being provided in effect with a central aperture through which the main arc stream passes. In other cases, the arc centering means may take the form of one or more centrally apertured annular members of refractory metal, ceramic material capable of withstanding high temperatures, or like material. Such a member or members can be mounted in any suitable manner either on the tube wall as in Fig. 2 or on the presses 12 as in Figs. 1 and 4. For example, one or more relatively thin flat rings or centrally apertured disks such as shown at 37 in Fig. 6 can be mounted between projections 38 on the inner surface of the tube in a plane or planes transverse to the axis of the tube. It will be understood that the size and shape of the central aperture 39 in the disk can be varied as desired, and also that the outer diameter of the disk may be substantially less than the inner diameter of the tube 11.

Upon increasing the thickness in the axial direction of a ring or disk such as the member 39, it becomes in efiect a short section of tubing. Such tubing sections can be of any desired length, provided that they should be made of material transparent to the desired radiation from the are if their axial extent is so large that they would otherwise decrease materially the radiation emitted by the burner. In the case of ultraviolet burners, for example, a suitable material that is both transparent to ultraviolet radiation and capable of withstanding the temperatures developed by a mercury arc is Vycor glass.

In some instances it is advantageous to employ tubing extending practically the entire distance between the electrodes and thus enclosing substantially the entire arc path. Such an arrangement is illustrated in Fig. 7 which shows an ultraviolet generator of the type described above having a bulb or tube 11, presses 12 at both ends, and electrodes 14, 16 and filaments 17, 18 mounted on the presses as described with reference to Fig. 1. Extending between the electrodes is an inner tube 40 which is open at both ends so that its interior is in free communication with the interior of the burner tube 11. The tube 40 may be mounted in any suitable manner, being shown as supported by the electrode lead-in wires 13 and 15 and by extensions 41 of the filament lead-in conductors 19 and 20. Thus the are which forms between the electrodes 14, 16 is completely shielded and prevented from contacting the tube 11. In the case of a mercury are used for sun lamp purposes, the tube 40 may be made of Vycor as mentioned above. The tube 11 may then be made of glass such as Corex which transmits the desired radiations but largely filters out the shorter and undesirable wave lengths generated by the are. No sealing problems are involved, since the two tubes are not sealed to one another. On the other hand, the more expensive Vycor need be used only for the inner tube 40, while less expensive but necessary filter glass such as Corex can be used in the burner tube 11 without danger of softcning due to excessive heating.

If shielding on only one side of the tube is required, then a suitably shaped and sized shield equivalent to a segment of the wall of the tube 40 may be mounted between the arc path and that side or part of the burner tube 11 which is to be protected. Such arrangements are illustrated by Figs. 8 and 9 wherein the upper part only of the burner tube is protected by an elongated shield 42. This shield is made of any suitable material such as Vycor glass or, if transparency on this side of the burner is not required, of ceramic or metal. As shown, the shield 42 is preferably curved in cross section and mounted in spaced substantially parallel relation with the tube wall, but the curved cross section is not necessary. The shield may be mounted in any suitable manner, as by means of one or more supports 43 secured to the shield and fused to the wall of the burner tube. If desired, one or more studs 44 may project from either the shield or the burner tube into engagement with the other.

It will be understood that the invention is not restricted to the embodiments illustrated in the drawings and described above but is capable of other embodiments, and also that various changes can be made in the form, details of construction, and arrangement of the parts without departure from its spirit. Reference therefore should be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. An arc lamp of the type comprising an elongated bulb containing at each end an electrode and a filament outwardly of the electrode, electric leads for the electrodes and filaments, extensions from the filament leads, and an ionizable gaseous atmosphere at sufiicient pressure to maintain a concentrated arc discharge between said electrodes, means for preventing contact of said are with the bulb wall including an open ended tubular member of refractory material mounted substantially concentrically within said bulb, said member extending the distance between said electrodes to enclose said are, said material and the material of said bulb being transparent to radiations from said are, the open ends of said member providing free and direct communication between the bulb atmosphere and the arc path at points immediately adjacent the electrodes at the ends of thearc path and said tubular member having its open ends engaging the electrode leads and extensions of the filament leads to maintain the position of said tubular member within said bulb, said tubular member surrounding the electrodes and the filaments being exposed to the atmosphere in the bulb.

2. An are lamp of the type comprising a substantially tubular lamp bulb containing an ionizable gaseous atmosphere containing mercury and having at each end an arc electrode, and a filament outwardly of the electrode, electric leads for the electrodes and filaments and extensions from the filament leads, means for energizing the lamp comprising supply leads and a circuit including ballast resistance in series with the arc path said ballast resistance providing heat to assist in maintaining the operative temperature of the bulb and means for preventing contact of said are with the bulb wall including an open ended tubular member mounted substantially concentrically within said bulb and surrounding the arc path, said tubular member and said bulb being transparent to radiations from said are, said tubular member extending the distance between said electrodes and its open ends providing free and direct communication between the bulb atmosphere and the arc path at points immediately adjacent the electrodes at the ends of the arc path, the open ends of said tubular member engaging the extensions of the filament leads and the electrode leads to maintain the position of said tubular member in said bulb, said tubular member surrounding the electrodes and the filaments being exposed to the atmosphere in the bulb.

References Cited in the file of this patent UNITED STATES PATENTS 1,971,944 Wiegand Aug. 28, 1934 2,025,934 Brett Dec. 31, 1935 2,133,206 McCauley Oct. 11, 1938 2,152,992 Francis Apr. 4, 1939 2,172,839 Francis Sept. 12, 1939 2,598,567 Lemaigre-Voreaux May 27, 1952

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