TWI566269B - Short arc high-pressure discharge lamp for direct current operation - Google Patents

Description

Short arc high pressure discharge lamp

This invention relates to a short arc high pressure discharge lamp that illuminates with nominal power greater than 1 kW.

Such lamps are commonly used in the manufacture of projectors for cinemas, semiconductors, and liquid crystal displays, as well as lithography. Such short arc high pressure discharge lamps comprise an anode and a cathode disposed within a discharge vessel. Generally, such a discharge vessel is provided with an enclosure containing a mixed gas of an inert gas or an inert gas. Generally, a mixed gas of an inert gas or an inert gas is argon (Ar) or krypton ( Kr) and / or 氙 (Xe). In most cases, this seal further contains mercury (Hg) in an amount generally ranging from 1 mg/cm ³ to 81 mg/cm ³ . The anode in such a short arc high pressure discharge lamp is generally formed of a tungsten-based material.

The short arc high pressure discharge lamp is an electron impact anode, and the anode is heated to a high temperature (generally between 2000 ° C and 3000 ° C). As a result, the anode material evaporates and adheres to the inner wall of the discharge vessel. This attached anode material can dim or blacken the discharge vessel, which in turn will absorb a portion of the beam from the discharge vessel, thereby reducing the utility beam. This effect generally becomes more pronounced during the durability of the discharge lamp. Therefore, if the operating time of the discharge lamp is increased, the practical light beam is reduced due to evaporation of the anode material.

In addition to the above effects, it also has the following effects: this short arc high voltage discharge The total durability of the lamp is short and may further reduce utility light. For example, the cathode quality is continuously deteriorated as the operation progresses. In particular, the cathode is worn or the front end of the cathode is further widened. Thus, in particular for short arc high pressure discharge lamps having a mercury containing enclosure, evaporation of the anode material is a decisive factor in the overall durability of the discharge lamp.

In particular, when the sealing pressure is higher than 3 bar, the evaporation of the anode material becomes more pronounced as the sealing pressure increases. In order to make the width of the arc short, the sealing pressure of such a high inert gas or a mixed gas of an inert gas (generally including Ar and/or Kr and/or Xe) is used. Accordingly, when the discharge lamp is used in an optical system, practical radiation is increased, and the discharge lamp has a higher luminance (high luminance lamp). As a result, a high thermal load is caused in the anode material, and it is possible to increase the stress due to heat, and further, it is possible to locally deform the functional surface region.

In general, the above-described short arc high pressure discharge lamps operate with direct current and constant electric power (watts). However, in some applications, this power cycle modulation is advantageous. The modulation of such power also increases the evaporation of the anode material.

In order to solve the above problems, in particular, to reduce the evaporation of the anode material and to reduce the occurrence of local deformation of the functional surface region, different attempts have been made. In particular, the diameter of the anode is increased to increase the heat flux at the point of exiting the anode by thermal radiation. Furthermore, different methods of coating the anode and/or structuring the anode have been proposed. For example, as the coating material for the functional surface region of the anode material, coarse-grained tungsten or dendritic ruthenium is used. but, Such short-arc high-pressure discharge lamps having a high sealing pressure with a low-temperature sealing pressure exceeding a certain value do not sufficiently suppress the evaporation of the anode material below the allowable value.

Further, a discharge lamp in which an anode is formed of a tungsten-based material containing potassium as an additive is described. The insoluble potassium particles impart sufficient durability with respect to dislocation at a very high temperature, whereby excellent shape stability can be obtained. Despite the excellent shape stability, when a tungsten-doped tungsten material is used at a high temperature exceeding 2,500 ° C, it is found that excessive crystal growth may occur along grain boundaries. Such crystal growth causes high porosity and lowers thermal conductivity.

Patent Document 1 describes a high-pressure mercury discharge lamp (including an anode) for a direct current lighting using a nominal electric power of more than 1.5 kW. At least a portion of the region of the anode is formed of at least a material comprising a plurality of tungsten. This material has a number of crystal grains of more than 200 grains per 1 mm ^{2 and} a density of more than 19.05 g/cm ³ . This material is doped with potassium. At this time, the amount of potassium is less than 50 ppm.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] International Publication No. 2008/077832A1

It is an object of the present invention to provide a short arc high pressure discharge lamp for DC lighting using a nominal electric power of more than 1 kW, which improves the shape stability and evaporation resistance of the anode, and in the manufacture, the anode material is provided even after high temperature processing. Excellent processability of the anode.

This object can be solved by a short arc high pressure discharge lamp for DC lighting using a nominal electric power of more than 1 kW as described in the first paragraph of the patent application. A further extension is defined in the scope of the patent application.

The short arc high pressure discharge lamp comprises: a discharge vessel having a low temperature sealing pressure of 0.5 bar or more, and an enclosure containing at least one inert gas and any mercury; and an anode comprising 5 ppm to 80 ppm of potassium. Formed by a tungsten material; and a cathode. The anode and cathode are disposed within a discharge vessel. The anode has a diameter d (where 10 mm < d < 70 mm) and includes a functional surface region where the anode interacts with the arc, and a bulk region adjacent to the functional surface region. The functional surface area has a crystalline grain area greater than 2 mm ² measured in a plane perpendicular to the longitudinal axis of the anode and contains at least one crystal grain. The number of crystal grains of the tungsten-based material in the main body region is more than 100 grains per 1 mm ² . In this case, the number of crystal grains is measured in a second plane perpendicular to the longitudinal axis of the anode, and the distance from the second plane to the surface of the functional surface region in the axial direction is s (where s is greater than d ). Between the functional surface region and the body region in a direction parallel to the longitudinal axis of the anode, the crystal grain size of the tungsten-based material of the anode has a rapid change.

The crystal grain region of at least one crystal grain in the functional surface region is determined by an optical microscope, for example, on the polishing surface of the functional surface region, and the number of crystal grains of the tungsten-based material in the main body region is ASTM E 112 is defined. The diameter d of the anode is determined by the maximum diameter of the anode. In the representative example in which the anode includes a cylindrical portion and an adjacent conical portion, the diameter of the cylindrical portion is determined as the diameter d of the anode. The term "low-temperature sealing pressure" is interpreted as the sealing pressure of the discharge vessel at room temperature. Moreover, the tungsten-based material of the anode further contains an additive which can be added in the form of an oxide, particularly containing bismuth (Si) or aluminum (Al), with respect to a potassium content of 5 ppm to 80 ppm. The longitudinal axis of the anode corresponds to the axis of the arc expansion. The functional surface region is preferably formed of only one crystal grain of a tungsten-based material or a crystal grain of a predetermined amount of two or more. It is preferable that when the functional surface region contains two or more crystal grains, all the crystal grain regions of the tungsten-based material in the functional surface region have a crystal grain region larger than 2 mm ² . The number of crystal grains in the main body region is more than 100 particles per 1 mm ² , that is, the main body region is formed by a fine particle structure, and the crystal grains in the functional surface region are wider than 2 mm ² . Below is a correspondingly large crystal grain size, so there is an extreme difference between this functional surface area and the body area in terms of crystal grain size. This body region abuts the functional surface region, so the crystal grain size changes rapidly between this functional surface region and the body region. In particular, if the crystal grain size changes rapidly according to the above (this is a sign of discontinuous crystal grain growth in secondary recrystallization), a specific amount of potassium in the tungsten-based material of the anode, in the functional surface region The combination of the large crystal grain size and the fine crystal grain size in the bulk region is known to achieve a particularly high level of shape stability and a low risk of undesired crystal growth. Accordingly, the beam of the short arc high pressure discharge lamp is boosted during the durability of the entire short arc high pressure discharge lamp. In particular, the reduction of the practical light beam caused by the evaporation of the anode material can be particularly inefficient. Since the body region is adjacent to the functional surface region, there is no region containing the intermediate crystal grain size at all between the functional surface region and the body region. The short-arc high-pressure discharge lamp suitable for DC operation, for example, can be applied to a fixed-current DC operation or to a specific application for modulating power DC operation. The anode may, for example, also have a generally cylindrical shape (for example, a circular or conical shape in the vicinity of the functional surface area or in the vicinity of the functional surface area). In this case, the longitudinal axis coincides with the centerline of the cylinder.

In one embodiment, the tungsten-based material in the body region has substantially the number of crystal grains that are not affected by the position. In other words, in this case, the number of crystal grains is substantially uniform throughout the volume of the body region. In this case, there is a fine crystal grain size in the entire body region, and the crystal grain size has a particularly sharp change between the functional surface region and the body region. In this case, this body region has particularly excellent workability.

By way of an embodiment, the tungsten-based material of the anode comprises a density greater than 19.05 g/cm ³ . In this case, the anode is realized in a particularly dense manner in the presence of high thermal conductivity at the anode. Accordingly, in the operation of the short arc high pressure discharge lamp, it is possible to effectively suppress the stress generated by the anode due to heat.

By way of an embodiment, the functional surface area has a thickness t in a direction parallel to the longitudinal axis. In this case, d/20 < t < d/5, especially d/10 < t < d/5. Due to the aforementioned thickness of this functional surface area, a particularly advantageous property with this short arc high pressure discharge lamp is known.

By way of an embodiment, the functional surface region comprises at least one crystalline particle, wherein the crystalline particle has a crystalline particle region which is wider than 5 mm ² , in particular greater than 10 mm ² . When two or more crystal grains are contained in the functional surface region, it is preferred that all of the crystal grains in the functional surface region have such a wide crystal grain region. In particular, by such a wide crystal grain region, evaporation of the anode material is effectively suppressed, and therefore, the durability of the discharge lamp becomes long.

According to one embodiment, the functional surface area is composed of only one crystal grain. In this case, the grain boundaries are excluded from this functional surface region, so the arc does not interact regardless of the grain boundaries. Accordingly, the anode can be realized in a particularly stable manner.

By one embodiment, a tungsten-based material of the anode in said body region, comprising more than 1 mm ² per 200 crystal grains, particularly comprising ² to 350 or more crystal grains per 1 mm. In this case, the crystal grain size in the main body region is finer, and thus the workability of the anode is further improved. Moreover, the sharpness of the change in crystal grain size becomes more remarkable between the body region and the functional surface region. Accordingly, shape stability and evaporation resistance are further improved.

By way of an embodiment, the amount of potassium in the tungsten-based material of the anode is less than 50 ppm, particularly from 8 ppm to 45 ppm, more particularly from 10 ppm to 40 ppm. These values of the amount of potassium are particularly effective in preventing deformation of the anode due to the progress of the difference. In this case, the potassium-filled crystal affects the poor row due to the attractive interaction, whereby the anode material has high creep resistance.

By way of an embodiment, the tungsten-based material of the anode also contains Al and/or Si. Al and/or Si, for example, can be provided by adding a corresponding oxide in the powder metallurgy process of the anode. Al and Si have the advantage that in the powder metallurgy process of the anode, the potassium content in the tungsten-based material of the anode is stabilized, the high stability of the anode is achieved, and the progress of the difference is efficiently prevented.

By way of an embodiment, the short arc high pressure discharge lamp has a nominal power of greater than 4 kW, preferably having a nominal power of greater than 5 kW. By way of an embodiment, the enclosure comprises from 1 mg/cm ³ to 50 mg/cm ³ of mercury. Especially in these cases, evaporation of the anode material often occurs more and must be prevented efficiently.

By way of an embodiment, the low temperature encapsulation pressure is above 0.5 bar, in particular above 1.5 bar, and the short arc high pressure discharge lamp is suitable for operation at constant power. By means of other embodiments, the low-temperature sealing pressure is above 0.5 bar, in particular above 1.5 bar, and the short-arc high-pressure discharge lamp is suitable for operation with modulated electric power. In particular, when this short arc high pressure discharge lamp is applied to such a method, it is necessary to efficiently suppress evaporation of the anode material.

For further development and advantages, please refer to the following description, and the following description of an embodiment will be apparent.

Next, reference is made to these drawings and an embodiment will be described. Figure 1 shows a short arc high pressure discharge lamp 1. The short arc high pressure discharge lamp 1 comprises a discharge vessel 2. A cathode 3 and an anode 4 are provided inside the discharge vessel 2. As shown in Fig. 1, the side of the anode 4 facing the cathode 3 assumes a substantially cylindrical shape with an inclined end edge. The cathode 3 includes a conical front end portion. The operation of the short arc high pressure discharge lamp 1 is to form an arc between the conical front end portion of the cathode 3 and the anode 4. This arc expands in a direction substantially parallel to the longitudinal axis Z of the anode 4. In the illustrated embodiment, the longitudinal axis Z of the anode 4 coincides with the cylindrical centerline of the cylindrical portion of the anode 4.

As shown in Fig. 1, the anode 4 preferably includes a slanted shape on the side facing the cathode 3. The side of the anode 4 facing the cathode 3, including the arc Functional surface area 4a that interacts with anode 4. The anode 4 includes a body region 4b directly adjacent to the functional surface region 4a in a direction away from the cathode 3. Both the functional surface region 4a and the main body region 4b are formed of a tungsten-based material containing 5 ppm to 80 ppm of potassium as an additive. Preferably, the amount of potassium is less than 50 ppm, more preferably from 8 ppm to 45 ppm, still more preferably from 10 ppm to 40 ppm. Both the functional surface area 4a and the main body area 4b are formed of the same material and contain substantially the same density. However, as explained in further detail below, the crystal grain size in the functional surface region 4a is significantly different from the crystal grain size in the body region 4b. For example, the material of the anode 4 may be tungsten which is imparted with the above amount of potassium as an additive. However, other additives may be further imparted. For example, a small amount of aluminum (Al) and/or bismuth (Si) is added as another additive. For example, such additives can also be added in the form of an oxide. Preferably, the above-mentioned small amount of aluminum and/or cerium is the same as the amount of potassium.

In the above cylindrical portion, the anode 4 has a diameter d ranging from 10 mm to 70 mm. Moreover, the tungsten-based material of the anode 4 has a density greater than 19.05 g/cm ³ . Accordingly, heat can be efficiently removed from the functional surface region 4a by heat conduction and heat radiation during the operation of the short arc high pressure discharge lamp 1.

The body region 4b, this tungsten-based material comprising the fine grain size, each having more than 1mm ² 100 crystal grains, preferably having crystalline grains per 1mm ² of more than 200, and more preferably 1mm per ² has more than 350 grains of crystal grains. This crystal grain size is measured in a plane perpendicular to the longitudinal axis of the anode 4 in accordance with ASTM E 112. For example, the number of crystal grains is measured at a position which is only a distance s from the surface of the functional surface region 4a. Wherein the distance s is greater than the predetermined diameter d. The number of crystal grains is substantially constant in all the main body regions 4b of the anode 4. In other words, the number of crystal grains in the body region 4b is substantially not affected by the position.

The functional surface region 4a is widened from the surface of the anode 4 facing the cathode 3 to the main body region 4b. That is, between the functional surface area 4a and the main body area 4b, other areas (having an intermediate crystal grain size/crystal grain number) are completely absent. The functional surface region 4a contains a crystal grain size which is extremely different from the crystal grain size in the main body region 4b. The functional surface region 4a is composed of only one crystal grain or only a few crystal grains. It is preferable that the functional surface region 4a is composed of only one crystal grain. 4a functional surface area comprising at least one of the crystal grains, the crystal grains having a crystal grain area broader than 2mm ^2, more preferably having ² 5mm wide crystal grains in the region, and still more preferably having a 10mm wide in crystal grains ² region. This crystal grain region is determined by a micrograph of the functional surface region 4a. When the number of crystal grains is contained in the functional surface region 4a. All of the crystal grains preferably contain the above-mentioned predetermined wide crystal grain region. In the radial direction, the functional surface area 4a is formed at least in the surface portion of the anode 4 that intersects the longitudinal axis Z. In the direction parallel to the longitudinal axis Z, the functional surface area 4a has a thickness t of d/20 to d/5, preferably a thickness t of d/10 to d/5. Here d is the diameter of the above-mentioned determined anode 4.

By making the crystal grain region in the functional surface region 4a wide, and the number of crystal grains in the main body region 4b (directly adjacent to the functional surface region 4a) is large, the crystal grain size is at the boundary between the functional surface region 4a and the main body region 4b. There are significant rapid changes. In particular, such a rapid change in crystal grain size, that is, a case where there is no intermediate grain size, can be understood to produce characteristics for the anode 4 Favorable impact. The rapid change in crystal grain size between the functional surface region 4a and the main body region 4b is considered to be caused by the growth of discontinuous crystal grains in the functional surface region 4a.

The characteristics of the anode 4 described above can be achieved by forming the anode 4 from a tungsten-based material of a fine powder type, and a relatively low temperature (for example, less than 1300 ° C) of the anode material before the large deformation formed thereby. A large deformation is applied (for example, a specific degree of deformation ΔA/A > 66%), and energy of high deformation is collected into the anode before the large deformation. As a result, a large force generated in recrystallization is obtained, and growth is performed at a high-speed grain boundary, and potassium crystals are present inside the crystal grains. Accordingly, undesired crystal growth along such grain boundaries is suppressed.

[Examples]

A comparison was made between a short arc high pressure discharge lamp 1 according to an embodiment and two comparative samples. The results of this comparison are shown in Figure 3. Figure 3 depicts the relative lumen maintenance (expressed as a percentage) of the short arc high pressure discharge lamp 1 and the two comparative samples as a function of operating time (in terms of time) relative to this embodiment. This relative lumen maintenance rate gives a change in the beam compared to the initial beam. The measured values of this embodiment are indicated by circles, the measured values of the first comparative example are indicated by black triangles, and the measured values of the second comparative example are indicated by black squares.

In this embodiment and the comparative examples, the individual anodes are formed of tungsten to which potassium (K), aluminum (Al), or bismuth (Si) is added. The density of this anode material was 19.1 g/cm ³ in all three cases.

In this embodiment, the amount of potassium is 25 ppm and the amount of aluminum is 18 ppm. Further, the amount is 6 ppm.

In the first comparative example, the amount of potassium was 26 ppm, and the amount of aluminum was 18 ppm, and the amount of lanthanum was 7 ppm.

In the second comparative example, the amount of potassium was 24 ppm, and the amount of aluminum was 17 ppm, and the amount of lanthanum was 7 ppm.

In this embodiment, the main body region 4b contains about 350 crystal grains/mm ² , and the functional surface region 4a is composed of only one crystal grain having a crystal grain size of about 12 mm ² . Figure 2 shows a photomicrograph of a portion of the anode of a short arc high pressure discharge lamp of this embodiment. In Fig. 2, it can be used to clearly understand that the functional surface region 4a is formed of only one crystal grain, and the body region 4b contains fine particles. Therefore, there is a sudden change in the crystal grain size at the boundary between the functional surface region 4a and the main body region 4b. This is shown in the schematic diagram of FIG. The anode 4 of this embodiment can be obtained by forming an anode material with a tungsten-based powder having a desired composition and an average crystal grain size of 3.5 μm. The "raw" anode is subjected to cold pressure equalization at about 2000 bar and calcined at a temperature above 2200 °C. The anode 4 (or more appropriately, the anode material at this stage) is deformed at a temperature below 1300 ° C to a specific degree of deformation ΔA/A above 66%. The anode 4 thus formed was calcined at 2,200 ° C for 180 minutes. After the anode 4 is installed in the short arc high pressure discharge lamp 1, the anode 4 is heated to a maximum operating temperature of about 3000 °C. In this case, the heating is carried out continuously over a time interval of about 60 minutes.

In the above two comparative examples, both the main body region 4b and the functional surface region 4a contained approximately 350 particles of substantially the same number of crystal grains/mm ² .

The embodiment and the anodes of these comparative examples are all formed by a powder metallurgy process. As a result, the obtained anode shape is realized by a known technique such as rolling, grinding, milling, washing, and tempering. The anodes of these comparative examples used in comparison with the anode 4 of this embodiment did not receive a large deformation at a slightly lower temperature.

As shown in Fig. 3, the relative lumen maintenance rate of this embodiment of the short arc high pressure discharge lamp shows a significant upward lift as a function of the operating time. That is, this beam suppresses the degree of attenuation with time as compared with these comparative examples.

Therefore, the stability of the anode of the short arc high pressure discharge lamp of the present invention is compared with the prior embodiment, showing a substantial improvement. According to the essence of the invention, no matter what kind of grain boundary is reached, it does not interact with the arc. To some extent, it is considered to be caused by the growth of discontinuous crystal grains in secondary recrystallization. The discontinuous crystal grain growth proceeds at a high speed. Accordingly, the crystal grains are not subjected to substantial influence from the grain boundaries, and further coarsening of crystal grains due to the combination of the grain boundaries is avoided. The crystals filled with potassium affect the difference due to the attractive interaction, whereby the anode material has high latent resistance and avoids deformation due to the progress of the difference. Further, it is understood that in the operation of the short arc high pressure discharge lamp of the present invention, further growth of fine-grained crystal grains in the main body region 4b is prevented.

Although the invention has been described in a somewhat specific embodiment, these are not to be construed as limiting the scope of the claims.

1‧‧‧Short arc high pressure discharge lamp

2‧‧‧discharger

3‧‧‧ cathode

4‧‧‧Anode

4a‧‧‧Functional area

4b‧‧‧ body area

D‧‧‧diameter

S‧‧‧distance

T‧‧‧thickness

Z‧‧‧ longitudinal axis

Figure 1 shows a schematic view of a short arc high pressure discharge lamp.

Figure 2 is a photomicrograph of a portion of the anode of an embodiment of a short arc high pressure discharge lamp.

Fig. 3 is a line graph showing the relative lumen maintenance rate as a function of the operation time for the short arc high pressure discharge lamp and the two comparative examples of the embodiment.

Fig. 4 is a schematic view showing the difference in crystal grain size between the main body region and the functional surface region determined by the micrograph of Fig. 2.

1‧‧‧Short arc high pressure discharge lamp

2‧‧‧discharger

3‧‧‧ cathode

4‧‧‧Anode

4a‧‧‧Functional area

4b‧‧‧ body area

D‧‧‧diameter

S‧‧‧distance

T‧‧‧thickness

Z‧‧‧ longitudinal axis

Claims (13)

A short arc high pressure discharge lamp (1) comprising: a discharge vessel (2), an enclosure having a low temperature sealing pressure of 0.5 bar or more and containing at least one inert gas and mercury; and an anode (4) comprising 5 ppm to 80 ppm a potassium tungsten material; and a cathode (3), the anode (4) and the cathode (3) are disposed in the discharge vessel (2), and the anode (4) has a diameter d (where 10 mm < d) <70 mm), and the functional surface region (4a) including the anode (4) interacting with the arc and the body region (4b) adjacent to the functional surface region (4a) are suitable for DC operation with a nominal electric power of more than 1 kW. The functional surface region (4a) includes at least one crystal grain, and the crystal grain region measured in a plane perpendicular to the longitudinal axis (Z) of the anode (4) is wider than 2 mm ² . The number of crystal grains of the tungsten-based material in the main body region (4b) is more than 100 per 1 mm ² , and the number of crystal grains is perpendicular to the longitudinal axis (Z) of the anode (4). 2 measured in-plane, and the second plane has a surface distance from the functional surface region in the axial direction a distance s (where s is greater than d) between the aforementioned functional surface region (4a) parallel to the longitudinal axis (Z) and the aforementioned body region (4b), the aforementioned tungsten material of the anode (4) There is a rapid change in the crystal grain size. The short arc high pressure discharge lamp according to claim 1, wherein the tungsten-based material in the body region (4b) substantially includes a number of crystal grains which are not affected by the position. The short arc high pressure discharge lamp of claim 1 or 2, wherein the tungsten material of the anode (4) comprises a density greater than 19.05 g/cm ³ . The short arc high pressure discharge lamp according to claim 1 or 2, wherein the functional surface region (4a) has a thickness t in a direction parallel to the longitudinal axis (Z), and at this time, d/20<t <d/5. The short arc high pressure discharge lamp of claim 1, wherein the functional surface area (4a) comprises at least one crystal grain, wherein the crystal grain has a crystal grain area of more than 5 mm ² . The short arc high pressure discharge lamp according to claim 1 or 2, wherein the functional surface region (4a) is composed of only one crystal grain. The short arc high pressure discharge lamp according to claim 1 or 2, wherein the tungsten material of the anode (4) in the body region (4b) contains more than 200 crystals per 1 mm ² Number of grains. The short arc high pressure discharge lamp according to claim 1 or 2, wherein the amount of potassium in the tungsten material of the anode (4) is less than 50 ppm. The short arc high pressure discharge lamp according to claim 1 or 2, wherein the tungsten material of the anode (4) further contains aluminum (Al) and/or bismuth (Si). Short-arc high-pressure discharge as described in item 1 or 2 of the patent application scope An electric lamp having a nominal power of greater than 4 kW. The short arc high pressure discharge lamp of claim 1 or 2, wherein the enclosure comprises 1 mg/cm ³ to 50 mg/cm ³ of mercury. The short arc high pressure discharge lamp according to claim 1 or 2, wherein the aforementioned low temperature sealing pressure is 0.5 bar or more, and is suitable for operating at a constant electric power. The short arc high pressure discharge lamp according to claim 1 or 2, wherein the aforementioned low temperature sealing pressure is 0.5 bar or more, and is suitable for operating in a modulated electric power.