JPH0626110B2 - High color rendering high pressure sodium lamp - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high color rendering high pressure sodium lamp having an increased sodium vapor pressure in a translucent arc tube, and more particularly to improvement of an electron emitting material used for an electrode.

[Conventional technology]

Generally, in a high-pressure sodium lamp, in order to compensate for the disappearance of sodium during the lamp travel, an excessive amount of sodium, and mercury and xenon as a rare gas for starting are enclosed in an alumina arc tube to compensate for the loss of sodium. ing.

A high-pressure sodium lamp equipped with such an arc tube has a saturated vapor pressure type characteristic, and the vapor pressure of sodium in the arc tube during lighting depends on the temperature of the coldest part of the arc tube.

Recently, in this type of high-pressure sodium lamp, by increasing the vapor pressure of sodium in the arc tube when the lamp is operating, the so-called high color rendering high-pressure sodium lamp (average color rendering) in which the emission spectrum is spread over the entire visible region to improve the color rendering The evaluation index _Ra = 80 to 90) has been commercialized.

[Problems to be solved by the invention]

However, the biggest problem with such a high-pressure sodium lamp is that the lamp voltage rises during the operation of the lamp and eventually the lamp extinguishes, which causes the vapor pressure to increase as described above. This is more noticeable for high color rendering high pressure sodium lamps.

This increase in lamp voltage is mainly due to the following reasons.

(1) The wall of the arc tube near the electrode is blackened due to evaporation and scattering of the electron emitting material from the electrode, and as a result, the temperature of the coldest part of the arc tube rises, the vapor pressure inside the tube rises, and the lamp The voltage rises.

(2) As the electron emission material attached to the electrode evaporates, scatters and is exhausted, the electron emission characteristic deteriorates, which increases the electrode drop and increases the lamp voltage.

(3) Since sodium reacts with the alumina arc tube and the electrode structural material and disappears, the proportion of mercury in sodium amalgam increases, resulting in an increase in lamp voltage.

Examination of the above causes reveals that in all cases (1), (2), and (3), the electron emitting material used for the electrode is involved in the rise of the lamp voltage.

Next, a specific mode of increasing the lamp voltage in the conventional high-pressure sodium lamp will be described. In an arc tube of a conventional high color rendering high pressure sodium lamp, an electrode having a structure as shown in FIG. 5 is used. That is, around the electrode core rod 1 made of a heat resistant metal such as tungsten,
Inner single coil 2 and outer single coil 3 made of tang ten wire
Holding the two-layer coil formed in
3 has a structure in which the electron emitting substance 4 is simultaneously adhered to the surface and the voids and the electron emitting substance on the outer surface is removed by brushing or the like so that the electron emitting substance is not directly exposed to the discharge. .

The electrode with such a structure has been conventionally used in high-pressure sodium lamps, but the electrode temperature rises slowly when the lamp is started and the glow discharge time is as long as 10 to 20 seconds. When applied to a high color rendering high pressure sodium lamp with a higher vapor pressure than before, it causes blackening of the tube wall near the electrodes of the arc tube early (within 6000 hours), resulting in an increase in lamp voltage. It is remarkable.

As a means for preventing the lamp voltage from rising based on such a reason, a method of shortening the glow discharge time at the time of starting the lamp by decreasing the size of the electrode, that is, the heat capacity to speed up the rising rate of the electrode temperature at the time of starting the lamp (Japanese Patent Publication Sho 5
No. 6-56189), and a method of making it possible to stabilize the electrode spot for a short time in the initial stage of lamp lighting without reducing the size of the entire electrode (JP-A-56-78057).

And, the structure of the electrodes applied to these methods is composed of an electrode core rod, an inner coil surrounding the electrode core and having an electron emissive substance attached thereto, and an outer coil surrounding the inner coil, The inner coil is composed of a double-winding coil or more.

However, since the electrode having the above structure uses a tungstate-based oxide containing an alkaline earth metal oxide as an electron emitting substance, the electron emitting substance is significantly consumed due to thermal evaporation and scattering.

Therefore, it is necessary to hold an amount of 10 mg or more in the inner coil in order to prevent depletion of the electron emitting substance due to exhaustion until the end of its life, and there is a limit to the miniaturization of the electrode to reduce the heat capacity. Is. In addition, the tungstate-based oxide containing an alkaline earth metal oxide is about 13
It has the drawback of decomposing and evaporating at 00 ° C to form a compound with sodium.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional high-pressure sodium lamp. By coating and baking an electrode with an electron-emitting substance that does not easily react with sodium and has a high melting point, Suppresses the blackening of the tube wall and the disappearance of sodium near the electrode caused by evaporation / scattering, thereby suppressing the rise in lamp voltage and the decrease in luminous flux during the lamp travel, maintaining excellent light color and color rendering characteristics throughout the life of the lamp. At the same time, it is an object to provide a high color rendering type high pressure sodium lamp having a long life of more than 9,000 hours.

[Means and Actions for Solving Problems]

In the present invention, as a result of conducting various experiments and investigations in order to solve the above problems, yttrium oxide (Y ₂ O ₃ ) is used as an electron emitting substance of the electrode.

When selecting the above-mentioned yttrium oxide as the electron emitting substance of the electrode, the present inventors have studied, as a basic experiment, a metal oxide for the electron emitting substance which satisfies the following conditions.

(1) It must have a high melting point of at least 1600 ° C so that it will not decompose at the arc tube sealing temperature of a high color rendering high pressure sodium lamp.

(2) It has a low vapor pressure at the electrode operating temperature.

(3) The work function for thermionic emission is relatively small.

(4) Does not easily react with sodium at the temperature when the lamp is on.

In this basic experiment, barium oxide, which is currently widely used as an electron emitting material for high pressure sodium lamps, is used.
BaO, calcium oxide CaO, etc., or a composite oxide containing them (eg barium calcium tungstate)
Ba ₂ CaWO ₆ etc.) has a low decomposition temperature and is likely to react with sodium. In addition, thorium oxide ThO ₂ and complex oxides containing thorium oxide have a problem that thorium is one of radioactive elements. In consideration of the points, the above metal oxides were excluded.

As a result of the above experimental examination, electron-emitting materials satisfying the above conditions (1) to (4) are scandium oxide Sc ₂ O ₃ , yttrium oxide Y ₂ O ₃ , lanthanum oxide La ₂ O ₃ , praseodymium oxide.
Pr ₂ O ₃ , neodymium oxide Nd ₂ O ₃ , samarium oxide Sm ₂ O ₃ ,
It was found to be an oxide of a rare earth element such as gadolinium oxide Gd ₂ O ₃ and dysprosium oxide Dy ₂ O ₃ .

Then, it was found that the melting points of these oxides were lowered in the following order. That is, Y ₂ O ₃ (2693 ° K), Sc
₂ O ₃ (2678 ° K), Gd ₂ O ₃ (2668 ° K), Dy ₂ O ₃ (2658 ° K), Sm ₂ O ₃ (2593 ° K), Nd ₂ O ₃ (2588 ° K), La ₂ O ₃ (25
73 ° K) and Pr ₂ O ₃ (2563 ° K) in that order.

It was also found that the vaporizability of these oxides increased in the following order. That is, Y ₂ O ₃ , Sc ₂ O ₃ , Gd
_{The order is 2} O ₃ , Dy ₂ O ₃ , La ₂ O ₃ , Sm ₂ O ₃ , Pr ₂ O ₃ , and Nd ₂ O ₃ .

It was also found that the work functions of these oxides increased in the following order. That is, Y ₂ O ₃ (2.0e
V), Gd ₂ O ₃ (2.1 eV), Dy ₂ O ₃ (2.1 eV), Nd ₂ O
_{3 (2.3eV), La 2 O} 3 (2.8eV), Pr 2 O 3 (2.8e
V), Sm ₂ O ₃ (2.8 eV), and Sc ₂ O ₃ (3.2 eV) in that order.

Among these rare earth element oxides, particularly when yttrium oxide Y ₂ O ₃ was used as the electron emitting material, the rise in lamp voltage and the deterioration of luminous flux were significantly suppressed, and the starting characteristics were relatively good.

Therefore, the present invention uses yttrium oxide Y ₂ O ₃ as the electron emitting material of the electrode for the high color rendering high pressure sodium lamp. This yttrium oxide Y
By using _{2 3,} rise and luminous flux deterioration of the lamp voltage is considerably suppressed, although why even startability becomes relatively good is not clear, as described above, the melting point, all aspects of evaporative and work function It is superior to other oxides, and therefore suppresses the blackening of the arc tube and the depletion of the electron emitting substance due to the evaporation and scattering of the electron emitting substance, and it is the most difficult to release the free oxidation. It is considered that the reactivity with sodium is low and the effect of suppressing the disappearance of sodium becomes remarkable.

As described above, when yttrium oxide Y ₂ O ₃ is used as the electron emitting material of the high color rendering high pressure sodium lamp electrode, the lamp voltage is increased and the luminous flux is deteriorated while maintaining excellent light color and color rendering characteristics throughout the life of the lamp. It is suppressed, the lamp life is improved, and the intended purpose can be achieved.

〔Example〕

Hereinafter, an example in which the present invention is applied to a 50 W high color rendering high pressure sodium lamp will be described in detail. The electrode structure of the arc tube used has the structure shown in FIG. In other words, the inner coil 2'contacts the outer circumference of the electrode core rod 1 made of tungsten and has a diameter of 0.5 mm.
A double coil formed by winding a secondary coil made of 05mm tungsten wire in advance is wound, and an outer coil 3 made of tungsten and having a diameter of 0.3mm is wound around the inner coil 2 '. .

On the other hand, as the electron emitting substance 4, butyl alcohol and nitrocellulose lacquer as a binder are added to a commercially available powder of yttrium oxide Y ₂ O _{3 having} a purity of 99.99% and well stirred to form a suspension.

Next, the electrode is dipped in this suspension to apply an electron emitting substance and dried, and then the electron emitting substance on the surface of the outer coil is removed by brushing. Then, it was fired at a temperature of about 2200 ° C. in a hydrogen atmosphere to form an electrode. In this firing step, since the melting point of yttrium oxide is as high as 2400 ° C., the firing temperature is preferably at least 2000 ° C. or higher in order to improve the binding property with the electrode constituent member.

In addition, as a method of applying and firing the electron emitting substance, there is also a method of immersing the electrode in an yttrium alkoxide solution to dry it and then heating it. According to this method, it is possible to obtain a uniform filmy crystallized glass Y ₂ O ₃ electron-emitting substance having a good binding property to the electrode.

FIG. 2 shows an arc tube for a 50 W high color rendering high pressure sodium lamp which incorporates the electrodes prepared as described above. In the figure, 5 is an arc tube main body made of polycrystalline alumina having an inner diameter of 4.0 mm, and both ends of the arc tube main body 5 are
Conductive heat-resistant metal tube 6a having main electrodes 7a, 7b,
6b is arranged such that the distance between the main electrodes 7a and 7b is 9.0 mm, and the gap between the heat-resistant metal tubes 6a and 6b and the arc tube body 5 is hermetically sealed by a sealing frit. . One of the heat-resistant metal pipes 6a also serves as an exhaust pipe.

Sodium 1.
It contains sodium amalgam 8 consisting of 67 mg and mercury 5.0 mg, and xenon 60 Torr as auxiliary gas for starting.
It is a so-called saturated vapor pressure type in which a part of is evaporated.

Usually, in the arc tube of a high color rendering high pressure sodium lamp, a metal foil made of tantalum or the like is wrapped around the end of the arc tube where sodium amalgam is present to increase the vapor pressure in the arc tube. It has been turned.

However, in this embodiment, the coldest part is as shown in FIG.
Since the heat-resistant metal tube 6a is formed on the conductive heat-resistant metal tube 6a, the heat-retaining effect of the heat-retaining means is small. Therefore, in order to increase the vapor pressure in the tube, it is necessary to raise the temperature of the heat-resistant metal tube 6a by other means. In this embodiment, the temperature of the entire arc tube is raised by setting the tube wall load to 40 w / cm ² or more. It is adopted. With such an arc tube structure, the temperature of the coldest portion located in the heat-resistant metal tube can be set to 850 ° C. or higher, and desired color characteristics (color temperature T _c = 2
500K, _Ra = 85) can be obtained. In this case, the effective lamp voltage Vl of the arc tube is 45 V and the lamp current Il is 1.25.
It is A.

The arc tube constructed in this manner was housed in an outer bulb (not shown), and a lamp life test was performed with a ballast for a 50 W high-pressure sodium lamp in a cycle of 7.5 hours of lighting-0.5 hours of extinction. Lamp voltage V after lighting for 1 hour and after lighting for 9,000 hours
The ascending state of 1, the total luminous flux F, the color temperature T _c, and the average color rendering index R _a were measured. Further, the stabilization time T _{B · A} of the electrode spot at the time of starting the lamp was also measured.

For comparison, the same measurement as above was performed for a conventional lamp using barium calcium tungstate Ba ₂ CaWO ₆ and thorium oxide ThO ₂ as electron emitting materials as a reference example.

Table 1 shows the measurement results for each type of electron emitting material. 3 and 4 show Y ₂ O ₃ (invention), ThO ₂ and Ba ₂ CaW as electron emitting materials, respectively.
The changes in the lamp voltage Vl and the luminous flux maintenance factor of the high color rendering high pressure sodium lamp using O _{6 up} to 9000 hours are shown. 3 and 4, A shows data of the present invention (Y ₂ O ₃ ), B shows ThO ₂ and C shows data of a reference example using Ba ₂ CaWO ₆ , respectively. It should be noted that no data is shown after a lamp using Ba ₂ CaWO ₆ as an electron-emitting substance after 9000 hours of operation has shown that the F value has already dropped to about 50% after 6000 hours of operation of this lamp, and _Ra is
This is because the color rendering property was reduced to 50 or less and the color rendering property was lost, and the measurement after that was stopped.

Table 1 As can be seen from Table 1, the lamp according to the present invention, which uses Y ₂ O ₃ as the electron emitting material, maintains excellent color characteristics during the entire life, and the increase of Vl at 9000 hours is 1
At V, the luminous flux maintenance factor is 85%, which is a very excellent characteristic as compared with other lamps using electron emitting materials.

After observing the blackening state of the end portion of the arc tube after 9000 hours of operation, the lamp according to the present invention using Y ₂ O ₃ as an electron emitting substance is blackened as compared with a lamp using another electron emitting substance. Was very few. Therefore, it was found that the blackening of the tube wall at this end had a significant influence on the increase in Vl and the luminous flux maintenance factor.

Thus Y ₂ O ₃ from the end blackening of electron emitting materials attached to electrodes attached to the arc tube is very small comprising, as described above, Y ₂ O ₃ has a high melting point, the electrode This is because there is little evaporation / decomposition at the operating temperature.

The excellent characteristics of Vl and luminous flux maintenance rate in a lamp using Y ₂ O ₃ as an electron emitting substance are that the starting characteristics of an arc tube using Y ₂ O ₃ are higher than those of a lamp using another electron emitting substance. However, this is an excellent effect that is more than compensated for the disadvantage of being slightly worse.

Moreover, in general, if the starting time is long, in addition to evaporation / scattering of the electron emitting substance of the electrode, back arc phenomenon from the root of the electrode becomes frequent, and cracks due to heat shock are generated in the seal part and the pipe end pipe wall. As a factor, in the examples according to the present invention, there was no leak due to cracks by 9000 hours.

〔The invention's effect〕

As described in detail based on the above examples, the high color rendering high pressure sodium lamp according to the present invention has a high melting point as an electron emitting substance, a high evaporation / decomposition temperature, and a relatively small work function. Since Y ₂ O ₃ is used, the evaporation and scattering of the electron emitting material of the electrode is greatly suppressed, and therefore the blackening of the tube wall at the end of the arc tube is suppressed, and the lamp voltage rise during the lamp life is small. It has many excellent effects such as improving the luminous flux maintenance factor.

Furthermore, since Y ₂ O ₃ used as an electron emitting substance does not easily react with sodium, a change in the sodium amalgam ratio due to the disappearance of sodium is suppressed, and excellent color development and color rendering properties can be maintained throughout the life of the lamp.

[Brief description of drawings]

FIG. 1 is a sectional view of an electrode of an arc tube in an embodiment of a high color rendering high pressure sodium lamp according to the present invention, FIG. 2 is a sectional view of an arc tube of an embodiment of the present invention, and FIG. FIG. 4 is a graph showing the range of the lamp voltage Vl up to 9000 hours in the embodiment of the invention and the reference example, FIG. 4 is a graph showing the range of the luminous flux maintenance rate up to 9000 hours, and FIG. FIG. 3 is a cross-sectional view of the high pressure sodium lamp electrode of FIG. In the figure, 1 is an electrode core rod, 2 is an inner single coil, 2'is an inner double coil, 3 is an outer coil, 4 is an electron emitting substance,
5 is the arc tube body, 6a and 6b are heat-resistant metal tubes, and 7a and 7b
Indicates a main electrode, and 8 indicates sodium amalgam.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomoyuki Hanyu 1-20 Fujimi-cho, Gyoda-shi, Saitama Iwaki Electric Co., Ltd. Development Center (72) Inventor Yasuharu Yamamoto 1-1 Iriyama-cho, Gyoda-shi, Saitama Iwasaki Electric Saitama Seisakusho Co., Ltd. (56) Reference JP-A-55-122353 (JP, A)

Claims (1)

[Claims] 1. A saturated vapor pressure type in which xenon as a starting auxiliary gas is enclosed together with sodium and mercury in a translucent arc tube having electrodes at both ends to increase the sodium vapor pressure in the tube during lamp operation. A high-color-rendering high-pressure sodium lamp, wherein yttrium oxide is used alone as an electron-emitting substance of the electrode in the high-color-rendering high-pressure sodium lamp.