CA1179726A - Incandescent lamp with infrared reflecting coating and with envelope made of several sections and method of manufacturing same - Google Patents

Abstract

INCANDESCENT LAMP WITH INFRARED REFLECTING
COATING AND WITH ENVELOPE MADE OF SEVERAL
SECTIONS AND METHOD OF MANUFACTURING SAME

Abstract An electric lamp whose envelope has at least two sections which are joined together in which the envelope preferably has a coating 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.

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Description

117~37~
INCANDESCENT LAMP WITH INFRARED REFLECTING
COATING AND WITH ENVELOPE MADE OF SEVERAL
1 SECTIONS AND METHOD OF ~ANUFACTURING SAME
Background of Invention Various types of energy conserving incandescent lamps having means, such as a coating, thereon for reflect-ing infrared (IR) radiation back to the filament and fortransmitting visible light are known. One such lamp is shown, for example, in U.S. Patent 4,160,929 granted July 19, 1979 to Thorington, et al and assigned to the same assignee.
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 reflective-visible energy transmissive 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 neecled to raise the filament to its operating temperature thereby improving the operating efficiency oE 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. It is also possible to produce a satisfactory lamp in which the filament is deliberately placed off center of the envelope optical axis~ While in the latter type of lamp, the ..

~7~726 1 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 homogenous 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 inhomo-geneities develope 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 ~i'7972~
and valleys, wh}ch are p;oducc-d when the en~elope is m~nufdct~.red by conventional processes. Such surface irregularities are of no consequence in a cvnventional incandescent lamp. 'ow~ver, ~here the IR Leflective-visible tranmissive coating is to be de?osLted on s~cn a surface, the efficiency of IR reflc-ctivity is reduced.
Accordingly, tne present invention relates to an incandescent laJrlp having an IR reflective-vis'ble transmissive ccating on its interior wall in which the erl~elope is foriied of multi-sections which are joined together and a method of making such a lamp. The use of an envelope formed of multi-sections permits various advantayes to be obtained. Fo{ example, the lnterior 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 1~ thereon. Further, it is also easier to aeposit 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 suppoft and filament mount configurations which reduce energy losses associ-ated 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.
It is, therefore, an object of the present invention to 2a provlde an incarldescent lamp having an envelope of multi-sections.
A further object is to provide an incandescent lamp having an infrared energy reflective-visible transmissive coating on the envelope inner wall in which the envelope is of multi-sections.

An additional object is to provide a ger,erally spherical ~ ~ 79726 I or generally ellipsoidal envelope for an incandescent la~!p ~,nich is -ade of several sections joined toge.her with the filanent mo-~nted therein.
Yet another further object is to p:ovide an incandescent lamp having an envelope of multi sections, in which the sections are jo ned together by laser welding.
A further object is to provide an ir~ccndescent la,llp with an IR reflective-visible transmissive coating on tne interior surface of an envelope made of multi-sections.
]0 Other objects and advantages of the present invention will become more apparent upon re-Eerence to the following speci-fication and annexed drawings in which:
Fig. 1 is an elevational view, partly in section, showing a prior art type incandescent lamp.
Fig. 2 is a view of a multi-section lamp in accordance with the invention in which the envelope is of generally spherical shape;
Fig. 3 is an incandescent lamp in which the envelope is multi-section and is of generally ellipsoidal shape; and

2~ Figs. 4-6 are views of various forms of filament mount-ing arrangements which can be used with multi-section envelopes;
and Referring to Fig. 1, there is shown a prior art type of incandescent lamp of the type under consideration. The lamp 10 2~ inciudes a generally spherical envelope 11 having thereon on the interior wall of the envelope a coating 12 of the types previo~sly 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 1~'79'726 I in a base which incl~des a threaa-d ~etallic SGc~et 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 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 which is located at the optical ccnter of the envelope or off of the axis. T},e filament is prefer2bly made colT,pact, i.e. h2s a small lenoth to diameter ratio. A reflector 25 of part spherical shape is ]0 mounted on the stem l9 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 fi-lament 22 to incan2esce and produce l~ energy in both the visible light range and in the infrared range of wavelengths . The coating 12 on the envelope ll reflects a large portion of the IR energy back toward the filament due to the curvature of the envelope ll and the location of the filament 22. The IR energy returned to the filament raises its operating ~0 temperature thereby improving the efficiency of the lamp since less current is needed to raise the ilament to its operating temperature. At the same time, the coating 12 permits a large portion of the visible 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.

117'~72~i I As explained previously, it is preferred that the coating 12 be placed on ~he inner surface of the envelope alti-,ough it can be located on the outer surface. ~owever, as also explained previously, due to the narrow neck of the envelope it is difficult to deposit a hornogeneous coating, particularly a multi-lRyer coating onto the envelope inner wall. ~lso, the finish of the interior wall is not optically precise.
Fig. 2 shows an illustrative errlhodilnent of a larllp 30 according to the present invention in which the envelope 32 is of ]0 generally spherical shape. The envelope has a plurality of sections, here shown as two, of generally hemispherical si-ape 33 and 34. i~ore than two sections can be used but an increase in the number of sections ma~es sealing more difficult. The envelope sections 33 and 34 are of a suitable glass material, for example, PYREX, 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. A further sup?ort lead 46 of conductive or non-conductive material is provided which is loosely placed around the elongated filarnent 40. The ~wo leads 42 and 44 and the support wire 46 are fastened to a base 50 which is shown in greater detail on Fig. 2A. 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 suppor-t wire 46 minimizes motion of the filament during shipping and also guards against excessive sag when the filament is in the horizontal 1 burning position. The base 50 is a circular "b~tton" of glass or glass-co~patible material. It includes a tubulation 52 through which the lamp can be exhausted and the tubulation tipped off in the usual m,anner.
Tne two envelope sections 33 and 34 are formed by any conventional glass makiny process, for exanlple, molding, vacuum forming, blowing, etc. By forming tne enJelope of two or more shaped pieces instead of one, it is possible to use glass fabri-cation 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 evapora-tion or chemical vapor deposition techniques without the constriction of plasma or restriction in gas flow characteristic of a one piece envelope construction.

In assembling the lamp of Fig. 2 the hemispheres 33,34 are formed. The lower hemisphere 34 is processed to cut out an opening at its bottom, or at some other loction, which conforms to the shape of the socket 50 and into which t}-e socket 50 is inserted and sealed by any suitable technique, for example, by metalization and soldering of the edges, by the use of an adnesive 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 3~ are placed 1 rogether. Prefe~ably, before this is done, the eoges of the hc-J-nispheres have been suitably treated, for exa}nple, by polishing, to proviàe a smooth finish without jagged edges so that a good seal can be formed. The seal is ~,ade by i,ietali~ation and solder-a ing at these edses, by the use of an adhesive, ror e~ample, apolyamide or high temperature epoxy resin, or by the use of frit or solder glass.
After the seam has been made, the cnvelope is exhausted through the tubulation 52. If a fill gas is required ror 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 tne lamp is completed.
In assembling the base 50 to the lower section 34, the 1~ 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 manufactur-ing 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 Fig. 1. It should be understood that internal surface irregu-larities underneath the coating detract from the homogeniety of the coating and the focussing effect of the reflector and thereby 2~ reduce the efficiency of the c-nvelope. 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.

117972/~

1 Fig. 3 shows a further embodiment of the invention wherein the envelope is ellipsoidal in shape. As described in copending application Serial No. 076,368, filed September 17, 1979, which is asslcJned to the assignee of the subject application, 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 abberational losses of the filament.
In Fig. 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 Fig. 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 76 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 Fig. 3 also can be used with the spherical shaped envelope of Fig. 2. The base constructions 50 of Fig. 2 and 70 oE
Fig. 3 have further advantages in that the usual stem 19 of Fig. 1 is not needed~ This reduces the light and heat loss within the envelope.

_9_ i~17~2~

I In the lamp of Fig. 3 or the ]amp of Fig. 2 ~sing the base of Fig. 3, final assembly is accomplisrled entirely within the machine used to seal the envelope. That is, as explained below, the sealing is accom?lished in a port~on of the machine a which is either a vacuurn or else is provided with the fill ~,as at tne a~propriâte pressure. This is described in yLeater detail below.
r~ulti-piece envelope constructiorls such as shown in Figs. 2 and 3 enables filament configurations where the support ~o leads can be eliminated or at least the removal of the obstruc-tion of the insulated support lead if the existing current leads are also used for support.
Referring to Fig. 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 e~uaiorial plane an 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. Fig. 4A shows mechanical retention in a groove 86 located at each end of a diametrical line with 2() 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 lalnp the support wire is slipped into position in the vicinity of the middle of the 2a filament and lies generally perpendicular to ~he filament The filament is mounted with conventional lead wires, such as shown in Fig. 2. More than one support wire may be employed to support or restrain filament movementr Figs. 5 and 5A show further ernbodiments of the invention which are possible with the multi-sectioned envelope construction.

~17~3~7Z~;
These embodiments eliminate some of the obstruction to IR reflec-tion from the lead-ins to the filament~ In Figs. 5 and 5A, a filarrlent is attached to current lead-ins 92,~4 which extend across the plane separating the two p eces. The leads 92, 94 can be exter,ded beyond the lamp to pLovide the ,ninilTium obstruction of radiation. This is shown in Fig. 5. The leads can also be directed alc,ng the s~rface to a convenient locat~on for a base.
This is snown in Fig. SA. The filarnc-nt arrarlgeliient of Figs. 5 and 5A may be conveniently combined with the strung wire support as shown in Fig. 5B to obtain an energy saving lamp configuration ~ith minimum radiation obstruction for a supported filament.
Considering tr,e lamp of Fig. 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 ~5 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 ar,d a hiyh vacuum pump, both connected through suitable valving to provide alternate roughing and high vacuum conditions.
Valving and connections to nitrogen and suitable filled 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 2~ retrieval system which is connected through a valve to a suitable pump, for example, a two stage diaphragm pump. T}le output staye 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 ~ ~9726 1 storage tank is also provided with cornectior;s to allow the continual replenishir,ent of the storage tank.
A suitable laser, for example, a carbon dioxide laser is connected thLo~gh beam benders in a suitable conduit to a focusing head having a lens. The laser system focusing head previously has been aligned with the la-r,p tubulation which is inside of the finishing chamber.
The lamps are rnoved into the fin~shing chamber where they are rough pumped and then purnped to a high vacuum. At this point the high vacuum valve is closed and the charnber is back-filled with the fill gas at a desired pressure. The lamp pressure and the chamber pressure are now e~,ual. The lamp exhaust tubu-lation is positioned by an externally actuated latching device - and bulb rotation is provided-by a lamp car on the inside of the 1~ chamber.
The lamp exhaust tubulation, which is of a heat sensi-tive glass material, ls 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 a~l have been tipped off, the fill gas retrieval system pumps out about 95% of the remain;ng 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 larnps shown in Fig. 2, whether these lamps are of ellipsoidal, 7~i 1 spnerical, or of some other shape.
A modified process is useful either wi~h the tubulated lamps of Fig. 2, in which the tubulation is sealed in the r"anner already described or with the lamp of Fig. 3 in which no tubulation is provided.
In both czses, it is assumed tnat the lamp is in the finishing chamber and has been pum2ed out and then oack filled with the fill gas at the required pressure. Thus, the environment within the finishing chamber is the fill gas which can be the ]0 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 chan,ber is vented and the finished lamps are removed.
As should be apparent, novel electrical envelopes 2~ for electrical lamps having energy reflective coatings have been provided which give rise to advantages in mounting filament, processing, etc.

Claims (22)

WHAT IS CLAIMED IS:

1. An electric lamp comprising:
an envelope of visible light transmissive material, said envelope being formed of at least two curved sections which are hermetically joined together, a source within said envelope for producing energy in the visible and infra-red range upon the application of electrical current thereto, means for supplying electrical current to said source, and a coating of a material on the interior wall of said curved sections for transmitting light in the visible range and for reflecting energy in the infrared range back to said source.

2. An electric lamp as in claim 1 wherein said curved envelope sections are shaped so as to redirect the incident infrared energy back to said source.

3. An electric lamp as in claim 2 wherein said source comprises an incandescent filament.

4. An incandescent lamp as in claim 1 wherein the interior of each of said sections on which said coating is located has an optical finish to improve its reflectivity property to the infra-red energy.

5. An electric lamp as in claim 2 wherein the interior of each said section beneath the coating has an optical finish to improve its reflectivity property.

6. An electric lamp as in claim 3 wherein said means for supplying electric current comprises a base of electrical insulating material formed as a separate unit, one of said envelope sections having an opening therein and said base being hermetically sealed in said opening, said base having current carrying lead means extending there-through, said filament being connected to said lead means interior of the envelope.

7. An electric lamp as in claim 6 comprising further means attached to said base for supporting said filament.

8. An electric lamp as in claim 3 further comprising means mounted to one of said sections for supporting said filament.

9. An electric lamp as in claim 8 wherein the said one section is formed with a groove at the intersection of a plane across the envelope, said support means comprising a wire mounted in said groove.

10. An electric lamp as in claim 9 wherein said wire is mounted under tension.

11. An electric lamp as in claim 8 wherein said support means comprise a wire which extends across the envelope section at the end thereof and is attached thereto.

12. An electric lamp as in claim 1 wherein said source comprises an elongated incandescent filament, a lead wire connected to each end of said filament, said lead wire extending across a section of the envelope.

13. An electric lamp as in claim 12 wherein said lead wires exit from the lamp generally radially with respect to the envelope section.

14. An electric lamp as in claim 12 wherein said lead wires are laid along the wall of the envelope section to generally follow its contour.

15. A method of manufacturing an electric lamp comprising the steps of providing an envelope of glass in the form of several sections, coating the interior of each said section with a material which transmits energy in the visible light range and reflects energy in the infrared range, placing a source of energy within said envelope, evacuating the envelope, and hermetically sealing the several sections together.

16. A method as in claim 15 further comprising the step of optically conditioning the interior of the sections prior to coating.

17. A method as in claim 15 wherein the step of evacuating the envelope comprises providing the envelope with a tubulation and exhausting the interior of said envelope through said tubulation after the section of the envelope have been hermetically sealed, and sealing said tubulation.

18. A method as in claim 17 further comprising the step of placing a fill gas within the envelope prior to sealing the tubulation.

19. A method as in claim 15 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.

20. A method as in claim 19 wherein the step of placing the desired gaseous environment in the chamber comprises placing a fill gas therein.

21. A method as in claim 20 wherein the step of sealing comprises heating the sections with energy from a laser beam.

22. A method as in claim 16 wherein the step of optically conditioning comprises grinding and/or polishing the interiors of the sections.