JP2005322575A - High-pressure sodium lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-pressure sodium lamp having high efficiency and long service life. <P>SOLUTION: In a high pressure sodium lamp 100, in which an arc tube 10 is housed in an outer tube 101 made of quartz glass, the housing of the arc tube 10 is made of polycrystalline alumina ceramics added with at least magnesium oxide and yttrium oxide; and if the minimum distance between the inner face of the outer tube 101 and the outer face of the housing is set to D (cm) and the tube wall load of the arc tube 10 is set to W<SB>e</SB>(W/cm<SP>2</SP>), the relational expressions W<SB>e</SB>≤28.4D+17.0 and W<SB>e</SB>>-6.8D<SP>2</SP>+10.6D+15.7 when D<0.7, and W<SB>e</SB>≥19.8 when D≥0.7 are satisfied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a high pressure sodium lamp.

High-pressure sodium lamps are widely used for road lighting, tunnel lighting, and the like because of their high efficiency and long life.
This type of high-pressure sodium lamp includes a quartz glass outer tube whose inside is in a vacuum state, and an arc tube that is housed in the outer tube and has a pair of electrodes disposed substantially opposite each other. ing.

As a material of the envelope constituting the arc tube, generally, a polycrystalline alumina ceramic having translucency is used. Usually, in order to obtain translucency, this polycrystalline alumina ceramic needs to appropriately control the growth of crystal grains at the time of firing, and for that purpose, a small amount of magnesium oxide (MgO) is added.
By the way, the lamp efficiency (lm / W) of this type of high-pressure sodium lamp is obtained by dividing the tube wall load of the arc tube (lamp input (W) by the inner area (cm ² ) of the portion forming the discharge space inside the arc tube. It is known that the measured value (W / cm ² ) increases as the value increases.

This is because the tube wall temperature of the arc tube rises as the tube wall load increases, the heat loss from the arc tube is reduced, and the radiation intensity of visible light increases.
On the other hand, it is known that the life time of the lamp becomes shorter as the tube wall load increases. This is also due to the fact that the tube wall temperature rises as the tube wall load increases, so that the proportion of sodium that is enclosed disappears due to reaction with the polycrystalline alumina ceramic and diffusion outside the arc tube during lighting. This is because the light flux maintenance factor is significantly reduced.

Therefore, in the conventional high pressure sodium lamp, high efficiency and in order to achieve both long life, the wall loading ^{_{W e 15W / cm 2 ~19W /}} cm 2 of (during stable lighting of the tube wall temperature 1000 ° C. to 1200 ° C.) It is set to work with a range.
Thus, among conventional high-pressure sodium lamps, for example, a double-piece high-pressure sodium lamp with a rated power of 400 W has an initial luminous flux of 46500 lm and a rated life of 12000 hours.

Here, the “initial luminous flux” refers to the luminous flux after 100 hours of lighting. “Rated life” indicates the elapsed lighting time when the luminous flux maintenance factor reaches 85%. However, “luminous flux maintenance rate (%)” indicates the ratio of the luminous flux of a certain lighting elapsed time to the luminous flux of 100 hours of lighting elapsed.
Recently, in view of energy saving and reduction of maintenance cost, it is desired to realize a high-pressure sodium lamp with higher efficiency and longer life.

Accordingly, as materials for the envelope constituting the arc tube of this type of high-pressure sodium lamp, magnesium oxide is 100 ppm to 800 ppm, zirconium oxide (ZrO ₂ ) is 200 ppm to 1200 ppm, and yttrium oxide (Y ₂ O ₃ ) is 10 ppm to It has been proposed to use a polycrystalline alumina ceramic added with 300 ppm (see, for example, Patent Document 1).

In particular, it is considered that zirconium oxide and yttrium oxide can improve the corrosion resistance against sodium even when the tube wall temperature is high. Therefore, even if the tube wall load is increased in order to realize further higher efficiency, it is possible to prevent the enclosed sodium from disappearing and the luminous flux maintenance rate from greatly decreasing, and to further increase the service life. It is expected that it can be realized.
JP-A-8-17396

In order to realize a high-efficiency, longer-life high-pressure sodium lamp, the inventors of the present invention are made of a polycrystalline alumina ceramic added with, for example, 500 ppm, 400 ppm, and 50 ppm of MgO, ZrO ₂ and Y ₂ O ₃ , respectively. An arc tube having an envelope was produced, and the produced arc tube was housed in a quartz glass outer tube having a vacuum inside as in the case of a conventional high-pressure sodium lamp, and a lamp was prototyped.

  Then, when the characteristics of the prototype lamp were evaluated, when the lighting elapsed time exceeded 14000 hours, the outer tube was deformed and the light distribution characteristics were changed, or in some cases, the deformed outer tube was in contact with the arc tube. Then, an unexpected problem occurred in which the arc tube was damaged by the heat of the arc tube and leaked. If the outer tube leaks, the temperature of the arc tube will drop and the desired lamp characteristics will not be obtained, or the metal holding the electrode (electrode holding member) will be oxidized and the conductivity will deteriorate, and the lamp will not turn on It becomes.

  The present invention has been made to solve such problems, and uses an envelope made of a polycrystalline alumina ceramic to which at least magnesium oxide and yttrium oxide are added as an envelope of an arc tube, High pressure that can prevent the outer tube from being deformed and the outer tube from being damaged and leaking due to the deformation in realizing higher efficiency and longer life. An object is to provide a sodium lamp.

  As a result of examining the cause of deformation of the outer tube when the lighting elapsed time exceeds 14000 hours, the inventors considered the cause of the damage of the outer tube as follows. In other words, as a result of increasing the tube wall load and increasing the tube wall temperature, heat loss is reduced, and instead, the radiation intensity of visible light emitted from the arc tube increases, while the radiation intensity of infrared light also increases. However, it is considered that the outer tube was excessively heated by the infrared radiation.

Therefore, the high pressure sodium lamp of the present invention includes an outer tube made of quartz glass, and an arc tube that is housed in the outer tube and has a pair of electrodes disposed substantially opposite to each other. The envelope is made of polycrystalline alumina ceramic to which at least magnesium oxide and yttrium oxide are added, and the minimum distance between the inner surface of the outer tube and the outer surface of the envelope is D (cm), and the light emission when the tube wall loading of the tube was ^{_{W e (W / cm 2)}} , < case of _{0.7, W e> W e ≦} 28.4D + 17.0 and ^{D, -6.8D 2 + 10.6D + 15.7} , In the case of D ≧ 0.7, it has a configuration that satisfies the relational expression of W _e ≧ 19.8.

Here, when the envelope of the arc tube is substantially cylindrical, the inner diameter is r ₁ (cm), the lamp input is W (W), and the distance between the electrodes is L (cm), the tube wall load We is assumed to be represented by the formula W / (πr ₁ L).
In particular, the present invention preferably further satisfies the relational expression W _e <13.4D + 19.0. Further, it is preferable that the relational expression W _e <26.5 is satisfied.

Minimum distance relationship between D a wall loading of (cm) and the light-emitting tube W _e (W / cm ²⁾ between the inner and the outer envelope of the outer surface of the outer tube as described above, W _e ≦ 28. 4D + 17.0, and <for ^{_{0.7, W e> D -6.8D 2}} + 10.6D + 15.7, if the D ≧ 0.7, by W _e ≧ 19.8 becomes satisfying, initial The luminous flux can be improved to increase efficiency, and the outer tube can be deformed over a long lighting elapsed time, or the outer tube can be damaged due to the deformation, causing leakage. Can be prevented, and the life can be extended.

In particular, W _e <By satisfying 13.4D + 19.0 relational expression, it is possible to suppress the scattering of aluminum which is one component of the envelope material, the light beam is colored by aluminum inner surface of the outer tube is scattered It is possible to prevent the maintenance rate from decreasing.
Further, by satisfying the relational expression W _e <26.5, it is possible to prevent the lamp voltage from being increased due to the disappearance of sodium, the luminous flux being decreased, and the luminous flux maintenance factor from being decreased.

The best mode for carrying out the present invention will be described below with reference to the drawings.
(1) Configuration of High Pressure Sodium Lamp 100 FIGS. 1A and 1B are a plan view and a front view showing the configuration of the high pressure sodium lamp 100 according to the present embodiment, respectively. In both figures, only the outer tube is shown in a sectional view with a part cut away.

This high-pressure sodium lamp 100 is of a double-cap type with a rated power (lamp input) of 400 W, and has sealing parts 102 that are pinched at both ends as shown in FIG. In addition, a substantially cylindrical outer tube 101 made of quartz glass evacuated so that the inside is in a vacuum state, and an arc tube 10 accommodated in the outer tube 101 are provided.
The central axis (tube axis) in the longitudinal direction of the outer tube 101 and the central axis (tube axis) in the longitudinal direction of the arc tube 10 substantially coincide with each other.

As shown in FIG. 2, the arc tube 10 is based on aluminum oxide (Al ₂ O ₃ ), and magnesium oxide (MgO), zirconium oxide (ZrO ₂ ), and yttrium oxide (Y ₂ O ₃ ) are each 500 ppm, It is made of polycrystalline alumina ceramic added with 400 ppm and 50 ppm, and is inserted into a substantially cylindrical envelope 11 having a total length T ₂ of 12.0 cm, and through holes 12 provided at both ends of the envelope 11. And an electrode holding member 9 hermetically sealed by the ceramic sealing material 13 and a pair of electrodes 14 provided at the tip of the electrode holding member 9.

Although not particularly illustrated, in the discharge space 15 of the arc tube 10, sodium as a luminescent substance and mercury as a buffer gas in the form of sodium amalgam (for example, sodium: 20% by weight, mercury: 80% by weight). , And a rare gas as a starting auxiliary gas, for example, xenon gas, is sealed in a predetermined amount.
Here, when the minimum distance between the inner surface of the outer tube 101 and the outer surface of the envelope 11 is D (cm) and the tube wall load of the arc tube is W _e (cm ² ), W _e ≦ 28.4 D + 17. 0.0 and D <0.7, the relational expression W _e > −6.8D ² + 10.6D + 15.7 and D ≧ 0.7 satisfies the relation W _e ≧ 19.8.

Further, in the case of satisfying this relational expression, it is preferable to satisfy W _e <13.4D + 19.0 relational expression. Furthermore, it is preferable to satisfy the relational expression W _e <26.5. Details will be described later.
As shown in FIGS. 1A and 1B, in the present embodiment, the central axis in the longitudinal direction of the outer tube 101 and the central axis in the longitudinal direction of the arc tube 10 (the central axis in the longitudinal direction of the envelope 11) Therefore, the minimum distance D is expressed by the equation (r ₂ −R) when the inner diameter of the outer tube is r ₂ (cm) and the outer diameter of the envelope 11 is R ₁ (cm). ₁ ) / 2. However, when the central axis in the longitudinal direction of the arc tube 10 is deviated from the central axis in the longitudinal direction of the outer tube 101, the “minimum distance D” is literally between the inner surface of the outer tube and the outer surface of the envelope. Take the minimum distance.

Also, the wall load W _e is determined by the value obtained by dividing the inner area (cm ²⁾ of the portion forming the discharge space in the arc tube portion of the lamp input (W) as described above, in this embodiment Represents the lamp input as W (W), the inner diameter of the envelope as r ₁ (cm), the distance between the pair of electrodes as L (cm), and approximates the expression W _e / (πr ₁ L). To.
The electrode 14 is composed of an electrode rod 14a made of tungsten and an electrode coil 14b made of tungsten which is wound around the electrode rod 14a and has an electron emitting material (not shown) attached thereto. The pair of electrodes 14 are substantially opposed to each other, and are arranged so that the central axis in the longitudinal direction of each electrode 14 is located on substantially the same axis as the central axis in the longitudinal direction of the envelope 11.

As shown in FIG. 3, the electrode holding member 9 is made of, for example, a bottomed cylindrical niobium tube having a length T ₃ in the longitudinal direction of the arc tube 11 of 20 mm and an outer diameter R ₃ of 4.0 mm. The tip (bottom) of the electrode holding member 9 and the electrode rod 14a are connected by welding or the like, and the end of the electrode holding member 9 opposite to the electrode 14 is connected to the outside of the envelope 11. Has been derived.
As shown in FIGS. 1A and 1B, an internal lead wire 106 is inserted into and electrically connected to the lead-out portion of the electrode holding member 9. End portions of the metal wire 105 bent in a U shape are connected to the electrode holding member 9 and the internal lead wire 106 by welding so that the internal lead wire 106 does not come out of the electrode holding member 9.

An external lead rod 108 made of molybdenum is also connected to the other end portion of the internal lead wire 106 via a metal foil 103 made of molybdenum sealed in the sealing portion 102 of the outer tube 101. The rod 108 is electrically connected to a terminal on the luminaire side (not shown).
The external lead rod 108 is provided with an insulating member 104 such as ceramic so as to cover the outer peripheral surface thereof.

In addition to the bottomed cylindrical niobium tube, various known electrode holding members such as a hollow member or a rod member can be used as the electrode holding member 9.
In FIG. 2, the ceramic sealing material 13 has a thickness t ₁ of 30 μm to 70 μm, and contains at least yttrium (Y) as its composition. At that time, it may be added in the form of a complex oxide or a phosphoric acid compound, but it is particularly preferred that it is added in the form of yttrium oxide (Y ₂ O ₃ ). By adding it in the form of yttrium oxide, it is possible to suppress the ceramic sealing material from reacting with sodium in the arc tube. As a result, it is possible to suppress the disappearance of sodium and improve the luminous flux maintenance factor. In addition, the product generated by the reaction with sodium is released into the discharge space, and it is possible to prevent the lamp voltage from rising due to this and causing the lamp to become unlit.

(2) Evaluation Experiment Next, an experiment was conducted to confirm the operational effects of the double-ended high-pressure sodium lamp 100 (hereinafter referred to as “the product of the present invention”) having a rated power of 400 W, which is an embodiment of the present invention. .
First, in the product of the present invention, the thickness t ₂ (see FIG. 1) of the outer tube is 0.15 cm, the thickness t ₃ (see FIG. 3) of the envelope 11 is 0.08 cm, and the distance L between the electrodes L Are set constant at 8.0 cm, the inner diameter r ₂ (cm) of the outer tube and the outer diameter R ₁ (cm) of the envelope, that is, the minimum distance D ((r ₂ −R ₁ ) / 2) and the tube wall load. Ten high-pressure sodium lamps each having a rated power of 400 W with various W _e (W / cm ² ) values were produced.

Each of the produced lamps was turned on at a rated power using a known copper iron ballast, and the initial luminous flux (lm) and the presence or absence of deformation of the outer tube after 18000 hours of lighting were examined. The results as shown were obtained.
In addition, as a lighting method, this was repeated for 5.5 hours lighting and 0.5 hour light extinction as 1 cycle.

ここで、「初期の発光光束」とは、１００時間点灯経過時の発光光束を示す。ただし、この１００時間とは上記点灯方法によって点灯した場合における累積点灯時間である。
また、初期の発光光束の評価基準として、その発光光束が従来の定格電力４００Ｗの両口金形の高圧ナトリウムランプの初期の発光光束（４６５００ｌｍ）に比して約５％以上、つまり４８８００ｌｍ以上得られことを合格基準とした。したがって、表1の「初期の発光光束の評価」欄において、「○」は前記評価基準を満たすことを、「×」は前記評価基準を満たさないことをそれぞれ示す。

Here, the “initial luminous flux” indicates the luminous flux after 100 hours of lighting. However, the 100 hours is the cumulative lighting time when the lamp is lit by the above lighting method.
As an evaluation standard for the initial luminous flux, the luminous flux is about 5% or more, that is, 48800 lm or more, compared with the initial luminous flux (46500 lm) of the conventional high-pressure sodium lamp with a rated power of 400 W. This was the acceptance criterion. Therefore, in the “Evaluation of initial luminous flux” column in Table 1, “◯” indicates that the evaluation criterion is satisfied, and “X” indicates that the evaluation criterion is not satisfied.

The “presence / absence of deformation of the outer tube” was determined visually.
(A) Improvement of initial luminous flux As is clear from Table 1, in Examples 1 to 15, Comparative Example 1 and Comparative Example 4, the initial luminous flux was 48800 lm or more, which is an evaluation standard. . On the other hand, in Comparative Example 2, Comparative Example 3, and Comparative Example 5, the initial luminous flux was lower than 48800 lm, which is the evaluation standard.

FIG. 4 is a diagram in which the results of Table 1 are plotted on a graph. In the graph, the horizontal axis indicates the size of the shortest distance D (cm) between the outer surface of the arc tube 10 and the inner surface of the outer tube 101, and the vertical axis indicates the tube wall load We (W / cm ² ) of the arc tube 10. Indicates the size.
The numbers in parentheses written beside the plotted points indicate the numbers of the examples in Table 1, and the numbers in <> indicate the numbers of the comparative examples in Table 1.

From this graph, the boundary for the initial luminous flux to be equal to or higher than the evaluation standard was obtained. When D <0.7, the curve F (W _e = −6.8D ² + 10.6D + 15.7) Can be approximated to a straight line E (W _e = 19.8) when D ≧ 0.7, and when D <0.7, the relational expression W _e > −6.8D ² + 10.6D + 15. When D ≧ 0.7, the relational expression W _e ≧ 19.8 is satisfied, and it is confirmed that the initial luminous flux becomes 48800 lm or more which is the evaluation standard.

By satisfying the above relational expression as described above, the initial luminous flux could be improved because the tube wall load was compared with the tube wall load (15 W / cm ^{2 to} 19 W / cm ² ) of a conventional high pressure sodium lamp. As a result of increasing the tube wall temperature of the arc tube, the heat loss from the arc tube is reduced, and the radiation intensity of visible light is increased instead. However, in the case of D <0.7, the arc tube and the outer tube are close to each other even if the tube wall load is about the same as the tube wall load of the conventional high-pressure sodium lamp. This is considered to be because the effect is high and the tube wall temperature of the arc tube substantially increases.

(B) About prevention of deformation of the outer tube In the case of Examples 1 to 15, Comparative Example 2, Comparative Example 3 and Comparative Example 5, the outer tube 101 is deformed at the time of lighting for 18000 hours. There wasn't. On the other hand, in the case of Comparative Example 1 and Comparative Example 4, the outer tube 101 is deformed before the lapse of 18000 hours, and in some of the samples of each comparative example, the deformed outer tube 101 is the arc tube 10. The arc tube 10 was broken and leaked by the heat of the arc tube 10 at that time. In these cases, the light distribution characteristics are changed due to deformation of the outer tube 101, or the temperature of the arc tube 10 is lowered due to leakage of the outer tube 101, and desired lamp characteristics cannot be obtained. In addition, the electrode holding member 9 is oxidized to deteriorate the conductivity, resulting in non-lighting.

Therefore, in the graph of FIG. 4, the boundary for preventing the outer tube from being deformed even when the lighting time is 18000 hours is obtained.
It can be approximated as a straight line A (W _e = 28.4D + 17.0), and it is confirmed that the outer tube can be prevented from being deformed by satisfying the relational expression W _e ≦ 28.4D + 17.0. It was.

  As described above, by increasing the tube wall load We of the arc tube 10 and increasing the tube wall temperature of the arc tube 10, the radiation intensity of visible light can be increased, while the radiation intensity of infrared rays also increases. It is thought that. Therefore, the outer tube 101 may be heated excessively to the extent that it is deformed by the infrared radiation in addition to the heat generated by the discharge in the arc tube 10 during lighting.

However, by satisfying the relational expression W _e ≦ 28.4D + 17.0, an increase in the infrared radiation intensity can be appropriately suppressed, and the outer tube 101 can be prevented from being deformed even after lighting for 18000 hours. did it.
As described above, when the minimum distance between the inner surface of the outer tube and the outer surface of the envelope is D (cm) and the tube wall load of the arc tube is W _e (W / cm ² ), W _e ≦ 28. When 4D + 17.0 and D <0.7, W _e > −6.8D ² + 10.6D + 15.7, and D ≧ 0.7, satisfying the relational expression W _e ≧ 19.8 As a result, the outer tube can be deformed over a long lighting elapsed time, or the outer tube can be damaged due to the deformation, resulting in leakage. As a result, the light distribution characteristics deteriorate due to the deformation of the outer tube, the desired lamp characteristics cannot be obtained due to the leakage of the outer tube, or the lamp is not lit. Can be prevented, and the life can be extended.

(C) Reduction of luminous flux maintenance factor due to coloring of outer tube Next, the luminous flux maintenance factor (%) in Examples 1 to 15 was examined, and the following results were obtained.
The luminous flux maintenance factor (%) indicates the ratio of the emitted light flux for a certain lighting elapsed time to the emitted light flux after 100 hours of lighting. As an evaluation standard of the luminous flux maintenance factor, 85% or more was set as an acceptance standard.

  In 15000 hours lighting progress that greatly exceeds the rated life of 14,000 hours of the conventional product, all luminous flux maintenance factors of Example 1 to Example 15 were 85% or more which is the evaluation standard, but at the time of 18000 hours lighting elapsed, About Example 6, Example 7, Example 10, and Example 14 except Examples 1 to 5, Example 8, Example 9, Example 11, Example 12, Example 13, and Example 15. It was found that the luminous flux maintenance factor was less than 85%.

When the outer tube of Example 6, Example 7, Example 10 and Example 14 in which the luminous flux maintenance factor deteriorated was observed by visual observation, something adhered to the inner peripheral surface of the central portion of the outer tube and blackish brown It is considered that this coloring causes a decrease in the luminous flux maintenance factor. Of course, such coloring is not preferable not only from the viewpoint of improving the luminous flux maintenance factor but also in terms of appearance quality.
When the deposit on the inner surface of the outer tube was analyzed, it was found to be aluminum which is a component of the material of the envelope 11 of the arc tube 10. That is, as the tube wall load of the arc tube 10 increases, the tube wall temperature of the arc tube 10 becomes excessively high. During lighting, aluminum which is one component of the envelope 11 is gradually scattered, It is considered that the light flux was blocked on the inner surface of the outer tube 101 as much as it was blocked.

Therefore, scattering of aluminum which is one component of the material of the envelope 11 is suppressed, the inner surface of the outer tube 101 is prevented from being colored by the scattered aluminum, and the luminous flux maintenance factor is not lowered, and the appearance quality is not impaired. 4 is obtained from the plot of each experimental result in FIG. 4, the approximate expression of the straight line B (W _e = 13.4D + 19.0) can be obtained, and W _e <13.4D + 19.0. When the following relational expression is satisfied, it was confirmed that the outer tube 101 was hardly colored even after 18000 hours of lighting.

(D) Decrease in luminous flux maintenance factor due to disappearance of Na On the other hand, there was no particular problem at the time of lighting for 16000 hours, but Example 7, Example 9, Example 10 were performed at the time of lighting for 18000 hours. Regarding Example 13 and Example 14, some of the samples of each Example were not lit. Among these examples, even in the samples that are continuously lit, in Example 9 and Example 10, the luminous flux maintenance factor after 18000 hours of lighting was extremely bad. Of course, as described in (c) above, in Example 10, the decrease in the luminous flux maintenance factor due to coloring of the outer tube 101 due to the scattering of aluminum in the envelope 11 is also superimposed. In Example 9 in which coloring is not recognized, it is surmised that the light flux maintenance factor is reduced, and that even non-lighting is caused by a factor different from (c).

  Thus, the cause was examined, and it was found that in these examples, the lamp voltage was increased by 20 V or more from the set value (100 V). Since each lamp is lit by a copper-iron ballast, when the lamp voltage increases, the lamp current decreases more than the increase, and the power input to the lamp becomes lower than the rated power, which decreases the luminous flux. Therefore, it is considered that the luminous flux maintenance factor is remarkably lowered. In extreme cases, lighting may not occur.

  In order to examine the cause of the increase in lamp voltage, the emission spectra of these lamps were measured with a spectrophotometer, and it was found that the self-absorption width of the sodium emission spectrum was reduced compared to the initial luminous flux. . That is, as the tube wall load of the arc tube 10 increases, the tube wall temperature of the arc tube 10 rises excessively, and the polycrystalline alumina ceramic that is the material of the envelope 11 reacts with sodium that is the luminescent material. Or, it diffused into the polycrystalline alumina ceramic and sodium disappeared excessively, so the mercury ratio in mercury sodium amalgam increased, and as a result, the vapor pressure of mercury increased and the lamp voltage increased. It is possible.

From the above results, on the graph of FIG. 4, it is possible to avoid the lamp from becoming non-lighted or reducing the luminous flux maintenance factor due to the increase in lamp voltage due to the disappearance of sodium even after 18000 hours of lighting. When seeking, can be approximated by the C-line (We = 26.5), by satisfying W _e <26.5 relational expression, it is possible to prevent non-lighting due to the increase of the lamp voltage, a decrease in luminous flux maintenance factor It was confirmed that it was possible.

(E) Summary The above results are summarized as follows.
(I) When the minimum distance between the inner surface of the outer tube 101 and the outer surface of the envelope 11 is D (cm) and the tube wall load of the arc tube is W _e (W / cm ² ), W _e ≦ 28 When 4D + 17.0 and D <0.7, when W _e > −6.8D ² + 10.6D + 15.7, and D ≧ 0.7, by satisfying the relational expression W _e ≧ 19.8 The initial luminous flux can be improved, and a rated life of at least 15000 hours can be obtained over a long lighting elapsed time without deformation of the outer tube.

(Ii) In addition, satisfies the W _e <13.4D + 19.0 relational expression, is less than the luminous flux maintenance factor of 85% due to adhesion to the outer tube 101 inner surface of the scattered aluminum even when 18000 hours of light passed There is nothing.
(Iii) Furthermore, by satisfying the relational expression W _e <26.5, the Na component in the arc tube is excessively reduced even after 18000 hours of lighting, and the luminous flux maintenance factor is less than 85%. There will be no lights off.

(F) Others In each of the above experimental examples, the wall thickness t ₂ of the outer tube 101 is set to 0.15 cm, but the wall thickness t ₂ of the outer tube 101 is generally used, for example, 0. Even when it was set in the range of 05 cm to 0.25 cm, the same effect as described above was obtained. This is because such a change in the thickness hardly affects the conditions for the occurrence of deformation of the outer tube 101.

Further, the wall thickness t ₃ of the envelope 11 of the arc tube 10 is also set to 0.08 cm. However, the wall thickness t ₃ is within a generally used range, for example, a range of 0.05 cm to 0.15 cm. Even when set, it is considered that the same effect as described above can be obtained. This is because a slight change in the thickness of the envelope 11 is considered to have little effect on the amount of infrared rays radiated toward the outer tube 101.

Furthermore, although the distance L between the electrodes 14 is also set to 8.0 cm, the distance L is generally used, for example, even when 400 W is set to a range of 6.0 cm to 10.0 cm. The same effect can be obtained.
In the above embodiment, a high-pressure sodium lamp with a rated power of 400 W has been described as an example. However, even when applied to a high-pressure sodium lamp with a rated power of 70 W to 1000 W, for example, the same effect as described above can be obtained. It is considered possible. This is because each relational expression in the present invention does not depend directly on the rated power and is defined by the tube wall load We. Actually, a confirmation experiment was also performed on lamps with various rated powers other than 400 W. As a result, almost the same results as the above-described effects were obtained.
(3) Modifications It goes without saying that the technical scope of the present invention is not limited to the above embodiment, and for example, the following modifications can be considered.

(3-1) In the above-described embodiment, the description has been given by taking the double-piece high-pressure sodium lamp as an example. However, even when applied to a single-piece high-pressure sodium lamp, the same effects as described above can be obtained. .
FIG. 5 is a view showing a configuration of the single-piece high-pressure sodium lamp 200. For convenience of explanation, a part of the outer tube 201 is cut away.

As shown in the figure, the high-pressure sodium lamp 200 is configured by housing the arc tube 10 inside an outer tube 201. The arc tube 10 is held by connecting the electrode holding members 9 on both sides thereof to internal lead wires 202 and 203 partially embedded in the sealing portion 204 of the outer tube 201. The arc tube 10 is disposed at a position where the tube axis thereof substantially coincides with the tube axis of the outer tube 201.
The internal lead wires 202 and 203 are connected to the pins 210 of the base 209 via molybdenum foils 205 and 206 sealed in the sealing portion 204 and external lead wires 207 and 208, respectively.

Even in such a single-piece high-pressure sodium lamp 200, the influence of heat applied to the outer tube 201 by the arc tube 10 is exactly the same as that of the double-piece high-pressure sodium lamp 100 of FIG. Each conditional expression described in the above embodiment is also applied as it is in this example.
(3-2) Moreover, in the said embodiment, as a material of the envelope 11 of the arc_tube | light_emitting_tube 10, the polycrystalline alumina ceramic which made aluminum oxide a base substance and was added with magnesium oxide, zirconium oxide, and yttrium oxide, respectively. In addition to these, even when an envelope to which scandium oxide, dysprosium oxide, terbium oxide, hafnium oxide or the like is added as an additive is used, the same effect as described above can be obtained. be able to. Of course, zirconium oxide is not always necessary, and only magnesium oxide and yttrium oxide may be added. Instead of zirconium oxide, scandium oxide, dysprosium oxide, terbium oxide, hafnium oxide, etc. may be magnesium oxide or yttrium oxide. Even when the envelope added together is used, the same effect as described above can be obtained.

  The amount of each additive added is appropriately determined according to the type and number of additives. For example, when magnesium oxide, zirconium oxide, and yttrium oxide are added as additives, oxidation is performed. It is preferable to add 100 ppm to 800 ppm of magnesium, 200 ppm to 1200 ppm of zirconium oxide, and 10 ppm to 300 ppm of yttrium oxide, respectively.

  The present invention relates to a high pressure sodium lamp using an envelope made of polycrystalline alumina ceramic to which at least magnesium oxide and yttrium oxide are added as an envelope of an arc tube. This is suitable as a technique for achieving the above.

(A) (b) is the top view and front view which notched a part of the double-piece-shaped high pressure sodium lamp which is embodiment of this invention. It is front sectional drawing of the arc_tube | light_emitting_tube used for the high pressure sodium lamp of FIG. It is a principal part expanded sectional view of the arc tube of FIG. Is a diagram showing the relationship between the minimum distance D between the outer surface and the inner surface of the outer tube of the arc tube (cm) and the tube wall of the arc tube load ^{_{W e (W / cm 2)}} . It is a figure which shows the structure of the high pressure sodium lamp of a single-piece metal mold | die as a modification of this invention.

Explanation of symbols

9 Electrode holding member 10 Arc tube 11 Envelope 14 Electrode 100, 200 High pressure sodium lamp 101, 201 Outer tube 102, 204 Sealing portion 106, 202, 203 Internal lead wire 108 External lead rod 207, 208 External lead wire 209 Cap

Claims (3)

An outer tube made of quartz glass, and an arc tube housed in the outer tube and disposed so that a pair of electrodes are substantially opposed to each other,
The envelope of the arc tube is made of a polycrystalline alumina ceramic to which at least magnesium oxide and yttrium oxide are added, and the minimum distance between the inner surface of the outer tube and the outer surface of the envelope is D (cm). When the tube wall load of the arc tube is W _e (W / cm ² ),
W _e ≦ 28.4D + 17.0,
And if D <0.7, W _e > −6.8D ² + 10.6D + 15.7,
In the case of D ≧ 0.7, W _e ≧ 19.8
A high pressure sodium lamp characterized by satisfying the following relational expression: Furthermore, W _e <high pressure sodium lamp according to claim 1, wherein a satisfying 13.4D + 19.0 relational expression. The high pressure sodium lamp according to claim 1 or 2, further satisfying a relational expression of W _e <26.5.

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