High pressure discharge lamp

Abstract: A high pressure discharge lamp comprises a vessel (4a) made of a non-conductive material which forms an inner space filled with an ionizable light-emitting material and a starting gas, the vessel having first and second opening portions (5a,5b) at both ends thereof, and a non-conductive member inserted into the first opening portion of the vessel and having an outer diameter which is smaller than inner diameter of the first opening portion so as to form a gap between the vessel and the non-conductive member, the non-conductive member further having a hole. An electrode unit (17) is inserted into the hole of the non-conductive member, the electrode unit has a first end which is exposed to the inner space of the vessel, and a second end which is exposed to outside of the vessel. A starting electrode (8) is arranged in the gap between the vessel and the non-conductive member, and has a first end which is exposed to the inner space, and a second end which is exposed to outside of the vessel. The vessel, the non-conductive member and the starting electrode are an integrated body which has been formed by a co-firing process.

Description: Background of the Invention Field of the Invention The present invention relates to a high pressure discharge lamp such as a sodium-vapor lamp, a metal halide lamp or the like. Background Art Conventionally, a high pressure discharge lamp includes a vessel made of a non-conductive material which forms an inner space filled with an ionizable light-emitting material and a starting gas, the vessel having first and second opening portions at both ends thereof; and a non-conductive member inserted into the first opening portion of the vessel and having an outer diameter which is smaller than inner diameter of the first opening portion so as to form a gap between the vessel and the non-conductive member, the non-conductive member further having a hole. An electrode unit is inserted into the hole of the non-conductive member. The electrode unit has a first end which is exposed to the inner space of the vessel, and a second end which is exposed to outside of the vessel. In this connection, GB-A-1421406, JP-U-52-19182 and US-A-5541480 each discloses such a high pressure discharge lamp which is further provided with at least one starting electrode which serves to reduce the starting voltage. In the high pressure discharge lamp according to GB-A-1421406, the non-conductive member is in the form of a ring which is inserted into a gap between an envelope and a cap, and a metal layer is provided on an inner face of the ring and acts as an starting electrode. In this instance, since the ring is arranged between the envelope and the cap, it is necessary to seal the gap between the envelope and the ring, and also seal the gap between the ring and the cap. Such a structure is not very appropriate from the viewpoint of the corrosion resistance and the tightness property. In the high pressure discharge lamp according to JP-U-52-19182 and US-A-5541480, a linear conductive material such as carbon, platinum, palladium or the like is provided on a light-emitting portion thereof. This structure is not very appropriate, either, because such a conductive material tend to decrease the luminous flux of the lamp. EP-A-28128 illustrates a sodium lamp having an arc tube of alumina with alumina end closures carrying electrode structures inserted in through-holes of the end closures. A starting electrode is provided in the form of a conducting ceramic coating on the inner wall of the arc tube. This coating extends from a fused conductive ceramic frit sealing the end closure to the arc tube. A ceramic frit also seals the electrode structure to the end closure. Disclosure of the Invention It is an object of the present invention to provide a high pressure discharge lamp which has excellent corrosion resistance and tightness property without reducing the luminous flux. According to the present invention, there is provided a high pressure discharge lamp as set out in claim 1. In the invention, the starting electrode is arranged between the vessel and the non-conductive member, it has a first end which is exposed to the inner space and a second end which is exposed to outside of the vessel and the vessel, the non-conductive member and the starting electrode is an integrated body which has been formed by a co-firing process. Therefore, it is not necessary to provide another member when the starting electrode is provided and seal gaps therebetween, so that the discharge lamp according to the invention has excellent corrosion resistance and tightness property. Also, as carbon, platinum, palladium or the like may be avoided on an outer surface of a light-emitting portion thereof, the luminous flux thereof may not decrease. Moreover, such an integrated body makes a strongly jointed structure. As used in the embodiment, word "the non-conductive member" includes a capillary, a disc or both of them. Preferably, the starting electrode is composed of a metal. By composing the starting electrode by a metal, the conductivity thereof, the connection between the starting electrode and an outer circuit, and the discharge by the starting electrode become good. The starting electrode can also be composed of a mixture of a non-conductive material and a metal. By composing the starting electrode by the mixture, the non-conductive material in the vessel and the non-conductive member is diffused into the mixture when having been subjected to a co-firing into an integrated body, so that a strongly jointed structure is formed among the starting electrode, the vessel and the non-conductive member. Therefore, the discharge lamp according to the invention have a fully tightness property while maintaining a fully conductivity. More preferably, the mixture contains 30 to 70 volumetric percentage of a metal. As the volumetric percentage of a metal increases, the conductivity of the starting electrode improves. On the other hand, as the volumetric percentage of a non-conductive material increases, the tightness property of the discharge lamp improves. To compromise these properties, it is found that 30 to 70 volumetric percentage of a metal is preferable. To form a strongly jointed structure among the starting electrode, vessel and/or the non-conductive member, it is desirable to select a metal having a melting point near that of the non-conductive material which composes the vessel and/or the non-conducive member, and a high halogen resistance. Also, the non-conductive material is best formed by the material which the vessel and/or the non-conductive member is formed. To fulfil such requirements, the metal contains not less than 50 volumetric percentage of molybdenum which has a high halogen resistance and a comparatively low melting point (2623°C), and the non-conductive material contains not less than 50 volumetric percentage of a material from which the vessel and/or the non-conductive member is formed. More preferably, the metal of the mixture forming the starting electrode comprises molybdenum, and the non-conductive material of the mixture is the same as the non-conductive material for said vessel and said non-conductive member. To form a strongly jointed structure among the starting electrode, vessel and/or the non-conductive member, it is preferable that the volumetric percentage of molybdenum in the metal is as high as possible, and that the volumetric percentage of the non-conductive material, of which the vessel and/or the non-conductive member is formed, is as high as possible. Therefore, it is preferred that the mixture comprises molybdenum and the material which the vessel and the non-conductive member are formed. As used herein, the word "molybdenum" includes not only pure molybdenum, but also molybdenum which contains a small amount of impurities. Also, the word "material which the vessel and the non-conductive member are formed" includes not only complete same as the material which the vessel and non-conductive member are formed but also the material which contains a small amount of impurities. Further, the starting electrode may comprise an exposed portion which is exposed to the inner space or outside of said vessel, and which is composed of a metal, and a non-exposed portion of the starting electrode which is not exposed to said inner space or outside of said vessel, and which is composed of a mixture of a non-conductive material and a metal. Such an starting electrode can form a strongly jointed structure among the starting electrode, the vessel and the non-conductive member, so that the discharge lamp according to the invention have a full tightness property while maintaining a fully conductivity, a good connection between the starting electrode and an outer circuit can be performed, and the discharge by the starting electrode become good. More preferably, the mixture contains 30 to 70 volumetric percentage of metal. As the volumetric percentage of metal increases, the conductivity of the starting electrode improves. On the other hand, the volumetric percentage of a non-conductive material increases, the tightness property of the discharge lamp improves. To compromise these properties, it is found that 30 to 70 volumetric percentage of a metal is preferable. Brief Description of the Drawings Fig. 1 is a schematic view showing a first embodiment of the high pressure discharge lamp according to the present invention; Figs. 2 to 9 are sectional views showing, in enlarged scale, various examples of one end portion of the vessel in the first embodiment of the present invention; Fig. 10 is a schematic view showing a second embodiment of the high pressure discharge lamp according to the present invention; Figs. 11 to 15 are sectional views showing, in enlarged scale, various examples of one end portion of the vessel in the second embodiment of the present invention. Fig. 16 to 21 are flow charts illustrating the process for manufacturing the high pressure discharge lamp of the present invention. Description of the Preferred Embodiments The embodiments of the high pressure discharge lamp according to the present invention will be explained with reference to the drawings. In the drawings, same reference number refers to same member. Fig. 1 is a plain view for schematically showing first embodiment of the entire structure of the high pressure discharge lamp. A ceramic discharge tube 2a is placed in outer tube 1 made of quartz glass or hard glass, and the center axis of the outer tube 1 is accurately aligned with that of the ceramic discharge tube 2a. Both ends of the outer tube 1 are tightly sealed with respective caps 3a, 3b. The ceramic discharge vessel 2 comprises a tubular vessel 4a made of alumina, capillaries 6a, 6b made of alumina as the non-conductive body which is provided at both ends 5a, 5b of the tubular vessel 4a, respectively, and composite electrodes 7a, 7b inserted into the capillaries 6a, 6b so that one end thereof is exposed to the inner space of the tubular vessel 4a and the other end thereof is exposed to outside of the tubular vessel 4a, respectively. In this embodiment, the tubular vessel 4a, the capillary 6a and an starting electrode 8a are an integrated body which has been formed by a co-firing process, with the starting electrode 8a arranged in a gap between the tubular vessel 4a and the capillary 6a such that a first end is exposed to the inner space of the tubular vessel 4a, a second end is exposed to outside of the tubular vessel 4a and the tubular surface of the capillary 6a is metallized. The starting electrode 8a is composed of a mixture of alumina and molybdenum. The mixture contains 30 to 70 volumetric percentage of molybdenum. The ceramic discharge tube 2a is held by the outer tube 1 via two lead wires 9a, 9b. The lead wires 9a, 9b are connected to the respective caps 3a, 3b via respective foils 10a, 10b. In this case, the starting electrode 8a is also connected to the cap 3a via a lead wire (not shown). Fig. 2 is a sectional view showing, in an enlarged scale, a first example of one end portion of the vessel in the first embodiment of the present invention. In Fig. 2, the composite electrode 7a comprises a substantially cylindrical member 11 made of niobium with a diameter smaller than an inner diameter of the capillary 6a, a cylindrical member 12 made of molybdenum with a diameter smaller than that of the substantially cylindrical member 11, the cylindrical member 11 has a first end which is jointed on the bottom of the substantially cylindrical member 11 exposed to the inner space of the tubular vessel 4a, and a second end which is jointed an electrode 13. The electrode 13 has a coil 14. A gap between the composite electrode 7a and a non-conductive member (i.e. the tubular vessel 4a and the capillary 6a) is tightly sealed by filling with frit seal 15. The end 5b has the same construction except that the tubular vessel 4a, the capillary 6a and an starting electrode 8a are an integrated body which has been formed by a co-firing process. In such a discharge lamp, discharge occurs between the composite electrode 7a and a protrusion 16 when the discharge lamp is ignited, which protrusion 16 protrudes at the inner space of the tubular vessel 4a so that the protruding direction thereof crosses central axis of the tubular vessel 4a. As a result, the starting voltage of the discharge lamp reduces due to the discharge. According to the embodiment, as the sealing such as the frit seal is not necessary when the starting electrode 8a is provided, the discharge lamp has excellent corrosion resistance and tight property. Further, carbon, platinum, palladium or the like is not provided on the tubular surface of the ceramic tube, so that the illuminance thereof does not decrease. Moreover, the tubular vessel 4a, capillary 6a and the starting electrode 8 are an integrated body which have been formed by a co-firing, so that such a integrated body makes a strongly jointed structure thereamong. Fig. 3 is a sectional view showing, in enlarged scale, a second example of one end portion of the vessel in the first embodiment of the present invention. In Fig. 3, a composite electrode 7c comprises a current conductor 17, and electrode 13 jointed by welding at a bottom of the current conductor 17 exposed to the inner space of a tubular vessel 4b. The current electrode 17 has a cylindrical member 17a made of alumina, and a metallizing layer 17 made of the mixture of alumina and molybdenum. A gap between the composite electrode 7c and a capillary 6c is tightly sealed by filling a frit seal 15. The tubular vessel 4b has a main body 18a and a disc 18b. In the embodiment, the tubular vessel 4b, capillary 6c and an starting electrode 8b are an integrated body which has been formed by a co-firing process, with the starting electrode 8b arranged a gap between the tubular vessel 4b and the capillary 6c so that a first end is exposed to the inner space of the tubular vessel 4b, a second end is exposed to outside of the tubular vessel 4b and a part of the tubular surface of the capillary 6c is covered with the composite electrode 8b. In such a discharge lamp, discharge occurs between the composite electrode 7c and a protrusion 19 when the discharge lamp is ignited, which protrusion 16 protrudes at the inner space of the tubular vessel 4b so that the protruding direction thereof crosses central axis of the tubular vessel 4b. As a result, the starting voltage of the discharge lamp reduces due to the discharge. In this case, the conductivity of the starting electrode becomes good, the starting electrode can be connect an outer circuit in a good manner, and good discharge by the starting electrode can be performed. Fig. 4 is a sectional view showing, in enlarged scale, a third example of one end portion of the vessel in the first embodiment of the present invention. In Fig. 4, a composite electrode 7d comprises a current conductor 20, and an electrode 13 buried in a concave portion at the bottom of the current conductor 17 which is exposed to the inner space of the tubular vessel 4b. The current electrode 20 has a substantially cylindrical member 20a made of alumina, and a metallizing layer 20b made of the mixture of alumina and molybdenum. A gap between an opening portion of a capillary 6d and the current conductor 20 is sealed by molybdenum and the mixture of molybdenum and alumina. The starting electrode 8c has a metal portion 21a exposed to the inner space of the tubular vessel 4b, a metal portion 21b exposed to outside of the tubular vessel 4b, a mixture portion 21c composed to alumina and molybdenum which covers over the inner surface of a disc 18b. The starting electrode 8c, the tubular vessel 4b and a capillary 6c are an integrated body which has been formed by a co-firing process, with the starting electrode 8c arranged a gap between the tubular vessel 4b and the capillary 6d. In such a discharge lamp, discharge occurs between a composite electrode 7d and the metal portion 21a. In this case, a strongly jointed structure is formed among the starting electrode 7d, the tubular vessel 4b and the capillary 6d, so that the discharge lamp has a fully tightness property while maintaining a fully conductivity, the starting electrode can be connect an outer circuit in a good manner, and good discharge by the starting electrode can be performed. Fig. 5 is a sectional view showing, in enlarged scale, forth example of one end portion of the vessel in the first embodiment of the present invention. In Fig. 5, a starting electrode 8d composed or the mixture of molybdenum and alumina, a non-conductive body 22 formed by a capillary 22a and a disc 22b, and a tubular vessel 4c are an integrated body which has been formed by a co-firing process, with the starting electrode 8d arranged a gap between the non-conductive member 22 and the tubular vessel 4c. A gap between a composite electrode 7e and the capillary 22a is sealed by welding. In such a way, the starting electrode 8d, the tubular vessel 4c and the disc 22b have been subjected to a co-firing into an integrated body, with the starting electrode 8d arranged a gap between the tubular vessel 4c and the disc 22b. Fig. 6 is a sectional view showing, in enlarged scale, a fifth example of one end portion of the vessel in the first embodiment of the present invention. In Fig. 6, a metallizing layer 25 is formed within a capillary 24, and a composite electrode 7f and the capillary 24 are jointed together with molybdenum 26. In the embodiment, a tubular vessel 4d, the disc 27 and an starting electrode 8e made of molybdenum are an integrated body which has been formed by a co-firing process, with the starting electrode 8e arranged a gap between the tubular vessel 4d and the disc 27 so that a first end is exposed to the inner space of the tubular vessel 4d, a second end is exposed to outside of the tubular vessel 4d, and the starting electrode 8e covers a part of the tubular surface of the disc 27. Fig. 7 is a sectional view showing, in enlarged scale, a fifth example of one end portion of the vessel in the first embodiment of the present invention. In Fig. 7, an starting electrode 8f has a metal portion 28a exposed to the inner space of the tubular vessel 4e, a metal portion 28b exposed to outside of the tubular vessel 4e, a mixture portion 28c composed of alumina and molybdenum which covers over the tubular surface of the disc 18b. The starting electrode 8f, the tubular vessel 4e and a disc 29 are an integrated body which has been formed by a co-firing process, with the starting electrode 8f arranged a gap between the tubular vessel 4e and the disc 29. Fig. 8 is a sectional view showing, in enlarged scale, a seventh example of one end portion of the vessel in the first embodiment of the present invention. In Fig. 8, a layer 32 for melting is provided between an extending conductive layer 31 for earth on a capillary 30 and a composite electrode 7g. The capillary 30, an starting electrode 8g composed of alumina and molybdenum, and a disc 33 are integrated body which has been formed by a co-firing process, with the starting electrode 7g covering over the inner surface of the disc 33. Fig. 9 is a sectional view showing, in enlarged scale, a eighth example of one end portion of the vessel in the first embodiment of the present invention. In Fig. 9, a composite electrode 7h is formed by a cylindrical member made of alumina which is provided with a layer of a mixture of molybdenum and alumina, and a disc 34 which have been co-firing into an integrated body with the cylindrical member. Also, the disc 34, an starting electrode 8h made of a mixture of alumina and molybdenum, and an tubular vessel 4f are an integrated body which has been formed by a co-firing process, with the starting electrode 8h covering over the tubular surface of the disc 34. Fig. 10 is a plain view for schematically showing a second embodiment of the entire structure of the high pressure discharge lamp, and Fig. 11 is a sectional view showing, in enlarged scale, a first example of one end portion of the vessel in the second embodiment of the present invention. In Figs. 10 and 11, a ceramic discharge tube 2b has a barrel shaped vessel 4g made of alumina, a disc 35 made of alumina which has a through-hole, and composite electrodes 7i and 7j, instead of the vessel 4a, capillaries 6a, 6b, and composite electrodes 7a, 7b (Fig. 1 and 2). In the embodiment, at one end portion 5c, the barrel shaped vessel 4b, a disc 35 and an starting electrode 8i made of molybdenum are an integrated body which has been formed by a co-firing process, with the starting electrode 8i arranged a gap between the barrel shaped vessel 4b and the disc 35 so that a first is exposed to the inner space of the barrel shaped vessel 4b and a second end is exposed to outside of the barrel shaped vessel 4b. In Fig. 11, the composite electrode 7i has a tubular electrode unit-holding member 36 made of molybdenum inserted into a through-hole of the disc 35, and an electrode 13 jointed at the bottom of the electrode unit-holding member 36 exposed to the inner space of the barrel shaped vessel 4b. At the end of the electrode-holding member 36 exposed outside of the barrel shaped vessel 4b, an opening portion sealed by laser welding or TIG welding after the ionizable light-emitting material and the starting gas are charged into the inner space of the barrel shaped vessel 4b, is provided. A gap between the disc 35 and the electrode unit-holding member 36 is tightly sealed by a metallizing layer 37. Fig. 12 is a sectional view showing, in enlarged scale, a second example of one end portion of the vessel in the second embodiment of the present invention. In Fig. 12, an starting electrode 8j has a metal portion 38a exposed to the inner space of a ceramic discharge tube 2b, a metal portion 38b exposed to outside of the ceramic discharge tube 2b, and s mixture portion 38c covering over a tubular surface of a disc 39. The mixture portion 38c is also composed of alumina and molybdenum, and contains 30 to 70 volumetric percentage of molybdenum. An electrode unit-holding member 41 applied an electrode 13 directly, is inserted into a tubular conductive member 40 inserted into the through-hole of the disc 39. This application method is disclosed in JP-A-6-3188435, to be concrete, outer ends of the tubular member 40 and the electrode unit-holding member 41 are welded together. Fig. 13 is a sectional view showing, in enlarged scale, a third example of one end portion of the vessel in the second embodiment of the present invention. In Fig. 13, a barrel shaped vessel 4b, a disc 42 and an starting electrode 8k are an integrated body which has been formed by a co-firing process, with the starting electrode 8k arranged a gap between the barrel shaped vessel 4b and the disc 42 so that a first end is exposed to the inner space of the barrel shaped vessel 4b and a second end is exposed to outside of the barrel shaped vessel 4b. Fig. 14 is a sectional view showing, in enlarged scale, a forth example of one end portion of the vessel in the second embodiment of the present invention. In Fig. 14, an starting electrode 8l made of a mixture of alumina and molybdenum, is provided so that a first end is exposed to the inner space of the barrel shaped vessel 4b, a second end is exposed outside of the barrel shaped vessel 4b, a part of the inner surface of the barrel shaped vessel 4b is covered with the starting electrode 8l, and a part of the tubular surface of capillary 43 is covered with the starting electrode 8l. A gap between the composite electrode 7j and the capillary 43 is tightly welded by welding. In such a way, the starting electrode composed of a mixture of alumina and molybdenum can be provided so as to cover a part of a tubular surface of an non-conductive body (i.e. the capillary 43). Fig. 15 is a sectional view showing, in enlarged scale, a fifth example of one end portion of the vessel in the second embodiment of the present invention. In Fig. 15, a composite electrode 7k has a tubular electrode unit-holding member 45 made of molybdenum which is inserted into a through-hole of a disc 44, and an electrode 13 jointed at a bottom of an electrode unit-holding member 36 which is exposed to an inner space of a barrel shaped vessel 4b. At the end of the electrode-holding member 36 exposed outside of the barrel shaped vessel 4b, an opening portion sealed by laser welding or TIG welding after the ionizable light-emitting material and the starting gas are charged into the inner space of the barrel shaped vessel 4b, is provided. In the embodiment, the barrel shaped vessel 4b, the disc 44 and an starting electrode 8m are an integrated body which has been formed by a co-firing process, with the starting electrode 8m arranged in the barrel shaped vessel 4b and the disc 44 so that a first end is exposed to the inner space of the barrel shaped vessel 4b, a second end is exposed to outside of the barrel shaped vessel 4b, and the starting electrode covers over the tubular surface of the disc 44. Next, a method of manufacturing the high pressure discharge lamp is described. Fig. 16 is a flowchart illustrating the process for manufacturing the high pressure discharge lamp of the present invention. In this process, first, alumina powder is mulled and extrusion molded, press molded or cast molded to obtain a molded body, and then, the molded body is cut and processed. In this case, the process is mainly outer peripheral process (centerless or the like), and the cutting can be done in advance of the processing or the processing can be done in advance of the cutting. Then, a binder is removed from the molded body, and the body is pre-fired by the request to obtain the pre-fired body of a non-conductive member (i.e. a capillary, a disc or both of them). Next, the pre-fired body is applied with a paste of the alumina powder and the molybdenum powder, and the body formed as such is pre-fired. On the other hand, a vessel (i.e. a tubular vessel, a barrel shaped vessel or a main body thereof) is molded, the molded body formed as such is dewaxed and pre-fired to obtain the pre-fired body of the vessel. The pre-fired body formed as such and the pre-fired body of the non-conductive member applied with a paste of the molybdenum powder are assembled and fired to obtain a fired body of the vessel and the non-conductive member having an starting electrode, with a first end exposed to the inner space of the vessel and a second end exposed outside of the vessel. Also, the composite electrode is processed and assembled at the same time of these steps, or before or after the steps, and the composite electrode and the fired body of the vessel and the non-conductive member are assembled, and a gap between the composite electrode and the fired body is welded or filled with frit seal. Fig. 17 is another flowchart illustrating the process for manufacturing the high pressure discharge lamp of the present invention. In this case, the cutting and processing is carried out after the firing or calcining step of the non-conductive member instead of performing the cutting and processing after the extrusion molding. Figs. 19 to 21 show alternative examples of the flow charts shown in Figs. 16 to 18, respectively. In those flow charts, a composite electrode composed of a cylindrical member made of alumina on which a layer made of a mixture of molybdenum and alumina is provided, is used. The pre-fired body of the non-conductive member, the pre-fired body of the vessel and the composite electrode are co-firing into an integrated body after the pre-fired body of the non-conductive member, the pre-fired body of the vessel and the composite electrode are assembled. While the present invention has been described above with reference to certain preferred embodiments, it should be noted that they were presented by way of examples only and various changes and/or modifications may be made without departing from the scope of the invention. For example, a non-conductive material other than alumina (e.g. cermet) can be used as a material of the vessel and the non-conductive member. Also, the vessel and the non-conductive member is formed by a same material, however the material forming the vessel can be different from that forming the non-conductive member (For example, the vessel is made of alumina and the non-conductive member is made of cermet.). The vessel may take any other form than the tubular form or the barrel form. The electrode does not have to have the coil. In the above embodiment, the composite electrode or the metal portion is made of molybdenum, however it can be any other metal (e.g. niobium or the like) than molybdenum. In manufacturing the discharge lamp of the present invention, after firing or calcining the vessel and the non-conductive member, these fired or pre-fired body formed as such are assembled with the composite electrode and these are fired, however, after firing or calcining the non-conductive member and the composite electrode, these fired or pre-fired body formed as such are assembled with the vessel and these are fired.

Claims: A high pressure discharge lamp comprising: a vessel (4a; 4b; 18a; 18b) made of a non-conductive material which forms an inner space filled with an ionisable light-emitting material and a starting gas, said vessel having openings at opposite ends thereof; a non-conductive member (6a; 6c; 22a, 22b; 24, 27; 6d; 30; 34; 35; 39; 42; 43) inserted into one of said openings of the vessel and having a through-hole; an electrode unit (7a - 7j) inserted into said through-hole of the non-conductive member, said electrode unit having a first end which is exposed to the inner space of the vessel, and a second end which is exposed outside of the vessel; and a starting electrode (8a - 8m) located between the vessel and the non-conductive member, and having a first end which is exposed to the inner space, and a second end which is exposed outside the vessel; wherein said vessel, said non-conductive member and said starting electrode are a co-fired integrated body, and (i) said starting electrode is composed of a mixture of a non-conductive material and metal, or (ii) said starting electrode comprises an exposed portion (21a, 21b; 28a, 28b; 38a, 38b) which is exposed to said inner space or outside of said vessel, and which is composed of metal, and a portion which lies between said vessel and said non-conductive member, and which is composed of a mixture of a non-conductive material and metal; characterised in that , in alternatives i) and ii), said metal of said mixture contains not less than 50 volumetric percentage of molybdenum and said non-conductive material thereof contains not less than 50 volumetric percentage of a material from which the vessel and/or the non-conductive member is formed. The discharge lamp according to claim 1, wherein said mixture contains 30 to 70 volumetric percentage of metal. The discharge lamp according to claim 1 or 2, wherein said metal of said mixture is molybdenum, and said non-conductive material of the mixture is the same as the non-conductive material of said vessel and said non-conductive member.

Inventors: NIIMI NORIKAZU, NIIMI, NORIKAZU
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1999
Main classification: H01J61
IPC codes: H01J61, H01J9