GB2083696A - Electric lamp and method of manufacturing same - Google Patents

Abstract

An electric lamp whose envelope 60 has at least two sections 62, 64 which are hermetically joined together, in which the envelope preferably has a coating 67 of a visible light transmissive and infrared reflective material thereon and in which the sections can be optically treated to accept and enhance the effectiveness of the coating. A method is also disclosed for making lamps using the multi-section envelope in which the envelope sections are hermetically sealed together after the envelope is exhausted or sealed in an environment the same as that to be contained within the envelope. <IMAGE>

Description

SPECIFICATION Electric lamp and method of manufacturing same Various types of energy conserving incandescent lamps having means, such as a coating, thereon for reflecting infrared (IR) radiation back to the filament and for transmitting visible light are known. One such lamp is shown, for example, in U.S. Patent 4,160,929 granted July 1979 to Thorington, et al.

The energy conserving incandescent lamps of the aforesaid patent, as well as others, for various reasons preferably place the coating on the inner surface of envelope, although it can be placed on the outer surface. Several coatings are shown, for example, in the aforesaid patent 4,160,929 to Thorington, et al.

Most incandescent lamps utilizing an IR reflectivevisible energytransmissive coating operate on the same general principle. That is, the coating is placed on an optically curved surface, generally the envelope, and the filament is located with respect to the envelope curved surface so that the infrared radiation will be reflected by the coating to impinge upon the filament and raise its operating temperature. This reduces the amount of power needed to raise the filament to its operating temperature thereby improving the operating efficiency of the lamp. The filament is preferably of a compact type, made as closely resembling a point source as possible. In theory, the filament should be optically centered with respect to the envelope to optimize the return of the IR radiation.In another type of lamp, the filament is deliberately placed off center of the envelope optical axis. While in the lamp of the latter application the impingement of IR energy on the filament occurs after two or more reflections of the IR energy from the coating, the IR reflective efficiency of the coating is sufficiently high so that the lamp is still energy efficient. The off-center mounting of the filament reduces manufacturing problems associated with centering the filament.

It is preferred to apply the IR reflective coating, sometimes called a heat mirror, to the envelope's interior wall. This eliminates mechanical and chemical reactions of the coating with the external environment, which are known to cause degradation of the coating, as compared to the relatively benign environment of inert atmosphere internal of the lamp. Also, a coating on the inner wall avoids the heat loss occurring when infrared radiation is partly absorbed by the lamp envelope.

Although a coating on the interior of the envelope is preferable, it is more difficult to deposit a homogeneous coating on the interior of a conventional envelope, of spherical, or some other, shape than on its exterior. For example, in a film having multi-layers, such as disclosed in U.S Patent 4,160,929, one method for depositing the coating, is by radio frequency (RF) sputtering. Substantial inhomogeneities develop with interior wall coatings when the targets are inserted and operated in the confined space of a conventional spherical envelope.

This is generally due to the physical constraint of positioning and moving the targets through the narrow opening of the neck and restriction of the gas flow. Consequently, in such conventional envelopes coatings are more readily laid down on the envelope outer surface. In addition, the inner surface of a lamp of conventional shape, has surface irregularities, such as peaks and valleys, which are produced when the envelope is manufactured by conventional processes. Such surface irregularities are of no consequence in a conventional incandescent lamp.

However, where the IR reflective-visible transmissive coating is to be deposited on such a surface, the efficiency of IR reflectivity is reduced.

Accordingly, the present invention relates to an incandescent lamp having an IR reflective-visible transmissive coating on its interior wall in which the envelope is formed of multi-sections which are joined together and a method of making such a lamp. The use of an envelope formed of multisections permits various advantages to be obtained.

For example, the interior wall of each section can more readily be processed with a higher quality optical finish to remove surface irregularities. This increases the IR reflectivity from the coating deposited thereon. Further, it is also easier to deposit the coating on the inner surface of each section since there is no constraint with respect to, for example, the narrow neck of a conventional incandescent lamp envelope. The multi-sectioned construction also lends itself to novel and improved filament support and filament mount configurations which reduce energy losses associated with conventional constructions. Further, the multi-section envelope approach also lends itself to new and novel techniques with respect to assembling lamps and for sealing the same.

In the drawings Figure 1 is an elevational view, partly in section, showing a prior art type incandescent lamp.

Figure 2 is a view of a multi-section lamp in accordance with the invention in which the envelope is of generally spherical shape; Figure 3 is an incandescent lamp in which the envelope is multi-section and is of generally ellipsoidal shape; and Figures 4-6 are views of various forms of filament mounting arrangements which can be used with multi-section envelopes; and Referring to Figure 1, there is shown a prior art type of incandescent lamp of the type under consideration. The lamp 10 includes a generally spherical envelope 11 having thereon on the interior wall of the envelope a coating 12 of the types previously considered with respect to U.S. Patent 4,160,929, having a multiplicity of discrete layers.

The lamp envelope has a narrowed down neck terminating in a base which includes a threaded metallic socket 14 and a conductive contact tip 16 which is insulated from the socket. Attached to the tip 16 and socket 14 are a pair of conductive leads 17 and 18 which pass through a stem 19 having a tubulation 20 which is used to seal off the envelope.

Connected to the leads 17 and 18 is a coiled-coil or triple coil type filament 22 which is located at the optical center of the envelope or off of the axis. The filament is preferably made compact, i.e. has a small length to diameter ratio. A reflector 25 of part spherical shape is mounted on the stem 19 to complete an overall spherical surface for the envelope.

In operation, current is supplied to the filament 22 through the electrical contacts 14 and 16 and the leads 17 and 18. The current causes the filament 22 to incandesce and produce energy in both the visible light range and in the infrared range of wavelengths.

The coating 12 on the envelope 11 reflects a large portion of the IR energy back toward the filament due to the curvature of the envelope 11 and the location of the filament 22. The IR energy returned to the filament raises its operating temperature thereby improving the efficiency of the lamp since less current is needed to raise the filament to its operating temperature. At the same time, the coating 12 permits a large portion of the energy in the visible light range produced by the filament to pass through for illumination purposes. The reflector 25 is also coated to reflect IR energy back toward the filament.

It is located at the base of the envelope where visible light cannot be transmitted and it need not transmit visible energy.

As explained previously, it is preferred that the coating 12 be placed on the inner surface of the envelope although it can be located on the outer surface. However, as also explained previously, due to the narrow neck of the envelope it is difficult to deposit a homogeneous coating, particularly a multilayer coating onto the envelope inner wall. Also, the finish of the interior wall is not optically precise.

Figure 2 shows an illustrative embodiment of a lamp 30 according to the present invention in which the envelope 32 is of generally spherical shape. The envelope has a plurality of sections, here shown as two, of generally hemispherical shape 33 and 34.

More than two sections can be used but an increase in the number of sections makes sealing more difficult. The envelope sections 33 and 34 are of a suitable glass material, for example, PYREX, (Registered Trade Mark) lime glass, optical glass, etc. The type of glass is not critical to the invention as long as it has cost effectiveness and also, preferably, it can be optically polished. The two sections 33 and 34 are joined together along a seam line 35 which defines a hermetic seal.

Located within the envelope 30 is the filament 40 which is held by stem leads 42 and 44. Afurther support lead 46 of conductive or non-conductive material is provided which is loosely placed around the elongated filament 40. The two leads 42 and 44 and the support wire 46 are fastened to a base 50.The filament is located on the base such that when the base is assembled to the lower section 34, the filament will be located at the proper position.

The support wire 46 minimizes motion of the filament during shipping and also guards against excessive sag when the filament is in the horizontal burning position. The base 50 is a circular "button" of glass or glass-compatible material. It includes a tubulation 52 through which the lamp can be exhausted and the tubulation tipped off in the usual manner The two envelope sections 33 and 34 are formed by any conventional glass making process, for example, molding, vacuum forming, blowing, etc.

By forming the envelope of two or more shaped pieces instead of one, it is possible to use glass fabrication techniques which yield superior reflectors compared with conventional blown bulbs, such as shown in Figure 1. For example, the internal surface of the reflector can be finished by grinding and polishing to produce an optical quality reflector.

The use of two or more sections to form the shaped envelope has further advantages in that it greatly simplifies the deposition of a uniform heat mirror coating on the inside surface since the coating can be done by a variety of sputtering, reactive evaporation or chemical vapour deposition techniques without the constriction of plasma or restriction in gas flow characteristic of a one piece envelope construction.

In assembling the lamp of Figure 2 the hemis pheres 33,34 are formed. The lower hemisphere 34 is processed to cut out an opening at its bottom, or at some other location, which conforms to the shape of the socket 50 and into which the socket 50 is inserted and sealed by any suitable technique, for example, by metalization and soldering of the edges, by the use of an adhesive or by the use of frit or solder glass. Hermetically sealed into the socket 50 are the lead wires 42 and 44 as well as the support lead wire 46.

The two hemispherical sections 33 and 34 are placed together. Preferably, before this is done, the edges of the hemispheres have been suitablytre- ated, for example, by polishing, to provide a smooth finish without jagged edges so that a good seal can be formed. The seal is made by metalization and soldering at these edges, by the use of an adhesive, for example, a polyamide or high temperature epoxy resin, or by the use of frit or solder glass.

After the seam has been made, the envelope is exhausted through the tubulation 52. If a fill gas is required for the lamp envelope, for example argon gas, it is inserted through the tubulation. The tubulation is then tipped off. After this is accomplished, the usual metal socket piece is connected, such as by an adhesive to the envelope, and the lamp is completed.

In assembling the base 50 to the lower section 34, the filament 40 is already precisely aligned so that when the base is inserted into the envelope and fastened thereto, the filament will be more or less at the optical center of the curved envelope.

As pointed out above, one of the advantages of manufacturing the envelope out of several sections is that a higher optical finish can be produced on the interior surfaces of the envelope than is possible with a conventional envelope with neck as shown in Figure 1. It should be understood that internal surface irregularities underneath the coating detract from the homogeniety of the coating and the focussing effect of the reflector and thereby reduce the efficiency of the envelope. It has been found that an envelope in which the interior surface on which the coating is laid down has been optically finished is substantially more efficient from the point of view of reflecting IR energy than a conventional blown envelope having surface irregularities.

Figure 3 shows a further embodiment of the invention wherein the envelope is ellipsoidal in shape. An ellipsoidal envelope in which an elongated filament is located such that the two foci of the ellipse are along the length of the envelope will minimize end and side aberrational losses of the filament.

In Figure 3, the envelope 60 is formed by two hemi-ellipsoid sections 62 and 64 which are joined together on a seam line 65 in the manner previously described. As before, sections 62 and 64 are preferably optically finished on the interior thereof to provide a better optical surface before the coating 67 is deposited.

In the embodiment of Figure 3, a different base 70 is shown which does not have a tubulation. The base 70 has two contact studs 76 and 78 sealed therein each having a head 80 at the lower end. The lead wires 42 and 44 are fastened for example, by spot welding, to the portion of the respective studs 76 and 78 which extend into the envelope. The support lead 46 is fastened only into the glass of the base 70.

Electrical contact is made for the filament 40 through the lead wires 42 and 44 and the respective stud connectors 80. The base 70 of Figure 3 also can be used with the spherical shaped envelope of Figure 2.

The base constructions 50 of Figure 2 and 70 of Figure 3 have further advantages in that the usual stem 19 of Figure 1 is not needed. This reduces the light and heat loss within the envelope.

In the lamp of Figure 3 or the lamp of Figure 2 using the base of Figure 3, final assembly is accomplished entirely within the machine used to seal the envelope. That is, as explained below, the sealing is accomplished in a portion of the machine which is either a vacuum or else is provided with the fill gas at the appropriate pressure. This is described in greater detail below.

Multi-piece envelope constructions such as shown in Figures 2 and 3 permit filament configurations where the support leads can be eliminated or at least the removal of the obstruction of the insulated support lead if the existing current leads are also used for support.

Referring to Figure 4, there is shown one-half of a section of an envelope in which a support wire 84 of non-conductive material is strung across the equatorial plane in approximately diametrical position and fastened to the envelope. The fastening is accomplished, for example, by adhesive or glass bonding to a surface of the envelope part. Figure 4A shows mechanical retention in a groove 86 located at each end of a diametrical line with each groove being covered during the final sealing process to make the lamp leak proof.

The support wire 84 can be tensioned with a spring member if necessary. On assembling the lamp the support wire is slipped into position in the vicinity of the middle of the filament and lies generally perpendicular to the filament. The filament is mounted with conventional lead wires, such as shown in Figure 2. More than one support wire may be employed to support or restrain filament movement.

Figures 5 and 5A show further embodiments of the invention which are possible with the multisectioned envelope construction. These embodiments eliminate some of the obstruction to IR reflection from the lead-ins to the filament. In Figures 5 and 5A, a filament is attached to current lead-ins 92,94 which extend across the plane separating the two pieces. The leads 92,94 can be extended beyond the lamp to provide the minimum obstruction of radiation. This is shown in Figure 5.

The leads can also be directed along the surface to a convenient location for a base. This is shown in Figure 5A. The filament arrangement of Figures 5 and 5A may be conveniently combined with the strung wire support as shown in Figure 6 to obtain an energy saving lamp configuration with minimum radiation obstruction for a supported filament.

Considering the lamp of Figure 2 which has the tubulation, to complete its processing, after the sections of the envelope have been joined together, the lamp is placed in a finishing chamber. At this time, the lamp has been sealed in, that is, the filament and the base 50 are joined to the envelope but the exhaust tubulation remains open.

The finishing chamber has attached to it a roughing pump and a high vacuum pump, both connected through suitable valving to provide alternate roughing and high vacuum conditions. Valving and connections to nitrogen and suitable fiiled gases are also provided along with an absolute pressure gauge for monitoring the fill pressure of the system.

The finishing chamber is also connected to a fill gas retrieval system which is connected through a valve to a suitable pump, for example, a two stage diaphragm pump. The output stage of the pump is connected to a diaphragm gas compressor which is in turn connected to a gas storage tank. The storage tank output is in turn connected back to the finishing chamber. The gas storage tank is also provided with connections to allow the continual replenishment of the storage tank.

A suitable laser, for example, a carbon dioxide laser is connected through beam benders in a suitable conduit to a focusing head having a lens.

The laser system focusing head previously has been aligned with the lamp tubulation which is inside of the finishing chamber.

The lamps are moved into the finishing chamber where they are rough pumped and then pumped to a high vacuum. At this point the high vacuum valve is closed and the chamber is back-filled with the fill gas at a desired pressure. The lamp pressure and the chamber pressure are now equal. The lamp exhaust tubulation is positioned by an externally actuated latching device and buib rotation is provided by a lamp car on the inside of the chamber.

The lamp exhausttubulation, which is of a heat sensitive glass material, is aligned with a window in the chamber through which the laser beam can enter. The window can be, for example, zinc selenide. The laser is actuated and the beam is directed to the tubulation. The tubulation is heat sealed and is now tipped off within the chamber and the fill gas at the proper pressure. If a number of lamps are being processed at the same time, when they all have been tipped off, the fill gas retrieval system pumps out about 95% of the remaining fill gas to the storage tank. The chamber is now vented back to the atmosphere with nitrogen and the tipped off lamps are removed.

The system and process described can be used to seal the lamps shown in Figure 2, whether these lamps are of ellipsoidal, spherical, or of some other shape.

A modified process is useful either with the tubulated lamps of Figure 2, in which the tubulation is sealed in the manner already described or with the lamp of Figure 3 in which no tubulation is provided.

In both cases, it is assumed that the lamp is in the finishing chamber and has been pumped out and then back filled with the fill gas at the required pressure. Thus, the environment within the finishing chamber is the fill gas which can be the only gas which will permeate into the lamp envelope. Pumping out is done with the two envelope sections spaced apart and open facing each other. The equatorial region of the hemispheres have previously been coated with a suitable joining compound, i.e., epoxy, solder glass, solder, etc., or alternatively, a simple glass to glass seal may be made.

The hemispheres are brought together in a line with each other vertically adjacent the window through which the laser beam enters the chamber.

The lamp is then rotated and subjected to a continuous or pulsed laser beam. The heat generated causes the coated or uncoated sections of the equatorial region to heat up and allows the hemispheres to be joined forming a lamp in a fill gas atmosphere at the correct pressure and gas mixture.

The chamber is vented and the finished lamps are removed.

As should be apparent, novel electrical envelopes for electrical lamps having energy reflective coatings have been provided which give rise to advantages in mounting filament, processing, etc.

Claims (25)

1. An electric lamp comprising: an envelope of visible lighttransmissive material, the envelope being formed of at least two curved sections which are hermetically joined together, a source within the envelope for producing energy upon the application of electric current thereto with at least a portion of the energy being in the visible range, and means for connection of electric current supply to the source to cause it to produce light.

2. An electric lamp according to claim 1 wherein the source also produces energy in the infrared region and further comprising on the inner wall of the envelope a coating of a material fortransmitting light in the visible region and for reflecting energy in the infrared region.

3. An electric lamp according to claim 2 wherein the envelope is shaped so as to redirect incident infrared energy back to the source.

4. An electric lamp according to any one of claims 1 to 3 wherein the source comprises an incandescent filament.

5. An incandescent lamp according to claim 1 wherein the interior of each of the sections is finished by an optical process to improve its reflectivity property.

6. An electric lamp according to claim 2 or 3 wherein the interior of each section beneath the coating thereon is finished by an optical process to improve its reflectivity property.

7. An electric lamp according to claim 4wherein the means for connection to electric current supply comprises a base of electrically insulating material formed as a separate unit, one of the envelope sections having an opening therein and the base being hermetically sealed in the opening, the base having electrically conductive lead means extending therethrough and the filament being connected to the lead means interior of the envelope.

8. An electric lamp accoding to claim 7 comprising further means attached to the base for supporting the filament.

9. An electric lamp according to claim 4,7 or 8 further comprising means mounted to one of the envelope sections for supporting the filament.

10. An electric lamp according to claim 9 wherein the said section is formed with a groove at the intersection of a plane across the envelope, and the support means comprises a wire mounted in the groove.

11. An electric lamp according to claim 10 wherein the wire is mounted under tension.

12. An electric lamp according to claim 9 wherein the support means comprise a wire which extends across the envelope section at the end thereof and is attached thereto.

13. An electric lamp according to claim 1 wherein the source comprises an elongate incandescent filament, a lead wire connected to each end of the filament, the lead wires extending across a section of the envelope.

14. An electric lamp according to claim 13 wherein the lead wires exit from the lamp generally radially with respect to the envelope section.

15. An electric lamp according to claim 13 wherein the lead wires are laid along the wall of the envelope section generally to follow its contour.

16. An electric lamp substantially as described with reference to and illustrated in any one of Figures 2 to 6 of the accompanying drawings.

17. A method of manufacturing an electric lamp, comprising the steps of providing an envelope of glass in the form of several sections, placing a source of energy within said envelope, evacuating the envelope, and hermetically sealing the several sections together.

18. A method according to claim 17 further comprising, prior to the step of sealing the sections together, the step of coating the interior of each section with a material which transmits energy in the visible light range and reflects energy in the infrared range.

19. A method according to claim 18 further comprising the step of optically conditioning the interior of the sections prior to coating.

20. A method according to any one of claims 17 to 19 wherein the step of evacuating the envelope comprises providing the envelope with a tubulation and exhausting the interior of the envelope through the tubulation after the sections of the envelope have been hermetically sealed, and sealing the tubulation.

21. A method according to claim 20 further comprising the step of placing a fill gas within the envelope prior to sealing the tubulation.

22. A method according to any one of claims 17 to 19 wherein the steps of sealing the sections and evacuating the envelope comprises placing the envelope sections unsealed in a chamber, placing a desired gaseous environment within the chamber and thereby also within the envelope, and then sealing the sections with the desired gaseous environment therein.

23. A method according to claim 22 wherein the step of placing the desired gaseous environment in the chamber comprises placing a fill gas therein.

24. A method according to claim 22 or 23 wherein the step of sealing comprises heating the sections with energy from a laser beam.

25. An electric lamp manufactured by the method claimed in any one of claims 17 to 24.