(12) United States Patent
`Eastlund et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,414,436 B1
`Jul. 2, 2002
`
`US006414436B1
`
`(54) SAPPHIRE HIGH INTENSITY DISCHARGE
`MP
`Inventors: Ben Eastlund, Spring, TX (US);
`vA<vs>
`.
`$:n(1UI§1)ght1ng LLC, Manakin-Sabot,
`
`(75)
`
`.
`
`(73) Assignee:
`
`.
`
`.
`
`5,451,553 A
`2923:7322:
`,
`,
`5540482 A
`2222:3332
`5,702,654 A
`5,829,858 A
`
`9/1995 Scott et 211.
`1;/1:3: E?“§f“‘
`ISC CI
`7/1996 L°Vi“5°“ 6‘ a1~
`13132: 3212,6251,
`12/1997 Ch
`1.
`11/1998 L65: : :1.
`
`OTHER PUBLICATIONS
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`USO 154(b) by 0 days.
`
`.
`(21) Appl' No" 09/241’011
`(22)
`Filed:
`Feb. 1, 1999
`
`.
`.
`.
`“
`S. Carleton et al., Metal. Halide Lamps ”VV1Ih Ceramic
`Envelopes: ABreahthrough in Color Control, Journal of the
`Illuminating Engineering Society, Winter
`1997,
`pp.
`139-145.
`S. A. R. Rigten, General Electric, Co. J. G. E. C. Journal, vol.
`32, N0- 1, 1965, 1313- 50-51-
`
`(51)
`Int. Cl.7 ............................................... .. H01J 17/16
`
`(52)
`,
`313/634; 313/572; 313/636
`(58) Field of Search ............................... .. 313/634, 572,
`313/635 636 573 570 571
`’
`’
`’
`’
`
`* cited by examiner
`Primary Examiner—Frank G. Font
`.
`.
`Asszstant ExamLner—AndreW H. Lee
`(74) Attorney, Agent, or Firm—Fay Kaplun & Marcin, LLP
`
`(56)
`
`References Cited
`
`(57)
`
`ABSTRACT
`
`U-S- PATENT DOCUMENTS
`3,608,050 A
`9/1971 Carman et al.
`4,013,374 A
`4/1977 Lee et a1.
`4,501,993 A
`2/1985 Mueller et a1.
`4,839,656 A *
`6/1989 Osteen ..................... .. 315/209
`4,855,879 A
`8/1989 8011311161 a1~
`5975587 A
`12/1991 Pabst 6‘ 31-
`592399230 A
`8/1993 Mathews ct 91‘
`5,336,968 A *
`8/1994 Strok et al.
`............... .. 313/571
`5,404,076 A
`4/1995 Dolan et al.
`5,424,608 A
`6/1995 Juengst et 211.
`5,427,051 A
`6/1995 Maxwell et al.
`
`A high intensity discharge lamp, especially for optical
`projection systems,
`in one embodiment ‘uses an anode
`electrode, a cathode electrode and a cylindrical envelope of
`single crystal (SC) sapphire. The fill may contain hydrogen,
`chlorine, sodium, scandium, sulfur and selenium and is
`under pressure exceeding 20 atmospheres. The lamp pro-
`duces a continuous non-flash arc and generates a correlated
`color temperature between 6500 and 7000 degrees Kelvin
`~
`and an efficacy exceeding 60 lumens/Watt.
`
`13 Claims, 7 Drawing Sheets
`
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`

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`U.S. Patent
`
`Jul. 2, 2002
`
`Sheet 1 of 7
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`US 6,414,436 B1
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`U.S. Patent
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`Jul. 2, 2002
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`Sheet 2 of 7
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`Jul. 2, 2002
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`Sheet 3 of 7
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`US 6,414,436 B1
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` Tinnerwallsapphirei = de|taT2i + 273- K + Touterwalli
`
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`U.S. Patent
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`Jul. 2, 2002
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`Jul. 2, 2002
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`Jul. 2, 2002
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`U.S. Patent
`
`Jul. 2, 2002
`
`Sheet 7 of 7
`
`US 6,414,436 B1
`
`
`
`Temperature Tensile Strength
`Sapphire
`
`Tensile Strength
`Quartz
`
`
`
`
`
`FOR TUBES
`
`Burst Pressure - (2 X Wall Thickness X Tensile Strength @ Temp)/ID
`
`TABLE 2
`
`THERMAL CONDUCTIVITY (W/CM ' K)
`
`
`
`TABLE 3
`
`

`
`US 6,414,436 B1
`
`1
`SAPPHIRE HIGH INTENSITY DISCHARGE
`PROJECTOR LAMP
`
`FIELD OF THE INVENTION
`
`This invention relates to optical projection lamps and
`more particularly to high intensity discharge (HID) electric
`lamps for optical projectors which lamps are presently
`generally constructed with quartz envelopes.
`
`BACKGROUND
`
`At the present time lamps (bulbs) for optical projectors
`are generally of the high intensity discharge (HID) type in
`which an arc is formed between two electrodes, the elec-
`trodes being positioned at opposite ends of a tubular enve-
`lope with a gap between them. The light from the lamp is
`reflected from a reflector and focused on an image gate, for
`example, an LCD (Liquid Crystal Display) plate, a slide
`projector film gate or motion picture film gate.
`HID lamps presently have light transmissive lamp enve-
`lopes with quartz or ceramic (polycrystalline). Many lamp
`patent claims are based on benefits arising from specific
`forms of these materials. For example,
`in U.S. Pat. No.
`4,501,993, relating to an electrodeless lamp bulb for pro-
`ducing deep ultraviolet (UV) “synthetic quartz which is
`substantially water free” is claimed as an advantage over
`“commercial quartz.” In the article “Metal Halide Lamps
`with Ceramic Envelopes: ABreakthrough in Color Control,”
`Journal of the Illuminating Engineering Society, Winter,
`1997, the advantages of translucent polycrystalline alumina
`ceramic envelopes over quartz envelopes are highlighted.
`However, the light transmissive envelope technologies in
`present use have limitations which affect the ability of such
`lamps to provide long life, flicker-free operation, color
`stability and high efficacy.
`The limitations quartz envelopes impose on HID lamp
`performance include the following:
`1. The envelope structures are physically delicate and
`subject to breakage in handling;
`2. Devitrification by water, and many different chemicals
`such as hydrogen and chlorine, limit the light output
`and the lifetime of electric lamps.
`3. Sodium, neon and hydrogen diffuse out of the bulb and
`so they cannot be used for fills.
`4. Pressure is limited by the tensile strength of 7000
`lb/in‘2 at room temperature.
`5. Large temperature gradients occur across the bulb wall,
`limiting the heat transfer capability of the wall to about
`20 watts/cm“2.
`Despite these limitations, quartz envelopes are generally
`used because ceramic (polycrystalline) envelopes present
`greater limitations. The limitations imposed by ceramic
`(polycrystalline) walls include:
`1. The ceramic is a translucent material which is unsuit-
`
`able for optical systems.
`2. The ceramic envelope is brittle.
`3. Such ceramic envelopes have a relatively low tensile
`strength of less than 25,000 lb/in32.
`Lamp systems of quartz and ceramic (polycrystalline)
`envelopes have been in commercial use for many years and
`in most application areas, lamp performance has been opti-
`mized to the physical limits of these materials.
`In some LCD (Liquid Crystal Display) projector electrode
`HID lamp applications it is desirable to have short (1-2 mm)
`arc gaps and 1-2 mm diameter for the light emitting volume.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`Such applications also need light emitting volumes that
`produce efficacy of 60 lumens/watt, or more, with good
`color stability, flicker-free operation and lifetimes of more
`than 2000 hours.
`
`An example of a system maximized to the physical
`properties of quartz is described in Matthews et al U.S. Pat.
`No. 5,239,230. This patent describes the maximum perfor-
`mance capabilities of a short arc HID discharge lamp with
`a Mercury, Bromine, Xenon fill. The inner bulb diameter is
`limited to dimensions greater than 3.8 mm for power levels
`of 70 to 150 watts. Limitations are due to hoop stress
`limitations and temperature limitations, on the inner wall of
`the quartz tube, which result in melting of the inner bulb
`surface causing failure in less than 100 hours.
`Another example of a system maximized to the physical
`properties of quartz is described in Fischer U.S. Pat. No.
`5,497,049. This patent describes the maximum performance
`capabilities of a specific HID high-pressure mercury (over
`200 bar) discharge quartz envelope design for LCD projec-
`tors having tungsten electrodes. Such a system suffers from
`premature failure due to devitrification and blackening of the
`inner bulb surface in the arc region and in the tip-off regions.
`Such lamps utilize bromine as an enhancer of efficacy but
`cannot use chlorine because of reactions with the envelope
`and cathode materials. The authors find the inner diameter of
`
`the bulb has to be greater than 3.8 mm for lamps in the
`70-150 watt range to avoid premature failure due to the
`physical properties of the quartz.
`Electrodeless lamps filled with sulfur and selenium have
`superior luminance properties. See, for example, U.S. Pat.
`No. 5,404,076 dated Apr. 4, 1995, and U.S. Pat. No. 5,606,
`220 dated Feb. 25, 1997. However, the envelopes are made
`of quartz, which has an operating temperature limitation of
`900° C. For example, the “Light Drive 1000” lamps devel-
`oped by Fusion Lighting Inc. utilize quartz envelopes and
`require constant rotation at high rpm to avoid development
`of hot spots that create temperatures of over 900° C. If the
`rotation stops, the bulb blows up in about 3 seconds.
`Lamp systems composed of ceramic (polycrystalline)
`material are translucent and are thus not usable for many
`optical systems applications. They are also brittle and have
`relatively low tensile strength. They do have advantageous
`features for lamp envelope applications in that they are
`chemically inert and impervious to elements like sodium,
`hydrogen, neon, chlorine, etc. For example, color stability
`and efficacy of over 90 lumens/watt of HID lamps with
`ceramic (polycrystalline) envelopes are described by Carle-
`ton et al in “Metal Halide Lamps With Ceramic Envelopes:
`ABreakthrough in Color Control”, published in the Journal
`of the Illuminating Engineering Society, Winter, 1997.
`Flash lamps, without continuous arcs, have been fabri-
`cated from single crystal (SC) sapphire by ILC Corporation
`of California and by Xenon Corporation of Massachusetts.
`SC sapphire is alumina (aluminum oxide) formed as a single
`crystal. These lamps have been demonstrated to have supe-
`rior lifetime and color maintenance over quartz. The end
`seals of these commercial lamps utilize metal brazing mate-
`rials and kovar components, which are unsuitable for HID
`lamp applications.
`There are examples in the literature of seals to ceramic
`(polycrystalline alumina)
`tubing which have proven
`adequate for “double wall” containment vessels which have
`an outside envelope of quartz. For example, Juengst et al
`U.S. Pat. No. 5,424,608, Pabst et al U.S. Pat. No. 5,075,587,
`and Bastian U.S. Pat. No. 5,455,480 describe such sealing
`arrangements using a variety of glass sealing materials
`optimized for sealing to polycrystalline materials.
`
`

`
`US 6,414,436 B1
`
`3
`U.S. Pat. No. 5,702,654 relates to manufacture of single
`crystal sapphire for windows and domes. U.S. Pat. No.
`4,018,374 relates to a sapphire-glass seal. U.S. Pat. No.
`5,451,553 relates to thermal conversion of polycrystalline
`alumina to sapphire by heating to above 1100° C. and below
`2050° C., and U.S. Pat. No. 3,608,050 relates to growing
`single crystal sapphire from a melt of alumina. The only
`mention we found in the patent literature of clear sapphire in
`a lamp is in a radio luminescent lamp application described
`in U.S. Pat. No. 4,855,879 in which clear sapphire planar
`window material is mentioned. The only mention we found
`in the technical literature is a diagnostic sodium discharge
`lamp described by S.A.R. Rigten, Gen. Elec. Co.J., Vol.32,
`p.37, 1965, in which a transparent sapphire tube is used for
`diagnostic purposes.
`One of the difficulties in utilizing single crystal (SC)
`sapphire in commercial lamp construction is the difficulty in
`growing the cylindrical crystals with suitable concentricity
`and a crystalline structure free of defects. The above-
`mentioned patents and articles are incorporated by refer-
`ence.
`
`SUMMARY OF INVENTION
`
`This invention significantly improves the efficacy,
`lifetime, and color stability of high intensity discharge (HID)
`lamps, especially projector lamps. It uses single crystal (SC)
`sapphire bulb envelopes which have physical properties
`superior to those of quartz and ceramic (polycrystalline)
`bulb envelopes. Its principal object is to provide a novel high
`intensity discharge (HID) lamp with a light
`transparent
`envelope of single crystal (SC) sapphire. The SC-sapphire
`HID lamp can be smaller, operate at higher power for equal
`size and be brighter with higher plasma luminance than
`quartz lamps with similar dimensions and fills. SC-sapphire
`HID lamps can also last four to five times longer with
`superior lumen maintenance. Such lamps may be easier to
`manufacture with superior manufacturing tolerances and at
`the same or lower cost as fused quartz envelopes, or poly-
`crystalline alumina envelopes. These sapphire lamps use
`metal to ceramic seals that can tolerate temperatures up to
`1300° C. as compared to fused quartz to metal seals that are
`limited to temperatures of about 250° C. The SC-sapphire
`HID lamp is preferably powered through two end electrodes
`or less preferably a combination of electrodes and micro-
`wave sources.
`
`OBJECTS OF THE INVENTION
`
`An object of the invention is to provide a novel sulfur or
`selenium-filled lamp with a light transparent envelope of
`single crystal (SC) sapphire.
`Another object of the invention is to provide a novel
`method of sealing lamps having SC-sapphire envelopes in
`such a way that the lamps can contain light emitting gaseous
`substances with pressures as high as 600 atmospheres.
`Another object of this invention is to provide a novel
`method of assembly of lamps with SC-sapphire envelopes in
`such a way that the manufacturing costs are low.
`This invention will make possible a wide range of new
`lamps based on SC-sapphire envelopes with application in
`optical projectors. The lamp may also be used in automobile
`headlamps and home and general lighting applications.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the drawings:
`FIG. 1A is a top plan view of the (SC) sapphire lamp
`envelope;
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`FIG. 1B is a side plan view of the bulb envelope of FIG.
`1A;
`FIG. 1C is an end plan view of the bulb envelope of
`Figure 1A;
`FIG. 2A is a side view of an LCD projector system using
`the (SC) sapphire bulb;
`FIG. 2B is a cross-sectional view of the first embodiment
`
`of the bulb using electrodes;
`FIG. 3 is a chart comparing heat effect on quartz and (SC)
`sapphire walls;
`FIG. 4 is a chart showing stress on a bulb as a function of
`tensile strength;
`FIG. 5 is a cross-sectional view of a second embodiment
`
`of the bulb using electrodes;
`FIG. 6 is a cross-sectional view of a third embodiment of
`the bulb, which is without electrodes;
`Table 1 is a comparison of sapphire to quartz;
`Table 2 is a comparison of tensile strength at various
`temperatures of quartz and sapphire; and
`Table 3 is a comparison of thermal conductivity between
`quartz and sapphire.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Embodiments of this invention will be described in detail
`
`with reference to the accompanying drawings.
`FIG. 1A is a top view that shows an SC-sapphire lamp
`envelope hollow tube envelope 100. The ID designated d
`can range from 1 mm to more than 20 mm. The OD
`designated D of the SC-sapphire tubing can range from 2
`mm to more than 23 mm. The length of the tube 100
`designated L can range from 3 mm to more than 40 cm. Such
`raw SC tubing is commercially available from a number of
`corporations, such as Saphikon in New Hampshire, and
`Kyocera in Japan. However, it must be machined to obtain
`the desired concentricity.
`Single crystal (SC) sapphire properties are compared with
`quartz and ceramic (polycrystalline alumina) in Table 1. The
`tensile strength of single crystal (SC) sapphire is compared
`with quartz as a function of temperature in Table 2. The
`thermal conductivity of single crystal
`(SC) sapphire is
`compared with quartz as a function of temperature in Table
`3.
`
`Sapphire is chemically inert and is insoluble in
`hydrofluoric, sulphuric and hydrochloric acid, and most
`important for HID lamp applications, it does not outgas or
`divitrify. It can be operated at higher temperatures than
`quartz and has significantly higher thermal conductivity.
`Raw SC tubing is presently available at reasonable prices
`from a number of vendors, such as Saphikon and Kyocera.
`Commercial and single crystal sapphire tubing, as delivered,
`has problems with holding circular cross-section tolerances.
`This can be taken care of by appropriate machining of the
`appropriate surfaces, i.e., reaming the interior and polishing
`the exterior using diamond tooling to obtain a uniform and
`specified wall thickness. A lamp envelope of SC-sapphire is
`capable of operating at a higher outer surface temperature
`than quartz and can handle conduction heat flux of greater
`than 150 watts/cm 2 compared to the 20 watts/cm“2 of
`quartz in HID lamp applications.
`FIG. 2A shows an optical projection system in which an
`SC-sapphire lamp (bulb) 10 is with a reflector 11. The
`lamp’s light is focused on the entry face 13 of a hollow light
`pipe 15, preferably of the type of U.S. Pat. No. 5,829,858
`
`

`
`US 6,414,436 B1
`
`5
`incorporated by reference. The beam is focused by lens 18
`and lens 19 onto Fresnel plate 20 and LCD plate 21 which
`forms an image. That image is focused on the screen by
`projector lens 23.
`FIG. 2B is a side view cross-section of a single crystal
`(SC) sapphire high intensity halide lamp. The sealing geom-
`etry is based on a design for sealing ceramic
`(polycrystalline) plugs to ceramic (polycrystalline) tubing as
`discussed by Juengst in U.S. Pat. No. 5,424,608. In the case
`of FIG. 2 a single crystal (SC) sapphire tube 100 is used.
`Plugs 200, which preferably are made of ceramic
`(polycrystalline) or single crystal (SC) sapphire, closes off
`the ends of the sapphire tube 100. The plugs 200 are sealed
`to the single crystal (SC) sapphire tube 100 to form a
`pressure and chemical resistant seal and contain the gases
`inside the region bounded by the inside diameter d and the
`surface facing the discharge of the plugs 200. The plugs are
`sealed to the single crystal (SC) sapphire tube 100 with
`halide resistant glass 202 to form a pressure and chemical
`resistant seal to contain the gases. The glass can be made
`from materials including aluminum, titanium or tungsten
`oxides as available from commercial vendors such as Ferro
`
`Inc. of Cleveland. The melting point of such materials is
`chosen to be about 800 to 1500 degrees Celsius, and most
`preferably about 1200 to 1400 degrees Celsius.
`The cathode base 202 and the anode base 203 are fitted
`
`into the cathode base receptacle 204 and the anode base
`receptacle 205 with sufficient clearance for wetting by the
`fill glass via capillary action. The cathode base 202 and the
`anode base 203 are composed of niobium or tantalum, which
`have coefficients of expansion close to that of sapphire
`(8><10‘—6 KA—1). The cathode stem 206 is attached to the
`cathode base 202 by welding. The cathode stem clearance
`hole 208 is sufficiently large to allow emplacement of the
`cathode stem with clearance too small to allow wetting of
`the clearance hole by glass through capillary action.
`The anode end is similar to the cathode end. The filling of
`the discharge volume takes place prior to insertion of the
`cathode stem 206 and the anode stem 210. The spherical
`anode tip 207 and cathode tip 209 are formed after assembly
`by heating with lasers or by drawing high current through
`the discharge. After assembly, the glass seal is applied by
`melting glass into the space between the cathode base
`receptacle 204 and the cathode base 202.
`This SC-sapphire halide lamp can be filled with a greater
`variety of halides and background gases than those fills
`which can be used in quartz lamps. For example, scandium
`and rare-earth halides can be used, with their favorite
`spectrum in the optical region. In quartz envelopes, such
`halides form reactions that lead to deposition of the silicon
`on the thoriated tungsten cathode and depletion of the
`scandium or rare earth fills. See, for example, Waymouth, J .
`F., “Electric Discharge Lamps,” MIT Press, Cambridge,
`Mass, 1971.
`Additionally, fills such as sulfur, sodium, hydrogen and
`chlorine can be used. The use of SC-sapphire envelopes, in
`combination with the various fills, more than doubles lamp
`efficacy to about 120 to 180 lumens per watt for arc gaps in
`the range of 1-2 mm. This improvement is due to increased
`plasma luminance. Lumen maintenance is improved dra-
`matically and the life of the lamp is extended to four or five
`times that of fused quartz envelope lamps.
`A short arc version of the lamp design in FIG. 2 is
`presented as an example. Lamps can match the optical
`systems of LCD projectors most favorably when the arc gap
`length s is on the order of 1-2 mm.
`
`6
`Short mercury arc HID lamps with quartz envelopes,
`which have been optimized to gap length s of 1.8 mm and
`inside diameter d of 3.8 mm with fill densities between 40
`
`and 65 mg/cm“3 operating at 70 to 150 watts are limited to
`about 70 lumens/watt output and are subject to “flicker” and
`premature failure of the quartz envelope due to divitrifica-
`tion. (See, for example, Matthews et al, U.S. Pat. No.
`5,239,230). Halide versions of such lamps are limited to
`about 70 lumens/watt with limitations due to the physical
`properties of the quartz envelope.
`A mercury filled HID lamp is described by Fischer et al
`in U.S. Pat. No. 5,497,049. They find for example, with an
`inside diameter d of less than 3.8 mm and a power level of
`70 to 150 watts, an outside diameter D of 9 mm and a
`pressure of 20 atm, the inside of the quartz begins to liquefy
`and devitrify leading to premature failure in less than 100
`hours.
`
`Quantitative analysis of the above-optimized quartz
`lamps is as follows:
`The data for quartz from Table 2 and Table 3 are used to
`parameterize the temperature behavior of the thermal con-
`ductivity and the tensile strength of the materials. The
`geometry of the lamp and the input parameters of pressure,
`power and fill amount of Hg and Xe and other gases are
`taken from the Fischer et al patent. The temperature drop
`across the tube wall is calculated as follows:
`
`10
`
`15
`
`20
`
`25
`
`AT=qWT/k
`
`30
`
`where
`
`AT=temperature drop between inner and outer wall
`q=heat flux in watts/cm“2
`WT=wall thickness in cm
`
`k=thermal conductivity in watts/cmK
`The total mechanical stress on the tube wall is determined
`
`by summing the thermal stress due to the temperature
`gradient and the mechanical hoop stress.
`The thermal stress on the low temperature surface on the
`tube is given by:
`
`0(thermal)=oLE(T/2(1—)
`
`where
`
`ot=coefficient of thermal expansion
`E=Young’s modulus
`y=Poisson’s ratio
`The Hoop Stress is given by:
`
`oL(Hoop)=Pressure d/2WT
`
`where Pressure=fill pressure
`Using the following values:
`WT=2.6 mm
`d=3.8 mm
`L=5 mm
`PWR=70 watts
`
`Pressure=20 atmospheres
`ot=0.5*10‘—6
`E=11*10”6 lb/in”2
`we find that when the outside wall temperature of the bulb
`is 25 degrees C. the inner wall temperature would be 1400
`degrees K; which is consistent with their description of
`failure at
`that small size of d at 3.8 mm. Under those
`conditions the total stress on the bulb would be 53% of the
`maximum stress of 7000 lbs/in 2.
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`

`
`US 6,414,436 B1
`
`7
`Comparison with SC-sapphire under the same conditions
`and with:
`
`oL=8><10”—6
`
`R=11><10”6
`
`and an outer wall temperature of 25 C. gives an inner wall
`temperature of 331 degrees K with a total stress on the bulb
`of 3.9% of the maximum allowable stress.
`
`The single crystal (SC) sapphire HID lamp is capable of
`being optimized with improved performance compared to
`quartz envelope HID lamps. FIG. 3 shows the inner wall
`temperature of quartz and single crystal
`(SC) sapphire
`envelope lamps compared as a function of the outerwall
`temperature. Note that up to 1273 degrees K the inner wall
`temperature stays within safe limits for the single crystal
`(SC) sapphire lamp, while the quartz lamp fails at room
`temperature. FIG. 4 is the safety factor defined as the actual
`total stress/maximum tensile strength. This factor should be
`a maximum of 0.3 to 0.4 for safe operation. Note that the
`quartz lamp would fail at room temperature, but that the
`sapphire lamp stays within feasible operating limits up to
`1273 degrees K.
`Improved efficacy of light output, with a gap sizes
`between 1 and 2 mm are desirable, especially in projector
`lamps. By allowing operation at higher fill pressures, the
`stronger single crystal (SC) sapphire tubing allows higher
`power density and thus higher efficacy. For example, the
`mercury HID quartz lamp described in Fischer et al above
`showed an increase in efficacy from 17 lumens/watt at
`pressures of about 20 atm to 70 lumens/watt at pressures of
`50 atm, with roughly a square root dependence on pressure.
`Basically, increased pressure resulted in increased efficacy
`until the discharge went unstable.
`The pressure at which the discharge goes unstable is
`determined by the Grashoft number:
`
`Gr=c"2(d/2)2(pressure)2
`
`in mg/cc (Note that 1
`where pressure=mercury content
`mg/cc of mercury is equivalent to 1 atm at 25° C.
`In quartz HID lamps in this range Gr/c must be less than
`1400 mg2/cc for stable operation. It can be seen from this
`relationship that a lamp with the inner diameter d smaller
`than 3.8 mm would have a value of Gr/c greater than 1400
`mg2 and would be unstable at mercury contents greater than
`60 mg/cc.
`Single crystal (SC) sapphire envelopes, in the lamp design
`of FIG. 2, can prevent “flicker” at smaller diameters and
`much higher pressure. For example, a single crystal (SC)
`sapphire HID lamp we designate as SC1, with a value of d
`of 2 and an arc gap s of 1.4 mm and a chamber length S of
`3 mm would have a value of Gr/c of less than 1400 for
`pressures of 120 to 135 mg/cc. This would result in flicker-
`free operation in this pressure range.
`Efficacy is also much improved for SC1. Based on the
`increase in efficacy with pressure observed by Fischer, we
`extrapolate the performance of this 2 mm ID lamp to be in
`the range of 70 to 90 lumens/watt. Thus, improvements in
`efficacy into the range of 90 lumens/watt can be achieved
`with Hg fill lamps alone. Further increases of efficacy can be
`expected by filling the bulb with alternative elements such as
`sodium, sulfur and selenium. These elements all increase
`luminous efficiency and can be expected to further increase
`output in other versions of the single crystal (SC) sapphire
`lamp.
`Larger lamps, which develop considerable pressure on the
`end plugs, can be built with the design shown in FIG. 5. In
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`this figure a second, metallic barrier is built into the lamp.
`This second barrier utilizes a new seal geometry in which the
`pressure from the lamp is taken in compression on the seal
`face rather than in tension, as in the design in FIG. 2. FIG.
`5 is a side cross-section of a single crystal (SC) sapphire
`high intensity halide lamp. In the case of FIG. 2, single
`crystal (SC) sapphire tube 100 is used and the two plugs 300
`preferably are made of ceramic (polycrystalline) or single
`crystal (SC) sapphire to close the ends of the SC-sapphire
`tube 100 as a “first” seal. The plugs 300 are sealed to the
`single crystal (SC) sapphire tube 100 to form a pressure and
`chemical resistant seal and contain the gases inside the
`region bounded by the inside diameter d and the surface
`facing the discharge of the plugs 300. The plugs are sealed
`to the single crystal (SC) sapphire tube 100 with halide
`resistant glass 301 to form a pressure and chemical resistant
`seal and to contain the gases. The glass can be made from
`materials including aluminum,titanium or tungsten oxides
`available from commercial vendors such as Ferro Inc. of
`
`Cleveland. The melting point of such materials is chosen to
`be about 1300 degrees Celsius.
`A “second” seal
`is provided in this design to further
`improve the lifetime of the lamps. A “cathode disc” is
`inserted in a groove in the tubing in such a way that the
`pressure on the ends is taken in compression by the single
`crystal
`(SC) sapphire tube, giving a more stable and
`pressure-resistant seal. The “first seal” takes the pressure in
`shear, and as bulb diameter increases the shear resistance of
`the seal does not scale with the diameter. The “second” seal
`
`being under compression can absorb much higher forces
`without flexing or tearing.
`The second seal is preferably formed as follows. The
`cathode base 302 is welded into the cathode disc 310. The
`cathode stem 306 is also welded into the cathode disc 310 as
`
`shown. The cathode base 302 is composed of nickel or
`molybdenum. The cathode disc 310 is composed of niobium
`or tantalum which have coefficients of expansion close to
`that of single crystal (SC) sapphire (8><10‘6 K‘1). The
`subassembly consisting of the cathode base 302, the cathode
`disc 310 and the cathode stem 306 is tapped into place. The
`cathode disc 310 is designed to be flexible enough to slip
`into the cathode seal receptacle 311. Upon assembly the
`lamp is first filled appropriately and then the cathode disc
`seal 312 is made with halide-resistant glass doped with
`titanium and tungsten.
`Similarly, the anode end comprises an anode base 303
`welded to anode disc 313 and anode stem 307. This new type
`of electrodeless lamp has advantages over the quartz tech-
`nology in typical commercial electrodeless lamp applica-
`tions. In particular, the high temperature capability of the
`envelope allows operation of the bulb at power densities
`much greater than 50 watts/cm 3 without rotation.
`FIG. 7 is a side view cross-section of a single-crystal
`electrodeless high intensity halide lamp with a disc seal to
`allow higher pressure and longer life operation.
`This design utilizes the disc seal concept described in
`FIG. 5, but only as a sealing device. This allows construction
`of a robust electrodeless lamp capable of operation at
`pressures over 300 atmospheres.
`The electrodes shown in the drawings are adapted for
`A.C. operation. Their shape and size would be changed for
`D.C. or pulsed operation.
`invention may maintain a
`The lamps of the present
`correlated color temperature of between 6500 and 7000
`degrees Kelvin with continuous non-flash operation.
`Preferably the lamp bulb envelope is cylindrical in shape,
`most preferably round-ring in shape, with an inner diameter
`
`

`
`US 6,414,436 B1
`
`9
`d of between 1 mm and 25 mm and an outer diameter D of
`4.8 or more. The fill emits uv or visible light; the fill density
`pressure is in excess of 10 mg/cm3; the fill pressure prefer-
`ably exceeds 20 atmospheres; the efficacy of light output
`exceeds 60 lumens/watt, and most preferably exceeds 75
`lumens/watt; the inside surface of the bulb is adapted to be
`up to 1400 degrees Celsius; and the arc in the gap has a
`temperature of at least 1000 degrees Celsius.
`What is claimed is:
`
`1. In an optical projection system, a high intensity dis-
`charge lamp for producing uv or visible light and having an
`anode electrode and a cathode electrode, wherein an effec-
`tive correlated color temperature is maintained of continu-
`ous non-flash operation thereby increasing the efficacy of the
`lamp radiation output comprising:
`(a) a lamp bulb envelope tube of single crystal (SC)
`sapphire tubing, having a tubular burst pressure of at
`least 155,000 psi at 25° C.;
`(b) wherein the lamp bulb envelope is cylindrical in shape
`with an inner diameter of between 1 mm and 25 mm
`and an outer diameter D of 2 mm or more; and
`(c) a fill in said envelope which emits uv or visible light
`radiation, having a color temperature between 6500 and
`7000 degrees Kelvin, when an arc is struck between the
`electrodes and whose fill pressure exceeds 120 atmo-
`spheres.
`2. The apparatus of claim 1 wherein said bulb includes
`tungsten electrodes.
`3. The apparatus of claim 1 wherein the efficacy exceeds
`60 lumens/watt.
`4. A high intensity discharge lamp for an optical projec-
`tion system, the lamp producing continuous uv or visible
`light, wherein loss of bulb transparency vs. time is substan-
`tially reduced, thereby increasing the useful life of the lamp,
`the lamp comprising:
`(a) a lamp bulb envelope tube of single crystal (SC)
`sapphire tubing the tubing being without microscopic
`surface undulations arising from conversion in place
`from polycrystalline alumina; and the tubing having a
`burst pressure of at least 155,0