JP2017098173A - Discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge lamp which enables the increase in light emission efficiency and the achievement of a longer life of a light-emitting part.SOLUTION: A discharge lamp according to an embodiment comprises: a light-emitting part having therein a discharge space in which a discharge medium containing a metal halide including a scandium haloid and an inert gas is sealed; and a pair of electrodes projected into the discharge space and opposed to and spaced by a predetermined distance apart from each other. When X (atm) is a pressure of the inert gas at a room temperature (25°C), T (mm) is a maximum of the thickness of the light-emitting part, D (mm) is a size of the discharge space at a position where the light-emitting part becomes the maximum in thickness, Mm (μgf) is a weight of the metal halide, and Ms (μgf) is a weight of the scandium haloid, "A" given by A=(X-10×T+7.3)×10-Dis 10 to 30, and "M" given by M=(Ms/Mm)×100 is 45-55 wt%.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a discharge lamp.

There is a discharge lamp provided with a light emitting part having a discharge space in which a discharge medium is enclosed, and a pair of electrodes protruding inside the discharge space and arranged to face each other at a predetermined distance.
Traditionally, discharge media have included metal halides, inert gases, and mercury. However, in recent years, mercury is not included in the discharge medium from the viewpoint of environmental protection.

  Here, if mercury is not included in the discharge medium, there is a problem that the total luminous flux becomes low and the luminous efficiency becomes low. Therefore, a technique for improving the light emission efficiency by increasing the temperature of the light emitting section (the arc tube temperature) has been proposed.

  However, simply raising the temperature of the light emitting part causes a new problem that the life of the light emitting part is shortened. Therefore, it has been desired to develop a discharge lamp that can improve the luminous efficiency and extend the life of the light emitting part.

JP 2011-134696 A

  The problem to be solved by the present invention is to provide a discharge lamp capable of improving the light emission efficiency and extending the life of the light emitting part.

A discharge lamp according to an embodiment includes: a light emitting portion having a discharge space in which a discharge medium containing a metal halide containing a scandium halide and an inert gas is sealed; and projects into the discharge space; And a pair of electrodes arranged to face each other at a predetermined distance.
The pressure of the inert gas at normal temperature (25 ° C.) is X (atm), the maximum value of the thickness of the light emitting portion is T (mm), and the dimension of the discharge space at the position where the thickness of the light emitting portion is maximum. Is D (mm), the weight of the metal halide is Mm (μgf), and the weight of the scandium halide is Ms (μgf), A represented by the following formula is 10 or more and 30 or less. M represented by the following formula is 45 wt% or more and 55 wt% or less.
A = (X−10 × T + 7.3) × 10−D ³
M = (Ms / Mm) × 100

  According to the embodiment of the present invention, it is possible to provide a discharge lamp capable of improving the light emission efficiency and extending the life of the light emitting part.

It is a schematic diagram for illustrating the discharge lamp 100 according to the present embodiment.

The invention according to the embodiment includes: a light emitting unit having a discharge space in which a discharge medium containing a metal halide containing a scandium halide and an inert gas is sealed; and projecting into the discharge space; A pair of electrodes arranged opposite to each other at a distance of
The pressure of the inert gas at normal temperature (25 ° C.) is X (atm), the maximum value of the thickness of the light emitting portion is T (mm), and the dimension of the discharge space at the position where the thickness of the light emitting portion is maximum. Is D (mm), the weight of the metal halide is Mm (μgf), and the weight of the scandium halide is Ms (μgf), A represented by the following formula is 10 or more and 30 or less. M represented by the following formula is 45 wt% or more and 55 wt% or less.
A = (X−10 × T + 7.3) × 10−D ³
M = (Ms / Mm) × 100
According to this discharge lamp, the luminous efficiency can be improved and the life of the light emitting part can be extended.

The metal halide may further include an indium halide. When the weight of the indium halide is Mi (μgf), M1 represented by the following formula is 0.1 wt% or more and 1.0 wt% or less.
M1 = (Mi / Mm) × 100
In this way, it is possible to suppress a decrease in the total luminous flux. Moreover, it can suppress that luminescent color comes to become yellowish.

The metal halide may further include a zinc halide. When the weight of the zinc halide is Mz (μgf), M2 represented by the following formula is 0.5 wt% or more and 3.0 wt% or less.
M2 = (Mz / Mm) × 100
In this way, it is possible to suppress a decrease in the total luminous flux. Moreover, it can suppress that lamp voltage (voltage applied at the time of stable lighting) falls.

In addition, when the volume of the discharge space is V (μL), S represented by the following formula can be 7 μgf / μL or more and 15 μgf / μL or less.
S = (Mm / V) × 100
In this way, it is possible to suppress a decrease in the total luminous flux. Moreover, it can suppress that it becomes difficult to take out light from a light emission part by being interrupted by a metal halide.

Further, the discharge medium may be substantially free of mercury.
According to this discharge lamp, even if the discharge medium does not substantially contain mercury, it is possible to improve the light emission efficiency and extend the life of the light emitting part.

Hereinafter, embodiments will be illustrated with reference to the drawings.
The discharge lamp according to the embodiment of the present invention can be, for example, an HID (High Intensity Discharge) lamp used for an automobile headlamp. Further, when the discharge lamp is an HID lamp used for a headlight of an automobile, so-called horizontal lighting can be performed.

  Although the use of the discharge lamp according to the embodiment of the present invention is not limited to a vehicle headlamp, here, as an example, a case where the discharge lamp is an HID lamp used for a vehicle headlamp is an example. Will be described.

FIG. 1 is a schematic diagram for illustrating a discharge lamp 100 according to the present embodiment.
In addition, in FIG. 1, when the discharge lamp 100 is attached to an automobile, the front direction is the front end side, the rear direction is the rear end side, the upper direction is the upper end side, and the lower direction is the lower end side. It is said.

As shown in FIG. 1, the discharge lamp 100 is provided with a burner 101 and a socket 102.
The burner 101 is provided with an outer tube 5, an inner tube 1, an electrode mount 3, a support wire 35, a sleeve 4, and a metal band 71.

The outer tube 5 is provided outside the inner tube 1 and concentric with the inner tube 1. That is, the burner 101 has a double tube structure including the outer tube 5 and the inner tube 1. The outer tube 5 is joined (welded) near the cylindrical portion 14 of the inner tube 1.
Gas is enclosed in a closed space formed between the inner tube 1 and the outer tube 5. The sealed gas can be a gas capable of dielectric barrier discharge. The gas to be sealed can be, for example, a kind of gas selected from neon, argon, xenon, and nitrogen, or a mixed gas thereof. The gas sealing pressure can be, for example, 0.3 atm or less at room temperature (25 ° C.). The gas sealing pressure is more preferably 0.1 atm or less at room temperature (25 ° C.).

  The outer tube 5 is preferably formed of a material having a thermal expansion coefficient close to that of the material of the inner tube 1 and having an ultraviolet blocking property. The outer tube 5 can be formed of, for example, quartz glass to which an oxide such as titanium, cerium, or aluminum is added.

The inner tube 1 has a light emitting part 11, a sealing part 12, a boundary part 13, and a cylindrical part 14. The light emitting part 11, the sealing part 12, the boundary part 13, and the cylindrical part 14 can be integrally formed.
The inner tube 1 (the light emitting part 11, the sealing part 12, the boundary part 13, and the cylindrical part 14) is formed from a material having translucency and heat resistance. The inner tube 1 can be formed from, for example, quartz glass.

  The light emitting unit 11 has a substantially ellipsoidal outer shape. The light emitting unit 11 is provided near the center of the inner tube 1. The dimension (sphere length) of the light emitting part 11 in the axial direction of the inner tube 1 can be set to about 8 mm, for example. The dimension of the light emitting unit 11 in the direction orthogonal to the axial direction of the inner tube 1 can be set to about 5 mm, for example.

  A discharge space 111 is provided inside the light emitting unit 11. The central portion of the discharge space 111 has a substantially cylindrical shape. Both end portions of the discharge space 111 have a substantially conical shape.

  A discharge medium is enclosed in the discharge space 111. The discharge medium includes a metal halide 2 and an inert gas.

  In the discharge lamp 100 according to the present embodiment, the discharge medium is substantially free of mercury from the viewpoint of environmental protection. In the present specification, “substantially free of mercury” not only does not contain mercury at all, but also allows mercury to be contained to the extent of impurities. For example, the discharge medium can contain mercury as long as it is less than 2 mg / cc in the discharge space 111.

The metal halide 2 may include, for example, scandium halide, indium halide, sodium halide, zinc halide, and the like.
As the halogen, for example, iodine can be exemplified. However, bromine or chlorine can be used instead of iodine.

  The inert gas sealed in the discharge space 111 can be xenon, for example. In addition to xenon, neon, argon, krypton, or the like, or a mixed gas in which these are combined can also be used. The filling pressure of the inert gas can be changed according to the purpose. For example, when increasing the total luminous flux, the sealing pressure is preferably 10 atm or more and 20 atm or less at normal temperature (25 ° C.).

  The sealing portion 12 has a plate shape and is joined to each of both end portions of the light emitting portion 11. The sealing portion 12 can be formed using, for example, a pinch seal method. Note that the sealing portion 12 may be formed by a shrink seal method and may have a cylindrical shape. A cylindrical portion 14 is joined to one sealing portion 12 via a boundary portion 13.

  The boundary portion 13 and the cylindrical portion 14 are joined to the end portion of the sealing portion 12 on the side opposite to the light emitting portion 11 side.

The electrode mount 3 is provided inside the sealing portion 12.
The electrode mount 3 includes a metal foil 31, an electrode 32, a coil 33, and a lead wire 34.

The metal foil 31 is provided inside the sealing part 12. The metal foil 31 is joined in the vicinity of the end of the electrode 32 on the side opposite to the discharge space 111 side.
The metal foil 31 has a thin plate shape and can be formed of, for example, molybdenum, rhenium molybdenum, tungsten, rhenium tungsten, or the like.

  The electrode 32 has a linear shape. The cross-sectional shape of the electrode 32 can be circular, for example. The thickness dimension (diameter dimension when the cross-sectional shape is circular) of the electrode 32 can be 0.2 mm or more and 0.4 mm or less.

  The thickness dimension of the electrode 32 may not be constant in the direction in which the electrode 32 extends. For example, the thickness dimension of the electrode 32 may be larger on the distal end side than on the proximal end side. Further, the tip of the electrode 32 may be spherical. Moreover, the thickness dimension of one electrode may differ from the thickness dimension of the other electrode like a direct current lighting type.

  One end of the electrode 32 protrudes into the discharge space 111. That is, one end of the electrode 32 is provided in the discharge space 111 and the other end is provided in the sealing portion 12. The pair of electrodes 32 are provided to face each other at a predetermined distance. The distance between the tips of the pair of electrodes 32 (interelectrode distance) can be, for example, 3.4 mm or more and 4.4 mm or less. The other end of the electrode 32 is bonded to the vicinity of the end of the metal foil 31 on the light emitting unit 11 side. The joining of the electrode 32 and the metal foil 31 can be performed by, for example, laser welding.

  The electrode 32 can be formed from, for example, pure tungsten, doped tungsten, rhenium tungsten, or the like. The electrode 32 may contain thorium or may not contain thorium.

  The coil 33 is provided to suppress the occurrence of cracks in the sealing portion 12. The coil 33 can be formed from, for example, a metal wire made of doped tungsten. The coil 33 is provided inside the sealing portion 12. The coil 33 is wound around the outside of the electrode 32. For example, the coil 33 can have a wire diameter of about 30 μm to 100 μm and a coil pitch of 600% or less.

  The lead wire 34 has a linear shape. The cross-sectional shape of the lead wire 34 can be circular, for example. The lead wire 34 can be formed from, for example, molybdenum. One end side of the lead wire 34 is joined to the vicinity of the end of the metal foil 31 on the side opposite to the light emitting unit 11 side. The lead wire 34 and the metal foil 31 can be joined by laser welding. The other end side of the lead wire 34 extends to the outside of the inner tube 1.

  The support wire 35 has an L shape and is joined to the end portion of the lead wire 34 extending from the front end side of the discharge lamp 100. The support wire 35 and the lead wire 34 can be joined by laser welding. The support wire 35 can be formed from nickel, for example.

  The sleeve 4 covers a portion of the support wire 35 that extends in parallel with the inner tube 1. The sleeve 4 has, for example, a cylindrical shape. The sleeve 4 can be formed from, for example, ceramics.

  The metal band 71 is fixed in the vicinity of the end portion on the rear end side of the outer tube 5.

The socket 102 has a main body 6, a mounting bracket 72, a bottom terminal 81, and a side terminal 82.
The main body 6 is made of an insulating material such as resin. Inside the main body 6, a rear end side of the lead wire 34, a rear end side of the support wire 35, and a rear end side of the sleeve 4 are provided.

  The mounting bracket 72 is provided at the end of the main body 6. The mounting bracket 72 is provided on the front end side of the main body 6. The mounting bracket 72 protrudes from the main body 6. The mounting bracket 72 holds the metal band 71. The burner 101 is held by the socket 102 by holding the metal band 71 by the mounting bracket 72.

  The bottom terminal 81 is provided inside the main body 6. The bottom terminal 81 is provided on the rear end side of the main body 6. The bottom terminal 81 is made of a conductive material. The bottom terminal 81 is electrically connected to the lead wire 34.

  The side terminal 82 is provided on the side wall of the main body 6. The side terminal 82 is provided on the rear end side of the main body 6. The side terminal 82 is made of a conductive material. The side terminal 82 is electrically connected to the support wire 35.

  The bottom terminal 81 and the side terminal 82 are electrically connected to a lighting circuit (not shown). In this case, the bottom terminal 81 is electrically connected to the high voltage side of the lighting circuit. The side terminal 82 is electrically connected to the low voltage side of the lighting circuit.

  When the discharge lamp 100 is used for a headlight of an automobile, the discharge lamp 100 has a central axis (tube axis) substantially horizontal and the support wire 35 substantially on the lower end side (downward). It is attached to be located. Note that lighting the discharge lamp 100 attached in such a direction is referred to as horizontal lighting.

Here, in the case of using a discharge medium that does not substantially contain mercury, there is a problem that the total luminous flux becomes low and the luminous efficiency becomes low. The luminous efficiency is “total luminous flux / lamp power (applied power during stable lighting)”.
In this case, if the temperature of the light emitting unit 11 (the arc tube temperature) is increased, the total luminous flux is increased, and the luminous efficiency is increased.

  This can be explained as follows. That is, when the temperature of the light emitting unit 11 is increased, the vapor pressure of the metal halide 2 is increased. If the vapor pressure of the metal halide 2 increases, the rate at which the electrons emitted from the electrode 32 collide with the molecules of the metal halide 2 increases. As the rate of collision between the electrons and the molecules of the metal halide 2 increases, the total luminous flux increases and the luminous efficiency also increases.

  According to the knowledge obtained by the present inventor, the temperature of the light emitting unit 11 is the pressure X (atm) of an inert gas (for example, xenon) contained in the discharge medium at normal temperature (25 ° C.), the thickness of the light emitting unit 11. And the dimension D (mm) of the discharge space 111 at the position where the thickness of the light emitting portion 11 is maximized.

  In this case, if the pressure X of the inert gas contained in the discharge medium at normal temperature (25 ° C.) is 10 atm or more and 20 atm or less, the temperature of the light emitting unit 11 is approximately proportional to the increase of the inert gas pressure X. Rises. The relationship between the pressure X of the inert gas and the temperature of the light emitting unit 11 can be obtained, for example, by performing an experiment. For example, when the pressure of the inert gas is 13.5 atm, the temperature of the light emitting unit 11 is about 920 ° C.

  Further, when the thickness of the light emitting unit 11 is reduced, it is difficult for heat to be diffused, and local temperature rise is likely to occur. In this case, the temperature of the light emitting unit 11 rises substantially in proportion to the decrease in the maximum thickness T of the light emitting unit 11. The relationship between the maximum value T of the thickness of the light emitting unit 11 and the temperature of the light emitting unit 11 can be obtained, for example, by performing an experiment. For example, when the maximum thickness T of the light emitting unit 11 is 1.85 mm, the temperature of the light emitting unit 11 is about 920 ° C.

  Further, when the size of the discharge space 111 is reduced, the distance between the discharge generated between the electrodes 32 and the inner wall 11a of the light emitting unit 11 is shortened. Therefore, when the dimension of the discharge space 111 decreases, the temperature of the light emitting unit 11 increases. In this case, the temperature of the light emitting unit 11 rises substantially in proportion to the decrease in the dimension D of the discharge space 111 at the position where the thickness of the light emitting unit 11 is maximum. The relationship between the dimension D of the discharge space 111 at the position where the thickness of the light emitting unit 11 is maximized and the temperature of the light emitting unit 11 can be obtained, for example, by performing an experiment. For example, when the dimension D of the discharge space 111 at the position where the thickness of the light emitting unit 11 is maximum is 2.5 mm, the temperature of the light emitting unit 11 is about 920 ° C.

As a result of investigation, the present inventor has obtained knowledge that the luminous efficiency can be improved by using A represented by the following formula.
A = (X−10 × T + 7.3) × 10−D ³
X (atm) is the pressure of the inert gas at room temperature (25 ° C.), T (mm) is the maximum value of the thickness of the light emitting unit 11, and D (mm) is the position where the thickness of the light emitting unit 11 is maximum. Is the dimension of the discharge space 111 in FIG.
As described above, X, T, and D are related to the temperature of the light emitting unit 11.
For example, when X = 15 (atm), T = 1.85 (mm), and D = 2.4 (mm), A = 24.176.

  In general, as shown in FIG. 1, the thickness of the light emitting unit 11 is maximized near the center of the light emitting unit 11. Further, the thickness of the light emitting unit 11 and the dimensions of the discharge space 111 can be obtained based on an X-ray photograph of the light emitting unit 11 taken. The pressure of the inert gas can be determined as follows. First, the light emitting unit 11 is cut in water, and the volume of the inert gas discharged from the light emitting unit 11 is measured. Next, the volume of the discharge space 111 is obtained based on the above-described X-ray photograph. Then, the pressure of the inert gas is obtained from the volume of the inert gas and the volume of the discharge space 111.

If “A” related to the temperature of the light emitting unit 11 is used, the luminous efficiency can be improved.
However, if the temperature of the light emitting unit 11 is too high, a new problem arises that the life of the light emitting unit 11 is shortened.
The reason why the lifetime of the light emitting unit 11 is shortened when the temperature of the light emitting unit 11 is excessively increased can be explained as follows. That is, if the temperature of the light emitting portion 11 is too high, the chemical reaction between the metal halide 2 and the inner wall 11a of the light emitting portion 11 is promoted. When the chemical reaction between the metal halide 2 and the inner wall 11a of the light emitting unit 11 is promoted, the inner wall 11a of the light emitting unit 11 is clouded and the total luminous flux is reduced. Therefore, if the temperature of the light emitting unit 11 is too high, the inner wall 11a of the light emitting unit 11 is likely to be cloudy, and the life of the light emitting unit 11 is shortened.

  In this way, it is difficult to improve the light emission efficiency and extend the life of the light emitting unit 11 only by “A” related to the temperature of the light emitting unit 11.

  Here, the luminous efficiency can be improved also by the composition of the metal halide 2. In this case, even if the composition of the metal halide 2 is changed, the temperature change of the light emitting portion 11 is small. Therefore, the luminous efficiency can be improved and the life of the light emitting part 11 can be extended depending on the composition of the metal halide 2.

As described above, the metal halide 2 includes scandium halide, indium halide, sodium halide, zinc halide, and the like.
In this case, if the amount of scandium halide is increased, the total luminous flux can be increased, and as a result, the luminous efficiency can be improved. However, if the amount of scandium halide is increased too much, the total luminous flux is decreased, and the luminous efficiency cannot be improved. Therefore, the ratio of the scandium halide must be in an appropriate range.

The proportion of scandium halide can be expressed by the following formula.
M = (Ms / Mm) × 100
Mm (μgf) is the weight of the metal halide 2, and Ms (μgf) is the weight of the scandium halide.
For example, when ScI ₃ : NaI: ZnI ₂ : InBr = 51.9 wt%: 46.9 wt%: 1.0 wt%: 0.2 wt%, M = 51.9 wt%.

Even if only “M” relating to the proportion of scandium halide is used, the luminous efficiency can be improved and the life of the light emitting portion 11 can be extended.
However, if only “M” relating to the proportion of scandium halide is used, high luminous efficiency cannot be obtained. For example, if only “M” relating to the proportion of scandium halide is used, it is difficult to achieve a luminous efficiency of 94 lm / W (lumen / watt) or more.

  Therefore, in the discharge lamp 100 according to the present embodiment, the “A” related to the temperature of the light emitting unit 11 and the “M” related to the ratio of the scandium halide improve the luminous efficiency and the length of the light emitting unit 11. The service life is to be extended.

なお、発光効率の評価においては、９４ ｌｍ／Ｗ（ルーメン／ワット）以上を「○」とし、９４ ｌｍ／Ｗ未満を「×」としている。
発光部１１の寿命の評価においては、放電ランプ１００を２０００時間点灯し、初期の全光束に対する２０００時間経過後の全光束の割合が６０％以上となった場合を「○」とし、６０％未満となった場合を「×」としている。 Table 1 is a table for illustrating the relationship between “A” and “M” and the light emission efficiency and the lifetime of the light emitting unit 11.

In the evaluation of luminous efficiency, 94 lm / W (lumen / watt) or more is “◯”, and less than 94 lm / W is “x”.
In the evaluation of the life of the light emitting unit 11, when the discharge lamp 100 is lit for 2000 hours and the ratio of the total luminous flux after the lapse of 2000 hours to the initial total luminous flux is 60% or more, “◯” is given, and less than 60% The case where it becomes becomes "x".

  As can be seen from Table 1, when “A” exceeds 30, the temperature of the light emitting section 11 becomes too high. In this case, since the temperature of the light emitting unit 11 is high, the evaluation of the light emission efficiency is “◯”. However, since the temperature of the light emitting unit 11 becomes too high, the evaluation of the life of the light emitting unit 11 is “x”.

When “A” is in the range of 10 or more and 30 or less, the temperature of the light emitting unit 11 does not become too high, and thus the life evaluation of the light emitting unit 11 is “◯”. However, a high luminous efficiency cannot be obtained only by the temperature of the light emitting unit 11, and the evaluation of the luminous efficiency is “x”.
However, in the range where “M” is 45 wt% or more and 55 wt% or less, the improvement of the light emission efficiency due to “M” contributes, and thus the evaluation of the light emission efficiency is “◯”.

If “A” is less than 10, the temperature of the light emitting section 11 becomes too low. In this case, since the temperature of the light emitting unit 11 is low, the evaluation of the life of the light emitting unit 11 is “◯”. However, since the temperature of the light emitting unit 11 becomes too low, the evaluation of the light emission efficiency is “x”.
In the range where “M” is 45 wt% or more and 55 wt% or less, the improvement of the light emission efficiency due to “M” contributes, but since the improvement of the light emission efficiency due to “A” is small, the evaluation of the light emission efficiency becomes “×”. .

  Therefore, as can be seen from Table 1, if “A” is 10 or more and 30 or less and “M” is 45 wt% or more and 55 wt% or less, the luminous efficiency is improved and the light emitting section 11 has a long lifetime. Can be achieved.

Here, the halide of indium and the halide of zinc contained in the metal halide 2 also contribute to the improvement of luminous efficiency, although not as much as the scandium halide.
According to the knowledge obtained by the present inventor, it was found that the total luminous flux decreases when “M1” represented by the following formula exceeds 1.0 wt%. It was also found that when “M1” was less than 0.1 wt%, the emission color became yellowish. Therefore, “M1” is preferably 0.1 wt% or more and 1.0 wt% or less.
In this way, it is possible to suppress a decrease in the total luminous flux. Moreover, it can suppress that luminescent color comes to become yellowish.
M1 = (Mi / Mm) × 100
Mm (μgf) is the weight of the metal halide 2, and Mi (μgf) is the weight of the indium halide.

Further, according to the knowledge obtained by the present inventor, it was found that the total luminous flux decreases when “M2” represented by the following formula exceeds 3.0 wt%. Further, it has been found that when “M2” is less than 0.5 wt%, the lamp voltage (voltage applied during stable lighting) decreases. Therefore, “M2” is preferably 0.5 wt% or more and 3.0 wt% or less.
In this way, it is possible to suppress a decrease in the total luminous flux. Moreover, it can suppress that lamp voltage (voltage applied at the time of stable lighting) falls.
M2 = (Mz / Mm) × 100
Mm (μgf) is the weight of the metal halide 2, and Mz (μgf) is the weight of the zinc halide.

Further, the amount of the metal halide 2 also contributes to the improvement of the luminous efficiency. For example, if the amount of the metal halide 2 is too small, the amount of the metal halide 2 that contributes to light emission is reduced, so that the total luminous flux is reduced and the light emission efficiency cannot be improved. If the amount of the metal halide 2 is too large, the light is blocked by the metal halide 2 inside the light emitting portion 11. For this reason, it is difficult to extract light to the outside of the light emitting unit 11.
According to the knowledge obtained by the present inventors, “S” represented by the following formula is preferably 7 μgf / μL or more and 15 μgf / μL or less.
In this way, it is possible to suppress a decrease in the total luminous flux. Moreover, it can suppress that it becomes difficult to take out light from a light emission part by being interrupted by a metal halide.
S = (Mm / V) × 100
Mm (μgf) is the weight of the metal halide 2, and V (μL) is the volume of the discharge space 111.

  As mentioned above, although several embodiment of this invention was illustrated, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, changes, and the like can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and equivalents thereof. Further, the above-described embodiments can be implemented in combination with each other.

  DESCRIPTION OF SYMBOLS 1 Inner tube, 2 Metal halide, 5 Outer tube, 11 Light emission part, 12 Sealing part, 32 Electrode, 100 Discharge lamp, 101 Burner, 102 Socket, 111 Discharge space

Claims (5)

A light emitting part having a discharge space in which a discharge medium containing a metal halide containing a scandium halide and an inert gas is enclosed;
A pair of electrodes protruding into the discharge space and arranged to face each other at a predetermined distance;
Comprising
The pressure of the inert gas at normal temperature (25 ° C.) is X (atm), the maximum value of the thickness of the light emitting portion is T (mm), and the dimension of the discharge space at the position where the thickness of the light emitting portion is maximum. Is D (mm), the weight of the metal halide is Mm (μgf), and the weight of the scandium halide is Ms (μgf),
A represented by the following formula is 10 or more and 30 or less,
A discharge lamp in which M represented by the following formula is 45 wt% or more and 55 wt% or less.
A = (X−10 × T + 7.3) × 10−D ³
M = (Ms / Mm) × 100 The metal halide further includes an indium halide,
When the weight of the indium halide is Mi (μgf),
The discharge lamp according to claim 1, wherein M1 represented by the following formula is 0.1 wt% or more and 1.0 wt% or less.
M1 = (Mi / Mm) × 100 The metal halide further comprises a halide of zinc;
When the weight of the zinc halide is Mz (μgf),
The discharge lamp according to claim 1 or 2, wherein M2 represented by the following formula is 0.5 wt% or more and 3.0 wt% or less.
M2 = (Mz / Mm) × 100 The discharge lamp according to any one of claims 1 to 3, wherein when the volume of the discharge space is V (µL), S represented by the following formula is 7 µgf / µL or more and 15 µgf / µL or less. .
S = (Mm / V) × 100   The discharge lamp according to any one of claims 1 to 4, wherein the discharge medium does not substantially contain mercury.

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