EP3700296A1

EP3700296A1 - Heater

Info

Publication number: EP3700296A1
Application number: EP19207350.0A
Authority: EP
Inventors: Masaaki TAKATSUKA
Original assignee: Toshiba Lighting and Technology Corp
Current assignee: Toshiba Lighting and Technology Corp
Priority date: 2019-02-21
Filing date: 2019-11-06
Publication date: 2020-08-26
Also published as: JP2020136118A

Abstract

A heater according to an embodiment includes a tubular portion, a coil which is provided inside the tubular portion and extends along a tube axis of the tubular portion, and a coating which is provided on an outer surface of the tubular portion and in which a first film and a second film having a higher refractive index than a refractive index of the first film are alternately superposed. A gas containing krypton as a main component or a gas containing xenon as a main component is sealed inside the tubular portion. When a tube outer diameter of the tubular portion is set to D (mm) and a wall thickness of the tubular portion is set to T (mm), the following expression is satisfied:T/D≥0.09and D≥11.8mm.

Description

FIELD

Embodiments described herein relate generally to a heater.

BACKGROUND

There is a heater for heating an object by radiant heat. Such a heater emits light in a visible light region to the outside when heat is generated. For this reason, for example, when such a heater is used for space heating, etc., it is required to prevent a user from being dazzled, which is a so-called anti-glare property.
Therefore, a heater is proposed in which a coating that hardly transmits visible light is provided on an outer surface of a bulb. In this case, it is preferable that the coating easily transmits an infrared ray and hardly transmits visible light. For this reason, a technology is proposed to use a superposed film, in which a low refractive index film and a high refractive index film are alternately superposed, as the coating.
Meanwhile, a coil that is a heating element and an anchor that supports the coil are provided inside the bulb. Since the anchor supports the coil, one end side of the anchor is in contact with the coil, and the other end side is in contact with an inner wall of the bulb. For this reason, heat generated in the coil is transmitted to the bulb through the anchor, and the heat transmitted to the bulb is transmitted to the coating. Here, since the high refractive index film provided in the coating contains a metal such as iron, discoloration of the coating may occur when a temperature of the coating becomes excessively high. In recent years, a heater of higher power is demanded. For example, when the heater has 2,000 W (watts) or more, there is concern that discoloration of the coating is likely to occur.
Therefore, there is a desire for development of a heater capable of suppressing discoloration of the coating.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view for illustrating a heater according to the present embodiment.
FIG. 2 is a schematic enlarged view of a portion A of FIG. 1.
FIG. 3 is a schematic cross-sectional view of the heater of FIG. 2 in a direction of a B-B line.
FIG. 4 is a schematic cross-sectional view for illustrating a coating as a superposed film.

DETAILED DESCRIPTION

A heater according to an embodiment includes a tubular portion, a coil which is provided inside the tubular portion and extends along a tube axis of the tubular portion, and a coating which is provided on an outer surface of the tubular portion and in which a first film and a second film having a higher refractive index than a refractive index of the first film are alternately superposed. A gas containing krypton as a main component or a gas containing xenon as a main component is sealed inside the tubular portion. When a tube outer diameter of the tubular portion is set to D (mm) and a wall thickness of the tubular portion is set to T (mm), the following expression is satisfied: $T / D \geq 0.09 and D \geq 11.8 mm .$
Hereinafter, an embodiment will be illustrated with reference to drawings. Incidentally, in the respective drawings, a similar component is denoted by the same reference symbol, and a detailed description thereof is omitted as appropriate.
A heater 1 according to the present embodiment can heat an object and a space where the object is placed. For example, the heater 1 can be used in a heating device that heats a space such as a store. However, the use of the heater 1 is not limited to the example illustrated.
FIG. 1 is a schematic view for illustrating the heater 1 according to the present embodiment.
FIG. 2 is a schematic enlarged view of a portion A of FIG. 1.
Incidentally, to avoid complication, in FIG. 1 and FIG. 2, a coating 50 is not illustrated.
FIG. 3 is a schematic cross-sectional view of the heater 1 of FIG. 2 in a direction of a B-B line.
As illustrated in FIG. 1 and FIG. 2, a bulb 10, a filament 20, a metal foil 30, a lead 40, and the coating 50 can be provided in the heater 1.
The bulb 10 can include a tubular portion 11, a sealing portion 12, a protrusion 13, and a dimple 14. The bulb 10 can be configured by integrally forming the tubular portion 11, the sealing portion 12, the protrusion 13, and the dimple 14. The bulb 10 can be formed from, for example, quartz glass. In this case, the bulb 10 can be formed from, for example, quartz glass that is transparent, that is, not colored.
The tubular portion 11 can have, for example, a cylindrical shape. The tubular portion 11 can have a form in which a total length L (length in a tube axis direction) is longer than a tube outer diameter D which is an outer diameter of the tubular portion 11. Incidentally, the total length L of the tubular portion 11 can be referred to as an effective light emission length. In this case, when a tube wall load of an inner wall of the tubular portion 11 becomes excessively high, a temperature of the tubular portion 11 becomes excessively high. Thus, there is concern that the tubular portion 11 may be deformed or durability of the tubular portion 11 may be lowered. For this reason, the tube outer diameter D and the total length L (effective light emission length) of the tubular portion 11 can be appropriately determined so as not to exceed a predetermined tube wall load depending on the power of the heater 1. For example, when the power of the heater 1 is 2,000 W (watts), the tube outer diameter D can be set to about 12 mm, and the total length L (effective light emission length) can be set to about 280 mm.
Gas can be sealed in an internal space of the tubular portion 11. The gas can be sealed to inhibit heat generated in the coil 21 from being transmitted to the tubular portion 11. For this reason, the gas is preferably a gas having a low heat conductivity. The gas can correspond to, for example, xenon (Xe), krypton (Kr), a gas mixture of krypton, nitrogen gas, etc. When the gas mixture of krypton and nitrogen gas is adopted, a ratio of krypton can be 90% or more. In this case, when xenon is used, it is possible to effectively inhibit the heat generated in the coil 21 from being transmitted to the tubular portion 11. When krypton or the gas mixture of krypton and nitrogen gas is used, a manufacturing cost can be reduced.
In addition, the gas can contain a halogen substance such as bromine or iodine. For example, a small amount of dibromomethane (CH₂Br₂), etc. can be included in the aforementioned xenon, krypton, etc.
As described above, a gas mainly containing krypton or a gas mainly containing xenon can be sealed in the tubular portion 11.
A gas pressure (sealing pressure) at 25°C in the internal space of the tubular portion 11 can be set to, for example, a pressure range from 0.6 bar (60 kPa) to 0.9 bar (90 kPa). Here, the gas pressure (sealing pressure) at 25°C in the internal space of the tubular portion 11 can be obtained from a standard state of gas (standard ambient temperature and pressure (SATP): temperature 25°C, 1 bar).
The sealing portion 12 can be provided at both ends of the tubular portion 11 in the tube axis direction. By providing sealing portions 12 at both ends of the tubular portion 11, the internal space of the tubular portion 11 can be hermetically sealed. For example, a pair of sealing portions 12 can be formed by crushing both ends of the heated tubular portion 11. For example, the pair of sealing portions 12 can be formed using a pinch seal method or a shrink seal method. When the sealing portion 12 is formed using the pinch seal method, a plate-like sealing portion 12 illustrated in FIG. 1 and FIG. 2 can be formed. When the sealing portion 12 is formed using the shrink seal method, a cylindrical sealing portion 12 can be formed.
The protrusion 13 can be provided on an outer surface of the tubular portion 11. The protrusion 13 can be provided to exhaust the internal space of the tubular portion 11 or introduce the gas into the internal space of the tubular portion 11 when the heater 1 is manufactured. The protrusion 13 can be formed by burning off a tube formed from quartz glass after exhaust and gas introduction.
The dimple 14 can be formed by locally projecting the inner wall of the tubular portion 11. The dimple 14 can be formed by heating the tubular portion 11 and locally pressing the outer surface of the tubular portion 11. For this reason, the outer surface of the tubular portion 11 at a position where the dimple 14 is formed is recessed toward the inside of the tubular portion 11.
The dimple 14 protrudes from the inner wall of the tubular portion 11 into the tubular portion 11 and can come into contact with an anchor 23. The dimple 14 can be provided to regulate a position of the anchor 23. Since the dimple 14 protrudes toward the inside of the tubular portion 11, the internal dimension of the tubular portion 11 at the position where the dimple 14 is formed is smaller than the internal dimension (inner diameter) of the tubular portion 11 at a position where the dimple 14 is not formed. For this reason, the anchor 23 can be held by the dimple 14. For example, as illustrated in FIG. 3, a pair of dimples 14 facing each other can be provided in a tube diameter direction, and the anchor 23 can be held by the pair of dimples 14. When the anchor 23 is held by the pair of dimples 14, a contact length between the anchor 23 and the inner wall of the tubular portion 11 can be reduced. For this reason, it is possible to inhibit heat generated in the coil 21 from being transmitted to the tubular portion 11 via the anchor 23.
When a plurality of anchors 23 is provided, the plurality of dimples 14 can be provided in the tube axis direction. In this case, the dimples 14 can be provided for each of the plurality of anchors 23, or the dimples 14 can be provided at a predetermined interval. In the case of the heater 1 illustrated in FIG. 1 and FIG. 2, a pair of dimples 14 is provided for three anchors 23. Incidentally, the number and arrangement of the dimples 14 can be changed as appropriate according to the total length L of the tubular portion 11, the number of anchors 23, etc. Further, depending on the total length L of the tubular portion 11, the number of anchors 23, etc., the dimple 14 can be omitted. That is, the dimple 14 may be provided as necessary.
The filament 20 can have the coil 21, a leg 22, and the anchor 23.
The coil 21 and the leg 22 can be integrally formed. The coil 21 and the leg 22 can be formed from, for example, tungsten, etc.
The coil 21 can have a spiral shape. The coil 21 can be formed by, for example, winding a tungsten wire in a spiral shape. A general shape of the coil 21 can be a cylindrical shape. The coil 21 can be provided in the internal space of the tubular portion 11. The coil 21 can be formed by extending a central region of the tubular portion 11 along the tube axis of the tubular portion 11. The coil 21 generates heat when electric conduction is performed and can emit light including an infrared ray.
The leg 22 is provided at each of ends on both sides of the coil 21. The leg 22 has a linear shape and can extend from the end of the coil 21 along the tube axis of the tubular portion 11. One end of the leg 22 is connected to the end of the coil 21 in the internal space of the tubular portion 11, and the other end is connected to the metal foil 30 inside the sealing portion 12. The vicinity of the end of the leg 22 can be laser-welded with the metal foil 30. The leg 22 may be used as a part that supplies power to the coil 21.
As illustrated in FIG. 3, the anchor 23 can be provided in the internal space of the tubular portion 11. For example, the one end 23a side of the anchor 23 can be provided on the outer surface of the coil 21. For example, the end 23a side of the anchor 23 can be wound around the outer surface of the coil 21 several times. For example, the end 23a side of the anchor 23 can have a spiral shape. For example, the other end 23b side of the anchor 23 can be brought into contact with the inner wall of the tubular portion 11. For example, the end 23b side of the anchor 23 can have a curved shape along the inner wall of the tubular portion 11. When the end 23a side of the anchor 23 is provided on the outer surface of the coil 21, and the end 23b side of the anchor 23 is in contact with the inner wall of the tubular portion 11, the coil 21 is supported on the internal space of the tubular portion 11 by the anchor 23. That is, the anchor 23 can be used as a support member that supports the coil 21 against the inner wall of the tubular portion 11.
The anchor 23 can be formed from, for example, tungsten, etc. The anchor 23 can be formed, for example, by bending a tungsten wire. Incidentally, even though a case where the coil 21 and the anchor 23 are separately formed is illustrated, the coil 21, the leg 22, and the anchor 23 can be integrally formed from the same wire. However, when the coil 21 and the anchor 23 are separately formed, a wire diameter of the anchor 23 can be made smaller than a wire diameter of the coil 21. In this way, it is possible to inhibit heat generated in the coil 21 from being transmitted to the tubular portion 11 via the anchor 23. For example, the wire diameter of the anchor 23 can be set to 0.35 mm or less.
When the anchor 23 is provided, the coil 21 can be positioned in the central region of the internal space of the tubular portion 11. For this reason, it is possible to inhibit the coil 21 from fully coming into contact with or fully coming close to the inner wall of the tubular portion 11. In this case, at least one anchor 23 can be provided. When a plurality of anchors 23 is provided, the plurality of anchors 23 can be provided at an equal interval at a predetermined pitch, or the plurality of anchors 23 can be provided at an arbitrary pitch. The number and arrangement of the anchors 23 can be appropriately changed according to the length, rigidity, etc. of the coil 21.
As described above, since the dimple 14 protrudes toward the inside of the tubular portion 11, the end 23b side of the anchor 23 is elastically deformed by the dimple 14. For this reason, the position of the anchor 23 can be maintained by an elastic force. Further, when the dimple 14 is formed, a part on the end 23b side of the anchor 23 is provided inside the dimple 14. For this reason, the position of the anchor 23 can be maintained by the dimple 14.
One metal foil 30 can be provided for one sealing portion 12. The metal foil 30 can be provided inside the sealing portion 12. A planar shape of the metal foil 30 can be a square. For example, the metal foil 30 can be formed from molybdenum.
One lead 40 can be provided for one metal foil 30. The lead 40 can have a linear shape. One end side of the lead 40 is connected to the metal foil 30 inside the sealing portion 12. For example, the one end side of the lead 40 can be laser-welded to the metal foil 30. The other end side of the lead 40 can be exposed to the outside of the sealing portion 12. A power source, etc. provided outside the heater 1 can be electrically connected to a pair of leads 40. For example, each of the pair of leads 40 is connected to a connector, and the pair of leads 40 can be electrically connected to the power source, etc. via a cable provided to the connector. The lead 40 can be formed from, for example, molybdenum, etc.
The coating 50 can be provided on the outer surface of the tubular portion 11. For example, the coating 50 can be provided to cover the outer surface of the tubular portion 11. Here, when an average transmittance of the coating 50 in a visible light region (wavelength region of 380 nm to 780 nm) is higher than 24%, glare increases in visibility evaluation. On the other hand, when this average transmittance is 24% or less, glare is reduced in the visibility evaluation. In this case, when this average transmittance is 21% or less, no glare is felt in the visibility evaluation. For this reason, it is preferable that the coating 50 has an average transmittance in the visible light region of 24% or less.
Incidentally, when the average transmittance in the visible light region in a case where the tubular portion 11 and the coating 50 are combined is higher than 22%, glare increases in visibility evaluation. On the other hand, when this average transmittance is 22% or less, glare is reduced in the visibility evaluation. In this case, when the average transmittance is 19% or less, no glare is felt in the visibility evaluation. For this reason, the coating 50 is preferably formed so that the average transmittance in the visible light region when the tubular portion 11 and the coating 50 are combined is 22% or less.
The average transmittance in the visible light region can be obtained using, for example, a spectrophotometer V-570 manufactured by JASCO Corporation. For example, the average transmittance in the visible light region can be obtained by measuring the transmittance of light every 5 nm using the spectrophotometer V-570 in a wavelength range of 380 nm to 780 nm, and averaging the measured transmittances.
In addition, it is preferable that the coating 50 easily transmits an infrared ray and hardly transmits visible light. For example, the coating 50 can be configured as a superposed film, in which a low refractive index film 51 (corresponding to an example of a first film) and a high refractive index film 52 (corresponding to an example of a second film) are alternately superposed.
FIG. 4 is a schematic cross-sectional view for illustrating the coating 50 as the superposed film.
As illustrated in FIG. 4, the coating 50 can be configured as the superposed film, in which the low refractive index film 51 and the high refractive index film 52 are alternately superposed. The low refractive index film 51 and the high refractive index film 52 can be formed using, for example, a dipping method, a vacuum deposition method, a sputtering method, etc.
For example, the low refractive index film 51 can be provided on the outer surface of the tubular portion 11. That is, the low refractive index film 51 can be set as the first layer. The thickness of the low refractive index film 51 can be set to, for example, about 80 nm. For example, the low refractive index film 51 can contain silicon oxide such as silicon dioxide (SiO₂), or silicon oxide (SiO), magnesium fluoride (MgF₂), etc. In this case, since the tubular portion 11 is formed from quartz glass, it is preferable that the low refractive index film 51 contains a component as close as possible to quartz glass as a main component. In this way, it is possible to improve the bonding strength between the low refractive index film 51 provided on the outer surface of the tubular portion 11 and the outer surface of the tubular portion 11. For example, when the low refractive index film 51 contains silicon dioxide as a main component, the bonding strength between the low refractive index film 51 and the outer surface of the tubular portion 11 is increased. Further, since silicon dioxide has chemical stability, heat resistance, and high mechanical strength, even when the low refractive index film 51 containing silicon dioxide as a main component is provided directly on the outer surface of the tubular portion 11 having a high temperature, a possibility of peeling or damage is low.
For example, the high refractive index film 52 can be provided on the low refractive index film 51. That is, an odd-numbered layer starting from the first layer directly formed on the outer surface of the tubular portion 11 can correspond to the low refractive index film 51, and an even-numbered layer starting from the second layer can correspond to the high refractive index film 52. The thickness of the high refractive index film 52 may be the same as or different from the thickness of the low refractive index film 51. The thickness of the high refractive index film 52 can be set to, for example, about 57 nm. The high refractive index film 52 includes, for example, iron oxide such as iron(III) oxide (Fe₂O₃), copper oxide such as copper(I) oxide (Cu₂O) or copper(II) oxide (CuO), etc. In this case, since copper(I) oxide easily transmits an infrared ray, the high refractive index film 52 containing copper(I) oxide as a main component can improve emission efficiency of an infrared ray.
The number of superposed layers of the low refractive index film 51 and the high refractive index film 52 (the total number of layers of the low refractive index film 51 and the high refractive index film 52) can be appropriately changed according to the required anti-glare property. For example, when the so-called high-glare type heater 1 is used, the number of superposed layers of the low refractive index film 51 and the high refractive index film 52 can be set to about ten. Further, in a case where the coating 50 has the low refractive index film 51 containing silicon dioxide as a main component and the high refractive index film 52 containing iron(III) oxide as a main component, when the heater 1 is not subjected to electric conduction, a color of the coating 50 is gold.
Here, the heat generated in the coil 21 is transmitted to the coating 50 through the tubular portion 11. In this case, one end 23a side of the anchor 23 is in contact with the coil 21, and the other end 23b side thereof is in contact with the inner wall of the tubular portion 11. For this reason, the heat generated in the coil 21 is easily transmitted to the tubular portion 11 via the anchor 23, so that a surface temperature of the coating 50 at the position where the anchor 23 is provided is likely to increase. Further, since the dimple 14 holds the anchor 23, the surface temperature of the coating 50 at the position where the dimple 14 is provided is likely to further increase.
Since the surface of the coating 50 is exposed to the environment where the heater 1 is installed, when the surface temperature of the coating 50 becomes excessively high, gas, dust, etc. contained in the environment may react with a component contained in the coating 50 to discolor the surface of the coating 50. For example, when an uppermost layer of the coating 50 is the high refractive index film 52, metal contained in the high refractive index film 52 may react with gas, dust, etc. When discoloration occurs in the coating 50, a commercial value is lowered. In recent years, a heater having higher power is demanded. For example, when the heater 1 has 2,000 W (watts) or more, discoloration of the coating 50 is likely to occur.
In this case, when the outer diameter of the coil 21 is reduced, a distance between the coil 21 and the coating 50 can be increased, so that an increase in the surface temperature of the coating 50 can be suppressed. However, in this way, the anti-glare property is degraded.
In addition, when the tube outer diameter D of the tubular portion 11 is increased, the distance between the coil 21 and the coating 50 can be increased, so that an increase in the surface temperature of the coating 50 can be suppressed. However, in this way, the heater 1 is increased in size.
In addition, when the tube outer diameter D of the tubular portion 11 is constant and the wall thickness of the tubular portion 11 is increased, a distance between the inner wall of the tubular portion 11 and the coating 50 can be increased, and thus an increase in the surface temperature of the coating 50 can be suppressed. However, when the wall thickness of the tubular portion 11 is merely increased, there is concern that the distance between the coil 21 and the inner wall of the tubular portion 11 may decrease and the surface temperature of the coating 50 may increase.
Therefore, in the heater 1 according to the present embodiment, an increase in the surface temperature of the coating 50 is suppressed by a combination of a ratio (T/D) of the wall thickness T (mm) of the tubular portion 11 to the tube outer diameter D (mm) of the tubular portion 11 and a size of the tube outer diameter D (mm).

Table 1 is a table for showing a relationship between the ratio (T/D) of the wall thickness T (mm) of the tubular portion 11 to the tube outer diameter D (mm) of the tubular portion 11 and occurrence of discoloration of the coating 50 when the tube outer diameter D of the tubular portion 11 is changed from 10.0 mm to 15.0 mm.

[Table 1]

T/D	Occurrence of discoloration
T/D	D = 10.0 mm	D = 11.0 mm	D = 11.8 mm	D = 12.0 mm	D = 12.2 mm	D = 13.0 mm	D = 14.0 mm	D = 15.0 mm
0.05	Present	Present	Present	Present	Present	Present	Present	Present
0.08	Present	Present	Present	Present	Present	Present	Present	Present
0.09	Present	Present	Slightly present	Slightly present	Slightly present	Slightly present	Slightly present	Slightly present
0.10	Present	Present	Not present	Not present	Not present	Not present	Not present	Not present
0.12	Present	Slightly present	Not present	Not present	Not present	Not present	Not present	Not present
0.15	Present	Not present	Not present	Not present	Not present	Not present	Not present	Not present
0.20	Present	Not present	Not present	Not present	Not present	Not present	Not present	Not present

Table 1 shows a case where the power density of the heater 1 is 7.14 W/mm or more.
Moreover, the tubular portion 11 contains quartz glass.
The number of superposed layers of the low refractive index film 51 and the high refractive index film 52 is set to ten. The low refractive index film 51 contains silicon dioxide as a main component, and the high refractive index film 52 includes iron(III) oxide as a main component.
As can be seen from Table 1, when "T/D ≥ 0.09" and "D ≥ 11.8 mm" are set, it is possible to suppress occurrence of discoloration of the coating 50. In addition, when "T/D ≥ 0.10" and "D ≥ 11.8 mm" are set, it is possible to further effectively suppress occurrence of discoloration of the coating 50.
In addition, according to a knowledge obtained by the present inventor, when the surface temperature of the coating 50 can be set to 722°C or less, the occurrence of discoloration in the coating 50 can be suppressed.

Table 2 is a table for showing the surface temperature of the coating 50. Incidentally, Table 2 is a result of a case where electric conduction is performed 3,000 hours. In addition, the heater 1 was provided in the atmosphere. The pressure of the gas sealed in the tubular portion 11 was about 0.8 atm (81 kPa).

[Table 2]

	Experiment (1)	Experiment (2)	Experiment (3)	Experiment (4)
Power	2000 W
Tube diameter D (mm)	φ12
Sealed gas	Xe		Kr
Wall thickness T (mm)	1.0	1.2	1.0	1.2
Surface temperature of coating (°C)	769	678	762	708

As can be seen from Table 2, in a case where the tube outer diameter D of the tubular portion 11 is 12 mm, when the wall thickness T of the tubular portion 11 is set to 1.2 mm or more, the surface temperature of the coating 50 can be set to 722°C or less. For this reason, it is possible to suppress occurrence of discoloration in the coating 50. Incidentally, in the case of considering a manufacturing tolerance, when the tube outer diameter D of the tubular portion 11 is 12 mm ± 0.2 mm, it is sufficient that the wall thickness T of the tubular portion 11 is set to 1.2 mm ± 0.15 mm or more.
In addition, as can be seen from Table 2, when the gas sealed in the tubular portion 11 is set to xenon, the surface temperature of the coating 50 can be further lowered. On the other hand, when the gas sealed in the tubular portion 11 is set to krypton, the cost can be reduced to about 1/19 when compared to xenon. For this reason, the type of gas to be sealed can be selected according to the environment where the heater 1 is installed, etc.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. Moreover, above-mentioned embodiments can be combined mutually and can be carried out.

Claims

A heater (1) comprising:
a tubular portion (11);

a coil (21) which is provided inside the tubular portion (11) and extends along a tube axis of the tubular portion (11); and

a coating (50) which is provided on an outer surface of the tubular portion (11) and in which a first film (51) and a second film (52) having a higher refractive index than a refractive index of the first film (51) are alternately superposed,

a gas containing krypton as a main component or a gas containing xenon as a main component being sealed inside the tubular portion (11),

when a tube outer diameter of the tubular portion (11) is set to D (mm) and a wall thickness of the tubular portion (11) is set to T (mm), the following expression being satisfied: $T / D \geq 0.09 and D \geq 11.8 mm .$
The heater (1) according to claim 1, wherein a power density of the heater (1) is 7.14 W/mm or more.
The heater (1) according to claim 1 or 2, further comprising:
an anchor (23) having one end side provided on the coil (21) and the other end side in contact with an inner wall of the tubular portion (11); and

a dimple (14) protruding from the inner wall of the tubular portion (11) into the tubular portion (11) and coming into contact with the anchor (23).