CA2135686A1 - Incandescent lamp having hardglass envelope with interference filter - Google Patents

Abstract

ABSTRACT

An incandescent lamp having an envelope of hardglass. The envelope encloses a tungsten filament and contains a fill material including an inert fill gas and a halogen additive. An interference filter for selectively reflecting and transmitting selected portions of the light spectrum emitted by the filament is disposed on the envelope. A barrier coating of silicon dioxide is preferably disposed on a substantial portion of the internal surface of the envelope. The barrier coating prevents the halogen additive from combining with alkaline ions of the hardglass envelope.

Description

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.` '~1 3~68 6 ~, INCANDESCENl~ LAMP HAVING HARDGL.ASS ENVELOPl~
WIl'H IN~ERFERENCE FILI'ER

CROSS-REFEREN(:E TO RELATED
APPLICATIONS

' U.S. patent application Serial No. (Attorney Docket No. D-93-1-452) ~iled concurrently herewith and assigned to the same assignee of the present invention, relates to the present invention.

FIELD OF THE INVENTION
This invention relates in general to electric incandescent lamps and pertains, more particularly, to incandescent lamps operating by a tungsten-halogen cycle.
BACXGROUND OF THE INVENTION :

Thin film optical coating~ known as interference -~
filters which comprise alternating layer-~ of two or ~: 25 more materials of different indices of refraction are ~;
well known to those skilled in the art. Such coatinqs or films,are used to selectively reflect or transmit light radiation from various portions of the :~;
I electromagnetlc radiation spectrum such as ~;l ~13~686 . , , .
, D-93-1-453 -2- PATENT APP~ICATION
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: ultraviolet, vi,ible and infrared radiation. These films or coating~ are u~ed in the lamp industry to , coat reflectors and lamp envelopes. One application in which these thin film optical coatings are useful , 5 is to improve the illumination efficiency or efficacy ~ of incandescent lamps by reflecting infrared energy ,l emitted by a filament bac}; to the filament while transmitting the visible light portion of the , electromagnetic spectrum emitted by the filament.
' 10 Thls lower~ the amount of electrical energy required to be supplied to the filament to maintain its operating temperature. In other lamp applications 3 where it is desired to transmit infrared radiation, ~, such filteri can reflect the shorter wavelength portions of the spectrum, such as ultraviolet and visible light portions emitted by the filament and transmit primarily the inrared portion in order to provide heat radiation with little or no visible light radiation. Such an application of this latter type would include a typical radiant heater for residential or indu~trial use where visible radiation emitted by the heater is unneeded or undesirable.
Interference filters for application where the filter will be exposed to high temperature (in excess of 500- C. or so) have been made of alternating layers of tantala (tantalum pentoxide Ta2Os) and silica SiO2~, wherein the ,ilica is the low refractive index material and the tantala i3 the high refractive index material. Such filters and lamps employing same are ~, .;: , . ! ~ ' ~13~686 ., I

disclosed, for example, in U.S. Patent Nos. 4,588,923;
4,663,557 and 4,689,519. In such lamp applications the interference filters, which are applied on the outside surface of the vitreou~ lamp envelope containing the filament within, often reach operating temperatures in the range o~E from about 800- to 900 C.
When such interference filters are applied to a tungsten halogen lamp, the operating temperature of the envelope wall of the lamp increases. This increaqe in the lamp wall temperature can be in excesR
of 100- C. for certain lamp shapes and wattages. The wall temperature can be lowered by increasing the distance from the filament to the envelope wall, however, due to the effects of imperfect geometries of the envelope wall and the coil, it i8 desirable to have the envelope wall as close to the filament as is practical. Due to the combination of hiqh wall ~;
temperatures and small capsule sizes, high efficiency infrared conserving tungsten halogen lamps have heretofore been limited to the use of quartz for their envelope material. ~
When selective interference filters such as ;
alternating layers of tantalum pentoxide and silica are deposited on quartz using a process that is suitable for formlng unlform coatings on complex shapes,jthe resulting film is sub~ected to stress that can cause the film to crack and peel. Methods for reducing the stress in the films are described, for .~3 ~, ~

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j example, ln U.S. Patent Nos. 4,701,663 and 4,949,005.
'f For example U.S. Patent No. 4,949,005 teaches a method of heat treating the films to produce a randomized crack pattern ln the film which results in a film with strong adherence to the substrate and good optical properties. However, any cracks in the optical film will cause the light which strikes the crack to scatter, thus compromising the integrity of the optical system of which the lamp is a part and reducing the magnitude of the efficiency gain.
In operation, tungsten-halogen lamps normally contain a non-reactive qas filling such as neon, nitrogen, argon, krypton or xenon or combination thereof together with iodlne, bromine, chlorine or fluorine vapor which combines with the evaporated tungsten escaping from the incandescent filament. An equilibrium concentration is attained by the qaseous species within the lamp between the temperature limits defined by the incandescent filament and coldest spot in the lamp envelope. The cold spot temperature must be sufficiently high to prevent any tungsten halide from condensing, and providing that this condition ls met a continuous tunqsten transport cycle operate~
which keeps the envelope free from tungsten. The minimum envelope temperature depends upon the halogen or halogens taking part in the cycle.
Hardglasses, such as borosilicate or aluminosilicate glass, have been successfully used for the envelope in certain generally low-wattage, ~11 3~686 ., , . `~ !
O--93-1-453 -5- PATENI' APPLICATION

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tungsten-halogen lamps. However, as the lamp wattage is increased or the size of the lamp envelope is decreased, the increased wall temperature causes an increase in the rate of diffusion of the alkaline ions of the hardglass (i.e., barium, strontium and calcium ions) to the inner surface of the glass where they are able to react with ~he halogen gas. The result is a permanent condensation of the thus reacted halogen gas on the inner walls of the lamp, which reduces the available halogen in the lamp to a level where the -tungsten/halogen cycle no longer operates, causing the lamp to blacken. After the onset of blackening, the ~ wall temperature of the blackened portion of the bulb 'j wall will increase, causing a more rapid diffusion, and further blackening in a "runaway" type reaction.
These high temperature reactions have often limited the use of hardglass in tungsten-halogen lamps where , the glass will be sub~ected to high temperatures.
;I "FT-IR Diagnostics of Tungsten-Halogen Lamps: Role of ;
Halogen Concentration, Phosphorus, Wall Material, and i Burninq Environment", (1991~, by Laurence Bigio et al, shows that for a tungsten-halogen capsule burning in a Parabolic Aluminized Reflector (PAR) lamp with a "hot spot" temperature of 600- C., the level of hydrogen bromide available in the gas phase decreases with burning time in a hardglass tungsten-halogen lamp, whereas the level of hydrogen bromide available in' the '~'A' gas phase remained at or above its initial levels in a quartz tungsten-halogen lamp.

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It ls undesirable to manufacture the lamps with excess halogen to compensate for the halogen which may react during the life of the lamp. This is because the excess halogen will react with the cooler portions of the filament and the lead wires over time, which will cause short life in larnps with long rated life, for example, greater than 750 hours.
The problem of excess activity is even more pronounced in lamps with fine wire filaments, for example, 50 wat~, 120 volt filaments, since these thinner filaments have smaller cross sections and will not withstand halogen attack for very long before they -fail.
In view of the limitations of using hardglass for the envelope of a tungsten-halogen ~ncandescent lamp, the envelope of such lamps is often made from vitreous fused silica ~i.e., quartz) or a high silica content glass such as one composed of ninety-six per cent silica and sold under the trademark Vycor.
However, quartz and ninety-six per cent silica glass are difficult to process and require special seallng techniqua~ to introduce the lead wires into the lamps because of their low coefficients of expansion, and thus leave something to be desired from an economic standpoint.
To prevent the reaction of the halogen constituents of the filling gas with various constituent~ of the lamp envelope, it is well known to use special glasses and/or a protective barrier layer.

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U.S. Patent No. 4,50~,991, which isisued to Wurster et al on April 2, 1985, teaches a halogen-cycle incandescent lamp with an envelope of a special j soft glass wherein the inner surface of the bulb is depleted of alkali lons (i.e., sodium and potassium ~
ions) to avoid a reaction between the halogen ;
constituents of the filling gas and the alkali constituents of the lamp envelope. The vacancies thus generated in the glass lattice may be filled by ` 10 replacement ions such as lithium, magnesium and calcium. In another emibodiment, the soft glass ~`
envelope having its inner surface depleted of sodium and potassium ion~ is coated with a protective layer of a metal and/or semi-metal oxide such as silicon lS dioxide (SiO2), titanium dioxide (TiO2) or barium ¦ oxide (B2O3). According to Wurster et al, reaction between the halogen constituent of the filling gas and alkali ions i5 avoided in prior known halogen cycle incandescent lamps because the lamp bulb was manufactured from quartz or hard glass which both contaln either no or only minor proportions of alkali ion~
U.S. Patent No. 3,496,401, which issued to Dumbaugh on February 17, 1970, teaches an iodine-cycle incandescent lamp having a lamp envelope consistinq e~sentially of an aluminosilicate qlass composition `~
containing a low level o~ alkali metal oxide (e.gJ, `~
sodium oxide). According to ~he patent, no white coatings will be formed in such a hardglass envelope ~13~686 ., -` D- 9 3 -1- 4 5 3 - 8 - PATE~ APPLICATION
~.i, ., containing a maxlmum amount of 0.10% by welght of ~i alkali and having a strain ]point of at least the .l envelope wall temperature. Upon incandescence of the lamp filament, the envelope of the iodine-containing q 5 lamp reaches an operating t~mperature of between 500-,~ 700 C.
U.S. Patent No. 4,256,988, which issued to Coaten et al on March 17, 1981, teaches a fluorine-,j cycle incandescent lamp wherein the internal surface of the lamp envelope and optionally also the exposed surface of internal components of the lamp is coated with a continuous imperforate coating composed of a metal oxide such as aluminum oxide. The aluminum oxide coating prevents free fluorlne from reacting with solid tungsten and the fluorides from reacting with the silica contained in the lamp envelope.
U.S. Patent Nos. 3,900,754; 3,902,091 and 3,982,046 teach the use of glassy coatings of metal pho~phate~ or arsenates as protective coatings for the internal surfaces of halogen-containing electric lamps, and describe a process for the formation of defect free coatings by deposition of a solution of compounds of the metal and phosphorus or arsenlc, followed by evaporation of the solvent and baking o~
the resulting layer.
Although the above-described techniques may be effective to some degree, there i3 a need in the industry for alternative ~olutions.

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~ ~13.S686 D--93-1-453 --9-- Pl~TENT APPLICATION

~, SUMMARY OF ~{E INVENTION

It is, therefore, an ob~ect of the present invention to obviate the disadvantages of the prior art.
It ii~ still another ob~ect of the invention to provide an improved incandescent lamp.
It is another ob~ect of the invention to provida an incandescent lamp which can be more easily `
manufactured and does not re~uire special sealing techniques to introduce the lead wires into the lamps. ~
It is still another ob~ect of the invention to ~`
provide an incandescent lamp having a hardglass envelope which can effectively operate at higher wall temperatures than normal for a tungsten/halogen lamp and will be suitable for use in higher wattage and/or `~
more compact lamp designs. ~;~
These ob~ects are accomplished in one aspect of `i the invention by the provision of an incandescent lamp including a hermetically sealed envelope of hardglass composed of a predetermined quantity of alkaline ions.
A fill material including an inert fill gas and a halogen additive i~ contained within the envelope. A
coating of silicon dioxide iq disposed on a portion of the internal surface of the envelope for preventing the halogen additive from combining with the alkaline ions of the envelope. At least one tungsten filament is sealed in the envelope and supported by a pair of ;--lead-ln wlre~. A coatlng for selective1y reflectlng .
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and tranismitting iselected portionis of the light spectrum emltted by the filament is disposed on an ? external surface of the envelope.
;' In accordance with further teachings of the present invention, the coating of silicon dioxide is disposed on substantially the entire internal surEace of the envelope. Preferably, the thickness of the silicon dioxide coating is within the range of from about 100 to 3000 Angstroms.
~ 10 In accordance with further aspects of the i~ present invention, the lamp may include an outer ~ envelope of a molded light-transmissive glass body or;~ a reflector (e.g., elliptical or paxabolic). A base may be disposed at one end of the lamp.
Additional ob~ects, advantages and novel featureis of the invention will be set forth in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The aforementioned objects and advantages of the invention may be realized and attained by means of the instrumentallt1es and combination particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more readily apparent from the following exemplary description in connection with the accompanying drawings, wherein:

~:l3~6g6 FIGS. 1 illu~trates a sectional view of an incandescent lamp in accordance wlth a preferred embodiment of the present invention;
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FIG. 2 shows a sectional view of an incandescent lamp having an elliptical reflector in accordance with another embodiment of the present invention;
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FIG. 3 shows a sectional view of an incandescent lamp having an outer envelope in accordance with ~-another ambodiment of the present invention; and FIG. 4 shows a sectional view of a PAR
incandescent lamp having a parabolic reflector in accordance with another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION
For a better under~tanding of the present invention, together with other and further ob~ects, ~-advantages and capabilitie~ thereof, reference is made to the following disclo~ure and appended clalms in connection with the above-described drawing~.
Referring to the drawings with greater particularity, FIG. 1 shows a preferred embodiment of the present invention. In particular, FIG. 1 illustrates an incandescent lamp 10 comprising an ,:.
`, ~ ~1 3~686 t elliptical-shaped hardglas~ envelope 12 having a first lead-ln wire 14 and a second lead-in wire 16. A
tungsten filament 18 extend~s axially and between the internal terminations of lead-in wires 14 and 16.
Filament 18 is electrically connected to a pair of contact wireq or pins 20 and 22 which project from the lamp envelope. More than one filament may be contained within envelope 12. Envelope 12 is hermetically sealed, in this instance, by a press seal 24.
Envelope 12 in FIG. 1 is provided with the usual tubulation 26 (shown tipped off in the drawings) whereby air is exhausted and an inert fill gas and one or more halogen~ (i.e., iodine, bromine, chlorine and fluorine) is introduced. In a preferred embodiment of a low volta~e lamp (e.g., 12 volts), the lamp fill compri~es (by volume) 0.3% hydrogen bromide, a phosphine getter, with the balance being krypton. The total fill pressure is about 5 atmospheres absolute at room temperature. In a preferred embodiment of a 120 volt lamp, the lamp fill compri~es (by volume) 0.17%
hydrogen bromide, a pho_phine getter, with the balance belng a 95~ krypton/5% n$trogen blend. The total fill pressure ls about 5 ~tmosphere~ absolute at room temperature. It is to be recognized that the envelope and filament structure of the incandescent lamp of the present invention may have configurations other than that which i~ shown in FIG. 1.

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By h~rdgla~ meant a materlal havlng a 11near coefficient of thermal expansion of from about 30 to 50X10 7 in/in/ C. Such glasses have softenlng temperatures of from about 750- C. to about 1020- C.
and a strain point of about 650- C. to 760- C.
Exemplary of such materials are the borosilicate or l aluminosilicate glasses.
`~t One suitable glass for the present invention is GE 180 glass manufactured by General Electric Company and generally described in U.S. Patent Nos. 4,060,423 and 4,105,826. This particular glass has the following properties:

Softening point, C. 1020 , 15 Annealing point, C. 805 ;~ Strain point, ' C. 755 Z Expansion (0--300 C.)X10 7 in/in/ C. 43 As the lamp w~ttage i8 $ncrea~ed or the size of the lamp envelope iq decreased, the wall temperature increases which increases the diffusion rate of some of the alkaline ion~ of the hardglass (i.e., barium, ~-strontium and calcium ions) to the inner surface of the glass where they are able to interact with the ;
halogen gas. The result is a permanent condensation of the thus reacted halogen gas on the inner walls of the lamp, which reduces the available halogen in the lamp to a :Level where the tungsten/halogen cycle no longex opexates, which causes the lamp to blacken.

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These high temperature reaction~ have often limited the use of hardglass in tungsten-halogen lamps where the glas~ will be sub~ected to high temperatures.
All references herein to alkaline ions refer to the common alkaline component~ of hardglass. In aluminosilicate and borosilicate glas~es, these alkaline components may include magnesium, calcium, strontium, and barium, and mixtures thereof.
As further ~llustrated in FIG. 1, a barrier layer 40 is disposed on the internal surface of envelope 12 in order to limit the rate at which halogen gas combines with the alkaline ions of the hardglaRs at elevated temperatures.
Preferably, barrier layer 40 consists of a single thin film or coating consisting of silicon dioxide (i.e., ~ilica). This coating forms a continuous and glassy barrier on the inner surface of the lamp envelope which prevents the alkaline ions of the hardglass from reaching the atmosphere in the lamp. As a result, the halogen (e.g., fluorine, iodine, bromine, and/or chlorine) i8 prevented from reacting with these components of the hardglass, which lQaves the halogen in a gaseous state where it can continue the tungsten-halogen regenerative cycle.
The coating of silicon dioxide need not be free from defects such as pinholes~ nor must it cover the entire internal surface of the lamp. The coating should generally cover those portions of the internal surface of the envelope which are sub~ected to :`

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D-93-1-453 -15- PA~ENT APPLICATION
;, ,. , temperatures known to be excesslve for hardglas~ -tung~ten-halogen lamps. For example, for lamps in a vertical-ba~e down burning position when the wall temperature of the upper portion of the envelope is i 5 hotter than the lower portion of the envelope, it may ;, only be necessary to apply the barr~er layer to the ~ upper half of the envelope. The amount of surface j~ area coated with silicon dioxide will depend upon the maximum temperature encountered as a result of the size of the envelope, the lamp wattage, and the lamp's intended burning position.
The thickness of the silicon dioxide layer I should be within the range of from about 100 to 3000 ? Angstroms. Preferably, the layer thickness is about 1000 Angstrom Greater temperature resistance and longer life may be achieved when a more thorough portion of the in~erior of the lamp envelope is coated with the silicon dioxide layer. In FIG. 1, the entire internal ~urface of envelope 12 is shown coated with the sllicon dioxide layer.
Sllicon dioxide offers an advantage over metal oxides in that its index of refraction (1.46) more closely matches, and is lower than that of hard~lass (1.54). Metal oxides typically have an index of refraction which i~ higher than that of silicon dioxide. For example, aluminum oxide has an index!of refrac~ion of 1.76. Metal oxide coatings with the higher refractive indexes will cause an increased 3~686 ,`.~- .
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amount of light to be reflected internally off of the glas~ surface, thus causing an effective decrea~e in ~' the lamp performance. Experimental test~ showed that '"!
a layer of silicon dioxide on hardglass resulted in an approximately 93~ transmis~ion of visible light through the hardglass in one pass. In contrast, a layer of aluminum oxide on the hardglass resulted in only an approximately 91% transmission of visible light through the hardglass in one pass.
;,i 10 The silicon dioxide coating of the present invention effectively increa~es the upper operating temperature limit of hardglass in a tungsten-halogen lamp. More specifically, it was discovered that a long life ti.e., greater than 750 hours) tungsten-halogen lamp having an envelope formed from GE 180 hardgla~s without the barrier layer of the present lnvention had a maximum operating wall temperature of about 500- C. Above this wall temperature, the halogen gas will be depleted during the life of the ' 20 lamp, evantually causing the lamp to blacken. The same glass with the internal barrier layer of silicon dioxide was found to have a maximum operating wall temperature greater than about 700- C. Due to this allowable increase in operating temperature, the 25 hardglass envelope with the internal barrier layer of silicon dloxide can be used in higher wattage and/or more compact lamp design~.
The silicon dioxide ~oating can be formed on the internal ~3urface of the lamp by many different ~ ~ 135686 D-93-1-453 -17- PATEN~ APPLICATION
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technique~. In one embodiment, a 301ution i9 formed from a mixture of tetraethylortho~ilicate, ethanol, ~ distilled water and nitric acid. The rela~ive amounts 3 of the variou~ components may be varied to yield a 5 coating with the de~ired properties. The solution can ~-then be applied to a hardglass envelope before it i~
pressed into a lamp by dipping method~, spraying methods, pipettes, or by drawing the solution into the envelope with a vacuum. Surprisingly, despite the 10 mi~match in thermal expansions between the coating and the glass, it is not neces~ary to avoid coating the ~eal area of the envelope because the lamp can be sealed in with the coating in this area. After the solution is applied, it is then air dried at room temperature and fired at 450- C.- 550- C. for 30 minute~ in air. Alternatively, vapor deposition techniques, ~uch a~ chemical vapor deposition, can be employed to produce the ~ilicon dioxide coating. The glass envelope can then be pressed in and proces~ed ln the normal manner.
As be~t shown in FIG. 1, the external surface of envelope 12 is coated with an interference filter 44.
Filter 44 selectively reflects infrared energy emitted by fllament 18 back to the filament wherein at least a portion of the lnfrared radiation is absorbed by the fllament. This reflected energy help~ to heat the filament which reduces the amount of energy required to maintain the filament at its designed operating temperature. Interference filters are well known in ;~' ..~j 3 ~ 6 8 6 .
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the art and con4ist of alternatinq layers of a low refractory index material such as silica and a high reractory index material such as tantala, titania, niobia and the like for selectively reflecting and transmitting different port.ion~ of the electromagnetic spectrum emitted by the filament. Such filter~ and the manner in which such coatings may be applied are ; found, for example, in U.S. Patent Nos. 4,229,066;

4,588,923; 4,663,557; 4,701,663; 4,949,005 and 5,138,219.
FIG. 2 lllustrates another embodiment of the present invention wherein lamp 10 of FIG. 1 is disposed within a reflector 52. Reflector 52 of ` combination 50 may be made of hardglass (e.g., borosilicate), and includes a forward concave reflecting portion 54 and a rear neck portion 56 l ad~acent ~hereto. Reflecting portion 54 i8 preferably i elliptical or parabolic in confiquration and hai a 'l concave reflecting surface that may be formed with a plurality of facet~ 58. Alternatively, the reflector may have a smooth and highly polished reflecting surfac~. The reflector may also have a lens attached.
Lamp 10 may be secured to reflector 52 by means of a suitable cement 60. Contact pin3 20 and 22 extend from the press seal of envelope 12 and pro~ect from rear neck portion 56 of reflector 50.
FIG. 3 illustrates another embodiment of the present invention wherein lamp 10 of FIG. 1 is disposed within a light-transmissive outer qla~

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jl !1 envelope 72. Outer glass envelope 72 of combination ~, 70 forms a cavlty 74 and includes a neck portlon 76 !l and an opposite dome portion 78. A lamp base 80 is S connected to neck portion 76 of outer envelope 72. In partlcular, lamp base 80 includes an electrically ,j conductive first region and an electrically conductive ~, second region insulated therefrom. In the preferred j embodiment, as depicted in FIG. 3, the electrically conductive first region includes a conventional threaded metal shell 82 and the electrically conductive qecond region includes a metal eyelet 84.
An insulating means such as a glass insulator 86 is provided between metal shell 82 and metal eyelet 84.
Contact wire 20 from lamp 10 is electrically connected to a wire support frame 88 which is electrically connected to threaded metal shell 82. Contact wire 22 from lamp 10, which iq spaced from wire support frame 88, i~ electrically connected to metal eyelet 84.
As further illustrated in FIG. 3, the in~ide surface of outer glais envelope 72 may include a light-diffusing coating 64. Coating 64 may comprise a quspension of ~ilica particles and a soluble ~ilicate binder a~ disclosed ln U.S. Patent No. 5,036,244 to Shaffer.
FIG. 4 illu~trates another embodiment of the present inventlon wherein lamp 10 of FIG. l i~
disposed within a parabolic reflector 92. Reflector 92 of combination 90 may be made of hardglass (e.g., borosilicate). The reflector forms a cavity 94 and 3~686 ,. ^ , D-93--1-453 -20- PATENI' APPLICATION

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include~ a forward concave xeflectlng portion 96 and a rear neck portion 9~ ad~acent thereto. An upper skirted portion 102 of a lannp base 100 is secured to neck portion 98 of reflector 92. A lower lamp base portio~ 104 include~ a threaded metal shell 106 and a metal eyelet 108. Contact wires 20 and 22 from lamp 10 are electrically connected to threaded metal shell 106 and metal eyelet 108, respectively. A lens or cover 110 is attached or hermetically sealed in a conventional manner to the opposite end of reflector 92.
In a typical but non-limitative example of an incandescent lamp made in accordance with the teachings of the present invention, a solution was j 15 made ucing 50 ml of tetraethylorthosilicate mixed with 183 ml of ethanol, 16ml of di~tilled water, and 3 ml of nitric acid. This solution was coated on the internal ~urface of pieces of aluminosilicate hardglas~ tubing having an elliptical portion by drawing the solution up through the neck area of the tubing into the elliptical portion of the tubing using a vacuum. The lower portion of the tubing which forms the press was not coated with solution. The solution was then expelled back out through the neck. The coating was then air dried by blowing a light stream of air through the necXed tubing, and the coating was ~
' ! I fired at 450 C. for 30 minutes in air. ! ';
A 74 watt 12.8 volt coil was pressed into each bulb to which the coating of silicon dioxide had been ....
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applied to sub3tantlally the entire internal surface of the bulb, and a second clroup of 74 watt 12.8 volt coils were pressed into similar elliptical bulbs which ;~ did not have an internal barrier coating applied to ;t 5 them. Both of the lamp groups were exhausted and finished identically in the normal manner. Both groups of lamps were then coated with a light transmitting, IR-reflecting interference filter and ~ were burned at 14.0 volts in clear outer ~ackets in a ;~ 10 horizontal position. The lamps were determined to ;j have an outer wall temperature near 720- C at the "hot spot" when burned in a horizontal position at 14.0 ; volts in a clear outer ~acket. An interference filter comprisinq, for example, alternating layers of tantala and silica can be deposited on the external surface of each bulb using PVD (physical vapor deposition), CVD
`! (chemical vapor deposition) or LPCVD (low-pressure ;l chemical vapor deposition) technology. Examples of sultable filters and methods of applying the filters are disclosed in U.S. Patent Nos. 4,229,066;
4,587,923; 4,663,557; 4,701,663; 4,949,005 and 5,138,219.
` After 50 hours of burning in a horizontal position, a white haze and areas of slight blackening appeared on the internal envelope walls of the lamps assembled without the lnternal silicon dioxide , ! ~ coating. The blackening of the envelope walls is due to evaporated tungsten condensing on the walls of the lamp because of a breakdown in the regenerative cycle.

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iD-93-1-453 -22- PATENT APPLICA~ION

:,, In contra~t, the group of lamp~ with the internal silicon dioxide coating showed no evidence of white haze or blackening. After 230 hours, the group of lamps without the lnternill silicon dioxide layer S had turned very black, while the group of lamp~ coated with the sllicon dloxide internal layer remained free from white haze and any signs of blackening.
Although the above described drawings illustrate single-ended incandescent lamps, it is to be recognized that the silicon dioxide coating can alternatively be applied to the internal surface of an envelope of a double-ended incandescent lamp.
There has thus been shown and described an improved incandescent lamp. The hardglass lamp of the present invention can be more easily manufactured than a quartz lamp and does not require special sealing techniques to hermetlcally seal the lead wires into the lamp~. The envelope can effectively operate at higher wall temperatures than normal and will be ;
sultable for use ln higher wattage and/or more compact lamp designs.
While there have been ~hown and described what i are at present considered to be the preferred embodiment~ of the invention, it will be apparent to ;
those skilled in the art that various changes and modification~ can be made herein without departing -~
!i from the scope of the invention. The actual scope of ; the invention is ~ntended to be defined in the ii;

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':~ following claims when view~d in their proper perspective based OA the prlor art.

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Claims (23)

1. An incandescent lamp comprising:
a hermetically sealed envelope of hardglass composed of a predetermined quantity of alkaline ions;
a fill material including an inert fill gas and a halogen additive contained within said envelope;
a barrier coating disposed on a portion of the internal surface of said envelope for preventing said halogen additive from combining with said alkaline ions of said envelope;
at least one tungsten filament sealed in said envelope and supported by lead-in wires; and a coating for selectively reflecting and transmitting selected portions of the light spectrum emitted by said filament disposed on an external surface of said envelope.

2. The incandescent lamp of claim 1 wherein said barrier coating is disposed on substantially the entire internal surface of said envelope.

3. The incandescent lamp of claim 2 wherein said barrier coating consists of silicon dioxide.

4. The incandescent lamp of claim 3 wherein the thickness of the silicon dioxide coating is within the range of from about 100 to 3000 Angstroms.

5. The incandescent lamp of claim 4 wherein the thickness of the silicon dioxide coating is about 1000 Angstroms.

6. The incandescent lamp of claim 1 wherein said envelope is borosilicate glass.

7. The incandescent lamp of claim 1 wherein said envelope is aluminosilicate glass.

8. An incandescent lamp comprising:
an outer envelope including a molded light-transmissive glass body enclosing a cavity, a hermetically sealed inner envelope of hardglass disposed within said cavity and composed of a predetermined quantity of alkaline ions;
a fill material including an inert fill gas and a halogen additive contained within said inner envelope;
a barrier coating disposed on a portion of the internal surface of said inner envelope for preventing said halogen additive from combining with said alkaline ions of said inner envelope;
at least one tungsten filament sealed in said inner envelope;
a coating for selectively reflecting and transmitting selected portions of the light spectrum emitted by said filament disposed on said envelope;
a base disposed at one end of said outer envelope; and means for electrically connecting said tungsten filament to said base.

9. The incandescent lamp of claim 8 wherein said barrier coating is disposed on substantially the entire internal surface of said inner envelope.

10. The incandescent lamp of claim 8 wherein said barrier coating consists of silicon dioxide.

11. The incandescent lamp of claim 10 wherein the thickness of the silicon dioxide coating is within the range of from about 100 to 3000 Angstroms.

12. The incandescent lamp of claim 11 wherein the thickness of the silicon dioxide coating is about 1000 Angstroms.

13. The incandescent lamp of claim 8 wherein said envelope is borosilicate glass.

14. The incandescent lamp of claim 8 wherein said envelope is aluminosilicate glass.

15. An incandescent lamp comprising:
a reflector defining a cavity a hermetically sealed envelope of hardglass disposed within said cavity of said reflector, said envelope composed of a predetermined quantity of alkaline ions;
a fill material including an inert fill gas and a halogen additive contained within said envelope;
a barrier coating disposed on a portion of the internal surface of said envelope for preventing said halogen additive from combining with said alkaline ions of said envelope.
at least one tungsten filament sealed in said envelope; and a coating for selectively reflecting and transmitting selected portions of the light spectrum emitted by said filament disposed on said envelope.

16. The incandescent lamp of claim 15 wherein said barrier coating is disposed on substantially the entire internal surface of said envelope.

17. The incandescent lamp of claim 15 wherein said barrier coating consists of silicon dioxide.

18. The incandescent lamp of claim 17 wherein the thickness of the silicon dioxide coating is within the range of from about 100 to 3000 Angstroms.

19. The incandescent lamp of claim 18 wherein the thickness of the silicon dioxide coating is about 1000 Angstroms.

20. The incandescent lamp of claim 15 wherein said envelope is borosilicate glass.

21. The incandescent lamp of claim 15 wherein said envelope is aluminosilicate glass.

22. The incandescent lamp of claim 15 further including a base disposed at one end of said reflector and means for electrically connecting said tungsten filament to said base.

23. Each and every novel feature or novel combination of features herein disclosed.