US2561868A - Gaseous electric discharge lamp - Google Patents

Description

July 24, 1951 H. G. JENKINS El AL GASEOUS ELECTRIC DISCHARGE LAMP Filed Dec. 15, 1947 lnven't'ors: Henr G. Jenkins, Edward E. MiLes,

Their Ab torneg.

Patented July 24, 1951 2,581,868 GASEOUS ELECTRIC DISCHARGE LAMP Henry Grainger Ernest Miles,

New York Application December 15, 1947,

Jenkins, Pinner,

England, asslgnors to any, a corporation of London, General Electric Comp and Edward Serial No. 791,678

Great Britain December 20, 1946 1 Claim. (Cl. 313-190) This invention relates to positive column electric discharge lamps of the type having a gas and/or vapor filling at a pressure much less than atmospheric but such that in operation the discharge path, or each discharge path if there is more than one, is occupied mainly by the positive column, and in which each electrode that is adapted to act as cathode in operation, either continuously for D. 0. operation, or intermittently for A. C. operation, is preferably an activated cathode of the pre-heated type, i. e., is activated with electron emissive material and is adapted to be heated prior to the starting of the discharge.

The invention relates more particularly, but not exclusively, to lamps of the type specified comprising luminescent material adapted to be excited to luminescence by the discharge; such lamps are usually known as low-pressure fluorescent lamps and the filling used with them is usually mercury vapor admixed with a few millimeters pressure of a rare gas such as argon.

For obtaining high efilciencies and high lumen output lamps of the type specified are usually arranged to have discharge paths of considerable length, often several feet, and for convenience in mass production the envelopes of the lamps at present generally consist mainly of straight lengths of glass tubing. But long straight dis charge lamps have several practical disadvantages; thus they are often inconveniently long for handling purposes and are difllcult to deal with in fixtures, such as for street lighting, owing to the large size of fixture required. Furthermore since the electrodes are situated at opposite ends of the tube, a long straight tube will require two widely separated external contacts or bases which may need to be very accurately spaced apart to enable the lamp to fit into a housing with pre-set sockets for the supply of electrical power to the lamp.

One method of avoiding the difiiculty is to use a number of shorter lamps in place of one long lamp, but this entails the provision of an increased number of sockets in the fixture and multiplication of auxiliary apparatus, which is often inconvenient.

It has therefore been proposed to construct compact lamps in which the discharge path in non-linear and the longest dimension of the lamp is considerably less than the total length of the discharge path; one method of achieving this is to bend the tubular envelope of the lamp into a curved shape such as a spiral or zig-zag, but such methods do not lend themselves readily to mass 2 tube bending in general reby skilled craftsmen or comproduction as such quires manipulation plicated machinery.

Other proposals have also been made for producing compact discharge lamps without requiring the bending of glass tubing; thus it has been proposed to form a tortuous channel for the passage of the discharge by the abutment of two initially separate glass components one or both of which is or are provided with one or more upstanding ridges which separate adjacent parts of the discharge passage; it has also been proposed to form a tortuous discharge channel by pressingin suitable parts of the sides of a fiat lozengeshaped bulb.

The object of this invention is to provide an alternative form of compact low-pressure electric discharge lamp which is well suited to mass production methods.

According to the invention an electric discharge lamp of the type specified comprises an hermetically sealed light transmissive envelope containing the filling of gas and/or vapor and within which are supported a plurality of preferably straight glass tubes each closed at one end, open at the other end, and having an electrode mounted within the tube at the closed end of the tube, the tubes being arranged with their closed ends all near one end of the said envelope and their open ends all near the opposite end of the envelope, and wherein leads for supplying the said electrodes, and possibly also one or more other electrodes which may be mounted within the envelope near the said opposite end thereof, pass to the exterior of the envelope, the arrangement being such that the lamp is adapted to be operated with a discharge passing along the length of each said glass tube.

Preferably each electrode at the closed end of a said glass tube is an activated cathode of the pre-heated type; then for D. 0. operation one or more anodes must be provided near the open ends of the glass tubes; for A. C. operation each such anode may be replaced by another activated cathode of the pro-heated type, but in some cases electrodes at the open ends of the glass tubes may be omitted altogether, so that the electrodes at the closed ends of the glass tubes are the only electrodes within the envelope. For convenience the electrodes at the closed ends of the glass tubes will hereinafter be referred to as the tube-electrodes.

Preferably the hermetically sealed envelope is a tubular glass bulb closed at one end by the sealing in of a closure member, for example a pinched or pressed stem tube, and the glass tubes are mounted with their closed ends near to the closure member and with the leads to the tube-electrodes passing through the closure member or its seal with the envelope.

The closing of the ends of the glass tubes need not necessarily be completely gas tight and need only be suflicient to prevent short-cutting of the discharges between the closed ends of the tubes. It is found with the arrangement in accordance with the invention that when one tube-electrode is adapted to cooperate with another, the discharge still takes the longer U-shaped path including the lengths of the tubes instead of taking the much shorter path between the leads to these electrodes, even without completely gas tight sealing of the closed ends of the tubes, providing the voltage between the leads is not too great; in practice we have found it desirable with exposed leads for the voltage between the leads to be not greater than 140 volts, but higher voltages might be used if the leads are adequately screened, e. g., sheathed in glass. This somewhat surprising feature enables the leads to the tube electrodes to be sealed through a pinched glass stem tube or other closure member of conventional type which can readily be sealed to the main part of the envelope of the lamp in accordance with well known techniques, thereby simplifying production.

The inner wall of one or more of the glass tubes may be coated with luminescent material adapted to be excited to luminescence by the discharge, and combinations of colors may be obtained by the use in different tubes of different luminescent materials and/or by the omission of luminescent material from one or more of the tubes. If the filling comprises mercury vapor, preferably each tube is coated with luminescent material.

The said sealed envelope and/or the outer envelope of the lamp if the said sealed envelope is not itself the outer envelope, may if required be rendered translucent for mixing and diffusing the light from the individual glass tubes and/or improving the appearance of the lamp by obscuring the details of the internal structure.

- 4 ate at only a fraction of the voltage required for the longer lamp.

In using a lamp in accordance with the invention each pair of electrodes between which a discharge is required to pass in operation may be associated for .starting purposes with a starting switch, which may be of the automatically operated type, ,i. e., glow type or coil-heated type. In some cases the same starting switch may be associated simultaneously with two or more pairs of electrodes; thus, for example, when two tubecathodes both cooperate with a third electrode,

leads from the said two tube-cathodes may be As already indicated, the electrodes within the envelope may all be tube-electrodes so that the lamp is adapted to produce one or more substantially U-shaped discharges. When two tubeelectrodes both cooperate with the same third tube-electrode, the corresponding U-shaped discharges will be in parallel and will have one limb in common; when the electrodes are all activated cathodes this arrangement has the advantage that the loss of power owing to cathode fall is reduced as compared with the case when each discharge terminates on separate electrodes, since there are four cathode falls in the latter case but effectively only three in the former; this advantage is of course obtained to an even greater extent if there aremore than two discharges in parallel in this way.

The same kind of advantage is obtained in the case where two or more tube-cathodes both cooperate with a further activated cathode mounted at the end of the envelope near the open end of the tubes so that the lamp is adapted to carry two or more substantially straight discharges in parallel. It may be noted that a further advantage of the arrangement having two or more discharges in parallel as compared with a lamp having a single straight discharge path of the equivalent length, is that it is adapted to operconnected together and the connection joined through a single lead to the third electrode; a starting switch placed in the said single lead will then serve to start both discharges.

One or more starting switches of the automatically operated type may if required be included within the sealed envelope, as part of the lamp, to reduce the number of leads passing to the exterior of the envelope.

In order that a lamp in accordance with the invention may run stably with each glass tube carrying the required discharge current, i. e., so as to avoid concentration of the discharge in one or more tubes to the exclusion of another or others, it may be necessary to associate each electrode with the appropriate stabilizing impedance, but the necessary arrangement for any particular case will be obvious to those skilled inthe art.

. The invention will be further described with reference to the accompanying drawings in which:

Figure 1 shows schematically a circuit arrangement incorporating a lamp in accordance with the invention which has two glass tubes,

Figure 2 shows a circuit arrangement similar to Figure 1 but in which the lamp in accordance with the invention has four glass tubes,

Figure 3 shows a modification of Figure 2 in which the lamp has-a fifth cathode with which each of the tube-cathodes cooperates, and in which a single starting switch serves to start all four discharges,

Figure 4 shows in side elevation and by way of example the details of one lamp in accordance with the invention,

Figure 5 shows the end elevation of the lamp of Figure 4, and Fig. 6 is an elevation, partly in section, showing structural details of a lamp such as shown diagrammatically in Fig. 1 but having the starting switch incorporated therein.

or vapor filling at low pressure constituting an' ionizable gaseous medium and within which are arranged two glass tubes 2 and 3 each of which is closed at one end and open at the other; the closed ends of the tubes 2 and 3 are disposed together near one end of the envelope l and the open ends are disposed together near the opposite end of the envelope I. Within the tubes 2 and l at the closed ends thereof are mounted activated cathodes l and 5, each having a pair of leads which pass through the closed ends of the tubes and the adjacent end of the envelope I. One end of cathode 5 is connected, via the external leads to one end of the cathode 4 through a starting switch 6, and-theother ends of the cathodes are connected, via the external leads, through chokes I and 8 to the terminals 9 and i! respectively or a source of A. C. supply. Sepa- Referring now to Figure l, the lamp in acrate chokes have been shown merely in order to facilitate the understanding of the more com plicated embodiments of the invention later to be described.

In operation a discharge initiated by the closing of the switch 6, which completes a heating circuit for the preheating of the cathodes 4 and 5, followed by the opening of the switch, which produces an inductive kick, takes the path indicated by the dotted line H.

In the arrangement shown in Figure 2 the arrangement of Figure 1 is effectively doubled," a second pair of glass tubes 2' and 3' being included within the envelope I in addition to the tubes 2 and 3; the tubes 2' and 3' have activated cathodes 4' and 5' mounted within their closed ends and each cathode has a pair of leads passing to the exterior of the envelope I in the sameway as the cathodes 4 and 5.

One end of cathode 4' is connected, via the external leads, to one end of the cathode 5 through a starting switch 6' similar to the connection of cathode 4 to cathode 5 through the starting switch 6, and the other ends of the cathodes 4 and 5'- are connected through chokes I and 8, in parallel with the chokes I and 8.

to the terminals 9 and ID of the A. C. supply.

In operation two separate discharges, taking the paths indicated by the dotted lines II and II, are initiated by the closing and opening of the switches 6 and B.

It will be appreciated that the four tubes 2, 2', 3 and 3' need not be arranged side by side as indicated in Figure 2; it may often be more convenient to group them together in a bundle for the sake of compactness.

Figure 3 shows an arrangement in which there are included within a gas or vapor-filled envelope l2, four glass tubes I3, |4, l5 and I6 whose closed ends are disposed together near one end of the envelope 2 and whose open ends are disposed together near the other end of the envelope. Within the tubes at the closed ends thereof are mounted activated cathodes |'I, l8, l9 and 2!] each of which has a pair of leads passing to the exterior of the envelope I2. Within the envelope and facing the open ends of the tubes l3, I4, I5 and I6 is mounted a fifth activated cathode 2| which has a pair of leads passing to the exterior of the envelope.

One end of the cathode 2| is connected, via the external leads, to one end of each of the cathodes I8, l9 and 20 through a starting switch 22, and the other end of the cathode 2| is connected to one terminal 9 of an A. C. supply; the other ends of the cathodes l1, l8, I9 and 20 are connected in parallel through chokes 23, 24, 25 and 26 respectively to the other terminal of the supply.

In operation the lamp is ignited by closing the switch 22, which completes a heating circuit for all the cathodes. and then opening the switch. which gives rise to inductive kicks initiating four separate discharges which take the paths indicated by the dotted lines 21, 28, 29 and 30.

It will be appreciated that in any of the arrangements described with reference to Figures 1, 2 and 3 the starting switches may be of the automatically operating type conventionally employed in fluorescent lamps, for example glow switches, and that these switches could if required be included within the sealed envelope of the lamp to reduce the number of leads passing to the exterior thereof. Such a glow switch is disclosed in Patent 2,329,134, L. R. Peters.

One lamp in accordance with the invention, similar to inches long and three inches in diameter; the envelope is closed by the sealing into its originally open end of a stem tube terminated by a pinch or press 32; within the envelope is a bundle of four glass tubes 33, 34, 35 and 36 each about nine inches long and one inch in diameter; each of the glass tubes is closed at the end near the envelope stem tube by the sealing into the glass tube of a small stem tube terminated by a pinch or press on which is mounted a cathode 31, 38, 39 or 40 consisting of a tungsten helix: coated with thermionically emissive material similar to the cathode used in the well known commercial 40 watt 4 ft. long by 1 diameter fluorescent lamp; leads to the tungsten helix pass through the closed ends of the glass tubes and thence through a mica battle disc 4|, supported on stout wires 42, 43 embedded in the pinch 32 and which extends over substantially the whole of the crosssection of the envelope, to the envelope stem tube through the pinch 32 of which the leads pass to terminals carried by a base 44 fitted over the end of the envelope.

The bundle of glass tubes is held together and supported from the wall of the envelope by thin wire spring rings 45, 46 which abut against the inner wall of the envelope. The glass tubes are also partly located by the stems 41, 49, 49 and 50 (of which 50 does not appear in the drawing), of the stem tubes closing the glass tubes, passing through holes in the mica disc 4|; the stems 41, 49, 49 and 50 are used for centering purposes during the scaling in of the stem tubes and correspond to the exhaust tubes forming part of the conventional tipless" stems.

Each of the glass tubes has its inner wall coated with luminescent material, indicated by the dotted lines 52 in Fig. 5 and the lower boundaries of which are indicated by the lines 5|, excitable by the low-pressure mercury vapor discharge, and the filling within the envelope of the lamp consists of mercury vapor together with a few millimeters pressure of argon.

In operation of this lamp a stabilizing choke. to carry the lamp current of approximately 0.3 amp., should be included in the lead to each cathode and the impedances of these chokes should preferably all be the same; we have found that if each choke impedance is about 350 ohms. the lamp will operate satisfactorily on a 240 volt supply in a circuit as shown in Figure 2:, the lamp dissipating a total of about 30 watts.

In Fig. 6 we have shown a lamp of the type shown diagrammatically in Fig. 1 and having two glass tubes 2, 3 supported within the envelope I in the manner shown in Fig. 4. However, in this case the starting switch 6, of the type shown in the Peters Patent 2,329,134 hereinbefore referred to, is mounted within the envelope I under the mica disk 4| and is shown supported by a wire 53 having one end embedded in the stem press 32.

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

A gaseous electric discharge lamp comprising an elongated hermetically sealed envelope con taining an ionizable gaseous medium, a stem sealed to one end of said envelope, glass tubes within and spaced Irom said envelope and extending longitudinally thereof, closure members closing the ends of said glass tubes adjacent said stem and having stem tubes projecting outwardly therefrom towards said stem, a transverse disc member arranged adjacent the closed ends of said glass tubes, means supporting said disc member from said stem. the said stem tubes projecting through openings in said disc member whereby to assist in fixing the location of the said glass tubes, resilient means supporting said glass tubes from the wall of said envelope, an electrode in each of said glass tubes adjacent the closed end thereof, at least one of said electrodes being an activated preheated type cathode, lead-in wires extending from each electrode through the associated closure member and through said disc and said envelope stem exteriorly of the envelope, and an automatically operated starting switch mounted in said envelope between said disc and said stem and being connected in series with said cathode to complete a heating circuit therefor.

HENRY GRAINGER JENKINS. EDWARD ERNEST MILES.

REFERENCES CITED The following references are of record in the file of this patent:

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