Mercury-free high-pressure discharge lamp and luminaire using the same

Abstract

 A mercury-free high-pressure discharge lamp includes a light-transmissive airtight envelope enclosing therein a discharge space, a pair of electrodes sealed inside the light-transmissive airtight envelope and facing the discharge space, and an ionization medium substantially excluded mercury therefrom, which is filled in the light-transmissive airtight envelope, wherein the ionization medium contains, a principal metal halide including thulium (Tm) as primary constituent thereof and capable of emitting light mainly at a visible range, an accessory metal halide including zinc (Zn) as primary constituent thereof and capable of fixing lamp voltage, and rare gas.

Description

[0001] This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications JP2005-276883 filed on September 22, 2005 and JP2006-150886 filed on May 31, 2006, the entire contents of which are incorporated herein by reference.

[0002] Present invention relates to a high-pressure discharge lamp which is substantially excluded mercury therefrom and thus hereinafter referred to a mercury-free high-pressure discharge lamp), and a luminaire using the mercury-free high-pressure discharge lamp.

[0003] A high-pressure discharge lamp, for example, a metal halide lamp, which is substantially excluded mercury therefrom, is disclosed in Japanese laid-open patent JP11-238488A (hereinafter referred to as patent document 1) etc. In the metal halide lamp disclosed in the patent document 1, it is filled with two types of metal halides, i.e., a primary metal halide having relatively high vapor pressure and capable of mainly emitting light in visible range and an accessory metal halide hardly emitting light in the visible range in compared to the primary metal halide but contributing to fix lamp voltage, in place of mercury.

[0004] In the patent document 1, as a first practical example, a metal halide lamp for liquid crystal projectors designed to have 4mm inter-electrode distance and to operate at 150W input power is described. In this first practical example, dysprosium (DyI3) by 1mg and iodination neodymium (NdI3) also by 1mg are filled as a principal metal halide, respectively, and argon (Ar) by 500Torr is filled as rare gas. In this first practical example, when zinc iodide (ZnI₂) by 8mg is filled as an accessory metal halide, lamp voltage is 73V, luminous efficiency is 68lm/W, and color temperature is 9160K.

[0005] Further, in the patent document 1, as a first practical example, a metal halide lamp designed to have 30mm inter-electrode distance and to operate at 2KW input power is described. In this first practical example, 4mg dysprosium bromide (DyBr3), 4mg holmium bromide (HoBr3), and 4mg thulium bromide (TmBr3) are filled as the principal metal halide, respectively, and 100Torr argon (Ar) is filled as rare gas. In this second practical example, when 30mg zinc iodide (ZnI₂) is filled as the accessory metal halide, lamp voltage is 112V, luminous efficiency is 921m/W, color temperature is 5340K, and a average color rendition evaluation account is Ra73.

[0006] Further, a high-pressure discharge lamp, for example, a metal halide lamp, which is substantially excluded mercury therefrom, is disclosed in Japanese laid-open patent JP11-238488A (hereinafter referred to as patent document 1). A mercury-free discharge lamp filled with 2 to 6 microg/mm³ zinc iodide (ZnI₂) is disclosed in Japanese laid-open patent JP2003-303571A (hereinafter referred to as patent document 2). In this mercury-free discharge lamp disclosed in the patent document 2, 5.0 to 5.7microg/mm³ sodium iodide (NaI) and 2.7 to 3.3microg/mm³ iodination scandium (ScI3) are filled as main emission medium.

[0007] Furthermore, a high-pressure discharge lamp improved luminous efficiency, light color, and life duration is disclosed in Japanese laid-open patent JP2004-349242A (hereinafter referred to as patent document 3). By carrying out the mass percentage of the halide of Na, the halide of Tl, the halide of In, and the halide of Tm into a prescribed range, respectively. However, in this high-pressure discharge lamp disclosed in the patent document 3, mercury is used as buffer gas.

[0008] The metal halide lamp disclosed in the patent document 1 has acquired decent electrical property and luminescent property near those of the conventional metal halide lamp using mercury, without using mercury of high environmental burden. However, an appearance of mercury-free metal halide lamp having luminous efficiency sufficiently higher than conventional metal halide lamp is expected.

[0009] Although sodium is used as metal which contributes to emit white light high-efficiently, the sodium D line is a bright line of 589nm wavelength, which is separated from 555nm, i.e., peak wavelength of visibility curve. So, in order to further advance efficiency, it is necessary to raise a temperature of the coldest part.

[0010] However, since there are various restrictions, such as the heat-resisting property of a airtight envelope, the reactivity of sodium, etc. which constitute an arc tube, improvement in large luminous efficiency is difficult. In addition, in the case of the metal halide lamp which is substantially excluded mercury therefrom (hereinafter referred to as "mercury-free discharge lamp" for convenience), although sodium contributes to improve luminous efficiency, it triggers to make the inter-electrode potential gradient gentle, and thereby reduces lamp voltage. In order to input desired lamp power, it is necessary to make lamp current increase, since lamp voltage comes down in case of that a discharge medium contains large quantity of sodium. For making lamp current increase, it is necessary to thicken the diameter of rod-shaped electrode. However, if a rod electrode is made thick, not only the design of the electrode itself and an airtight envelope becomes difficult, but also the design of stabilizer will also become difficult.

[0011] By the way, in the patent document 1, although it is able to achieve metal halide lamp with electrical property and luminous efficiency almost equivalent to those of conventional metal halide lamp, its luminescence efficiency is only equivalent to that of metal halide lamp using mercury.

[0012] According to the patent document 2, although ZnI₂ has an effect on acquiring lamp voltage adequate to mercury-free discharge lamp, its luminous efficiency falls as lamp voltage rises. For this reason, if priority is given to maintenance of practical efficiency, the quantity of ZnI₂ is limited to the above-described range. As a result, lamp voltage becomes only around half that of discharge lamp containing mercury. Then, it is necessary to make a rod-shaped electrode thick for raising lamp voltage. By doing this, however, the evil of the airtightness of an electrode sealing part becoming insufficient, or circuit design becoming difficult since there is the necessity of enlarging the physical size of a lighting circuit will arise.

[0013] On the other hand, in the mercury-free discharge lamp of the patent document 3, since it is premised on using mercury as buffer gas, such a favorable luminous efficiency as described are not obtained.

[0014] According to researches by the inventors, it turned out that only a combination of that luminescence medium is thulium (Tm) halide and that primary constituent of a lamp voltage fixing medium is zinc halide, mercury-free high-pressure discharge lamp which has the luminescent property equivalent to or more excellent than that of high-pressure discharge lamp containing mercury is obtained. That is, although lamp voltage does not increase notably only with thulium (Tm) halide. When zinc (Zn) halide is added by a specific ratio, lamp voltage increases notably to about 2 times of the lamp voltage which is obtained in the case of zinc (Zn) halide being employed alone. When thulium (Tm) halide is used alone, since thulium (Tm) halide does not evaporate enough, luminous efficiency is low. However, when zinc (Zn) halide is added by a specific ratio, luminous efficiency improves notably.

[0015] Then, the inventors found out, as a result of research, a practically very advantageous combination of thulium (Tm) halide and zinc iodide (ZnI₂), that has the electrical property and luminescent characteristic equivalent to or more excellent than that of high-pressure discharge lamp containing mercury.

[0016] Further the inventors found that adequate electrical property is secured and that high luminous efficiency is also attained, by constraining the occurrence of white roiling phenomenon of a light-transmissive airtight envelope.

[0017] An object of the present invention is to provide a practically very advantageous high-pressure discharge lamp containing thulium (Tm) halide as principal metal halide and zinc (Zn) halide as accessory metal halide in combination and exhibiting electrical property and luminescent characteristic equivalent to those of high-pressure discharge lamp containing mercury and luminaire using this high-pressure discharge lamp.

[0018] Another object of the present invention is to provide a high-pressure discharge lamp reducing white roiling phenomenon occurring on a light-transmissive airtight envelope and luminaire using this high-pressure discharge lamp.

[0019] A further object of the present invention is to provide high-pressure discharge lamp in easy to manufacture, and a luminaire using this high-pressure discharge lamp.

<Description of Principal Metal Halide>

[0020] The principal metal halide is a metal halide which emits light mainly of visible range, and contains thulium (Tm) halide.

[0021] Since thulium has a innumerable emission spectrum near the peak of relative luminous efficiency curve, and proper amounts of spectrum agreeing with the peak of luminous efficiency curve in short wavelength range, thulium (Tm) halide is an emission medium very effective for raising luminous efficiency of a high-pressure discharge lamp in combination with zinc halide.

[0022] Especially thulium (Tm) halide has the operation which itself makes an inter-electrode potential gradient steep under coexistence with zinc halide in a range as described later. Therefore thulium (Tm) halide has an operation of raising lamp voltage remarkably. According to this operation, high-pressure discharge lamp containing thulium (Tm) halide is able to obtain high lamp voltage two times in compared to high-pressure discharge lamp containing only zinc (Zn) halide. Therefore, thulium (Tm) halide is an emission medium suitable for use in mercury-free discharge lamp.

[0023] To achieve the afore-mentioned object, in a high-pressure discharge lamp according to first aspect of the present invention, a mass percentage of charged thulium (Tm) halide is specified within a predetermined range as described later, in relation to charged mass percentage of zinc halide.

[0024] The principal metal halide may contain further halide of emission contributory metals other than thulium (Tm). As emission contributory metal other than thulium, there are thallium (T1), alkali metals, etc. These metals can be used for the purpose of further improving luminous efficiency, chromaticity and/or color temperature, etc.

<Description of Accessory Metal Halide>

[0025] Accessory metal halide contributes mainly to fix amp voltage. In a high-pressure discharge lamp according to the first aspect of the present invention, the accessory metal halide contains zinc (Zn) halide as a primary constituent. The accessory metal halide may contain one or more metal halides as an accessory constituent selected from following group as needed. Namely, it is a group containing magnesium (Mg), iron (Fe), cobalt (Co), chromium (Cr), zinc (Zn), nickel (Ni), manganese (Mn),The group of aluminum (Al), antimony (Sb), a bismuth (Bi), beryllium (Be), rhenium (Re), gallium (Ga), titanium (Ti), zirconium (Zr), and hafnium (Hf).

[0026] Zinc halide is specified that the sum of its mass percentage and the mass percentage of thulium (Tm) halide falls in a range as described below.

<Descriptions of Mass Percentages of Principal and Accessory metal Halides>

[0027] The mass percentage of thulium (Tm) halide to the whole ionization medium is labeled WTm. The mass percentage of zinc (Zn) halide to the whole ionization medium is labeled WZn. Mass of a zinc (Zn) halide is labeled A. Mass of a thulium (Tm) halide is labeled B. Then it is assumed that they satisfy following relations, respectively.

[0028] In Relation (1), if "WTm + WZn" is 5% or more, an effect of the present invention can be acquired. Here, whole of halide charged in the mercury-free high-pressure discharge lamp according to the present invention may be occupied by thulium (Tm) halide and zinc (Zn) halide. However, for a purpose of adjusting chromaticity, etc, the mercury-free high-pressure discharge lamp may be charged with ionization media other than thulium (Tm) halide and zinc (Zn) halide, for example, other metal halide and an elementary substance of metal, etc. Here. a preferable range is given by "WTm + WZn" > 33.

[0029] In Relation (2), when the mass percentage WZn to the whole ionization medium is less than 2.5%, effects of raising lamp voltage and improvement of luminous efficiency is no longer acquired fully. When the mass percentage exceeds 15%, although lamp voltage lifting will be acquired, improvement in luminous efficiency becomes insufficient. It is a range satisfying the relation (3); 0 <= WZn <= 10.

[0030] In the Relation (3), an effect of lamp voltage lifting and improvement in luminous efficiency declines rapidly that ratio A/B of mass A of zinc (Zn) halide and mass B of thulium (Tm) halide is less than 0.025. If the ratio A/B exceeds 0.23, although lamp voltage will rise, there is a tendency for luminous efficiency to fall. Therefore, the lamp becomes difficult for practical use. The suitable range of the A/B is given by a relation; 0.030 <= A/B <= 0.14.

[0031] Further to the mercury-free high-pressure discharge lamp according to the first aspect of the present invention, a mercury-free high-pressure discharge lamp according to the second aspect of the present invention, it is characterized by that the sum "WTm + WZn" of the mass percentage WTm of principal metal halide and the mass percentage WZn of the accessory metal halide to the whole ionization medium satisfies a relation; 5 <= "WTm + WZn" <= 100. It is further characterized by that the mass percentage WZn of the accessory metal halide to the whole ionization medium satisfies a relation; 2.5 <= WZn <= 15. It is still characterized by that the ratio A/B of mass A of the accessory metal halide and mass B of the principal metal halide satisfies a relation; 0.025 <=A/B <= 0.23.

<Description of Mass Percentages of Principal and Accessory Metal Halides)

[0032] In the mercury-free high-pressure discharge lamp according to the second aspect of the present invention, when the mass percentage of thulium (Tm) halide is labeled WTm and the mass percentage of zinc (Zn) halide is labeled WZn, quantity of the principal and accessory metal halides are decided so that the sum "WTm + WZn" of thulium (Tm) halide and zinc (Zn) halide satisfy a relation; "WTm + WZn" > 33, the mass percentage WZn of zinc (Zn) halide satisfies a relation; 0 < WZn < 5. When adding the accessory constituent in the mercury-free high-pressure discharge lamp according to the first aspect of the present invention, it is assumed that the mass percentage WZn of the zinc halide further contains an accessory constituent of zinc.

[0033] In the mercury-free high-pressure discharge lamp according to the second aspect of the present invention, when the sum "WTm + WZn" of thulium (Tm) halide and zinc (Zn) halide satisfy a relation; "WTm + WZn" > 33, under a proper mercury-free discharge lamp voltage fixed by contribution of zinc halide and thulium (Tm) halide contributing, an efficient luminescence of thulium (Tm) can be obtained. On the other hand, when the sum "WTm + WZn" of thulium (Tm) halide and zinc (Zn) halide lowers below 33%, lamp voltage will dip from proper range to very low state. Here, it is preferable that the sum "WTm + WZn" of thulium (Tm) halide and zinc (Zn) halide satisfies a relation; 100 > "WTm + WZn" > 50.

[0034] When the mass percentage WZn of the accessory metal halide to the whole ionization medium satisfies a relation; 0 < WZn < 5, an effect of proper lamp voltage is satisfied, the effect of rising proper lamp voltage will be acquired so that occurrence of white roiling phenomenon can be prevented. In the combination of the primary and the accessory metal halides, larger the charged quantity of zinc halide, higher lamp voltage can be obtained. However, when the mass percentage WZn of zinc halide becomes 5% or more, the white roiling phenomenon of light-transmissive airtight envelope makes progress so that the discharge lamp suffers from low efficiency and begets short life. Here, a preferable range of the mass percentage WZn of zinc halide is given by a relation; 1.5 < WZn < 4. More preferable range of WZn is given by a relation; 2.5 < WZn < 4.

[0035] Further to the mercury-free high-pressure discharge lamp according to the first aspect of the present invention, a mercury-free high-pressure discharge lamp according to the 3r aspect of the present invention, it is characterized by that the sum "WTm + WZn" of the mass percentage WTm of principal metal halide and the mass percentage WZn of the accessory metal halide to the whole ionization medium satisfies a relation; "WTm + WZn" > 33. It is further characterized by that the mass percentage WZn of the accessory metal halide to the whole ionization medium satisfies a relation; 0 <= WZn <= 5.

<Description of Principal Metal Halide>

[0036] In the mercury-free high-pressure discharge lamp according to the third aspect of the present invention, the principal metal halide contains thulium (Tm) halide and thallium (Tl) halide. Thulium (Tm) is an emission contributory metal very effective for improving the luminous efficiency of a high-pressure discharge lamp, as explained in the high-pressure discharge lamp according to the 1st aspect of the present invention. And thulium (Tm) is filled in the mercury-free high-pressure discharge lamp of the third aspect by a ratio which is later mentioned to thallium (T1). That is, when the mass percentage of thulium (Tm) halide is labeled WTm and the mass percentage of thallium (Tl) halide is labeled WT1, a ratio WTl/WTm satisfies 0.05 < WTl/WTm < 1.40

[0037] In the mercury-free high-pressure discharge lamp according to the third aspect of the present invention, luminous efficiency and light color are governed by thulium like the mercury-free high-pressure discharge lamp according to first aspect of the present invention. Luminous efficiency and light color are improved further by thallium.

[0038] When thulium (Tm) halide is iodination thulium, iodination thulium alone is difficult it to be pelletized, but iodination thulium has a feature that it becomes easy to be pelletized by adding thallium halide. Therefore, by using this pelletized iodination thulium high-pressure discharge lamp will become easy to manufacture.

[0039] If a ratio WTl/WTm of the mass percentage WTl of thallium and the mass percentage WTm of thullium satisfies a relation; 0.10 < WTl/WTm < 0.50, the luminous efficiency and the light color of the high-pressure discharge lamp get better.

[0040] On the other hand, when the ratio WTl/WTm is 0.05 or less the vapor pressure of thallium halide becomes insufficient, the ratio WTl/WTm does not contribute to improve luminous efficiency. When the ratio WTl/WTm is 1.4 or more, luminous efficiency falls notably. So that such a ratio, so that the ratio WTl/WTm not suitable.

[0041] By the way, since thallium (T1) has a bright line at a wavelength of 535nm, when thallium (Tl) is added, a green light spectrum zone can be increased.

[0042] In the mercury-free high-pressure discharge lamp according to the third aspect of the present invention, it is preferable to increase the quantity of thulium (Tm) halide more than other halide, and to make the mass percentage of thallium halide less than 30% to whole of the metal halide. If the mass percentage WTl of thallium halide becomes more than 30%, luminous efficiency will fall notably. Here, it is preferable that the mass percentage WTi of thallium halide is less than 15%.

[0043] The accessory metal halide is the same as the accessory metal halide in the mercury-free high-pressure discharge lamp according to first aspect of the present invention. A mercury-free high-pressure discharge lamp according to fourth aspect of the present invention is characterized by that further to the mercury-free high-pressure discharge lamp according to the first aspect of the present invention the principal metal halide includes thallium (T1) halide, and the ratio WTm/WT1 of the mass percentage WTm of the thulium (Tm) halide to the whole ionization medium to the mass percentage WTl of the thallium (Tl) halide satisfies a relation; 0.05 < WTl/WTm < 1.40.

<Description of Principal Metal Halide>

[0044] In the mercury-free high-pressure discharge lamp according to the fourth aspect of the present invention, the principal metal halide contains the thulium (Tm) halide and alkali metal halides as explained in the mercury-free high-pressure discharge lamp according to the first through third aspect of the present invention. And the charged quantity of the thulium (Tm) halide and alkali metal halide are specified to fall in a prescribed range. Namely, when the mass percentage of thulium (Tm) halide is labeled WTm, and the mass percentage of alkali metal halides is labeled WA, WTm and WA satisfy the relation; 30 < WTm < 90 and the relation; 10 < WA < 60, respectively.

[0045] Then, in the mercury-free high-pressure discharge lamp according to the fourth aspect of the present invention, when the thulium (Tm) halide satisfying the relation; 30 < WTm < 90 is charged as the principal metal halide, an alkali metal, for example sodium (Na) halide is added by the quantity satisfying the above relation; 10 < WA < 60, a curve of discharge arc in lighting operation is depressed. Since the temperature of the upper part of a light-transmissive airtight envelope decreases in connection with this, the reaction between thulium (Tm) halide and a light-transmissive airtight envelope is depressed. As a result, the white roiling phenomenon of light-transmissive airtight envelope decreases. Here, it is preferable that the WTm and WA satisfy the relation; 50 < WTm < 80 and the relation; 15 < WA < 30, respectively. When the mass percentage WZn of the accessory metal halide to the whole ionization medium satisfies a relation; 0 < WZn < 5, an effect of proper lamp voltage is satisfied, the effect of rising proper lamp voltage will be acquired so that occurrence of white roiling phenomenon can be depressed. When the WTm and WA fall in the above range satisfying the above relations, it is preferable that occurrence of white roiling phenomenon can be depressed, and the quantity of thullium (Tm) can be increased.

[0046] On the other hand, if the mass percentage WTm of thulium (Tm) halide becomes 30 or less, luminous efficiency will become disadvantageously lowered. When the mass percentage WTm of thulium (Tm) halide becomes 90 or more, other halides are decreased too much, so that for example, inconveniences such as white roiling phenomenon, etc, will improperly increase. When the mass percentage WA of alkali metal becomes 10% or less, a white roiling depression effect will become improperly insufficient. When the mass percentage WA of alkali metal becomes 60% or more, the quantity of other metal halides will decrease, so that luminous efficiency will improperly lowers.

[0047] Although the accessory metal halide is the same as the accessory metal halide in the mercury-free high-pressure discharge lamp according to first aspect of the present invention, in a third aspect of the present invention when the mass percentage of zinc halide to the whole of the charged halides is labeled WZn, the WZn is specified to fall in the range satisfying a relation; 0 < WZn < 20. However, in order to obtain proper lamp voltage and to obtain a highly efficient high-pressure discharge lamp, it is preferable that the WZn fall in a range satisfying a range given by the following relation; 5 < WZn < 15. A mercury-free high-pressure discharge lamps according to fifth aspect of the present invention is characterized by that further to the mercury-free high-pressure discharge lamps according to any one of the first to fourth aspects of the present invention the thullium (Tm) halide includes at least thulium bromide.

[0048] In the mercury-free high-pressure discharge lamp according to the fifth aspect of the present invention, there is an effect [that high-pressure discharge lamp manufacture becomes easy] that a emission spectrum of thulium can be used effectively, that a life duration is improved, by including thulium bromide.

[0049] That is, thulium (Tm) is an emission contributory metal very effective for improving luminous efficiency of high-pressure discharge lamp as described before. However, there is a problem in obtaining thulium (Tm) halide by using what sort of halogen.

[0050] That is, iodination halide heavily used in the high-pressure discharge lamp has too high melting point of 1030 degrees C, due to its reaction being moderate. For this reason, it is needed to raise operating temperature of a light-transmissive airtight envelope to obtain emission spectrum of Tm.

[0051] On the other hand, in the case of thulium bromide, a melting point is 952 degrees C, and its vapor pressure in this temperature is also high. For this reason, emission spectrum of Tm can be used more effectively than iodination thulium. Operating temperature of a light-transmissive airtight envelope can be reduced. Therefore, the life duration of a part and a high-pressure discharge lamp in which operating temperature fell is improved suitably.

[0052] Iodination thulium is difficult to pelletize when it is employed independently. However, in the case of thulium bromide, it can pelletize in the state where it mixed with its simple substance and iodination thulium. For this reason, a manufacturing process of an enclosure objects and, consequently manufacture of a high-pressure discharge lamp becomes easy.

[0053] However, if bromine exists in discharge space, bromine will react with tungsten of an electrode and tungsten will tend to form a compound with a low melting point. Therefore, if bromine is filled too much, since breakage to an electrode becomes large, it is necessary to mind.

[0054] In the mercury-free high-pressure discharge lamp according to the fifth aspect of the present invention, preferable constitutional examples of the ionization medium are as follows.

[0055] 

1. When the mass percentage of thulium (Tm) halide to whole halide in the ionization medium is labeled A, and the mass percentage of the accessory metal halide is labeled B, the mass percentage A satisfies a relation; 30 < A < 95, and the mass percentage B satisfies a relation; 0 < B < 20.

[0056] Thulium (Tm) halide and the accessory metal halide can be used the same thulium (Tm) halide and the same accessory metal halide in any one of the first through fourth aspects of the present invention as described above. The thulium (Tm) halide is constituted at least one constituent thereof by thulium bromide.

[0057] According to the first constitutional example, it is able to obtain a mercury-free high-pressure discharge lamp excellent in luminous efficiency in addition to the effects of the mercury-free high-pressure discharge lamp the according to the first through fourth aspects of the present invention.

[0058] 

2. When the mass percentage of the thulium (Tm) halide to whole of the halide is labeled A and the mass percentage of the accessory metal halide to whole of the halide is labeled B, a sum "A + B" of the mass percentage of the thulium (Tm) halide and the accessory metal halide, and the mass percentage B satisfy a relation; 50 < (A + B) < 90, and a relation; 20 < B < 90, respectively.

[0059] According to the second constitutional example, it is able to obtain a mercury-free high-pressure discharge lamp having steep potential gradient and thus excellent in electrical characteristics in addition to the effects of the mercury-free high-pressure discharge lamp the according to the first through fourth aspects of the present invention.

[0060] 

3. In the first and second constitutional examples, when a mass percentage of thulium bromide (TmBr) to the whole of the thulium (Tm) halide is labeled C, the mass percentage C satisfies a relation; 5 < C < 60. In this constitutional example, since the quantity of thulium bromide (TmBr) is sufficient, a preferable range of the mass percentage C of the thulium bromide (TmBr) satisfies a relation; 30 < C < 60.

[0061] According to the third constitutional example, it is able to obtain a mercury-free high-pressure discharge lamp which is easy to manufacture, excellent in luminous efficiency, and hard to electrode attrition causing serious damage.

[0062] 4. In the first through third constitutional examples, it is independent or the second aspect to which ionization potential adds metal halide of 5.4eV or more to the principal metal halide can be added with the first aspect.

[0063] According to the fourth aspect of the present invention, a mercury-free high-pressure discharge lamp capable of avoiding lowering of potential gradient is easily achieved.

<Description of other constitution in the mercury-free high-pressure discharge lamp according to the 1s through fourth aspects of the present invention>

[0064] 

(1) When temperature of the coldest part of a light-transmissive airtight envelope is labeled TC (degree C), the first aspect constituted so that temperature TC of the coldest part may become within the limits which satisfies a relation; 540 < TC < 660 can be added. However, temperature of the coldest part says temperature in the surface outside a light-transmissive airtight envelope which carries out a right opposite to the coldest part.

[0065] According to this constitution, a mercury-free high-pressure discharge lamp having proper lamp voltage and high luminous efficiency can be obtained.

[0066] 

(2) A metal halide with ionization potential of 5.4eV or more can add to the principal metal halide. This later constitution can be used with the former constitution, if needed.

[0067] According to this constitution, avoiding the fall of a potential gradient can obtain the mercury free high-pressure discharge lamp which becomes easy.

[0068] Fig. 1 is a front view showing a configuration example of the high-pressure discharge lamp according to the present invention;

[0069] FIG. 2 is a graph showing relations of lamp voltage and luminous efficiency to the mass percentages of zinc halide and thulium (Tm) halide according to one aspect of the present invention;

[0070] FIG. 3 is a graph showing a relation of lamp voltage to mass percentages of thulium (Tm) halide and zinc halide to whole of halides according to another aspect of the present invention;

[0071] FIG. 4 is a graph showing degree of white roiling of light-transmissive airtight envelope to the mass percentage of zinc halide to whole of halide according to still another aspect of the present invention;

[0072] FIG. 5 is a graph showing luminous efficiency to the temperature of the coldest part of the light-transmissive airtight envelope according to still another aspect of the present invention;

[0073] FIG. 6 is a graph showing luminous efficiency to a ratio WTl/WTm of the mass percentages WTl and WTm according to still another aspect of the present invention;

[0074] FIG. 7 is a graph showing a degree of white roiling of light-transmissive airtight envelope to the mass percentage of alkali metal halide to whole of halide according to still another aspect of the present invention;

[0075] FIG. 8 is a graph showing a relation of lamp voltage to the mass percentage of alkali metal halide to the whole of halide according to still another aspect of the present invention;

[0076] FIG. 9 is a graph showing a relation of degree of electrode attrition to the mass percentage WTBr of thulium bromide to whole of halide according to still another aspect of the present invention;

[0077] FIG. 10 is a block diagram showing an exemplary high-pressure discharge lamp lighting system for lighting the high-pressure discharge lamp according to the present invention; and

[0078] FIG. 11 is a schematic diagram showing an automobile headlight embodying the luminaire according to the present invention.

[0079] Referring now to attached drawings FIGS. 1preferred embodiments of the present invention will be described in detail in reference to attached drawings.

<First Embodiment>

[0080] Fig. 1 is a front view showing a first embodiment of the high-pressure discharge lamp according to the present invention.

[0081] This configuration example is a high-pressure discharge lamp for automobile headlight. In FIG. 1, high-pressure discharge lamp MHL is comprised of arc tube IT, insulation tube T, outer bulb OT, and bulb base B. Here, the high-pressure discharge lamp MHL is operated in a horizontal state.

[0082] Arc tube IT is comprised of a light-transmissive airtight envelope 1, a pair of electrodes 2, a pair of metal foils 3, a pair of lead wire 4 and ionization medium filled in the tube.

[0083] Light-transmissive airtight envelope 1 is formed by refractory material sustainable to normal yield temperature of the high-pressure discharge lamp MHL. Further the light-transmissive airtight envelope 1 just derives outside the visible light emitted by electric discharge. Therefore, as long as the material of the light-transmissiive airtight envelope 1 has refractoriness and can derive visible light outside, it may be formed with any kind of material. For example, quartz glass, light-transmissive ceramics, etc. can be used for the light-transmissive airtight envelope 1. As for the light-transmissive ceramics, light-transmissive alumina, yttrium-aluminum-garnet (YAG), yttrium oxide (YOX), polycrystal non-oxide such as aluminium nitride (AIN) or single crystal ceramics, etc. can be used. The light-transmissiive airtight envelope 1 may be coated a light-transmissive film on its inner surface, or the inner surface may be modified, as needed.

[0084] The light-transmissive airtight envelope 1 has discharge space 1c inside thereof. So as that, the light-transmissive airtight envelope 1 comprises envelope 1a for encampassing the discharge space 1c. Enclosure 1a defines proper shape, for example, ball-shape, axiolite shape, column-shaped discharge space. The volume of discharge space 1c may be defined in various widths according to the rated lamp wattage of the high-pressure discharge lamp MHL, inter electrode distance, etc. For example, in the case of the lamp for LCD projectors, the space can be made O.lcc or less. In the case of automobile headlights, it may be made 0.05 c or less. In the case of the lamp for common lighting, according to rated lamp wattage, it can be made into a width in the vicinity of 1cc.

[0085] A pair of sealing portions 1b and 1b are formed on both ends of the envelope 1a. These sealing parts 1b and 1b seal envelope 1a. An axis portion of the electrodes 2 is supported by these sealing portions 1b and 1b, respectively. These sealing portions 1b and 1b contribute to hermetically introduce lead wires 4 connected to the lighting circuit (not shown) into light-transmissive airtight envelope 1. Generally, these sealing parts 1b and 1b are allocated in the ends of envelope 1a.

[0086] In case of that the material of light-transmissive airtight envelope 1 is quartz glass, sealing portion 1b is made in solid quartz glass, and metal foil 3 is buried hermetically. Sealing portion 1b contributes to seal the enclosure 1a, and to support the axis portion of electrode 2 as mentioned later, and to introduce current from a lighting circuit hermetically to electrode 2. The base end of electrode 2 is welded to the end by the side of discharge space 1c of metal foil 3, and lead wire 4 is welded to the other end. Metal foil 3 is hermetically buried inside the sealing portion 1b and contributes to make the sealing portion 1b to keep the interior of the enclosure 1a airtight, and to serves as current conductor in cooperation with the sealing portion 1b. As for a material of the metal foil 3, molybdenum (Mo) is the optimal in case of that the light-transmissive airtight envelope 1 is comprised of quartz glass. Although a way of burying the metal foil 3 in the sealing portion 1b is not specifically limited, it may be employed by selecting appropriate one from evacuation sealing method, pinch sealing method, etc.

[0087] Here, after the sealing portion 1b shown on the left portion of FIG. 1 has been formed, a sealing tube 1a1 is extended integrally from the end of the sealing portion 1b to an interior of the bulb base B.

[0088] On the other hand, as for a sealing means for the case that the light-transmissive airtight envelope 1 is made of light-transmissive ceramics, a technique for sealing the metal foil 3 such as frit sealing by pouring frit into a gap between light-transmissive ceramics and lead wire and then sealing, or fusion bond homogeneous to the envelope 1 or the lead wire.

[0089] In order to maintain the temperature of the coldest part yielding in the light-transmissive airtight envelope 1 to relatively high desirable temperature, by holding sealing portion 1b of light-transmissive airtight envelope 1 to a necessary comparatively low temperature, a thin cylindrical portion communicating to the envelope may be formed. While sealing portion 1a is allocated by the end part of a byway cylinder part in the case of such a structure, it is common to form narrow clearances in which electrode shank may extend and form a narrow gap called capillary between the electrode shank and a thin cylinder portion along the axial direction of the thin cylinder portion. The base end of electrode 2 is connected to a feed conductor, i.e., lead wire.

[0090] Pair of electrodes 2, 2 is hermetically sealed to the light-transmissive airtight envelope 1, and they are allocated so that their head ends oppositely face the discharge space 1c. In case of LCD projectors, the distance between the pair of electrodes 2, 2 may be preferably 2mm or less, while it may also be 0.5mm. As for the automobile headlights, an inter-electrode distance of 4.2mm in central value is standardized. In the case of the lamp for general lighting, the inter-electrode distance in small size lamp may be set to 6mm or less, and that in middle size lamp to large size lamp may be set to 6mm or more.

[0091] As for configuration material of the electrode, refractory and conductive metal, for example, pure tungsten (W), doped tungsten containing one or more dopants selected from a group of, for example, scandium (Sc), aluminium (Al), potassium (K), silicon (Si)), etc., treated tungsten containing thorium oxide, rhenium (Re), or tungsten-rhenium (W-Re) alloy may be employed.

[0092] In the case of small size lamp, straight wire rod or wire rod with large-diameter head are employed for electrode 2. In the case of a middle size to large size electrode, a coil made of same material with the electrode may be wound around the tip end of the electrode. In the case of operating by AC electricity, a pair of electrodes 2, 2 are formed in same configuration. In the case of operating by DC electricity, since the temperature rise of anode is intense, generally it makes the heat dissipation area of anode is made wider than cathode. Therefore, a thick wire rod is employed for anode.

[0093] In FIG. 1, electrode 2 is consisted of a doped tungsten wire. The diameter of the axis portion of the electrode 2 is the same over the tip end, intermediate portion, and base end. Further, the tip end and a part of the intermediate portion expose in the discharge space 1c. The base end of the electrode 1b is welded to the metal foil 3 at the end thereof on the side facing the discharge space 1c. The intermediate portion of the electrode 1b is allocated in a predetermined position in the envelope 1b by being loosely supported by sealing portion 1.

[0094] Metal foil 3 is configured by molybdenum as mentioned above. Pair of lead wires 4, 4 is derived outside through the ends of sealing portions 1b, 1b.

[0095] As shown in FIG. 1, as for the lead wire 4 derived to right side from the arc tube IT, its intermediate portion is folded along the outer bulb OT and introduced into the bulb base B. The lead wire 4 is then connected to ring-shape bulb base terminal t1 allocated on outer surface of the bulb base B. On the other hand, lead wire 4 derived to left side from the arc tube IT is connected to the other pin-shape bulb base terminal allocated in the center of the bulb base B along the axis of the tube.

[0096] The ionization medium is the characteristic constituent in the present invention as described above. The ionization medium contains the principal metal halide, the accessory metal halide and rare gas, but it is substantially excluded mercury therefrom.

The principal metal halide contains thulium (Tm) halide.

[0097] As to the accessory metal halide, zinc (Zn) halide serves as a primary constituent. The filling quantity of the thulium (Tm) halide and zinc (Zn) halide are regulated in prescribed range as described below.

[0098] Namely, the sum "WTm + WZn" of the mass percentage WTm of thulium (Tm) halide and the mass percentage WZn of zinc (Zn) halide to the mass of whole of the ionization media filled in the arc tube IT satisfies a relation; 5 <= "WTm + WZn" <= 100. Similarly, the mass percentage WZn of zinc (Zn) halide satisfies a relation; 2.5 <= WZn <= 15, and a ratio A/B of the mass A of zinc (Zn) halide and the mass B of thulium (Tm) halide satisfies a relation; 0.025 <= A/B <= 0.23.

[0099] Rare gas serves as starting gas and buffer gas. The rare gas is used by selecting one or a combination of two or more from a group of xenon (Xe), argon (Ar), and neon (Ne), etc. The charged pressure of the rare gas can be suitably set as usage of the high-pressure discharge lamp.

[0100] Since the atomic weight of xenon is higher than other rare gas and thus its heat conductivity is relatively small. By charging xenon by 0.6 atmospheric pressures or more, or preferably 5 atmospheric pressures or more, xenon contributes to fix lamp voltage just after the start of lighting. Xenon also contributes to quicken luminous flux rising time by emitting white visible light at the low vapor pressure stage of halide. Therefore, xenon is advantageous for high-pressure discharge lamp for headlight. In this case, it is preferable that xenon is charged by 6 atmospheric pressure or more. It is more preferable that xenon is charged in the range from 8 to 16 atmospheric pressures. For this reason, xenon may contribute to improve luminous flux rising time and light color rising time just after the start of lighting. Therefore, xenon contributes to satisfy the standard of white light as a HID light source for automobile headlights.

[0101] Although it is preferable that mercury (Hg) is completely excluded for reducing environmental burdens, it is permitted that few amounts exist as impurities.

[0102] Outer bulb OT has ultraviolet radiation blocking function. The outer bulb OT accommodates therein arc tube IT. The small diameter portion 5 (only right-side one is shown in FIG. 1) of the outer bulb OT is glass-welded to the sealing portion 1b of the arc tube IT. However, the outer bulb OT is not hermetically sealed and thus communicates to ambient air.

[0103] Insulating tube T is configured by ceramic tube and coats the lead wire 4.

[0104] Bulb base B is standardized for the usage of automobile headlights. The bulb base B then supports the arc tube IT and the outer bulb OT in standing attitude along the center axis thereof. The bulb base B is then mounted in removable on the backside of automobile headlight. Further, the bulb base B is provided with a ring-shape bulb base terminal T1 allocated on cylindrical outer surface so as to be connected to power supply side lamp socket (not shown) at the time of mounting to the automobile headlight. On the other hand, the other side bulb base (not shown) is provided with pin-shape bulb base terminal projecting in a depressed portion defined inside of cylindrical portion.

<Practical example I>

[0105] Shown in FIG. 1 is a practical example I of metal halide lamp for the usage of automobile headlight according to the present invention.
Light-transmissive airtight envelope 1: This is manufactured from light-transmissive ceramics by integral molding. Envelope; 8.0mm in length of tube axis direction, the maximum inner diameter of 2.9mm, the thickness of 0.5mm, the linear transmissivity of 30%, the average particle diameter of 0.5-1.0 micrometers of material, the byway cylinder part; bore of 0.7mm, and the thickness of 0.5mm, 12mm in length, linear transmissivity of 20%, average particle diameter of 0.5-1.0 micrometers of material A pair of Electrodes: The product made from doped tungsten, 4.2mm of inter electrode distances

Ionization medium :TmI3-NaI-ZnI₂(70:20:10 mass %)2mg, 10 atmospheric pressures of Xe(s)

Lighting direction : Level lighting

Lamp power :30W

Electrical property : lamp voltage 85V

Luminescent characteristic : luminous efficiency 1101m/W

<Practical example II>

[0106] 

Ionization medium :TmBr3-NaI-ZnI₂(70:20:10 mass %)2mg, 10 atmospheric pressures of Xe(s)

Electrical property : lamp voltage 88V

Luminescent characteristic : luminous efficiency 110lm/W

Others are the same as Embodiment 1.

<Practical example III>

[0107] 

Ionization medium :TmBr3-TlI-NaI-ZnI₂(50:20:20:10 mass %) 3mg, 10 atmospheric pressures of Xe(s)

Electrical property : lamp voltage 75V

Luminescent characteristic : luminous efficiency 100lm/W

Others are the same as Embodiment 1.

<Comparative example I>

[0108] 

Ionization medium :TmI3-NaI(80:20 mass %)2mg, 10 atmospheric pressures of Xe(s)

Electrical property : lamp voltage 27V

Luminescent characteristic : luminous efficiency 45lm/W

Others are the same as Embodiment 1.

<Comparative example II>

[0109] 

Light-transmission airtight envelope 1: The product made from quartz glass, 8.0mm in length of an enclosure part, the maximum inner diameter of 2.4mm, the thickness of 1.8mm

Ionization medium :ScI3-NaI-InBr-ZnI₂ (20:50:1:29 mass %) 0.5mg, 10 atmospheric pressures of Xe(s)

Lamp power :35W

Electrical property : lamp voltage 42V

Luminescent characteristic : luminous efficiency 90lm/W

Others are the same as the practical example I.

[0110] FIG. 2 is a graph showing relations of lamp voltage and luminous efficiency to the mass percentages of zinc halide and thulium (Tm) halide according to one aspect of the present invention. In FIG. 2, horizontal axis represents a ratio A/B of the mass A of zinc (Zn) halide, and mass B of thulium (Tm) halide; a vertical axis represents lamp voltage (relative value) and luminous efficiency (relative value), respectively. Curve Vl represents lamp voltage, and curve fÅ represents luminous efficiency, respectively.

[0111] It increases as zinc halide of lamp voltage (curve VI) increases in quantity, so that as seen from FIG. 2, but if A/B especially becomes 0.025 or more, it rise up rapidly and around 0.15 the rising rate will become small. On the other hand, if, as for luminous efficiency (curve η), A/B becomes 0.025 or more, it rapidly rise and after passing peak around 0.15, the luminous efficiency gently decreases.

[0112] As mentioned above, it is seen that a high lamp voltage and high luminous efficiency are obtained in the range satisfying the relation; 0.025 <= A/B <= 0.23, which is range defined in the in the first practical example.

<Second Embodiment>

[0113] The mercury-free high-pressure discharge lamp according to the second embodiment of the present invention differs in the constitution of an ionization medium from the mercury-free high-pressure discharge lamp according to the first embodiment of the present invention. That is, as for the ionization medium, the sum "WTm + WZn" of the mass percentage WTm of the principal metal halide and the mass percentage WZn of the accessory metal halide to the whole of the ionization medium satisfies a relation; "WTm + WZn" > 33; and the mass percentage WZn of the zinc (Zn) halide satisfies a relation; 0 < WZn < 5. Rare gas permits that it is the same in the first aspect.

<Practical Example IV>

[0114] It is a halide lamp for automobile headlights shown in drawing 1.

Light-transmission airtight envelope 1: The maximum outer diameter of 6.0mm, the solid sphere length of 6.5mm, the maximum inner diameter of 2.4mm,

The temperature of the coldest part of 600 degrees C

Electrode of a pair : The product made from doped tungsten, the shaft diameters of 0.3mm, 10mm in full length,
4.2mm of inter electrode distances

Ionization medium :TmI3-TlI-ZnI₂ (70:26:4)0.6mg,

Figures in the brackets are the mass percentage, and 13 atmospheric pressures of Xe(s).

Electrical property : lamp voltage 74V when switching on the light with the temperature of the coldest part of 600 degrees C

Luminescent characteristic : white roiling reduction of the light-transmissive airtight envelope by total-luminous-flux 4900lm, luminous efficiency 100lm/W, and lighting was not able to be checked.

Hereafter, with reference to Figs. 3 through 5, the relation of white roiling between an enclosure object, lamp voltage, and a light-transmissive airtight envelope, and the coldest part of a light-transmissive airtight envelope and the relation of luminous efficiency are explained about the second embodiment based on experimental data.

[0115] FIG. 3 is a graph showing a relation of lamp voltage to mass percentages of thulium (Tm) halide and zinc halide to whole of halides according to the second embodiment of the present invention; In the drawing, a horizontal axis shows the ratio "WTm + WZn" of a mass percentage of thulium (Tm) halide and zinc halide (%), and a vertical axis shows lamp voltage (V), respectively.

[0116] If the ratio "WTm + WZn" of a mass percentage is more than 33% so that as seen from the drawing, equivalent to the case containing mercury and the lamp voltage beyond it will be obtained.

[0117] FIG. 4 is a graph showing degree of white roiling of light-transmissive airtight envelope to the mass percentage of zinc halide to whole of halide according to the second embodiment of the present invention, In the drawing, a horizontal axis shows the mass percentage WZn of zinc halide (%), and a vertical axis shows a white roiling grade, respectively. The grade of white roiling is the relative judgment by visual observation.

[0118] If the mass percentage WZn is less than 5% so that as seen from the drawing, the high-pressure discharge lamp controlled to such an extent that the white roiling occurring in a light-transmissive airtight envelope does not affect luminous efficiency and a life duration will be obtained.

[0119] FIG. 5 is a graph showing luminous efficiency to the temperature of the coldest part of the light-transmissive airtight envelope according to the second embodiment of the present invention. In the drawing, a horizontal axis shows a temperature of the coldest part (degree C), and a vertical axis shows efficiency (lm/W), respectively.

[0120] As seen from FIG. 5, as the coldest part more than 540 degrees C if it is less than 660 degree C, high luminous efficiency is acquired, and although it does not appear in the drawing, the high-pressure discharge lamp in which white roiling is controlled will be obtained.

<Third Embodiment>

[0121] The mercury-free high-pressure discharge lamp according to the third embodiment of the present invention is identical to the mercury-free high-pressure discharge lamp according to the first embodiment of the present invention as shown in FIG. 1, except the specification of the ionization medium.

[0122] As for the ionization medium according to the third embodiment, in addition to thulium (Tm) halide, the principal metal halide is constituted including thallium (Tl) halide. The ratio of the mass percentage WTl of thallium halide and the mass percentage WTm of thulium (Tm) halide to whole of the halide WTl/WTm satisfies a relation; 0.05 < WTm/WTl < 1.40.

[Practical Example 5]

[0123] 

Ionization medium: TmI3-TlI-ZnI₂ (72.6:14.9:12.5)0.8mg,
(The figures in brackets are mass percentage (%))

Xe: 13 atmospheric pressures

Others are the same as Embodiment 4.

[0124] 

Electrical property: lamp voltage 85V; lamp power 35W

Luminescent characteristic: Total-luminous-flux 3500lm: luminous efficiency 100lm/W

Decreasing of white roiling phenomenon of the light-transmissive airtight envelope by lighting was not able to be checked.

[0125] FIG. 6 is a graph showing luminous efficiency to a ratio WTl/WTm of the mass percentages WTl and WTm according to the third embodiment of the present invention.
In FIG. 6, a horizontal axis a ratio a vertical axis shows efficiency (1m/W) for WTl/WTm, respectively.

[0126] As seen from FIG. 6, as a ratio if WTl/WTm is within the limits which satisfies the relation, it turns out that high luminous efficiency is acquired.

<Fourth Embodiment>

[0127] The mercury-free high-pressure discharge lamp according to the fourth embodiment of the present invention is identical to the mercury-free high-pressure discharge lamp according to the first embodiment of the present invention as shown in FIG. 1, except the specification of the ionization medium.

[0128] As for the ionization medium according to the fourth embodiment, in addition to thulium (Tm) halide, the principal metal halide is constituted including the alkali metal, for example, sodium (Na) halide. While the mass percentage WTm of thulium (Tm) halide and the mass percentage WA of alkali metal halide to whole of the halide satisfy relations; 30 < WTm < 90 and 10 < WA < 60, respectively, the mass percentage WZn of zinc halide satisfies a relation; 0 < WZn < 20.

[Practical Example 6]

[0129] 

Ionization medium: TmI3-TlI-NaI-ZnI₂ (58.4:9.9:23.3:8.3)1.2mg
(The number in a parenthesis is a ratio of a mass percentage (%))

Xe: 13 atmospheric pressures

Others are the same as Embodiment 4.

[0130] 

Electrical property: lamp voltage 55V; lamp power 35W

Luminescent characteristic: Total-luminous-flux 3500lm

Luminous efficiency: 100lm/W

White roiling reduction of the light-transmissive airtight envelope by lighting was not able to be checked.

[0131] FIG. 7 is a graph showing a degree of white roiling of light-transmissive airtight envelope to the mass percentage of alkali metal halide to whole of halide according to the fourth embodiment of the present invention. In FIG. 7, a horizontal axis shows the mass percentage WA of alkali metal halide (%), and a vertical axis shows a white roiling grade, respectively. White roiling is similarly estimated as FIG 4.

[0132] As seen from FIG. 7, as a ratio if WTl/WTm is within the limits which satisfies the relation, the occurrence of white roiling can be controlled effectively.

[0133] FIG. 8 is a graph showing a relation of lamp voltage to the mass percentage of alkali metal halide to the whole of halide according to the fourth embodiment of the present invention.
In FIG. 8, a horizontal axis shows the mass percentage WA of alkali metal halide (%), and a vertical axis shows lamp voltage (V), respectively.

[0134] As seen from FIG. 8, since it has a reverse proportion relation, in order to secure proper lamp voltage, the mass percentage WA and the lamp voltage of alkali metal halide are good to carry out the ratio of a mass percentage within the limits which satisfies the relation.

<Fifth Embodiment>

[0135] The mercury-free high-pressure discharge lamp according to the fifth embodiment of the present invention is identical to the mercury-free high-pressure discharge lamp according to the first embodiment of the present invention as shown in FIG. 1, except the specification of the ionization medium. As for the ionization medium according to the fifth embodiment, thulium (Tm) halide contains thulium bromide at least.

[Practical Example 7]

[0136] 

Ionization medium: TmI3-TmBr3-ZnI₂ (43.8:43.8:12.4)0.8mg,
(The number in a parenthesis is a ratio of a mass percentage (%))

Xe: 13 atmospheric pressures

Others are the same as Embodiment 4.

[0137] 

Electrical property: Ramp voltage 107V, lamp current 0.65A, lamp power 60W

Luminescent characteristic: Total-luminous-flux 6900lm and par general-color-rendering-index Ra91, color deviation + 0.0007

Although white roiling reduction of the light-transmissive airtight envelope by lighting was not able to be checked, the improvement in luminous efficiency has been checked.

[Comparative example 3]

[0138] 

Ionization medium: TmI3-TlI-ZnI₂ (72.6:14.9:12.5)0.8mg,
(The number in a parenthesis is a ratio of a mass percentage (%))

Xe: 13 atmospheric pressures

Others are the same as Embodiment 5.

[0139] 

Electrical property: Ramp voltage 93V, lamp current 0.86A, lamp power 60W

Luminescent characteristic: Total-luminous-flux 6800lm and par general-color-rendering-index Ra93, color deviation + 0.0016

Decreasing of white roiling phenomenon of the light-transmissive airtight envelope by lighting was not able to be checked.

[0140] FIG. 9 is a graph showing a relation of degree of electrode attrition to the mass percentage WTBr of thulium bromide to whole of halide according to the fifth embodiment of the present invention. In FIG.9, a horizontal axis shows the mass percentage WTBr of thulium bromide (%), and a vertical axis shows the degree of electrode attrition, respectively. The degree of electrode attrition is relative evaluation by visual observation.

[0141] If the mass percentage WTBr of thulium bromide is 60% or less so that as seen from FIG. 9, it turns out that it does not become the degree of electrode attrition of the grade which has serious influence.

[0142] FIG. 10 is a block diagram showing an exemplary high-pressure discharge lamp lighting system for lighting the high-pressure discharge lamp according to the present invention.
In this embodiment, its lighting circuit employs a low-frequency AC lighting system. In FIG. 10, DC denotes DC power source; BUT denotes step-up chopper; FBI denotes full-bridge inverter; IG denotes igniter; and MHL denotes the mercury-free high-pressure discharge lamp.

[0143] DC power source DC is comprised of, e.g., battery for automobile.

[0144] The step-up chopper BUT is connected its input terminal to the DC power supply DC.

[0145] The full-bridge inverter FBI is connected its input terminal to the output terminal of the step-up chopper BUT.

[0146] Igniter IG generates high-voltage starting pulse by being input with low-frequency AC electricity. At the time of starting operation, the high-voltage starting pulse is applied over a pair of electrodes of metal halide lamp MHL for automobile headlight as described later.

[0147] High-pressure discharge lamp MHL has a construction as shown in FIG. 1, and connected to output terminal of full-bridge inverter FBI to be lit up by low-frequency AC electricity.

[0148] FIG. 11 is a schematic diagram showing an automobile headlight embodying the luminaire according to the present invention. In FIG. 11, 11 denotes a headlight main body; 12 denotes a high-pressure discharge lamp lighting system; and 13 denote a metal halide lamps for automobile headlights.

[0149] Headlight main body 11 is formed in cup-shape, and provided with a reflection mirror 11a inside thereof, a lens 11b on its front and a lamp socket (not shown).

[0150] High-pressure discharge lamp lighting device 12 is provided with the circuit as shown in FIG 10, and has main lighting circuit 12A and starter 12B. Main lighting circuit 12A is mainly constituted by step-up chopper BUT and full-bridge inverter FBI as main components. Similarly starter 12B is constituted by igniter IG as main component.

[0151] The metal halide lamp 13 for automobile headlight is mounted to the lamp socket and then it is lit up.

[Effect of the Invention]

[0152] The present invention is able to provide a practically very advantageous high-pressure discharge lamp containing thulium (Tm) halide as principal metal halide and zinc (Zn) halide as accessory metal halide in combination and exhibiting electrical property and luminescent characteristic excellent to those of high-pressure discharge lamp containing mercury and luminaire using this high-pressure discharge lamp.

[0153] The present invention is also able to provide a high-pressure discharge lamp reducing white roiling phenomenon occurring on a light-transmissive airtight envelope and luminaire using this high-pressure discharge lamp.

[0154] While there have been illustrated and described what are at present considered to be preferred embodiments of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof without departing from the true scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teaching of the present invention without departing from the central scope thereof. Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed as the best aspect contemplated for carrying out the present invention, but that the present invention includes all embodiments falling within the scope of the appended claims.

[0155] It is explicitly stated that all features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original disclosure as well as for the purpose of restricting the claimed invention independent of the composition of the features in the embodiments and/or the claims. It is explicitly stated that all value ranges or indications of groups of entities disclose every possible intermediate value for intermediate entity for the purpose of original disclosure as well as for the purpose of restricting the claimed invention, in particular as limits of value ranges.

Claims

1. A mercury-free high-pressure discharge lamp comprising:

a light-transmissive airtight envelope enclosing therein a discharge space;

a pair of electrodes sealed inside the light-transmissive airtight envelope and facing the discharge space; and

an ionization medium substantially excluded mercury therefrom, which is filled in the light-transmissive airtight envelope;

characterized in that,

the ionization medium contains,

a principal metal halide including thulium (Tm) as primary constituent thereof and capable of emitting light mainly at a visible range;

an accessory metal halide including zinc (Zn) as primary constituent thereof and capable of fixing lamp voltage; and

rare gas.

2. A mercury-free high-pressure discharge lamp as claimed in claim 1, wherein
a sum "WTm + WZn" of the mass percentage WTm of the principal metal halide to the whole ionization medium and mass percentage WZn of the accessory metal halide satisfies a relation; 5 <= "WTm + WZn" <= 100;
the mass percentage WZn of the accessory metal halide to the whole ionization medium satisfies a relation; 2.5 <= WZn <= 15;
and
a ratio A/B of the mass A of the accessory metal halide and mass B of the principal metal halide satisfies a relation; 0.025 <= A/B <= 0.23.

3. A mercury-free high-pressure discharge lamp as claimed in claim 1, wherein
the sum "WTm + WZn" of the mass percentage WTm of the principal metal halide to the whole of the ionization medium and the mass percentage WZn of the accessory metal halide to the whole of the ionization medium satisfies a relation; "WTm + WZn" > 33; and
the mass percentage WZn of the accessory metal halide satisfies a relation; 0 < WZn < 5.

4. A mercury-free high-pressure discharge lamp as claimed in claim 1, wherein
the principal metal halide further contains thallium (Tl) halide, and
the ratio WTl/WTm of the mass percentage WTm of the thulium (Tm) halide to the whole of the ionization medium and the mass percentage WTl of the thallium (Tl) halide to the whole of the ionization medium satisfies a relation; 0.05 < WTl/WTm < 1.40.

5. A mercury-free high-pressure discharge lamp as claimed in claim 1, wherein
the principal metal halide further contains alkali metal halide; and wherein
the mass percentage WTm of the thulium (Tm) halide to the whole of the ionization medium satisfies a relation; 30 < WTm < 90;
the mass percentage WA of the alkali metal halide to the whole of the ionization medium satisfies a relation; 10 < WA < 60; and
the mass percentage WZn of the zinc (Zn) halide to the whole of the ionization medium satisfies the relation; 0 < WZn < 20,

6. A mercury-free high-pressure discharge lamp as claimed in any one of claims 1 through 5, wherein,
the thulium (Tm) halide contains at least thulium bromide.

7. A luminaire, comprising:

a luminaire main-body; and

the mercury-free high pressure discharge lamp as claimed in any one of claims 1 through 6, which is mounted on the luminaire main-body; and

a lighting circuit for lighting the mercury-free high pressure discharge lamp.

Drawing