US3514660A - Electric discharge flicker lamp - Google Patents

Description

May 26, 1970 B. KOPELMAN 3,514,650

ELECTRIC DISCHARGE FLICKER LAMP Filed July 10. 1968 FIG.3

INVENTOR BERNARD KOPELMAN BY ATTORNEY United States Patent 3,514,660 ELECTRIC DISCHARGE FLICKER LAMP Bernard Kopelman, Salem, Mass, assignor to Sylvanza Electric Products Inc., a corporation of Delaware Filed July 10, 1968, Ser. No. 743,753 Int. Cl. H01j 17/20 US. Cl. 313-185 8 Claims ABSTRACT OF THE DESCLOSURE The electrodes of a flicker lamp are coated with a mixture comprising an alkaline earth azide and an alkaline halide. The use of a halide enables the lamp to flicker in the presence of nitrogen and thereby permits such lamps to be manufactured on continuous sealing machines.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to electric dischargre lamps intended to simulate the flickering effect of a candle flame. Such lamps are primarily used for their aesthetic value, with the amount of illumination being a secondary consideration.

DESCRIPTION OF THE PRIOR ART Both patents emphasize the criticality of the heating process which breaks down the barium azide to an electron-emissive form of barium. In addition, the nitrogen content of the lamp fill must be extremely low, below readily detectable quantities, in order for the lamps to flicker satisfactorily. Amounts of nitrogen above a trace generally cause lamps to glow steadily rather than flicker randomly.

Such criticality and sensitivity to nitrogen reduces the likelihood of successfully manufacturing flicker lamps on automatic production sealing machines where rapid exhaust and flush cycles preclude the probability of complete removal of nitrogen, especially if, for economic reasons, nitrogen is used as a flush gas. In addition, the extreme dependency of the flickering effect on a minute nitrogen content in the lamp often results in low yields of first quality lamps. Or else, after several hundred hours of operation, the flickering or unstable glow discharge can become a steady or stable glow discharge, as nitrogen from the electrode coating is evolved in gaseous form into the lamp fill. The easily ionizable nitrogen lowers the high ionization potential of the gas fill, usually neon, sufliciently to cause the undesired stable glow discharge.

SUMMARY OF THE INVENTION This invention relates to a flicker lamp capable of being successfully manufactured on automatic exhaust and sealing machines. This result is attained by making a lamp which can flicker satisfactorily in the presence of small but readily detectable quantities of nitrogen. The toleration of the lamp for small quantities of nitrogen can result in higher production rates by permitting the use of gas flames in exhausting the lamp and breaking down the electrode coating. Gas flames are preferred on exhaust and sealing machines since they are faster heating and less cumbersome than, say, electrically operated heating ovens.

I have found that if a small quantity of a metal halide is included in an azide electrode coating, the breakdown of the coating need not be carried to completion in order to obtain a satisfactory flicker lamp. The halide enables the lamp to be operated satisfactorily in the presence of significant quantities of nitrogen. Such nitrogen can be present in the electrode coating as, probably, the nitride, or in the lamp fill as gaseous nitrogen. However it is likely that, in operation, the nitrogen would be present in both states since an equilibrium would be established between the nitride in the electrode coating and the gaseous nitrogen in the lamp fill.

Gas flames are applied to the lamp envelopes at a predetermined number of successive stations on the exhaust machine until the electrode coating changes from a white to a black color. After these stations, the breakdown process, that is, the heating, is discontinued. Even though, at this point, there is only incomplete evolution of nitrogen from the electrode coating, the remaining nitrogen will not be detrimental to lamps made according to this invention.

Lamps made in accordance with this invention will operate satisfactorily in the presence of significant quantities of nitrogen, expressed as a percentage of the lamp fill, of up to 0.05% or 0.10% or even higher. Such quan tities are readily detectable by means of a high frequency test coil applied to the lamp. The color of the glow discharge of lamps containing such quantities of nitrogen is bluer than that of lamps containing considerably less nitrogen. For example, in a flicker lamp filled with neon only, the color of the glow discharge is orange. In a lamp whose fill contains, in addition, 0.05% nitrogen, the color of the glow discharge is pink.

A flicker lamp made in accordance with this invention has electrodes coated with a low work function coating that includes about 0.5 to 50% by weight of a metallic halide. Preferably the metal constituent of the halide is an alkali or alkaline earth metal. For example, if the coating is a mixture of barium azide and cesium azide, then the halide can be that of barium, strontium, calcium, cesium and the like. Preferably, however, in this example, barium iodide is used, in an amount about 2% by weight of the barium-cesium azide.

After the electrodes have been coated and inserted in a lamp envelope, the azide must be decomposed by heat to an electron emitting state that is probably a combination of free barium and barium nitride; considerable amounts of nitrogen are evolved during decomposition. The transition is indicated by a change in the color of the coating from white to black. After the coating has been decomposed and the envelope exhausted, the lamp is filled and sealed. The fill can be a difiicultly ionizable gas such as neon or helium. The preferred filling however, is neon at a pressure of about 110 mm. of mercury.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front view of a flicker lamp in accordance with this invention, the envelope being transparent to show the electrodes.

FIG. 2 is a side view of the same lamp.

FIG. 3 is an elevational view of a lamp in which the envelope is covered with glass beads to diffuse the glow of the discharge.

DESCRIPTION OF THE PREFERRED EMBODIMENT function coating 8 which, under the influence of an electrical potential between electrodes 4, causes an unstable glow discharge therebetween. Coating 8 is deposited on electrodes 4 from a solution having the following compositions:

552 ml. of barium azide solution 15 ml. of cesium azide solution 2 gm. of barium iodide 100 ml. of anhydrous ethyl alcohol The barium azide solution consists of 17% by weight of barium azide in water and the cesium azide solution is 50% by weight of cesium azide in water.

Electrodes 4 are made of mil thick perforated iron sheet and are about one inch long; the ends are rounded and the width tapers from inch to A1 inch. The perforations increase the viewable amount of the discharge. The large end of electrode 4 is welded to lead-in wire 5 which is embedded in stem mount 7.

The electrodes are coated by dipping about A of their length into the coating solution, mount 7 serving as a convenient holder for this purpose. During this operation the gap between electrodes 4 is greater than the desired finished gap to avoid excessive solution pickup therebetween. Electrodes 4 are then dried in an oven at 90 C. for about minutes. The resultant coating 8 on electrodes 4 consists of a thin uniform layer, about 1 mil thick, of white crystals. Electrodes 4 are then pressed together to a spacing, substantially parallel, of /2 mm.

Mount 7 is then sealed to envelope 2 with electrodes 4 protruding into the interior of the envelope. The sealing flames used are small and pointed in order to avoid overheating the electrodes.

Envelope 2 is then placed in the head of an exhaust machine operating at the rate of 900 indexes per hour and, by means of an exhaust tube (not shown) on mount 7, envelope 2 is exhausted to a vacuum of about microns. The envelope is then flushed with nitrogen and after repeated steps of exhausting and flushing, the last two flushes being with neon, the envelope is heated with gas flames at four successive stations on the machine. The strength of the flames is adjusted so that, at the fourth station, the color of coating 8 changes from white to black.

The envelope is then filled with neon to a pressure of 110 mm. and tipped ofi. Base 3 is then attached to the tipped-off end of envelope 2, with the usual electrical connections being made to lead-in wires 5. In the electrical circuit between base 3 and one of lead-in wires 5, but attached to mount 7 within the envelope, is located 7000 ohm carbon resistor 6. The resistor is necessary to limit the current between electrodes 4 and to obtain a satisfactory flickering effect in the finished lamp.

In order to ditfuse, and enhance the appearance of, the flickering glow discharge, the exterior surface of envelope 2 may then be covered with glass beads as shown in FIG. 3, a process such as that disclosed in patent application 634,542 filed on Apr. 28, 1967 by Russi.

In order to show the advantage of the halide in the electrode coating, especially in lamps containing small but detectable quantities of nitrogen, the following test was made: 25 lamps, designated as Lot A, were made as described above. The electrode coating was the abovementioned barium-cesium azide mixture, containing 2% barium iodide. The fill gas was 99.95% neon0.05% nitrogen at a pressure of mm. Twenty-five lamps, designated as Lot B, were identically made, but without the barium iodide.

All 50 lamps were operated continuously at their rated voltage, volts, for hours and then examined. Twenty-four of the 25 lamps in Lot A continued to flicker satisfactorily versus only 12 of the 25 lamps in Lot B. Expressed as percentages, 96% of the Lot A lamps were still good against only 48% of the Lot B lamps. The lamps that failed had either a steady glow discharge or no discharge at all.

Moreover, the flickering rate, after 150 hours of operation, of the Lot A lamps was higher than that of the Lot B lamps. The Lot A lamps averaged about 120 to 150 flickers per minute versus only about 20 to 60 for the Lot B lamps. Since the initial flickering rate for all lamps was generally over 100, the rate decrease for the Lot B lamps was appreciable, averaging about two-thirds.

It is apparent that modifications and changes may be made within the spirit and scope of the invention, but it is our intention only to be limited by the spirit and scope of the appended claims.

I claim:

1. A gas discharge flicker lamp comprising: a glass envelope having a fill including neon or helium; two metal electrodes disposed within but spaced from said envelope, said electrodes having a coating thereon comprising a mixture of alkaline earth or alkali halide and partially decomposed alkaline earth azide; and means for electrically energizing said electrodes.

2. The lamp of claim 1 wherein the weight of said halide is about 0.5 to 50% of the weight of said alkaline earth azide.

3. The lamp of claim 2 wherein said halide is barium iodide.

4. The lamp of claim 2 wherein said alkaline earth azide is barium azide.

5. The lamp of claim 2 wherein said electrodes comprise parallel perforated sheet metal plates.

6. The lamp of claim 2 wherein said fill includes a significant quantity of nitrogen.

7. The lamp of claim 6 wherein said quantity of nitrogen is less than about 0.1% of said fill.

8. The lamp of claim 7 wherein the pressure of said fill is about 110 mm.

References Cited UNITED STATES PATENTS 3,238,408 3/1966 Kayatt 313 RAYMOND F. HOSSFELD, Primary Examiner US. Cl. X.R.

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