CA2066604A1 - Variable color lamp - Google Patents

Abstract

A variable color lamp of which the chromaticity of the light can be varied. The variable color lamp (1) has first, second, and third arc tubes (3, 4 and 5), each being a metal halide tube, in an outer tube (2). Main electrodes enclosed in the respective arc tubes are connected with a power controlling circuit (20). The first arc tube (3) in which indium halide is sealed emits light of a strong line spectrum in bluish violet. The second arc tube (4) in which thallium halide is enclosed has a strong line spectrum in green. The third arc tube (5) in which sodium halide is enclosed has a strong line spectrum in yellowish red. The color of light of the lamp can be adjusted to any color in the almost whole range of visible rays on x-y chromaticity diagram by changing the relative intensities of light of the respective arc tubes through the use of the power controlling circuit, etc.

Description

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DESCRIPTION
VARIABLE COLOR LAMP

Technical Field The present invention relates to a variable color lamp with a dimmer function Background Art When a light source includes a number of lamps with t0 diffPrent luminous colors, the color of the light e~itted from the source is varied by switching over the lamps.
Several devices have been proposed fo~ continuously changing the chromaticity of light emitted from a discharge lamp; for example, Japanese Patent Publication Gazette No.
ls Sho-53-42386 and Japanese Patent Laying-Open Gazette No.
Sho-63-198295~ In such devices, gas or vapor sealed in a discAarge lamp as a luminescent material varies its luminous color corresponding to the intensity o~ electxonic energy, that is, the waveform o~ a pulse, in the discharge lamp.
20 When the ratio of power supplying time to idle period is rela-tively large, the color o~ the light emitted from the lamp is blua; o~ the other hand, when the ratio is relati~ely small, the color of the.light emitted from the lamp is red.
The former method, howeverr re~uires a large num~er of luminous lamp corresponding to various color~ and there~ore makes a device bul~y. Such a device occupies large space and .

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is not ~1itable ~or private purposes, that is~ lighting in or out o~ the houses or illuminatio~ at shop w.indows.
In the latter method, on the other hand, since a longer idle period is required for red light emission, power supplied s to the discharge lamp becomes rather small and luminance of the light may be insufficient for illumina-tion.
The objective o~ the invention i~ thus to provide a space-saving variable color lamp which emits light of ~arious chromaticity and sufficient luminance.
1 0 ~' ' Disclosure Invention The invention attains the foregoing and other objectives with a variable color lamp with a dimmer function, which - includes: plural emission tubes each emitting light of different chromaticity; and control means for regulating power supplied : to each of the plural emission tubes.
Power supplied to each of the emission tubes i5 regulated by the control means, and each amission tube ~mits light of self-luminous color corresponding to the power.
~0 'rhe variabl~ color lamp of the invention occupies smaller space khan the conventional light source including a ! large number of lamps with different lumi~ous color~. The color lamp o~ the invention does not require idle period ~or ~ :
light emission of. any color or tint and can thus emit light of neutral tints with sufficient l~minance.
The simple structure of the invention attains light 2~66Q~
~3--em.ission of a wide range o:E color varia-tion at relatively low c~st.
The control means includes a relative output control unit for varying the relative output or the quantity of light emitted from each of the plural emission tubes. The variable color lamp of the invention thus emits light of a neutral tint according to the relative outputs of the plural emission tubesO Namely, the luminous color of the lamp is varied corresponding -to color matching functions of chromaticity coordinates.
In another aspect, the invention comprises a variable color lamp including: ~ first emission tube far emitting blue light of a first wavelength rang2; a second emission tube for emitting green light of a second wavelength range; and a third emission tube for emitting red light of a third wavelength range.
The color lamp of the invention has the three emission tubes each discharging light of one of the additive p~imaries proper to the tube, thus attai~ing a wider color variation and reproducing the color of irradiated objects vividly.
The first through the third emission tubes are all di~charge tube~; the fix~t emission tube includes indium halide sealed therein, the se~ond emission ~ube includes thallium halide ~aled therein; and the third emission tube include~ sodium halide sealed thérein.
In the variable color lamp including the first through ., .. , ., ~ ., . , . . ,, . ,~ , . . . . ~ , . .

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the third ~mission tubes each emitting light of one o~
additive primaries proper to the kube or discharging color light d~termined by the metal halide sealed in the tube, th~
first through the third emission tubes are arranged adjacent to and parallel to one another.
The three emission tu~es may he arranged in parallel on the same plane such that the first emlssion tube is p~aced in between the second and the thixd emission tubes. The emission tube disposed in the middle is the first emission tube with indium halide seal~d therein which has a narrow dimmer range than thallium halide or sodium halide.
The three emission tubes disposed adjacent to and par~llel to one another or arranged in parallel on the same plane in the predetermined order may be integrally formed in the variable color lamp of the invention. Such strllcture enables the adjacent emission tubes t9 trans~er thermal ~ ;~
energy generat~d from the tubes to each other and to attain uniform temperature riseO ~ach emission tube thus reaches stable lighting conditions ~ithin a short time period.
Th~ emission tub~ di~posed in the middle receives thermal en~xgy generated from both khe side tubes. Namely, the middle tube with indium halide receives thermal energy from both the adjacent emission tubes and is thereby maintained at high temperature.
This structure of the invention at~ains a wider range of color variation of the emission tubes as described below.

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A hi~h intensi-ty discharge lamp including one emission tube generally ha~ a dimmer range of approximately ten percent. The dimmer range o -the discharge lamp i5 narrower than incandesc~nt lamps and tungsten halogen l~mps because of the followiny reasons. In th~ high intensity dischaxge lamp, when input to the emission tube i5 limited in order to decrease -the light flux, the temperature in -the emission tu~e is lowered and the luminesce~t material such as In (indium~, Tl (thallium), or Na (sodium) sealed in -the emission -tube varies its partial vapor pressure, When the partial vapor pressure drops down to a predetermined threshold ox lower value, the lamp does not discharge any light but is in 'OFF' state. In the conven-tional high intensity discharge lamp with only one emis~ion tube, the possible dimmer rang~ i~
within approximately ninety percent of the rated output~
In the ~ariable color lamp of the invention, on the other hand, plural emission tubes are disposed adjacent to and parallel to each other, and thermal en~rgy generated from each emission tube is transferred tQ the other emission tubes through the common side wall of the tubes. Even when input ko one emi~sion tube is limite~, thermal energy generated from the adjacent emission tubes is given to that one tubeO
A~cordingly the emission tube with limited input in the structure of the invention is maintained at higher temperature than the only one emission tube with limited input in the conventional high intensity discharge l~mp. The partial - . : . - . : . . - . .

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vapor pressure of the luminasce~t material sealed in the emission tube with limited input do~s not vary bu-t i5 Xept relatively constant, so -that the possible dimmer range of the emission tube becomes wider.
Input to one emission tube may be decre~sed while input to ~he other two emission tubes is increased. This allows the total input to the whole variable color lamp to be kept constant and thereby prevents the temperature fall of the emission tube with limited lower input so as to attain 2 wider dimmer range.
The variable color lamp of the invention can emit light o~ a wider chromaticity range corresponding to the wider dimmer range of the emission tube.
In the variable color lamp of the invention, the emission tube disposed in the middle contains indium halide emitting bluish purple line spectrum and having a relatively nar~ow dimmer range. Thallium halide emitting green line spectrum and having a relatively wide dimmer range and sodium halide emitting reddish orange line spiectrum and having a relatively wide dimmer range are reæpectivaly ~ealed in the side emission tube~ arranged in parallel with the middle tube.
When input to the middle emission tube with indium halide having a relatively narrow dimmer range is decreased and the same to the side emission tuhes with thallium halide or sodium halide having a relatively wide dimmer range is ,;, . ~, - . : . , ....... , , . , ...... : . ; : . ~ . . - .: . - . . .. - :: :

- . . . - :- -: .... : . ~ :.:,: : :-. -.. ... .. : ,- . .

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increased, thermal ~nergy generated ~xom the side tubes i~
transferred to tha middle emission tube so as to maintain the middle tube at high temperature. The possible dimmer range of the middle emi~sion tube i~ thus made wider than the original dimmer range of the sealed luminescent matexial.
The plural emission tubes of the invention axe composed of translucent alumina ceramic~ prepaxed by sintering fine powdery alumina of at least 99.99 mol~ in purity. TAe average grain diameter of the translucent alumina particles is not greater than one micrometer and the maximum grain - diameter is not greater than two micrometer.
Since high purity of alumina does not virtually ~orm the grain boundary phase, the emission tube of translucent alumina ceramics has improved mechanical strength (bending strength and Weibull coef~icient) at ambient to discharge temperatures, compared with an emission tube of conve~tional translucent ceramics prepared by sintering and growi~g grains with a sintering accelerator such as MgO. The improved mechanical strength allows the emission tube to have thinner wall and thereby ~maller thermal capacity. Accordinqly the luminous part of the emission tube is heated to a predetexmine~
temperature at a high ~peed and warm-up tLme o~ the tube is ~hortened. ~ere the warm-up tLme represen~s a time period until di~charging metal component (metal halide) ~ealed in the tube vaporizes to ~aturated vapor pressure.
The emission tube may be any discharge ~ube wi*h high , ,. ,: , . . . . . .. .. .

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lc~mp efEicacy; for example, metal halide tubes, high-prassure sodi~ tubesl and fluorescent tubes.
Japanese Industrial Standard JIS Z8110 deines the rel~tionship between the salf-luminous color of a monochromat.ic light source and the wavelength range as follows:
380 to 455 nm: bluish purple 455 to 485 nm~ blue 485 to 495 nm: blue green 495 to 548 nm: green 548 to 573 nm: yellow green 573 to 584 nm: yellow 584 to 610 nm: reddish orange 610 to 780 nm: red In the invention, the wavelength range of blue light ~ :
denotes 380 to 49~ nm; the wavelength range of green ligh-t represents 485 to 573 nm; and the wavelength range of red light i~ 573 to 780 nm. ~ :

Brief De~cription Of Dra~ing~
Fig. 1 i~ a v~rtical cross sectional view showing a var.iable color lamp of a ~ir~t embodiment according to tha inventlon; -~
Fig. 2 is an x-y chromaticity diagram showing the relationship betwee~ the relative output of an emission tube .:
and the luminous color in the variable color lamp of the first embodiment .. . ~ . ~ . .. . . . ' , . . ! .

9 2 ~

Fig. 3 .i.s a block diag.ram showing the electric s-tructure of the variable color lamp of the first ~mbodimenk;
Fig. 4 is a perspective view illustra-tiny an emis ion tube lM built in a variable color lamp according to a second embodiment;
Fig. 5 is a process chart showing manufacturing process of the emission tube lM;
Fig. 6 is a perspe~tive view illustrating another emission tube lN;
lOFig. 7 is a graph showing distribution of the grain diameter of translucent alumina constituting the emission tube lM; : .
Fig. 8 is a persp~ctive vi~w illustrating another emission tube lL applied to modification of the second e~bodiment;
Fig. 9 is a perspective view illustrating another emission tube lR applied to modi~ication of the second e~bodiment and a mold used -for manufacturing the tube lR;
Fig. lO is a perspective view illustrating another ~0 emis~ion tube 15 appli~d to modi~ica~ion of the second embodiment;
Fig. ll(a) i~ a perspective vlew illustrating another emission tube lA used in place o~ the emissio~ ~ubes lR and lS;
25Fig. ll~b) is a Y-plane cros~ sectional view o~ Fig.
ll~a);

,: . ... ... .

.. :. ' - '' ' ' -lo- 2~

Fig. l~ is a process chart showing manuEac-turing pro~ss of the emission tube lA;
Figs. 13(a) and 13(bl are perspectiva views showing a mold used in manufacture of the emission tube ~A; :
Fig. 14 is an explanatory view illustrating manu~acture of the emission tube lA; and Fig. 15 is an explanatory view also illustrating manufacture of the emission tube lA.

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Best Mode for Carrying Out the Invention Preferred embodiments of the invention are hereinafter described in detail according to the drawings.
Fig. 1 is a vertical cross sectional view showing a variable color lamp of a first embodiment according to the invention.
A variable color lamp 1 includes a first emission tube

3, a sPcond emission tube 4, and a third emission tube 5 via a support 15 i~ an outer bulb 2 havin~ a reflector mirror 17 on the upper side thereof. The outer bulb 2 is composed of a txanslucent matexial having light æcattering abilityj for example, ~rosted gla~s, milky glass or acrylic resin~ Metal halide (luminescent material) for emitting ligh~ of a different luminous color is sealed with mercury and starting noble gas in e~ch of the ~mission tubes 3 through 5. A pair of primary electrodes 6 and 9, 7 and 10, or 8 and 11 are ~dhered to either end of the emission t~be via molybde~um foils. ~uxiliary '. ~:

:-- - : -: .::
. : . .: -. , 2 ~

startin~ electrodes 12, 13~ and 14 are also fixed Lo the lower end of the emission tubes, respectively. The primary electrodes and the auxiliary starting electrodes are connected to a power control circuit 20 (described later) through pins 16.
The emiission tubes 3 through 5 are composed of quartz glass, and the primary electrodes mounted on both the ends of the emission tube are coils of tungsten and the like. The outer bulb 2 may be evacuated or filled with gas.
The first emission tube 3 contains indium halide such as InI3 with mercury and star ting no~le gas, and emits bluish purple line spectrsm at the wavelength around 411 nm or 451 nm. The second emission tubP 4 contain~ thaIlium halide such as TlI with mercury and starting noble gas, and emits green line spectrum at the wavelength around 535 nm. The third emission tube 5 contains sodium halide such as NaI with mercury and staxting ~oble gasy and emits reddish oran~e line spectrum at the wavelength around 589 nm. .
Fig. 2 .is an x-y chrvmaticity diagram showing the relation~hip between the relative output o the emis~ion t~e and the luminou~ color; In the diagramr point~ A, Bt and C
3 repre~e~t luminou~ colors of the emission tubes 3 through 5, respe~tively. Th~ l~minou~ color of t~e variable color l~mp 1 may be varied within a triangle of the three points A, B, and C in conformity with the rule of color addition (the additive mixture of color~). For example, when outputs of : . ..

,. . . - - . , , ~. . - -. . . . ::: ~ :

'. ~ ' ' A , .' , .' ' . . ' ' ' , ' ~12- 2~60~

the second and the third emission tubes 4 and 5 a.re set greater than that of the first emission tube 3, -the luminous color of light emitted from the variable color lamp 1 is pale yellowish green shown by a point D.
S The electric structure of the variable color lamp 1 of the first embodiment is explained based on the block diagram of Fig. 3. The auxiliary starting electrodes a~e omitted in the diagram since they are not essential for the scope of the invention.
The power control circuit 20 includes three dimmers 21, 22, and 23 and three ballasts 24, 25, and 26 corresponding to the three emission tubes 3, 4, and 5. The dimmers 21 through 23 are semi-conductor phase control circuits connected to an ~C power source 18 in series. When the emi~sion tubes 3 through 5 have different rated voltages, each dimmer may be connected to an individual AC power source for applying a different rated voLtage~
A color control circuit 30 includes an input area 31, an output distribution calculator 32~ an emission tube ou~put calculator 33, and three d.immer signal output areas 34, 3 and 36.
A remote control unit 40 include~ a chromaticity setting area 42 and a lamp output setting area 43. The remote - , . .- .
control unit 40 has a series of keys for inputting commands 25 and a display for showing operati~n of the lamp. ~.

TAe luminous color or the light flux of the lamp may be ..

- . . , - . . . : , . . ~ . : .. - . : ~ . . .

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v~ried b~ settin~ the chromaticity and output oE the lamp through th~ keys of the remote control unit 40. The chromaticity i5 ~ for example r input as coordinate values on the x-y chromaticity coordinates. The coordinates of the point D in Fig. 2 are (0O37~ 0.45) in the x-y chromaticity coordinatP system. The output of the lamp is, for example, input as a percentage relative to the maximum output of the lamp at each chromaticity. The chromaticity setting area 42 and the lamp output setting area 43 of the remote control lo unit 40 respectively generate a chromaticity signal Sc and a lamp output signal Sp corresponding to the input values, and transfer data to the input area 31 of the color control circuit 30.
The chromaticity ~ignal Sc is sent from the input area 31 to the output distribution calculator 32, which determines the relative value of the total luminous flux emitted from each of the three emission tubes 3 through 5 according to the additive mixture of colors so as -to attain th~ chromaticity shown by the chromaticity signal Sc.
The emission tub~ output calculator 33 determine~ the output level of each emission tube based on the relative ,l value of the total luminous flux, thak is~ the relative output, of the emis~ion tube detsrmined ~y the output distribution calculator 3~ and the lamp output signal Sp.
The output level of the emission tu~e having the m~ximal relative olltput determined by the output distribution calculator 2~6~
--1'}-32 i5 set ~qual to a value multiplying the rated output of the emiss.ion tube by the relative output (percent) shown by the lamp output signal Sp. For example, when the ~elative output values of th~ three ~mission tubes are 0.6: 0.4~ 1.0 and the relative output of the lamp output signal Sp is seventy percent, the output levels o~ the emission tubes are respectively set to 42%, 28%~ and 70~.
Signals representing the output levels of the emission t~bes are sent from the emission tube output calculator 33 to the three dimmer signal output areas 34 through 36, which -generate dimmer si~nals (fade signals) for controlling the dimmers 21 through 23. Each of the dimmers 21 through 23 controls a continuity phase angle of current supplied to the emission tube coxresponding to the dimmer signal output from 15 the dimmer signal output area 34, 35, or 36. Current running -: through the emission tube and the total luminou~ flux of the emission tube are thus adjusted. Since the efficiency of the emission tube Yaries with the current, the total luminous 1ux is not always proportional to the feed quantity. The emission tube output calculator 33 corrects the ~ig.nals, which are sent to the dimmer signal output areas 34 through 36, with a predetermined calibration curve according to the relation~hip between th~ total luminous flux of the emis~ion t~be and the feed quantity, such that the ratio of the output signals is equAl to the ratio of the total luminous fluxes of the emission tubes determined by the output distribution ,~ -.: . ,- .. . : ... -. . .: . ... , ., - ... . . -.. -. .. .-,. ,.. ;.,., .. - . .. .... . . .

:: : .: . . .- :: - -: . - ,, .- , ",, , .- - - .. . . . ..

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calculator 32.
The emission tub~s 3 through 5 are installed in the outer hulb 2 composed of a translucent material with light scattering function, for example, frosted glass, milky glass or acrylic resin. Mixing ~ailure of the luminous fluxes of the plural colors due to mi~alignment of the emission tubes is hence well prevented by the blurring of such a translucent material.
The variable color lamp 1 of the first embodiment tO includes three emis~ion tubes each discharging color light similar to one of addi-tive primaries, that is, Red, Green, and Blue. The luminous color o~ the variable color lamp 1 is adju~table within almost the whole visible ligh-t on the x-y chromaticity diagram by varying the relative outputs of the 15 emission tubes. Namely, the luminous color of the lamp i5 varied corresponding to color matching functions of the chromaticity coordinate system~ The li~e spectra o~ the - emission tubes are also close to the additive primaries , and the color o~ an irradiated object i~ there~y repxoduced 20 vividly.
The emission tube~ 3 thro~lgh 5 of the variable color lamp 1 may be any discharge tube ~uch as incandescent tubes, ~luorescent tube~, hi~h pressure sodium t~be~, and n~on tu~es as well a~ the metal halide tubes used in the first ~bodiment.
25 For example, when a neon tube emitting red li~e ~pectrum is r u~ed for the third emission tube 5 tthe metal halide tube ,'. ' "
'' " .
;. . .

2~6604 con~aining sodium halide such as NaI in the first embodiment), wider color variation i~ implementad.
Emission tubes emitting continuous spectrum may be used in place of thos~ with line spectrum in a certain wavelength range.
In ~nother aspect, certain additives may be mi~ed with alumina to give specific spectral charactPristics to the tran~lucent alumina emission tube with hydrogen, iodine, and starting noble gas sealed therein. When chromium compound is add~d to alumina, red line spectrum is obtained; cobalt compound for blue line spectr~n; and nickel or zinc compound for green line speetrum. The speci~ic spectral characteristics may be attained by coloring the whole emission tubP or forming a colored layer on the surface of the emission tube.
In the first method, solid solution of the metal oxide tadditive) i9 mixed with alumina while translucent alumina is sintered. In the latter method~ on the other hand, solid solution of the me-tal oxide is painted on the circumferel1ce o~ the alumina emission tube.
The number of th2 ~mi~ion tubes is det~rmined according to the reguirement. Two emission tubes are, for example, us~d when th~ coloring range is a lins, while four tube~ are used when a wider band range should be covered.
Another variable color lamp of a second embodIment according to the invention is described hereinaf~er. In the following description, mem~ers having the ~ame functions as -17- 2 0 ~

the first e~bodiment may not be explained, nor may symbols or numerals ass:igned to such members be omitted.
In the first emhodiment~ the three emission -tubes 3 through 5 are independently installed in the outer bulb. The second embodiment, on the other hand, includes an emission tube lM consisting of three emission pipes intesrally formed in parallel on the same plane as shown in Fig. 4.
The emission tube lM, composed of translucent alumina, is a multi-pipe tube consisting of three single emission pipes lml, lm2, and lm3 which are integrally formed adjacent to and parallel to one another. Each emission pipe has a pair of primary electrodes and generates linear electric discharge spaceO The side wall of the single emission pipPs lml and lm2 or lm2 and lm3 is in common as indicated by - ~5 shaded parts in Fig. 4.
The inner diameter of each single emission pipe lml, lm2, and lm3 ('d' in Fig. 4) is ~pproximately 4.0 mm, and the wall thickness ('dO' in Fig. 4) is about 0.2 mm. The distance between the primary electrodes adhered in each em.is~ion p.ipe is approxLmately 30 mm.
Manufac~ure of the emission tube lM is described according to the process chart vf Fiy. 5~
Fine powdery alumina, material o~ the emission tube lM
is first synthesized. Aluminum salty which gives at least 9g.99 mol~ in purity of alumina by pyrolysis, is used as a starting material. Examples of such aluminum salt for ..

, . - ......... : . - . - ............. ~ .. .. ~ - .,. - . ,:

: - :. . , . . : : ~- - ~ - . -: .:

20~0l1 yielding high purity o~ alumina include ammonium alum and aluminum ammoni~n carbonate hydroxida ~NH~AlCO3(O~1) 2 ) .
The aluminum salt i5 weighed, mixed with distilled wa-ter and a dispersing agent to a suspension, and dried by spray drying. The dried salt is then pyrolyzed to fine powdery alumina at the temperature between 900 and 1200C, -for examplP, 1050C, in the atmosphere for two hours. Through the process of spray drying and pyrolysis, fine powdery alumina (average grain diame-ter: 0.2 to 0.3 micrometer, purity: at least 99.99 mol~) is prepared. Secondary aggreqate of alumina fine powder, which has a greater diameter than the powder, is actually yielded.
An organic binder mainly consisting of acrylic thermoplastic resin is mixed with the secondary aggregate of alumina fine powder. The mixture in an organic solve~t such as benzene is wet stirred with a plastic or nylon ball mill for approximately twenty-four hours, so that the organic binder and alumina fine powder are sufficiently wet. The mixture is then evaporated ox removal of the solvent and ~0 kneaded to yield a compound of a desired ~iscosity (50~000 to 150~ 000 cp~) (process ~
,1 The organic binder con~ists o~ acrylic thermopla~tic resi~ paraffin wax, and atactic polypropylene, and the total quantity of th~ binder is 25 g with respPct to 100 g of alumina f ine powder . ~ :
The content of each component of the organic binder is -, ; . . - , , " - , . .

. - . - ... ~ .- .: - . . . . . . . . .

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as follow~:
Ac~ylic thermoplastic resin: 20 to 23 g ~pre~erably 21.5 g) Paraffin wax: not greater than 3 g 5(preferably 2.0 g~
~tactic polypropylene: not qreater than 2 g (preferably L.5 g) Here, the tvtal of the contents should be 25 g.
The mixture is evaporated at 130C for twenty four hours and kneaded at 130C with an alumina roll mill to yield a compound.
The compound is in~ ected into a cavi-ty of a mold on an injection molding device ~not shown) and molded to a multi-pipe body W0, shown in Fig. 4, consisting of three cylindrical emission pip~s integrally formed adjacent to and parallel to one another (process 2). The compound is previou~ly hea-ted to 130 to 200C (preferably 1809C), and then injected from a no~zle of an injection device under the pressure of 900 to 1,800 k~/cm2.

20The compound i~ solidified in the inj~ction cavity to the molded body W0 under ~he certain pre~sing conditions; khe ! pre~ure of 180 to 800 kg~cm2 is kept for 0.5 to 5 seco~d~.

The mold2d body W0 thus obtained h~s 0.99 or higher transfsrability (~imensions of the molded body J those of the mold), 0.99 or higher circularity, and O.g9 or high~r con~raction ratio (i~ the dir~ction of th diameter / that of the ~xis~

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The lnner ~iameter of each cylindri~al pipe of the molded ~ody WO is determined t~ be ~pproximately 4.~5 mm hy considPring ..
volume shrinkage on sintering. The wall -thickness ('dO' in Fig. 4) of each cylindrical pipe is se-t to be approximately 0.3 mm by considering volume shrinkage on sintering and grinding margin.
After completion of the injection molding proce~s (process 2), the molded body WO is parted from the mold on the injection molding device ~process 3).
The molded body WO is heated in nitrogen atmosphere to a temperature at which the oxganic binder containing acrylic thermoplastic resin is pyrolyzed and completely carbonated.
Namely, th~ molded body WO is degreased (process 4). The upper limit of the heating temperature in this initial heat treatment is determined according to the performanca of the heat treatment furnace and the pyrolytic temperature of the organic binder. In this embodiment~ khe molded body WO is heated from the room temperature (20C) to 450C ~or seventy-two hours. The conditions of the initial heat treatment are as follow~:
Pre~sure: l to 8 kg/cm2 (optimal pressure is 8 kg/cmX~
Time period for heating Erom 20C to 450CJ not longer than seYenty-tWO hours.
Here, the pres~ure i~ kept constant during heating Up to 450C.

~ --21- 2~6~60~

The organic binder o acrylic thermoplastic resin, paraffin wax, and atactic polypropylene mixed in the compound is pyrolyzed and carbonated through this initial heat treatment, so that the molde~ body W0 is sufficiently degreased.
The degreased body W0 is again applied to heat treatm~nt in the atmosphere so as to be sintered (proce~s 5). The conditions of the secondary heat treatment are given below;
here the heating rate is 100C J hour ~; Temperature: 1,200 to 1,300C
(optimum temperature~ 1,235C) Time period of treatment at the above temperature:
zero to four hours (optimum time period: two hours~
The ~intering temperature is s~t in the range of 1,200 to 1,300C so as to make the actual density of the sintered body not less than 95% of the theoreti al density for the following hot isostatic pressing and prevent growth of undesirable rough crystals. When the temperature is 1,200C
or lower, the density of the sintered body drops to the level unsuitab~e for hot i~ostatic prassing, that is, less than 95~
of the theoret~aal density. When the temperature i~, on the other hand, over 1,300C, forMation of rough crystals d~creases the strength of the sinterad body.
Through the initial and secondary h~at treatment for - degreasing and sintering, the volume of the molded body is shrunk to 82.5%, and the packing factor of the sintered body becom~s approximately 100% tbul~ density: 3.976). Carbides ,, .

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.
:.
produced in the process of the initial heat treatment are completely burned out and removed from the sintered body through the sinkering process.
The sintered body is exposed to hot isostatic pressing in argon atmosphere or the atmosphere of argon with o~ygen of ,~ not greater than 20vol% (process 6). The conditions of the hot isostatic pressing are given below; here the heating rate is 200C / hour:
.. . . .
! j Temperature: 1,200 to 1,250C

(optimum temperature: 1l230~C) Pressure: 1,000 to 2,000 atm ~optimum pressure: 1,000 atm) Time: one to four hours ~optimum time: two hours) sf :, .
l The sintered body acquires translucency through this process, 15 and the multi-pipe emission tube lM of translucent alumina is thus obtained.
The temperature~and pres~ure ranges for hot isostatic pressi~g are~determined~ so as to give desirable translucency to ~the~ sintered~;body and improve the mechanical strength 20~ thereof. ~When the hot~i sos~atic pre.ssing is implemented at the~temperature~lower~than ~1,200C or~ under ~he pressure lower than l,OOO;~atm,~sufflcient traDslucenay is not siven to the sintared body. When the temperature is over 1,250C, on the other hand,~ abnormal grain ~rowth lowers both translucency 2S and mechanical strength. When the pressure is over 2,000 atm, even~very;small pares ar scratahes in the sintered body 2~6~

may cause ~atal craoks due to stress concentration.
sOth ends of the mul-ti-pipe amission tube lM of translucent alumina are then ground with a di~nond grinding wheel, and the inner and outer surface of the emission tube lM is ground and polished to have the wall thickness not greater than 0.2 mm by u~ing a brush with diamond abrasive grains (grain diameter: O.5 micrometer) (process 7). This grinding process smooths the surface of the emission tube to prevent scattering of light on the surface, thus improving lo the linear transmittance.
Through the process 1 to 7, obtained is the emission tube lM shown in Fig. 4, consisting of three :single emission pipes lml, lm2, and lm3, which are integrally formed adjacent to and parallel to one another and have the common side wall shown by the shaded parts in the drawing. The emission tube 1~ thus prepared has the inner diameter of about 400 ~m (wall thickness: approximately 0.2 mm) and the total length of approxLmately 40 mm.
The emi~ion tube lM with pairs of primary electrodes 20 i3, in u~e, installed in the outer bulb o~ the va.riable color lamp. Luminescent materials are individually sealed in each of the ~ingle ~mission pipes lml, lm2, and lm3 o~ the emi~ion tube lM. ~xample~ of such luminescent materials include: indium halide emitting bluish purple line spectr~m, thallium halide emitting green line spectrum, and sodium halide emitting reddish orange~lLn~ spectrum. In one embodiment, o ~

indium halide is sealed in the single emission pipe lml;
thallium halide in the single emission pipe lm2; and sodium halide in the single emission pipe lm3.
The variable color lamp of the second embodiment has the multi-pipe emission tube lM consisting of the three single emission pipes lml, lm2, and lm3 integrally formed adjacent to and parallel to one another, while the first embodiment has three independent emission tubes 3 through 5 installed in the outer bulb. The second embodiment has the following effects as well as those of the first embodiment including variation of the luminous color corresponding to the color matching functions of the chromaticity coordi~ate system.
In the integral emission tube lM of the variable color lamp, the side wall of the adjacent single emission pipes lml and lm2 or lm2 and lm3 is formed in common~ Th~rmal energy is freely transferred between the adjacent single emission pipes through the common side wall~ thus allowing the wall - temperature of ~th2 sin~le emission pipes lml, lm~, and lm3 ~o rise uniformly. The whole emi~sion tube lM is accordingly stabilized within a short tLme period, an~ the warm-up time is ~a~orably shortened.
When plural emission tubes axe axranged not in contact with or adjac~nt to one another in the lamp, arc discharge between the pair of primary electrodes starts at a different ~5 moment in each emission tube, and heat generation due to arc discharge is made different among the ~ube~. The plural ,~ .

- ,. , . .- , , - .

-~5 emission tubes di~fer in the heating time period for raising the wall temperature of the emission tube to ~ predetermined value (the temperature at which sealed discharge material is evaporated in the emission tube to give saturated vapor pressure). Accordingly the plural emission tubes are not stabilized at the same time or on the whole within a short tLme.
On the contrary, in the structure of the multi-pipe emission tube lM, the temperature of the single emission 10 pipes increase uniformly to a predetermined value based on .:
heat transfer through the common wall. The plural emission pipes or the whole emission tube lM is thus stabilized almost simultaneously and the warm-up time of the variable color lamp is significantly shortened.
Heat transfer between the adjacent ~ingle emission pipes lml and lm2 or lm~ and lm3 of the emission tube lM expands the possible di~mer range of each sin~le emission pipe~
A high inkensity discharge lamp including an emission tube ~enerally has a dimmer ranga of approximately ten percent. The dimmer range of the discharge lamp is signific~ntly narrower than inca~descent lamps and tungsten halogen lamps b~cau~e of the following reasons. In the hi~h intensity discharga lamp, when input ko the emission tub2 is limited in order to decrease the light flux, the temperature in the emission tube is lowered and the luminescent material ~uch ~s In, Tl, or Na sealed in the emls~ion t~be varies i~s partial ~'~

.. . . . . ... ..

, , , . . .. ...... .. ~ . ..
: - : .. ... .. ~. . ..
- . - - - : , -..... ... -- :

-26~ 4 ~ ~ ~

vapor pressu~e~ When the partial vapor pressure drops down to a predetermined threshold or lower value, ~he lamp does not discharge any light but is in 'OFF' state. In the conventional high inten~ity discharge lamp with only one emission tubs, the possible dLmmer range is within approximately ninety percent of the rated output. In the variable color lamp 1 of the fir~t embodiment including independent three ami~sion tubes, the possible dimmer range is also about ninety percent~
In the emission tube lM of the second embodiment, on the other hand, since three single emission pipes are arranged adjacent to and parallel to one another and have the common side wall, thermal energy generated from each emission pipe is transferred to the other emission pipes through the side wall. Even wh~n input to one emission pipe is limited, thermal energy generated from the adjacent emi~sion pipes is given to that one pipe. Accoxdingly the single emission pipe with lLmited input in the emission tube lM of the varia~le color lamp is maintained at higher temperature than the only one emis~ion tub~ with limited input in the conv~tional high intensity discharge lamp. The partial vapor pres~ure of the lumine~cent material sealed in t~e single emission pipe with limited input does not vary ~ut is kept rela~ively constant, so that the po~sible dimmer ra~ge of the variable color lamp becomes wider~
I~put to on~ emis~ion pipe may be decreased while inpl~t ' ' ' -27~

to the other two emission pipes is increased. This allows the total input to the whole emission tube to be kept constant and thereby prevents the tempera-ture fall of the single emission pipe with limited lower input so as to attain a wider dimmer range.
The variable color lamp with the emission tube lM has wider variation of chromaticity of -the emitted light corresponding to the wider dimmar range of the emission tube.
Arrangement of the single emission pipes wi-th metal halides sealed therein attains the following effects besides the wider dimmer range.
In the emission tube lM of the embodiment, the single emission pipe lm2 disposed in the middle contains indium halide emitting bluish purple line spectrum and having a narrower dimmer range than thallium and sodium. Thallium halide emitting green line spectrum is in the single emission pipe lml, and sodium halide emitting leddish orange line - spectrum in the single emission pipe lm3. When input to the middle emission pip~ lm2 with indium halide having a relatively ~0 narrow dimmer range is decreased and the same ~o the adjacent emission pipes lml and lm3 is increased, thermal energy ~; generated from the adjacent emi~sion pipes lml and lm3 is tran~ferred to the middle emission pipe lm2 so as to maintain the middle emission pipe at high temperature. The possible dimmer range of the middle emission pipe lm2 is thus made wider than the original dimmer range of indium. Another . : ... .- - . . ::

2~6~60~

emission tube lN shown in Fig. 6 may be used ~or the emission tube 1~ to give the similar effects.
The properties of the emission tube lM are given below:
Linear tran~mittance to visible light (wavelength: 380 --5 to 760 nm): not less than 70% . .
hinear transmittance to light having the wavelength of 500 nm: B2~ (~all thickness: 0.5 mm) Average grain diameter: approximately 0.7 micrometer (maximum grain diameter: 1.4 micrometer) Mechanical strength (JIS R1601~ :
Bending strength St: (room temperature) - 98 kg/cm (9oooc) = 81 kg/cm2 Weibull co2fficient: (room temperature) - 3.3 (~00C) - 8.1 :; l5 Above data including the grain diameter and the ~ .
mechanical strength was determined not for the emission tube ;
1~ itself of the embodiment but for a sample prepared under the variou~ conditions specified in the above manufacturing process (the shape and the thickness of the sample were ln ; ;
conformity with ~IS R1601)~
The grain diameter wa~ determ.i~ed in the following . . ~ .
.il mannar. The suxface of the sample prepared to have the shape and thicknes~ in accordance with JIS Rl601 was lapped with diamond abxasive grains and exposed to molten potaæsium hydroxide for intergranular etchin~. The image of the grain was analyzed based on observation of the surface of the :'' ;- :
- ,::

20B660~

sample with a scanning electron microscope. For the image analysis~ the grain was assumed to be spherical or polygonal, and the maximum value of the diameter or the distance between vertexes was used for calculation of the grain diameter.
Fig. 7 shows a distribution diagram of the grain diameter determined by assuming the spherical grain.
The sample was cut to have the thickness oE 0.5 mm and finished by lapping th~ surfaca, and the linear transmittance was measured with a double beam spectrophotometer.
lo Observation of the tissue with a transmission electron microscope (TEM) did not show any grain boundary phase, undesirable pore in the grain, nor lattice defec-t, which may cause scattering of light.
The emission tube lM is composed not of the conventional tr nslucent alumina, which is sintered with a sintering accelerator such as MgO to make large rough grains, but of fine powdery alumina. The excellent translucency of the alumina o the embodiment may be ascribed to the following reasons.
Since alumina (before sintering) contain~ only a very little amount of impurity ~maximum: 0.01 mol~, all the impurity is molten in the alumina and does not substantially form any grain boundary phase such as a spinel phase.
Effects of the grain boundary phase, which causes scattering of light, are thus eliminated, and the linear transmittance to the visible light is sufficiently improved.

~, . . . . . . . . .. . ..

~66~

Another possib:Le reason is ~u.rther ~iven below.
When hoth the cross sections o~ the gxain and the grain element are assumed to be circular, the following equation (1) is held. Here, the grain of the diameter D consists of n grain elements of the diameter d.
(1) n = (DJd)2 ::~
The ~alue of n determined by the equation (1) repre~ents the n~ er of the interface between grain elements contained in the cross section of a grain.
- 10The lattice constant was determined with an X-ray diffractometer for various translucent alumina grains (average grain diameter: 0.72, 0.85, 0.99, 1.16, i.35, and 1.52 micrometex) of highly pure alumina. The diameter d of the . .
translucent alumi~a grain element was then determined for the 15 various.translucent alumina grains above by su~stituting the ; .
value of the (012) diffraction peak in Scherrer's expression which defines the relationsh.ip between the diameter d of the grain element and the width of the diffraction line. The results show that the diameter d of the grain element is 1 20 constant irrespective o~ the size of the grain. The Scherrer's : expre~ion i~ ~hown in 'P. Gallezot, Catalysis, Science, and 1 Technology; vol. 5, p2~1, Springer-Verlag (1984)' or 'P. ..
5cherrer; Gnttinger Nachrichen, 2; 98, tl918)'. ~
The above equation (1) accordingly proves that the smaller average diameter D of the grain implies the smaller number of the interface between grain elements in one grain.

, . . . ., ,. . . ,:,: .. , : ., ~ :

-31~

When li~ht enters polycrystal such as ceramics, it is scattered on the face with the discontinuous refractive index or discontinuous atomic arrangement. The interface between the grain elements in the grain has discontinuous atomic arrangement and thus causes scattering of light. The smaller number of the interface between the grain elements in the grain, that is, the smaller diameter D of the grain eliminates undesirable effects of the interface, which cause scattering ; of lightr and improves the linear transmittance to the lo visible lightO
Some modification of the above embodiment is described hereinafter.
The three emission pipe~ are arranged in parallel on the same plane in the second embodimentO Three single emission 15 pipes may, however, be disposed in contact with and parallel to one another to have the commo~ side wall as shown in FigO
8. In this structure, an emission tube lL consists of the thre emission pipes integrally form~d with the excessi~e wall around the pipesO Indium halide, thallium halide, and ~0 sodium halide ar~ separately sealed in the emission pipes o~
the amission tuba lL in the same manner as the ~econd q embodiment.
A variable color lamp with the emisgion tube lL has the following effects as well as expa~sion of the pos~ible ~immer 25 range and the shortened warm-up tLme described in the second embodiment. The circumf~rence of the emission tube lL does -- , , .......................... . . ~

,, , . ~ : - . - . . : . :. . - . :
. , , :. : ,. .- ~ . , . :: . :

-32- 2 ~

not have any conv~x or concave but is smooth, and the cross section of the whole emission tube is a round -triangleO The smooth surface efficiently prevents concentration of the thermal stress generated on sint~ring or switchi~g, which may cause early rupture of the lamp, and the life o~ the variable color lamp is elongated.
Although each emission pipe of the emission tube is linearly formed in the second embodiment and the above ; modification, a U-shaped emission pipe may be used instead~
An emission tube lR or lS which consists of three U-shaped emission pipes integrally formed adjacent to and parallel to one another as shown in Figs. 9 and 10 may, for example, be installed in the outer bulb of the lamp.
A variable color lamp with the emission tube lR or lS
has the following e~fects as well as expansion of the possible dimmer range and the shortened warm-up time described in the ~econd embodiment. The center o~ emission having the maximum luminous ~lux is located on a curved portion in the emi~sion tube lR or lS~ When such an emission -tube i8 ~0 installed i.n the outer bulb, the emission center faces the end o~ the lamp. The variahle color lamp can thus be formed ~; relatively small and space-saving in the direction of emission.
Manufacture of the emission tube lR or lS is briefly described. The emission tube lR is prepared with a combination mold shown in Fig. 9, which include~ an upper mold 50, a lower mold 51, and a sliding mold 52 slidably disposed .. . , ~ , . ...

- . . -- . .. . . , , .,. ~ ., - . : .

2~6~

between tha upper and the lower ~olds 50 and 51~ Each mold has thrae arc-shaped grooves to form the cavity corresponding to the outer face of the emission tube lR. ~nother combination mold with rectangular grooves is used for manufacturing the emission tube lS having the polygonal or rectangular cross section.
The emission tube lS or lR is prepared with such a mold according to the following process. Here manufactur2 of a 1single U-shaped emission tube 1~ shown in FigsO ll~a~ and ll(b) is ~escribed based on the process chart of Fig. 12 for clarity and simplicity of the description. Fig. ll(b) is a Y-plane cross sectional view of Fig. ll(a).
High purity (at least 99.99 mol%) of fine powdery alumina (secondary aggregate) prepared by spray drying in the ;15 same manner as the second embodiment is mixed with an organic binder such as acrylic emulsion, a d~flocculant such as sodium polyacrylate, an antifoamer such as octanol, and distilled water. The mixture i~ wet stixred with a plastic or nylon b~ll mill for approximately twenty four hours, so that exces~ive aggregation of alumina is eliminated and alumina uniforml~ di~persed in the sol~ent, that i9, slurry, is prapared (process 1).
The con~ents of the additives with respect to lQQ g of - fine powdery alumina are as follow~:
Organic binder- 3g Deflocculant: lg -:

.~, . . .

Antifoamer: O.lg Di~tilled water : 55g Blow holes are then removed from the slurry (process 2).
Slurry taken out of the ball mill is placed in a resin vessel in a vacuum de~iccator and stirred with a magnetic stirrer while air in the desiccator is aspirated with a vacuum pump for several minu-tes ~for example, fiv~ minutes).
The molded body lA shown in Figs. ll(a) and ll(b) is prepared with a combination mold ~0 shown in Fig~ 13(a) through the following process. As described above, the emission tube lR, which is actually applied -to the embodiment, is formed with the combination mold consisting of the upper mold 50, the lower mold 51, and the sliding ~old 5~. :
The combination mold 60 includes symmetrical molds ~la and 61b, which are composed of a porous inorganic material such as plaster or a porous xesin containing pores having the ~:
similar function to plaster, as shown in Fi~. 13~a). A
cavity 63 for slurry pour is formed between the joint ~aces of the molds 61a and 61h.
Each mold 61a or 61b has a U-shaped groove or cavity 63a or 63b on a ~oint face 65a or 65b thereof as seen in Fig.
I 13~b). The groova 63a or 63b has a ridge ~4a or 64b on the center thereof, which is a little lower than the joint face : .
~5a or 65b. The grooves may pr~viously be molded or cut by usi~g an end mill with spherical teeth on the edge (not shown).

:. ' .~

., :: , . .

~6~0~

After r~moval o:E blow holes from the slurry at process 2, the slu.rry i~ poureA into the cavi-ty 63 of the combination mold 60 and stood for a predetermined time period ~process 3). An excessive amount (more than the volume of the cavity 63~ of slurry is poured into a cylindrical body 67 mounted on ~he upper face or the combination mold 60 as shown in Fig.
14. The lower face of the cylindrical body 67 a.nd the upper face of th~ combination mold 60 are se~led with ~lay or rubber 69.
The solvent (distilled water in the embodiment) contained in the ~lurry, which is poured into the cavi-ty 63, is absorbed into the pores of th~ porous molds 6la and 6lb while the slurry is stood for the predetermined time period.
Alumina grains ~ound to one another via the organic binder are uniformly aligned along the wall of the cavity 63, and an alumina layer SA is formed as shown in Fig. 15.
The thicknes~ o~ tha alumina layer SA or the inner diameter of the molded body depends on the standing time period. The standing time is thus previously determined through experim~nt~ such that the alumina layer SA formed has a desirable inner diameter. The ~tanding time and the dimen~ion~ of th~ groove should be determined ~y con~idering the volume ~hrinkage on sintering. In one embodiment, the ~tanding time i~ three minutes or ghorter to make the inner ~5 di~meter of th~ alumina layer SA around 4.8~ mm, and the packing ratio appxoximately 58%D The outer diameter of the : - . . -. ......... . . - , - - ~ - ..................... ,- :
- - -.. . ~ - -. ~. , . . -. - . : - ~ . .

- : . : . - - : :.: . - . . : .: . . . : . : .:
.. - ,. . . .,. . :~ . .: : :.. , . ~ - . : , : :

2~1666~L
-36~

alumina layer SA is determined by the dim~nsions of the cavity 63, and is around 5.54 mm in the embodimen-t.
The mold may be s-tood under the nega~ivP pressure so that the solvent in the slurry is forcibly aspirated out of the mold. This system attains shorter standing time, direct removal of blow hoies from the slurry, and higher packing ratio.
After elapse of -the predetermined standing time, slurry ramaining in the cylindrical body 67 or on the inner face of the alumina layer SA is removed (process 4~. The com~ination mold 60 is separated into two parts, and the molded body lA
shown in Figs. ll(a) and ll(b) is parted from the mold. The molded body is dried until the solvent is completely eliminated . therefrom (process 5).
The molded body is sintered through heat treatment at a - predetermined sintering temperature between 1,200 and 1,300C, for example, at 1,235C for four hours (procass 6). ~lere the heating rate is 100C / hour. Through the sin~ering process, the volume of the molded body is shrunk to approximately 83~, and the paeking facto.r of the sintered body become~ approximately 100% (bulk density: 3.976).
The sintering temperatuxe is set in the range of ly200 to ~,300C 50 as to make the actual de~sity of the sintered :. body not less than 95~ of the theoretical density for the following hot isos~atic pressing and prevent growth of undesirable rough crystals. ~When the temperature is 1,200 . , ~, . . -- ~ . . ~ , . ,. - ,- . . .,,.-- . . . . , . -', ,: . - ' ~
. - - . , ~; - ~, ,, . ~ - - :- - . : :. . .- .

_37~ 2~66~

or lower, the dens.ity of the sintex~d bo~y dr~ps to the level unsuitable for hot i50static pressing, that is, less than 95%
of the theoretical density. When the t mperature is, on the other hand, over 1,300C, ~ormation of rough crystals decreases the strength of the sintered body.
The sintered body is exposed to hot isostatic pressing in argon atmosphere or the atmosphere of argon with oxygen of not greater than 20vol% (process 7~. The conditions of the hot isostatic pressing are given below; here the heating xate is 200C / hour:
Temperature: 1,200 to 1,250C
(optimum temperatur2: 1,230C) Pressure: 1,000 to 2,000 atm (optimum pressure: 1,OOO atm) Time: one to four hours ~optimum time: two hours3 The sintered ~ody acquires translucency through this process, and the emission tube lA of translucent alumina is thus obtained. The sintered body is embedded in sapphire beads (diameter: 2 mm) or titanium sponge during ~he hot isostatic 20 pressing. .
The temperature and pressure ranges for hot iso~tatic pressing ars detarmined so as to give desirable translucency to th~ sintered body and improve the mechanical strength thereo~ h~n the hot isostatic pressing is implemen-ted at the -temperature lower than 1,200C or under ~he pressure.
lower th~n 1,000 atm, sufficient translucency is not given to ,, , - , , . . . : --3~- 2~ 4 the sinter~d body. When the temperature i6 over 1~250C, on the other hand~ abnormal yrain growth lowers both translucency and mechanical strength. When the pressure is over 2,000 atm, even very small pores or scratches in the sintered body may cause fatal cracks due to stress concentration.
The emission tube lA thus prepared has tha inner diameter of about 4.0 mm, the wall thickness of approximately 0.3 mm, and the length between the op~ning and the curv2 of approximately 20 mm, that is, the total length of approximately 40 mm. Observation of the tissue with a transmission electron microscope (TEM) did not show any grain boundary phase, undesirable pore in the grain, nor lattice defect, which may cause scattering of light.
The inner and outer surface of the emission tube lA is ground and polished to have the wall thickness not greater than 0.2 mm by using a brush with diamond abrasive grains [grain diameter: 0.5 micrometer) (pro~ess ~). Thi~ grinding process smooths the sur~ace of the emission tube to prevent scattering of light on the surface, thus Lmproving the linear transmittance~ The wall of the tube may be ground to the thicknes~ o~ 0.05 mm according to the requirements.
! The emi~sion tube lA th~s prepared, that is, the emission tube lR or lS~ has almost the s~me linear transmittance and average grain diameter as the emission tube 1~ of the second e~bodiment, and possesses the mechanical strength of approximately 80% of the emi~ion tube lM.

~ - . - . . ~ . .

- ,: , . . , . . .. .. - . - : .. ,.. , ~ , -_39_ 2 ~ 0 ~

Industrial Applicability The variable color lamp of the invention described above may be applied to neon signs as well as lighting in or out of S the houses or illumination at shop windows.

!:

Claims (8)

1. A variable color lamp with a dimmer function, which comprises:
plural emission tubes each emitting light of different chromaticity; and control means for regulating power supplied to each of the plural emission tubes.

2. A variable color lamp in accordance with claim 1, wherein said control means comprises a relative output control unit for varying the relative output from each of said plural emission tubes.

3. A variable color lamp in accordance with either claim 1 or claim 2, wherein said plural emission tubes comprise: a first emission tube for emitting blue light of a first wavelength range; a second emission tube for emitting green light of a second wavelength range; and a third emission tube for emitting red light of a third wavelength range.

4. A variable color lamp in accordance with claim 3, wherein said first through third emission tubes are all discharge tubes; said first emission tube includes indium halide sealed therein; said second emission tube includes thallium halide sealed therein; and said third emission tube includes sodium halide sealed therein.

5. A variable color lamp in accordance with either claim 3 or claim 4, wherein said first through third emission tubes are arranged adjacent to and parallel to one another.

6. A variable color lamp in accordance with claim 5, wherein said first through third emission tubes are arranged in parallel on the same plane such that the first emission tube is placed in between the second and the third emission tubes.

7. A variable color lamp in accordance with either claim 5 or claim 6, wherein said plural emission tubes are integrally formed.

8. A variable color lamp in accordance with claim 7, wherein said plural emission tubes are composed of translucent alumina ceramics prepared by sintering fine powdery alumina of at least 99.99 mol% in purity; the average grain diameter of the translucent alumina particles being at most one micrometer and the maximum grain diameter being at most two micrometer.