US2467687A

US2467687A - High-pressure discharge lamp

Info

Publication number: US2467687A
Application number: US681824A
Authority: US
Inventors: Edward B Noel
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1946-07-08
Filing date: 1946-07-08
Publication date: 1949-04-19
Anticipated expiration: 1966-04-19

Description

48 PERCENT ECADM/UM AM4LGAM v E. B. NOEL nununo' r'ill- HIGH-PRESSURE DISCHARGE LAMP Filed July 8, 1946 MERCURY FIG. 1

April 19, 1949.

BY W dum PLUS ' AMALGAM INVENTOR: EDWARD B. NOE

52 PE ENTCA M/U 52 PERCENT ZINC HIS ATTORNEY 4 FIG 5| WAVELENGTH //v ANGSTROM u/wrs 4a PERCENT Z/NC AMALGAM Patented Apr. 19, 1949 HIGH-PRESSURE DISCHARGE LAMP Edward B. Noel, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application July 8, 1946, Serial No. 681,824

7 Claims.

My invention relates. to electric discharge devices, and more particularly to electric discharge lamps of the high pressure type such as high pressure capillary lamps.

Heretofore, where it has been desired to modify or supplement the radiation produced by an electric discharge through mercury by the addition of metals such as zinc or cadmium or both, much difllculty has been encountered due to the tendency of the amalgams to solidify thereby interfering with and hindering the initiation and maintenance of the arc discharge. In some types of prior art lamps employing amalgams, such as capillary lamps, upon solidification and formation into globules, the amalgam tended to form and roll into positions away from the electrodes, in which situations starting of the lamps was difficult. Furthermore, the prior art attempts to modify the mercury arc spectrum by the use of amalgams in place of mercury alone have left much to be desired from the standpoint of approximating a continuous spectrum where it is desired to produce a concentrated high intensity light source suitable for use in connection with picture projection such as in colored motion picture projection systems, and the like, wherein a well balanced spectrum is desired or required.

It is an object of my invention to provide a new and improved electric discharge device.

It is another object of my invention to provide a new and improved high pressure electric discharge lamp.

It is a further object of my invention to provide a new and improved high pressure electric discharge lamp of the capillary type employing an ionizable medium comprising mercury, zinc and cadmium in optimum proportions to produce an improved spectrum.

In accordance with my invention, I provide a new and improved electric discharge lamp of the high-pressure, high-intensity compact source type, wherein mercury, zinc and cadmium are used as an ionizable medium. By the use of optimum percentages of zinc and cadmium, I have obviated the prior art difficulties previously encountered in initiating and maintaining an arc discharge in amalgams. In addition, I have found that the spectrum of the radiation produced nicely approximates or approaches a continuous spectrum, and contains a marked line of radiation within the green region of the spectrum as well as substantial radiation in the red region, without incurring an inordinate reduction in efficiency, which has heretofore been considered a serious disadvantage in the use of amalgams.

More particularly, I have found in the development of my invention, that I can use greater amounts of both zinc and cadmium, than would normally be expected on the basis of prior art investigations, without encountering difliculties in starting and maintaining an arc discharge in the amalgam. As an example, I have found that where mercury, zinc and cadmium are employed as an ionizable medium, I obtain highly satisfactory arc starting and maintenance conditions where the individual percentages by weight of the zinc and cadmium with reference to the total amalgam, do not exceed 11.1 per cent.

In operation of electric discharge lamps employing the above described amalgam, highly satisfactory results are obtained when the operating pressure of the lamp is at or above '75 atmospheres, and preferably in the neighborhood of atmospheres. Under such conditions, and in view of the physical structure incident to capillary lamp design, it is seen that the interior wall loading of my lamp is greatlyin excess of that present in the prior art devices using amalgams. For example, in one type of lamp built in accordance with my invention, the interior wall loading of the lamp is approximately 4000 watts per square inch. In view of this fact, I may use cooling means for the lamp in order to dissipate the incident heat and maintain the wall temperature within a suitable range.

A still further feature of my invention is the greatly improved spectrum produced by the use of an amalgam containing zinc and cadmium within the above stated range. I have found that by the Joint use of zinc and cadmium, the spectrum of visible radiation contains substantial improvements not present when either Zinc or cadmium is used alone in an amalgam. More specifically, by using both zinc and cadmium in amounts within the above mentioned range, I have observed in tests conducted on lamps built in accordance with my invention, that there is a marked line of radiation within the green region, i. e., within the vicinity of the 5000 Angstrom unit line and particularly at and above this line, which is not present when either zinc or cadmium is used alone in an amalgam. Moreover, there is a substantial increase in radiation within the red region of the spectrum over that present where either zinc or cadmium is used alone in an amalgam.

For a better understanding of my invention reference may be had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the 3 appended claims. Fig. 1 illustrates one type of high pressure lamp construction to which my invention may be applied. Figs. 2-5 inclusive represent spectra data predicated on high pressure lamps which data serve to explain the improvements in spectra obtained by using particular amalgams; andFig. 5 is a spectrum of a high pressure lamp constructed in accordance with my invention showing the increased radiation within the green and red regions of the spectrum.

In Fig. 1, I have illustrated one type of electric discharge lamp in which my invention may be used, together with supporting and cooling structure therefor. The electric discharge lamp I may be 01. the general type disclosed and claimed in U. S. Patent No. 2,094,694, granted October 5, 1937, upon an application of Cornelius 301 et 81., and which is assigned to the assignee of this application. A pair of electrodes are constituted by the inner extremities of suitable high temperature resisting wires or conductors, such as

tungsten conductors

2 and 3, and sealed into the ends of an elongated tubular envelope 4 which is constructed of a high temperature resisting and transparentmaterial such as highly refractory glass, quartz or the like. The ends 01' each of the electrodes project short distances from the amalgam, described hereinafter, and which is preferably positioned about the electrodes.

Supporting and coolin structure for the lamp assembly may include a pair of end members or plates 6 and I, the former of which is constructed of insulating material such as Textolite and the latter of which may be of metal such as brass to serve as one of the electrical connections to the lamp assembly. The plates 6 and 1 are held in position by retaining bolts 8 and 9 which are insulated from the metal plate I by ceramic bushings l and II. Rubber gaskets (not shown) are inserted between the ends of a glass tube i2 to provide a water-tight enclosure and seal about the lamp 1 and external electrode supporting structure to be described presently.

A water intake tube 13 of metal is mounted on and extends into and is seated in plate 6, and communicates with the interior of tube i2. A spring biased socket I4 is mounted in the intake tube [3 and extends into the glass tube i2 to accommodate and engage a metallic cylindrical terminal i of the lamp, which terminal is electrically connected to the conductor 2 and is cemented to the associated end tubulation of the lamp. The other end of lamp I is supported in the position shown by means of a slotted metal sleeve socket l6 which serves as a stationary contact adapted to receive lamp terminal I! which is connected to conductor 3 and constitutes an I ing and cooling structure for the lamp i, the velocity tube construction disclosed and claimed in U. S. Patent No. 2,295,046, granted September 8, 1942, on my application, and which is assigned to the assignee of this application.

Electrical connections to the assembly may be made to the lamp through plate 1 and the exposed portion of the intake tube iii, the latter of which may be electrically insulated by a rubbet water-inlet tube (not shown) to eliminate personnel hazard. If desired, an insulating cap 19 and a contact assembly including an insulated bushing 20 containing a brass terminal connector 2| in contact with the tube It and socket It may be employed to serve as one connection to the lamp. An insulated conductor (not shown) may be connected to connector 2 l.

I provide an ionizable medium 22 which aflords improvements in the radiation in the visible range and which approximates a continuous spectrum. In addition the ionizable medium, described immediately hereinafter, also radiates in the longwave ultraviolet. Heretofore, where cadmium and zinc were added to mercury in attempts to improve the spectrum of the emitted radiation, difliculties were encountered due to the fact that the amalgamssolidifled thereby preventing the lamp or lamps from being started in a normal and satisfactory manner.

I have found that by using both zinc and cadmium in an amalgam, I can add larger quantities of these metals than could be added separately heretofore, and still obtain a liquid amalgam which will permit the lamp to start and operate in a normal manner. I also employ a charge of gas, preferably rare gas, at a low pressure to facilitate starting of the discharge across the space operating the electrodes. A charge of argon, for example, at a pressure of a few millimeters to several centimeters of mercury is satisfactory for this purpose.

The amalgam may be located as illustrated in slightly enlarged spaces at the ends of the discharge chamber, and the ends of the electrodes extend short distances beyond the amalgam, defining therebetween the arc discharge path.

In order to prevent devitrification of the enclosing envelope 4, where it is constructed of quartz, I may employ as an internal coating the glaze or protective coating disclosed and claimed in my icopending patent application Serial No. 560,775, filed October 28, 1944, now abandoned, and which is assigned to the assignee of this application.

I have found that by adding zinc and cadmium at the same time I can add more of these metals to the mercury than previously could be employed separately without encountering the above mentioned difficulties in maintaining the atrial-- gam in liquid form. In other words, I maintain the amalgam in liquid form even though relatively high percentages of zinc and cadmium are employed, and still obtain satisfactory starting and operation of the high pressure lamp.

Furthermore, I have found that zinc and cadmium influence each other so that lines appear very prominent in the spectrum, which lines are insignificant in the spectrums of either cadmiummercury or zinc-mercury amalgams. This fact is substantiated by reference to Figs. 24 inclusive which are based on observed values obtained from tests conducted on lamps containing as ioni'zable mediums mercury, cadmium-amalgam and zinc-amalgam, respectively. More particu-- larly, in connection with Fig. 2 it will be observed that the mercury spectrum is deficient in radiation in the green region of the spectrum, that is within the vicinity of the 5000 Angstrom unit line. Furthermore it is to be observed that the radiation within the red region of the spectrum, is also relatively low. The above-mentioned deiiciencies in the green and red region are also apparent in the cadmium-amalgam spectrum shown in Fig. 3. Moreover. in the zinc-amalgam spectrum shown in Fig. 4 it is also evident that there is relatively little radiation within the green and red regions of the spectrum.

However, as is supported by Fig. 5, the particular combination of mercury, cadmium and zinc produces a spectrum with lines spaced at conveniently close intervals throughout the spectrum and with improved amounts of radiation within the green region, that is at 5000 Angstrom units and above, as well as improved radiation within the red region.

I have found that the improved spectrum with augmented radiation in the green and red regions is obtained by employing amalgams in which the individual percentages by weight of the zinc and cadmium do not exceed 11.1 per cent of the total and wherein the lamp operates at pressures at or above 75 atmospheres. As supported by Fig. 5 it is also clear that the improved spectrum is obtainable by employing amalgam wherein the individual percentages by weight of the zinc and cadmium are in the neighborhood of 5 per cent of the total amalgam. Tests conducted in accordance with my invention indicate that the above-described improvements in spectrum without sacrificing starting and operating conditions are readily obtainable by operating the lamps at pressures within the neighborhood of 100 atmospheres.

In one type of discharge lamp in which my invention has been incorporated, the internal bore of the envelope 4 is approximately 1.8 to 2.2 mm., and the distance between the electrodes or the discharge path is about 25 millimeters. Such lamps have been operated at 1000 watts input, producing spectra such as that shown in Fig. 5. Due to the relatively high internal wall loading, which is approximately 4000 watts per square inch, the cooling structure as shown in Fig. 1 is entirely satisfactory to maintain the wall temperature within a range of values which afford satisfactory life for the lamps.

The above-described lamps offer important ad vantages for those fields of application where it is desired to use a mercury type lamp with a modified color. I have also found that some of the lines in the long-wave ultraviolet have been enhanced so that a lamp of this type will afford improved results in the field of blue-printing and photo-engraving as well as in the colored motion picture field.

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

1. In a high pressure electric discharge lamp of the capillary type, the combination comprising an envelope transparent to visible radiation and capable of defining an arc discharge chamber at pressures at or above 75 atmospheres, a pair of electrodes sealed in the ends thereof, an ionizable medium comprising mercury, and zinc and cadmium in about equal percentages which obviate the formation of solid amalgams to permit normal starting and operation of the lamp and to produce substantial radiation within the region of the 5000 Angstrom unit line, the internal wall loading of said envelope being in the neighborhood of 4000 watts per square inch.

2. In a high pressure electric discharge lamp of the capillary type, the combination comprising an envelope, a pair of electrodes within said envelope, and an ionizable medium for supporting an arc discharge and operable at pressures within the neighborhood of 100 atmospheres, said medium comprising mercury, zinc and cadmium wherein the individual percentages by weight of 6 zinc and cadmium are approximately equal and do not exceed 11.1 per cent of the total to obtain substantial radiation within the vicinity of the 5000 Angstrom unit line, the internal wall loading of said envelope being in the neighborhood of 4000 watts per square inch.

3. In an electric discharge lamp of the capillary type for emitting radiation within the visible part of the spectrum, the combination comprising an envelope, a pair of electrodes sealed in said envelope, and employing an ionizable medium at an operating pressure at or above 75 atmospheres, said ionizable medium comprising mercury, zinc and cadmium, the individual percentages by weight of zinc and cadmium are approximately equal and not exceeding 11.1 per cent of the total to afford substantial radiation within the green and red regions of the spectrum, the internal wall loading of said envelope being in the neighborhood of 4000 watts per square inch.

4. In an electric discharge lamp of the capillary type, the combination comprising an elongated envelope pervious to visible radiation and capable of defining an arc discharge chamber at pressures in the neighborhood of atmospheres, a pair of electrodes sealed in the ends thereof, an ionizable medium comprising mercury, zinc and cadmium wherein the zinc and cadmium individual percentages by weight are approximately 5 per cent of the total to produce substantial radiation within the green portion of the spectrum.

5. In an electric discharge lamp of the capillary type, the combination comprising an elongated envelope transparent to visible radiation and capable of defining an arc discharge chamber at pressures above 75 atmospheres, a pair of electrodes sealed in the ends thereof, an ionizable medium comprising mercury, zinc and cadmium wherein the zinc and cadmium individual percentages by weight are about equal and are approximately 5 per cent of the total to afford substantial radiation within the green and red regions of the spectrum.

6. In an electric discharge lamp of the capillary type, the combination comprising an elongated envelope transparent to visible radiation and capable of defining an arc discharge chamber at pressures above 75 atmospheres, a pair of electrodes sealed in the ends thereof, an ionizable medium comprising mercury, zinc and cadmium wherein the zinc and cadmium individual percentages by weight are approximately equal and do not exceed 11.1 per cent of the total to produce substantial radiation within the red and green regions of the spectrum, the internal wall loading of said envelope being approximately 4000 watts per square inch.

7. A high pressure electric discharge lamp of the capillary type comprising an envelope transparent to visible radiation, a pair of spaced electrodes within said envelope, and an ionizable medium within said envelope and consisting of a starting gas, mercury, zinc and cadmium, the individual percentages by weight of zinc and cadmium being approximately 5 per cent of the total amalgam, the wall loading being such as to produce vaporization of the zinc and the cadmium to produce substantial radiation within th green and red regions of the spectrum.

EDWARD B. NOEL.

(References on following page) 1 REFERENCES CITED The following references are of record in the Number me of this patent: 495,632

UNITED STATES PA'I'ENTS 6 526340 Number Name Date 2,150,007 Ryde Mar. '7, 1939 2,152,987 Dorgelo et a1 Apr. 4, 1939 2,272,487 Kern et a1 Feb. 10. 1942 10 FOREIGN PATENTS Country Date Great Britain Nov. 16, 1938 Great Britain Sept. 28, 1940