US2208998A - Electric lamp - Google Patents

Description

July 23, 1940.

K. MEY

ELECTRIC LAMP Filed Nov. 8, 1937 2 m M Q n t i? n a A IK W/s Patented July 23, 1940 UNITED STATES ELECTRIC LAMP Karl Mey, Berlin-Charlottenburs", Germany, assignor to General Electric Company, a corporation of New York Application November 8, 1937, Serial No. 173,477 In Germany November 12, 1936 7 Claims.

My invention relates to electric lamps generally and more particularly to incandescent electric lamps containing a gaseous atmosphere. Still more particularly, my invention relates to 5 electric incandescent lamps containing a vaporizable metal which is vaporized during operation of the lamp.

It is well known in the lamp art that in the case of gas-filled electric incandescent lamps,

in whose filaments consist of metals having a high melting point such as tungsten, or metal alloys such as tantalum carbide, the vaporization of the filament is lessened the heavier the molecule of the filling gas and the higher the pressure 16 such gas attains during operating of the lamp. For this reason it has already been proposed to use, instead of nitrogen and argon, the heavier rare gases, such as krypton and xenon, as well as mercury vapor.

39 Although mercury vapor retards the vaporization of the coiled filaments considerably, be-

cause of its especially heavy atomic weight, it has so far not been practically utilized in electric incandescent lamps for several reasons. The 3; heavy mercury mass, whichrolls freely in the lamp bulb, is likely to damage the bulb or even the filament during transportation or manipula- .tion. Moreover, the mercury is apt to penetrate into the fine spaces between the coils of the fila- 30 ment so that short-circuits between turns and over-currents will occur. Such short-circuits and over-currents greatly shorten the life of the lamp, and on some occasionsmay even cause the lamp to explode, particularly when the over-cura rents, as a result of increased mercury vapor development, create an extraordinary rise in the vapor pressure. The danger that the vapor pressure will exceed the safety limit, as determined by the mechanical strength of the lamp bulb, may also occur when over-voltages appear in the network, and therefore over-currents in the lamps. This danger may also arise when the mercury vapor incandescent lamp is mounted in l or built into either a tightly closing lamp shade, a or one which dissipates the heat very slowly, so that even the normal current of the incandescent lamp will lead to an excessive bulb temperature and thus to excessive vapor pressure. Conversely, a comparatively slight drop in the; netgowork'voltage, or an especially strong or pronounced cooling at the point of utilization, will cause a more or less considerable amount of condensation of the mercury vapor, so as to form a layer against the bulb, thereby reducing the light 55 radiation. Coincidently, the pressure of the mercury vapor filling drops considerably, and, be, cause of insuflicient retardation of the filament vaporization, the life of thelamp is shortened. To the foregoing disadvantages must be added the consideration that in the case of a quantity '5 production of such metal filament lamps with mercury pools, the individual lamps will generally operate under vapor pressures which difier greatly from each other so that the lives and; the light outputs of such lamps will also differ. 10 This is due to the unavoidable differences in the dimensions of the lamp bulbs and to the differences caused thereby in the heat transfer conditions and characteristics.

One object of my invention is to provide an incandescent lamp in which a metallic vapor, preferably mercury vapor, is utilized to retard vaporization of the lamp filament, without the presence of the previously mentioned disadvantages.

Another object of my invention is to provide a metallic vapor incandescent lamp in which the pressure of the vaporizable metal, when thelamp is in operation, will remain very nearly constant under practically all conditions of bulb temperature variations.

According to the invention, the quantity of vaporizable material which is placed within the bulb, and which supplies the high pressure vapor atmosphere, is made'so slight that during operation of the lamp the said material is completely vaporized. After the lamp is switched in, all of the vaporizable metal filling is evaporated before the lamp bulb has attained its operating temperature. With such a lamp, the pressure of the vapor increases with increasing temperature, only as long as new additional metallic vapor is developed. After the. vaporization of the last trace of the metal, the vapor pressure remains nearly the same regardless of a continuous rise in the bulb temperature. This is because the vapor pressure curve of the superheated metallic vapor that has been formed has a very fiat shape with the result that with a lamp constructed in accordance with the invention, voltage fluctuations and temperature conditions at the place of utilization, as well as difierences in the size, may have much less harmful results. Inasmuch as the vaporizable metal in the lamp exists, as a rule, in the form of a fine" sediment covering the bulb wall, and this even in the cases where the operating vapor pressure attains only a few atmospheres, no damage to the lamp bulb and to the filament need be feared. l

Further objects and advantages of my invention will appear from the following description of species thereof and from the accompanying drawing, in which:

Fig. 1 is a longitudinal sectional view of a double-ended tubular lamp comprising my'invention; Fig. 2 is a view similar to .Fig. l of a single-ended tubular lamp comprising my invention; Fig. 3 is a longitudinal sectional view of a I modification of my invention in which discharge electrodes and an incandescent filament are connected in series within the same bulb; Fig. 4 is a longitudinal sectional view of another modification of my inventionin which discharge electrodes are connected in series with and between two incandescent filaments within the same bulb; Fig. 5. is a modification of the lamp shown in Fig. 4 in which both tube ends, each of which encloses one of the filaments, are bent at right angles to the central portion to form a U-shaped tubular bulb; and Fig. 6 is still another modification of my invention in which an incandescent lamp, constructed in accordance with my invention, and a high pressure discharge lamp are mounted within a common bulb to provide a source of mixed light.

Referring to Fig. 1, the incandescent lamp there shown comprises a tubular bulb or envelope I, consisting of quartz or other heat-resisting glass, and an incandescent body orfilament 2 mounted within said bulb and consisting preferably of a single or multiple coiled tungsten wire or a small rod of tantalum carbide. The filament 2 is disposed along the axis of the bulb which surrounds the filament as closely as possible. The current for operating the lamp is supplied to the filament 2 through a pair of leads 3, 3 which are sealed tightly into fusing nipples l, I that protrude outwardly at both ends of ,the tubular bulb l. The nipples consist of a glass which provides a graded seal to facilitate the transition between the quartz glass of the bulb and the current leads 3, which consist preferably of molybdenum or tungsten. For this purpose, the sealing nipples may consist of 65 to 96rp'er cent, SiOz, 4 to 20 per cent A1203, and 0 to 30 per cent earth alkalies. ing of the lamp bulb are accomplished by means of a lateral tubular orifice which, after sealing 'ofi', leaves the tip 5. The lamp bulb contains a filling of a fixed gas such as nitrogen or argon or a mixture of argon or grypton with nitrogen at a sumcient pressure, for example, 300 mm. of mercury or more. In addition, the lamp bulb contains an exceedingly small, but very accurately measured quantity of vaporizable metal 6, preferably mercury, which appears mostly as a fine deposit on the walls of the lamp bulb. This quantity of mercury is so small that at approximately 90 per cent, at the most, of the power absorption of the lamp, hence much before the operating temperature of the lampbulb is attained, the entire amount of mercury will vaporize, so that the mercury vapor thus produced will be considerably superheated. The quantity of mercury to be introduced into the lamp bulb depends. each time upon the size of the bulb and also upon the value of vapor pressure which is to be attained. This value may range between one-half atmosphere and twenty atmospheres, and in certain cases it may be even higher.

Be ruse of the aforementioned superheating of the mercury vapor at the operating temperature, the pressure, which is mainly "dependent on the quantity of mercury, will be to a great extent independent of temperature variations in The evacuation and the fillthe lamp bulb, suchas may be caused by voltage fluctuations or changes in the cooling conditions, or by unavoidable dimensional differences in the manufacturing process. The vapor pressure, after complete vaporization of the mercury, remains nearly the same regardles of a continuous rise in the bulb temperature. This is due to the fact that the vapor pressure curve or the superheated mercury vapor has a very flat shape. Inasmuch as no mercury pool exists when the lamp is in service, and since no important pressure increases will occur any longer because of temperature variations, there exists the possibility of establishing an operating vapor pressure, by suit-.

ably apportioning the mercury quantity, which will be just-as high as the strength of the lamp bulb will warrant, taking safety into consideration.

The possibility that, immediately upon switching on an incandescent lamp of .the type described, i. e., before the high mercury vapor has been produced, the filament may vaporize excessively or may be subjected to a destructive discharge are between its individual parts, can be effectively prevented by a sufliciently high pressure, approximately 300 mm. of mercury and possibly more, of the aforementioned gas filling of nitrogen or argon, or mixture of argon or krypton with nitrogen. In many cases, however, it is advisable to operate the lamp in the well-known manner, by means of an adjustable or disconnectible rheostat which will reduce the starting current.

The lamp illustrated in Fig. 2 differs from that shown in Fig. 1 only in that it is of the singleended base type, so that both leads 3, 3 are sealed into the same end of the tubular lamp bulb. In this case the current lead 3, which extends to the top of the lamp bulb, must be surrounded by an insulating casing or tubing 1.

In the lamp shown in Fig. 3, in addition to the filament, there is mounted within the lamp bulb, a pair of electrodes 9 and III which are heated by an arc discharge therebetween and are provided with a highly electron emissive substance. In this modification, the filament 2 is .connectedin series with the arc gap between the electrodes and is supported from electrode I0 and separated from said arc path by a wall or partition 8. This partition is not made gas-tight and therefore the same vapor pressure and the same amount of vapor superheat exists in both chambers. In this case the application of the superheated mercuryvapor atmosphere is very important since only such an atmcsphere will make it possible to have an arcing voltage that is independent of voltage or temperature variations. Such an independence is absolutely necessary. It will provide a constant light fiux by the discharge are and a correct loading of the current-carrying. filament.

Referring more specifically to Fig. 3'the tubular lamp bulb i is subdivided into two chambers by a partition 8 which is not entirely gas-tight and may be perforated. One of the tube chambers contains the coiled filament 2, and the other chamber contains two glow cathodes 9 and II which are heated by thedischarge therebetween, and which are provided with substances that liberally emit electrons. Between these two electrodes a discharge arc ii is struck when the lamp is switched in. The incandescent filament 2 serves as a series resistance for the discharge are ll. However, it is frequently advisable to utilize an additional series resistance, mounted outside of the discharge space and arranged to be regulated or switched in or out. This resistance may also consist of a reactor or a condenser. The filament 2 and the discharge are ll burn or operate in a strongly superheated mercury-vapor filling, whose pressure is accurately determined by a suitable apportioning of the quantity of mercury 6, as described above in conto the opposite electrode ill by means ofa resistor I! having a high ohmic resistance.

As shown in Figs. 4 and 5,-it is also possible to have a discharge are arranged between and connected in series with two filaments. In this arrangement, each filament is separated from the are by a shielding wall which must not be gas tight. In this instance, the incandescent filament is subdivided into two halves 2 and 2,and

the discharge are is arranged between these halves. Two dividing barriers or partitions I and 8' shield the central discharge space from theend portions of the tube, each one of which contains one of the incandescent filaments 2 or 2'. For many purposes it is advisable to bend the end portions of the tubular lamp bulb at right angles to the central portion, as shown in Fig. 5, thereby providing a particularly practical shape.

Also, in the two lamps shown in Figs. 4 and 5, the striking of the discharge are I I may be facilitated by means of an auxiliary electrode I! with a high ohmic series resistance I3 inserted ahead of it.

In order to obtain a practical source of mixed light which has the shape of incandescent lamps, a mercury high-pressure incandescent lamp according to the inVention and one of the known high-pressure metal-vapor discharge lamps, may be mounted together in'one common glass bulb, as shown in Fig. 6, both light sources being then connected in series. A particularly good mixture of,light radiations of both light sources can be obtained by having a surrounding glass vessel or. bulb which will diffuse light and which may be provided with glass transparent to ultra-violet rays, or glass which may be colored, or altematively, glass provided with luminophores.

In this mixed-light lamp, (Fig. 6), a tubular mercury high-pressure incandescent lamp I, constructed according to the invention, and a tubular mercury vapor high-pressure discharge lamp I, such as is already known, are both mounted and housed within a common glass envelope i5 and are connected in series by means of a connecting wire l6. Both tubular lamps are arranged parallel with respect to each other and symmetrical with respect to the axis of the surrounding glass envelope it. The ignition of the discharge lamp It may be facilitated in this case by means of an auxiliary electrode l2 which is disposed adjacent one of the discharge-heated glow electrodes II and is connected through thehigh ohmic resistance I! with the other electrode 9. The singlebase glass envelope i 5 is provided, as is customary with incandescent lamps, with a stem l'l protruding inwardly and formed with a stem press it within which leads I! and 20 are sealed. Lead I! is connected to the incandescent lamp I while lead 20 is connected to the discharge lamp l4.

The bulb ll may be made either of glass that is transparent to ultra-violet light, or it may be provided with an inside frosting. Alternatively, the bulb may consist of clear glass, and its inner surface may then be coated with a luminophorous earliest, only after complete vaporization of the mercury in the incandescent lamp bulb l.

The novel high-pressure incandescent lamp disclosed herein may be double-walled, if desired, and the space between the two walls may be evacuated or may be filled with a gas which will equalize the temperature, such as nitrogen, oxygemhydrogen, or a rare gas. Under certain conditions it is advisable to use, for the lamp bulbs or for the external wa1l,a safety glass which will not splinter, or to surround the bulb with a wire netting that-will not reduce the luminous output to any great extent. The leads to the coiled filament may contain, as already known, suitable fuses What I claim as new and desire to secure by Letters Patent of the United States is:

v1. A high-pressure electric lamp comprising a sealed envelope divided into a plurality of chambers by at least one partition permitting gaseous intercommunication therebetween, a metallic filament mounted within one of said chambers and a pair of electrodes in another chamber, said filament being connected in series with the arc gap between said electrodes, and a predetermined amount of vaporizable metal within said envelope such that it is completely vaporized at a power absorption of the lamp amounting to not more than approximately ninety per cent of its rated 'power absorption.

2. A high-pressure electric lamp comprising a sealed elongated envelope divided into three longitudinally sp ced chambers, including a central chamber and end chambers, by a pair of partitions permitting gaseous intercommunication therebetween, a metallic filament mounted within each of said end chambers, a pair of electrodes located within said central chamber, said filaments being connected in series. with the arc gap between said electrodes, and a predetermined amount of vaporizable metal within said envelope such that it is completely vaporized at a power absorption of thelamp amounting to not m re than approximately ninety per cent of its rated power absorption. g

8. An electric lamp comprising an outer envelope, and a high-pressure incandescent lamp and a high-pressure discharge lamp mounted within said envelop and connected in series, said incandescent lamp comprising a bulb containing a metallic filament and a predetermined amount of vaporizable metal such that it is completely vaporized at a power absorption of the lamp less than its rated power absorption.

4. An electric lamp comprising in combination an incandescible metallic filament and a pair of electrodes, said filament being connected in series with the gap between said electrodes, means providing separate enclosing chambers for said filachamber enclosing said filament containing a predetermined amount of vaporizable metal such that it is completely vaporized during operation or the lamp.

5. A high-pressure electric lamp comprising a sealed elongated envelope divided into three longitudinally spaced chambers, including a central chamber and end chambers, by a pair of partitions permitting gaseous intercommunication therebetween, a metallic filament mounted within each of said end chambers, a pair of electrodes locatedwithin said central chamber, said filaments being connected in series with the arc gap between said'electrodes, and a quantity of vaporlzable metal in said envelope.

6. A high-pressure electric lamp comprising a sealed elongated envelope divided into three longitudinally spaced chambers, including a central chamber and end chambers, by a pair of partitions permitting gaseous intercommunication therebetween, said end chambers extending laterally of said central chamber to form a U-shaped envelope, a metallic filament mounted within each sealed elongated envelope divided into three longitudinally spaced chambers, including a central chamber and end chambers, by a pair of partitions permitting gaseous intercommunication therebetween, said end chambers extending y laterally of said central chamber to form a U- shaped envelope, a metallic filament mounted within each of said end chambers, a pair of electrodes located within said central chamber, said filaments being connected in series withthe arc gap between said electrodes, and a quantity of vaporizable metal in said envelope.

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