JP2005228520A - Electrodeless discharge lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a discharge part to efficiently emit light, in an electrodeless discharge lamp for emitting light by discharge light emission. <P>SOLUTION: This electrodeless discharge lamp includes: a waveguide part for transmitting electromagnetic waves; a discharge part formed separately from the waveguide part for carrying out discharge light emission by surface-wave plasma; and an electromagnetic wave radiation part formed between the waveguide part and the discharge part for radiating the electromagnetic waves received from the waveguide part to the discharge part at a gain higher than that in the case where the waveguide part radiates electromagnetic waves from an end. The waveguide part has a hollow tubular first conductor, and a linear second conductor installed in the first conductor. The electromagnetic wave radiation part has an external conductor electrically connected to the first conductor and extending in a tubular form toward the discharge part from the first conductor, an internal conductor electrically connected to the second conductor and extending toward the discharge part from the second conductor in the external conductor, and a heat insulation part having thermal conductivity smaller than that of either of the external conductor and the internal conductor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrodeless discharge lamp. In particular, the present invention relates to an electrodeless discharge lamp that emits light by discharge light emission.

2. Description of the Related Art Conventionally, an electrodeless discharge lamp that emits light by discharge light emission is known (see, for example, Patent Document 1). In this electrodeless discharge lamp, the discharge part is irradiated with an electromagnetic wave transmitted by a coaxial cable. The discharge unit emits light based on surface wave plasma generated by the irradiated electromagnetic wave.
JP 2003-197156 A

  In an electrodeless discharge lamp, in order to discharge light sufficiently as a light source, it is desired to generate a high-density plasma and to evaporate and excite a light-emitting substance in a discharge part. In order to generate high-density plasma, it is desirable to efficiently irradiate the discharge part with electromagnetic waves. In order to evaporate and excite the luminescent material in the discharge part, it is desirable to sufficiently heat and keep the discharge part by irradiation with electromagnetic waves.

  Then, an object of this invention is to provide the electrodeless discharge lamp which can solve said subject. This object is achieved by a combination of features described in the independent claims. The dependent claims define further advantageous specific examples of the present invention.

  In order to solve the above problems, in the first embodiment of the present invention, an electrodeless discharge lamp that emits light by discharge light emission, is provided with a waveguide section that transmits electromagnetic waves and spaced apart from the waveguide section. The discharge unit that discharges and emits light by surface wave plasma generated according to the electromagnetic wave to be irradiated and the electromagnetic wave that is received between the waveguide unit and the waveguide unit are received by the waveguide unit. An electromagnetic wave irradiation unit for irradiating the discharge part with a higher gain than that when the electromagnetic wave is applied from the end part, and the waveguide part is provided inside the hollow cylindrical first conductor and the first conductor The electromagnetic wave irradiation unit is electrically connected to the first conductor, and extends from the first conductor to the discharge unit in a cylindrical shape, and the second conductor and the electric conductor are electrically connected to the first conductor. Connected and extended from the second conductor toward the discharge part inside the outer conductor Has an inner conductor, which is formed in the gap between at least the outer conductor and the inner conductor, and a thermal conductivity than any of the outer conductor and the inner conductor is a small heat insulating section that.

  The outer conductor has a peripheral conductor portion formed in an annular shape on the outer peripheral portion on the upper surface facing the discharge portion in the electromagnetic wave irradiation portion, and the inner conductor is circular in the center portion on the upper surface of the electromagnetic wave irradiation portion. You may have the center conductor part formed in this.

  The inner conductor extends from the second conductor to the discharge portion in a straight or hollow cylindrical shape, and the electromagnetic wave irradiation portion has a gap between the outer conductor and the inner conductor and a hollow inside the inner conductor. The part may have a heat insulating part.

  According to a second aspect of the present invention, there is provided an electrodeless discharge lamp that emits light by discharge light emission, and is provided above a waveguide part that transmits electromagnetic waves and an upper end of the waveguide part. A discharge portion that has a height greater than the diameter of the lower surface facing the end portion and discharges and emits light by surface wave plasma generated in accordance with electromagnetic waves applied to the lower surface. The lower surface as a whole generates high-density plasma, receives an electromagnetic wave having an intensity at a temperature that excites the luminescent material in the discharge unit, and transmits the electromagnetic wave toward the lower surface of the discharge unit.

  When the discharge part emits light, the temperature of the lower surface is equal to or lower than the melting temperature of the lower surface, and the temperature of the upper surface of the discharge part that faces the lower surface is sufficient to allow the surface wave plasma to reach the upper surface. Good. Moreover, when the discharge part emits light, the temperature of the lower surface may be 1200 ° C. or lower, and the temperature of the upper surface may be 800 ° C. or higher.

  The above summary of the invention does not enumerate all the necessary features of the present invention, and sub-combinations of these feature groups can also be the invention.

  Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the scope of claims, and all combinations of features described in the embodiments are included. It is not necessarily essential for the solution of the invention.

  FIG. 1 shows an example of the configuration of a lamp 10 according to an embodiment of the present invention. The purpose of this example is to cause the electrodeless discharge lamp 20 used in the lamp 10 to emit light efficiently. The lamp 10 is a lamp for vehicles, for example, and includes an oscillating unit 102 that oscillates electromagnetic waves and an electrodeless discharge lamp 20 that emits light by discharge light emission.

  The oscillation unit 102 generates an electromagnetic wave for generating surface wave plasma in the electrodeless discharge lamp 20. In this example, the oscillating unit 102 generates an electromagnetic wave of about 10 MHz to 10 GHz with a power of about 100 W or less, for example, according to the power received from the in-vehicle battery. In this case, the oscillating unit 102 oscillates electromagnetic waves having such intensity that the entire lower surface of the discharge unit 108 in the electrodeless discharge lamp 20 has a temperature that generates high-density plasma and excites the luminescent material in the discharge unit 108. It is preferable to do this. The high density plasma is, for example, plasma having a density sufficient to generate surface wave plasma corresponding to the plasma. The oscillating unit 102 may be, for example, a magnetron, or a high frequency amplifier using an FET, a transistor, or the like. Moreover, it is preferable that the oscillation part 102 can oscillate electromagnetic waves in the temperature range in the vehicle lamp used outdoors, for example, about -20 degrees-120 degrees.

  The electrodeless discharge lamp 20 includes a waveguide unit 104, an electromagnetic wave irradiation unit 106, and a discharge unit 108. The waveguide unit 104 is, for example, a coaxial cable, and includes a shield conductor 204, a dielectric 206, and a core wire conductor 202 as shown in an enlarged sectional view 200. The shield conductor 204 and the core wire conductor 202 are examples of the first conductor and the second conductor. The shield conductor 204 is a hollow cylindrical conductor and is grounded. The dielectric 206 is provided between the core wire conductor 202 and the shield conductor 204, and insulates the core wire conductor 202 from the shield conductor 204. The material of the dielectric 206 is not particularly limited, and may be air, for example.

  The core wire conductor 202 is a linear conductor and is provided inside the shield conductor 204. One end and the other end of the core wire conductor 202 are connected to the oscillation unit 102 and the electromagnetic wave irradiation unit 106, respectively. Thereby, the waveguide unit 104 transmits the electromagnetic wave generated by the oscillation unit 102 toward the electromagnetic wave irradiation unit 106. Accordingly, the waveguide unit 104 transmits this electromagnetic wave toward the lower surface of the discharge unit 108 via the electromagnetic wave irradiation unit 106. The core wire conductor 202 is not limited to a solid line shape, and may be a hollow line shape (tubular shape).

  The waveguide section 104 preferably has flexibility. In this case, since the freedom degree of arrangement | positioning of the oscillation part 102, the electromagnetic wave irradiation part 106, and the discharge part 108 improves, the design property of the lamp 10 can be improved. The oscillation unit 102 includes a matching unit, and improves the efficiency by matching the wavelength of the electromagnetic wave to be transmitted. In this case, the waveguide unit 104 can supply the electromagnetic wave to the electromagnetic wave irradiation unit 106 with high efficiency.

  The electromagnetic wave irradiation unit 106 is provided between the waveguide unit 104 and the discharge unit 108, and includes an outer conductor 304, an inner conductor 302, and a slot 310 as shown in an enlarged perspective view 300. The outer conductor 304 is electrically connected to the shield conductor 204 and extends in a cylindrical shape from the shield conductor 204 toward the discharge portion 108. In this example, the outer conductor 304 has a peripheral conductor portion 314. The peripheral conductor part 314 is an annular outer peripheral part on the upper surface of the electromagnetic wave irradiation part 106. The upper surface of the electromagnetic wave irradiation unit 106 is a surface facing the discharge unit 108 in the electromagnetic wave irradiation unit 106.

  The inner conductor 302 is electrically insulated from the outer conductor 304 and electrically connected to the core wire conductor 202, and extends from the core wire conductor 202 toward the discharge portion 108 inside the outer conductor 304. In this example, the inner conductor 302 has a center conductor portion 312. The central conductor portion 312 is a circular central portion on the upper surface of the electromagnetic wave irradiation unit 106, and is provided with a gap between the central conductor portion 312 and the peripheral conductor portion 314. The slot 310 is an annular gap sandwiched between the peripheral conductor portion 314 and the central conductor portion 312. Note that the inner conductor 302 may have a hollow cylindrical shape.

  Here, the outer conductor 304 is grounded by being electrically connected to the shield conductor 204. The internal conductor 302 is driven to a potential corresponding to the electromagnetic wave generated by the oscillation unit 102 by being electrically connected to the core wire conductor 202. The outer conductor 304 and the inner conductor 302 are opposed to each other with the slot 310 interposed therebetween. Therefore, the electromagnetic wave irradiation unit 106 functions as a slot antenna and irradiates the lower surface of the discharge unit 108 with the electromagnetic wave received from the waveguide unit 104. Thereby, the electromagnetic wave irradiation unit 106 irradiates the electromagnetic wave with a gain higher than that in the case where the waveguide unit 104 directly irradiates the electromagnetic wave from the end.

  The discharge unit 108 is a discharge tube that discharges and emits light by surface wave plasma generated according to the irradiated electromagnetic wave. The waveguide unit 104 is located above the upper end of the waveguide unit 104 with the electromagnetic wave irradiation unit 106 interposed therebetween. It is provided away from. According to this example, the electromagnetic wave irradiation unit 106 can function as an exciton that excites the discharge of the discharge unit 108. Thereby, the discharge part 108 can be light-emitted efficiently.

  FIG. 2 shows an example of a detailed configuration of the discharge unit 108. The discharge part 108 has a tube wall 402 and a hollow part 404. The tube wall 402 is a hollow cylindrical body formed of a dielectric material such as quartz glass or translucent ceramics. The hollow portion 404 is a space sealed by the tube wall 402 and is filled with an inert gas such as xenon or argon and a light emitting metal such as sodium iodide or scandium iodide. This inert gas is sealed at a sealing pressure of 300 Torr or less so that the pressure in the hollow portion 404 at the time of lighting is 1 atm or less. In this case, as indicated by Paschen's law, the discharge unit 108 can be lit with good startability and can be lit continuously and stably. In another example, the hollow portion 404 may be filled with a light emitting substance such as sulfur.

  The discharge unit 108 receives the electromagnetic wave irradiated by the electromagnetic wave irradiation unit 106 (see FIG. 1) over almost the entire lower surface 406. When this electromagnetic wave enters the discharge portion 108, high-density plasma is generated, and the luminescent metal in the discharge portion 108 is evaporated and excited, and surface wave plasma is generated. The surface wave plasma extends from the lower surface 406 of the discharge unit 108 serving as an excitation unit toward the upper surface 408 along the shape of the discharge unit 108. As a result, the discharge unit 108 emits light by surface wave plasma generated according to the electromagnetic wave applied to the lower surface 406.

  In this case, the shape of the discharge part 108 can be freely designed according to the required light source shape. Thereby, the discharge part 108 of the shape similar to the filament of a halogen bulb, for example can be provided. In this case, the light distribution design using the electrodeless discharge lamp 20 (see FIG. 1) can be performed by the same or similar method as the conventional light distribution design using a halogen bulb. Thereby, the lamp 10 (refer FIG. 1) can be utilized appropriately, for example as a headlamp of a motor vehicle. The inner diameter L of the discharge part 108 may be 5 mm or less, for example. Moreover, the height H of the discharge part 108 may be 10 mm or less, for example.

  In this example, the discharge part 108 has a height H greater than the diameter L of the lower surface 406 facing the end of the waveguide part 104. Thereby, the discharge part 108 has a vertically long line shape. Further, in this case, the surface wave plasma generated on the lower surface 406 having a small area is grown over a long distance to the upper surface 408, whereby the discharge unit 108 can emit light efficiently. Here, the diameter L of the lower surface 406 is, for example, the inner diameter of the hollow portion 404 on the lower surface 406. Further, the height H of the discharge part 108 is, for example, the height of the hollow part 404 and the distance between the lower surface 406 and the upper surface 408. The upper surface 408 is a surface facing the lower surface 406 across the hollow portion 404 in the discharge unit 108.

  In order to cause the discharge unit 108 to emit light, for example, a method of uniformly irradiating the entire discharge unit 108 with electromagnetic waves may be considered. However, in this case, the upper surface 408 is heated to a high temperature due to the convection generated in the discharge portion 108, and the temperature of the lower surface 406 does not increase so much. Further, the light emission efficiency of the discharge unit 108 depends on the temperature of the coldest spot. Therefore, in this case, the efficiency of the discharge unit 108 may not be appropriately increased. Further, when the intensity of the electromagnetic wave is increased so as to increase the temperature of the lower surface 406, the temperature of the upper surface 408 excessively increases, and the discharge unit 108 may be damaged, devitrified, or blackened.

  However, according to this example, the lower surface 406 can be appropriately heated by irradiating the lower surface 406 of the discharge unit 108 with electromagnetic waves. In this case, the entire discharge unit 108 can be appropriately heated by the convection generated in the discharge unit 108. Therefore, according to this example, the discharge part 108 can emit light efficiently.

  Moreover, in this example, the discharge part 108 does not have an electrode. Therefore, various substances can be used as the trace additive enclosed in the hollow portion 404. In this case, even if no harmful substance such as mercury is used, light with high color rendering properties can be generated. In addition, since the discharge unit 108 does not have a consumable part such as a filament, it can have a long life. Furthermore, since no heat loss from the filament or electrode occurs, the discharge unit 108 can generate light with high efficiency.

  FIG. 3 shows an example of a detailed configuration of the electromagnetic wave irradiation unit 106 by a BB vertical sectional view and an AA horizontal sectional view. In this example, the electromagnetic wave irradiation unit 106 further includes a hollow part 316 and a heat insulating part 308. The hollow portion 316 is a region where neither the outer conductor 304 nor the inner conductor 302 is formed in the electromagnetic wave irradiation unit 106. The heat insulating portion 308 is formed by a heat resistant member 318 having a lower thermal conductivity than the outer conductor 304 and the inner conductor 302 throughout the hollow portion 316. Thereby, the heat insulation part 308 reduces heat conduction from the discharge part 108 to the waveguide part 104. The heat-resistant member 318 is formed of an insulating material that can withstand a temperature rise accompanying light emission of the discharge unit 108 (see FIG. 1), such as glass or ceramic. Therefore, the heat resistant member 318 does not melt even when the discharge part 108 emits light. The heat insulating unit 308 preferably has a lower thermal conductivity than the dielectric 206 in the waveguide unit 104. In another example, the air in the hollow part 316 may be used as the heat insulating part 308.

  Here, for example, it is conceivable to directly connect the waveguide unit 104 (see FIG. 1) and the discharge unit 108 without using the electromagnetic wave irradiation unit 106. However, in this case, a large amount of heat flows from the discharge unit 108 to the waveguide unit 104 during light emission. In this case, the discharge part 108 cannot be heated appropriately and efficiently, and the light emission efficiency of the discharge part 108 may decrease. In addition, the waveguide section 104 may be damaged by heat flowing from the discharge section 108.

  However, according to this example, the heat outflow from the discharge unit 108 to the waveguide unit 104 can be reduced by forming the heat insulating unit 308 in the electromagnetic wave irradiation unit 106 that is separate from the waveguide unit 104. In addition, as a result, the discharge part 108 can be sufficiently heated to emit light efficiently. The area occupied by the conductor in the horizontal section of the electromagnetic wave irradiation unit 106 is preferably smaller than the area occupied by the conductor in the horizontal section of the waveguide unit 104. In this case, heat outflow from the discharge unit 108 to the waveguide unit 104 can be further appropriately reduced.

  Note that the inner diameter of the peripheral conductor portion 314 may be about 5 to 10 mm in order to match the size of the discharge portion 108. The diameter of the central conductor portion 312 is preferably 5 to 70% of the inner diameter of the peripheral conductor portion 314, and more preferably about 30% (for example, 25% to 35%). In this case, the entire lower surface 406 (see FIG. 2) of the discharge unit 108 can be appropriately heated.

  In another example, the heat insulating part 308 may be provided in the discharge part 108. For example, when the discharge part 108 is formed of a double tube, the heat insulating part 308 may be formed between the outer tube and the inner tube. In this case, a gap between the outer tube and the inner tube may be used as the heat insulating portion 308.

  4 and 5 are diagrams for explaining an example of the operation of the lamp 10. FIG. 4 shows an initial process in which the electromagnetic wave irradiation unit 106 irradiates the discharge unit 108 with electromagnetic waves. The electromagnetic wave irradiation unit 106 emits the electromagnetic wave transmitted by the waveguide unit 104 (see FIG. 1) to the outside of the slot 310 as shown in the enlarged views 500a and 500b. As a result, the electromagnetic wave irradiation unit 106 irradiates the discharge unit 108 with electromagnetic waves, and raises the entire temperature of the lower surface 406 of the discharge unit 108. When this electromagnetic wave is irradiated, almost the entire lower surface 406 of the discharge unit 108 has a temperature that generates high-density plasma and excites the luminescent substance in the discharge unit 108.

  FIG. 5 shows a process in which electromagnetic waves generate surface wave plasma following FIG. The temperature of the lower surface 406 rises sufficiently, and as shown in FIG. 5A, high-density plasma is generated in the vicinity of the slot 310 in the hollow portion 404 by the electromagnetic wave irradiated from the slot 310 and the surface. A wave plasma 602 is generated. Then, light emission starts when the luminescent substance in the discharge unit 108 evaporates and is excited, and the surface wave plasma 602 appears on the upper surface along the inner surface of the tube wall 402 as shown in FIG. It grows towards 408. Therefore, according to this example, the discharge unit 108 can appropriately emit light by the surface wave plasma 602.

  Further, since surface wave plasma has extremely high electromagnetic wave absorption efficiency, according to this example, it is possible to block electromagnetic noise without preparing an electromagnetic wave shield separately.

  Here, in order to sufficiently grow the surface wave plasma 602, when the discharge unit 108 emits light, the temperature of the lower surface 406 is equal to or lower than the melting temperature of the lower surface 406, and the temperature of the upper surface 408 is the surface wave plasma. It is preferable that the temperature be sufficient to reach the upper surface 408. In this case, the temperature of the lower surface 406 is, for example, 1200 ° C. or lower, and the temperature of the upper surface 408 is 800 ° C. or higher. The electromagnetic wave irradiation unit 106 preferably heats the lower surface 406 to a temperature at which the surface wave plasma 602 just reaches the upper surface 408 within a range where the lower surface 406 does not melt. In this case, the entire discharge unit 108 can emit light efficiently.

  FIG. 6 shows another example of the configuration of the electromagnetic wave irradiation unit 106. FIG. 6A is a perspective view of the electromagnetic wave irradiation unit 106. FIG. 6B is a BB vertical sectional view of the electromagnetic wave irradiation unit 106. FIG. 6C is an AA horizontal sectional view of the electromagnetic wave irradiation unit 106. In FIG. 6, the configurations denoted by the same reference numerals as those in FIG. 3 have the same or similar functions as the configurations in FIG. In this example, the electromagnetic wave irradiation unit 106 includes an outer conductor 304, an inner conductor 302, a plurality of heat insulating portions 306 and 308, and a slot 310.

  The outer conductor 304 is a hollow cylindrical body, and accommodates the heat insulating portion 308, the inner conductor 302, and the heat insulating portion 306 therein. The heat insulating portion 308 is formed by a heat resistant member 318a in a hollow portion 316a that is a gap between the outer conductor 304 and the inner conductor 302. Moreover, the heat insulation part 308 accommodates the internal conductor 302 and the heat insulation part 306 inside.

  The inner conductor 302 is a hollow cylindrical body and houses the heat insulating portion 306 therein. The heat insulating portion 306 is a columnar body accommodated in the hollow portion 316b inside the internal conductor 302, and is formed by a heat resistant member 318b. The slot 310 is a gap between the outer conductor 304 and the inner conductor 302 on the upper surface of the electromagnetic wave irradiation unit 106. According to this example, the amount of heat that flows from the discharge unit 108 to the electromagnetic wave irradiation unit 106 can be further reduced by reducing the ratio of the conductor facing the discharge unit 108 on the upper surface of the electromagnetic wave irradiation unit 106.

  Also in this example, the electromagnetic wave irradiation unit 106 has a function of a slot antenna. Thereby, the electromagnetic wave irradiation part 106 can irradiate the electromagnetic wave received from the waveguide part 104 (refer FIG. 1) to the discharge part 108 (refer FIG. 1) with a high gain. Further, in this example, the electromagnetic wave irradiation unit 106 includes a heat insulating unit 308 and a heat insulating unit 306 in a gap between the outer conductor 304 and the inner conductor 302 and a hollow portion inside the inner conductor 302. Therefore, also in this example, heat conduction from the discharge unit 108 to the waveguide unit 104 can be reduced. One or both of the heat insulating part 308 and the heat insulating part 306 may be formed by air in the hollow part 316.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

It is a figure which shows an example of a structure of the lamp 10 which concerns on one Embodiment of this invention. 3 is a diagram illustrating an example of a detailed configuration of a discharge unit 108. FIG. 3 is a diagram illustrating an example of a detailed configuration of an electromagnetic wave irradiation unit 106. FIG. It is a figure explaining an example of operation | movement of the lamp. It is a figure explaining an example of operation | movement of the lamp. 6 is a diagram illustrating another example of the configuration of the electromagnetic wave irradiation unit 106. FIG. FIG. 6A is a perspective view of the electromagnetic wave irradiation unit 106. FIG. 6B is a BB vertical sectional view of the electromagnetic wave irradiation unit 106. FIG. 6C is an AA horizontal sectional view of the electromagnetic wave irradiation unit 106.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Lamp, 20 ... Electrodeless discharge lamp, 102 ... Oscillation part, 104 ... Waveguide part, 106 ... Electromagnetic wave irradiation part, 108 ... Discharge part, 200 ... Expansion Sectional view, 202 ... conductor for core wire, 204 ... conductor for shield, 206 ... dielectric, 300 ... enlarged perspective view, 302 ... inner conductor, 304 ... outer conductor, 306 ..Heat insulation part, 308... Heat insulation part, 310... Slot, 312... Central conductor part, 314 .. peripheral conductor part, 316. ... Tube wall, 404 ... Hollow part, 406 ... Lower surface, 408 ... Upper surface, 500 ... Enlarged view, 602 ... Surface wave plasma

Claims (6)

An electrodeless discharge lamp that emits light by discharge light emission,
A waveguide for transmitting electromagnetic waves;
A discharge part that is provided apart from the waveguide part, and discharges and emits light by surface wave plasma generated according to the electromagnetic wave to be irradiated;
An electromagnetic wave provided between the waveguide unit and the discharge unit, and receiving the electromagnetic wave received from the waveguide unit with a higher gain than the case where the waveguide unit radiates the electromagnetic wave from the end portion. An irradiation unit,
The waveguide section is
A hollow cylindrical first conductor;
A linear second conductor provided inside the first conductor;
The electromagnetic wave irradiation part is
An outer conductor electrically connected to the first conductor and extending in a cylindrical shape from the first conductor toward the discharge portion;
An inner conductor electrically connected to the second conductor and extending from the second conductor toward the discharge portion inside the outer conductor;
An electrodeless discharge lamp comprising: a heat insulating portion having a thermal conductivity smaller than any of the outer conductor and the inner conductor, formed at least in a gap between the outer conductor and the inner conductor. The outer conductor has a peripheral conductor portion formed in an annular shape on the outer peripheral portion on the upper surface facing the discharge portion in the electromagnetic wave irradiation portion,
2. The electrodeless discharge lamp according to claim 1, wherein the inner conductor has a central conductor portion formed in a circular shape at a central portion on the upper surface of the electromagnetic wave irradiation portion. The inner conductor extends from the second conductor toward the discharge part into a hollow cylindrical shape,
2. The electrodeless discharge lamp according to claim 1, wherein the electromagnetic wave irradiation unit has the heat insulating part in a gap between the outer conductor and the inner conductor and a hollow part inside the inner conductor. An electrodeless discharge lamp that emits light by discharge light emission,
A waveguide for transmitting electromagnetic waves;
A surface wave that is provided above the upper end of the waveguide and has a height that is greater than the diameter of the lower surface that faces the end of the waveguide, and is generated in response to electromagnetic waves that are applied to the lower surface. A discharge part that emits light by plasma,
The waveguide unit receives an electromagnetic wave having an intensity such that the entire lower surface of the discharge unit generates a high-density plasma and excites a light-emitting substance in the discharge unit from the oscillation unit. An electrodeless discharge lamp that transmits toward the lower surface.   When the discharge portion emits light, the temperature of the lower surface is equal to or lower than the melting temperature of the lower surface, and the temperature of the upper surface of the discharge portion facing the lower surface is sufficient for the surface wave plasma to reach the upper surface. The electrodeless discharge lamp according to claim 4 which becomes temperature.   The electrodeless discharge lamp according to claim 5, wherein when the discharge part emits light, the temperature of the lower surface is 1200 ° C. or lower, and the temperature of the upper surface is 800 ° C. or higher.

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