JP2011076805A - Cold-cathode fluorescent lamp and plane light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to obtain a small-diameter cold-cathode fluorescent lamp and a plane light source device having enhanced reliability with a simple construction. <P>SOLUTION: A cup-shaped discharge electrode (13) including a cylindrical electrode (15) is provided at an end part (11a) of a glass tube of the small diameter cold-cathode fluorescent lamp (10). A larger inner diameter part (17) of the glass tube is provided at the region close to the tip part of the cylindrical electrode (15) where the inner diameter of the glass tube is larger than that of the other part of the glass tube. Even when the discharge electrode (13) inclines, a shortest distance between the cylindrical electrode and the glass tube can be kept lengthened in comparison with the case in which the larger inner diameter part is not provided. Even if the discharge electrode is sputtered, generation of an abnormal discharge near the discharge electrode is lowered so that the reliable cold-cathode fluorescent lamp is obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a cold cathode fluorescent lamp using a cup-shaped electrode and a surface light source device using the fluorescent lamp.

  In recent years, fluorescent lamps have been used as backlights for liquid crystal display devices. For example, in a 20-inch diagonal liquid crystal display device, an edge light type backlight is used, and a small-diameter cold cathode fluorescent lamp is provided on an end surface of a light guide plate. In backlights for large-sized liquid crystal televisions having a diagonal size of 30 inches or more, direct type backlights are used, and a plurality of cold cathode fluorescent lamps are provided.

  Cold cathode fluorescent lamps are generated inside the arc tube by discharge, with a cup-shaped or plate-shaped metal electrode provided at both ends of the arc tube with the phosphor coated on the inner surface of the glass tube, and mercury inside. It is configured to obtain visible light by exciting the phosphor with ultraviolet light.

  In recent years, with the diversification of liquid crystal display devices, demands such as downsizing, diameter reduction, high brightness, long life, and cost reduction have increased, and various studies have been conducted. Generally, there are two types of fluorescent lamps, the hot cathode type and the cold cathode type described above, and the cold cathode type has a feature that the life is long. A cold cathode fluorescent lamp is also known in which a molybdenum foil excellent in sputtering resistance is processed into a cup shape in order to extend the life (see, for example, Patent Document 1).

  It is also known to increase the surface area of the electrode to reduce the current density in order to achieve a long life even when operated with a large current. For example, in Patent Document 2, the length of the electrode is increased.

JP 2007-48527 A JP 2005-327485 A

  However, in order to meet the recent demands for reducing the diameter and increasing the brightness, it is necessary to flow a relatively large lamp current of 10 mA. Further, when the inner diameter of the arc tube is extremely reduced to 1 to 4 mm, the cup-shaped electrode is sputtered by the discharge, and the sputtered electrode material increases. In particular, when the lamp current is 10 mA or more and the inner diameter of the arc tube is extremely reduced to 1 to 4 mm, the mercury in the lamp is consumed as the electrode material to be sputtered increases, and the cold cathode fluorescent lamp As compared with the case where the inner diameter is large, the life of the steel is reduced. In addition, the sputtered electrode material is deposited on the arc tube to cause a blackening phenomenon, thereby reducing the lamp life.

  In addition, when the electrode length is increased in order to increase the electrode area as in Patent Document 2, the arc tube has a cold cathode fluorescent lamp in which the inner diameter of the arc tube is extremely reduced to 1 to 4 mm. Since the distance between the tip of the electrode and the inner wall of the arc tube is small, the electrode is inclined and the distance from the inner wall varies. Also, the insertability is bad. Therefore, there is a problem that the yield decreases.

  Furthermore, the sputtered electrode material causes a blackening phenomenon that accumulates inside the arc tube near the electrode. In particular, when depositing on the inner wall of the arc tube at the tip of the electrode, the distance between the sputtered electrode material deposited on the inner wall of the arc tube and the electrode material approaches due to the inclination of the electrode caused by increasing the electrode length. It became easy to become the starting point of abnormal discharge. For this reason, there has been a problem that the abnormal arc discharge causes the glass arc tube to crack and the lamp is not lit.

  In view of the above, an object of the present invention is to realize a long life in a cold cathode fluorescent lamp having a long electrode length and a small diameter and a surface light source device using the cold cathode fluorescent lamp.

  Another object of the present invention is to provide a cold cathode fluorescent lamp capable of contributing to yield improvement due to electrode tilt and a surface light source device using the cold cathode fluorescent lamp.

The above object can be achieved by the following embodiments.
The invention described in claim 1 includes a cylindrical glass tube (11) and a discharge electrode (13, 23) long in the axial direction of the glass tube sealed at the end (11a) of the glass tube (11). The discharge / discharge electrode (13, 23) includes an electrode support lead (14) and a cylindrical electrode (15), and the glass tube (11) has a region close to the tip of the cylindrical electrode. A cold cathode fluorescent lamp (10), which is enlarged (17) than the inner diameter of the glass tube of the discharge light emitting part.

  According to the first aspect of the present invention, even when the cylindrical electrode is inclined and installed with a cold cathode fluorescent lamp provided with a cold cathode electrode having a long cylindrical electrode portion, the glass around the tip of the cylindrical electrode is provided. Since the tube has an enlarged portion, the shortest distance between the tip of the cylindrical electrode and the inner wall of the glass tube is wider than the case where a glass tube of the same diameter without an enlarged portion is used. Yield is improved. Also, even when deposits are generated on the inner wall due to electrode sputtering, there is a distance between the tip of the cylindrical electrode and the glass tube at the shortest distance, so that abnormal discharge is unlikely to occur and the lamp life is extended. Can do. In addition, a bright cold cathode fluorescent lamp with a reduced glass tube diameter can be obtained.

  Further, the glass tube (11) has a discharge light emitting portion inner diameter (D1) of 1 to 4 mm, and the cylindrical electrode (15) is 1.5 to 6 times as long as the discharge light emitting portion inner diameter (D1). Is preferred.

  In this way, although it is a cold cathode fluorescent lamp with a reduced diameter, it is a cold cathode that achieves higher brightness and longer life compared to the case of using a glass tube with the same inner diameter without an enlarged portion. It can be a fluorescent lamp.

  Further, the discharge electrode (13, 23) has a mortar shape in which the bottom surface (15b) of the cylindrical electrode is recessed toward the discharge light emitting part, and the electrode support lead is connected to the mortar-shaped recess (15c). Is preferred.

  By doing so, it is possible to reduce the axial displacement of the discharge electrode, thereby reducing the inclination of the discharge electrode in the cold cathode fluorescent lamp and improving the yield.

According to another aspect of the present invention, a cold cathode fluorescent lamp section (2) in which a plurality of the cold cathode fluorescent lamps (10) described above are arranged in the same direction and a back surface of the cold cathode fluorescent lamp section (2) are provided. A reflecting surface (7) and a diffusion surface (9) provided on the front surface of the cold cathode fluorescent lamp portion, and the cylindrical electrode portions on one terminal side of the cold cathode fluorescent lamp are arranged in a line. The surface light source device (1).
Thereby, a surface light source device can be made thin.

  As described above, according to the present invention, even when an elongated cup-shaped discharge electrode is used, abnormal discharge between the discharge electrode tip and the sputter deposit on the tube wall is less likely to occur. Thus, even when a large current is passed, a cold cathode fluorescent lamp that suppresses the shortening of the lifetime of the cold cathode fluorescent lamp and a surface light source device using the cold cathode fluorescent lamp are provided.

FIG. 1 is a sectional view schematically showing a cold cathode fluorescent lamp according to the present invention. FIG. 2 is an enlarged sectional view showing an end portion of the fluorescent lamp provided with the discharge electrode of FIG. FIG. 3 is an enlarged cross-sectional view showing an end portion of a fluorescent lamp according to another embodiment. FIG. 4 is a cross-sectional perspective view of the discharge electrode. FIG. 5 is an exploded perspective view schematically showing the overall configuration of a surface light source device using a cold cathode fluorescent lamp.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS.
The embodiments described below are preferable specific examples of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. As long as there is no description of the effect, it is not restricted to these aspects.

  FIG. 1 is a sectional view schematically showing a cold cathode fluorescent lamp, and FIG. 2 is an enlarged sectional view showing an end portion of the fluorescent lamp provided with the discharge electrode of FIG. FIG. 5 is an exploded perspective view schematically showing the overall configuration of a surface light source device using a cold cathode fluorescent lamp. The surface light source device 1 includes a fluorescent lamp unit 2, a housing 3, a diffusion plate 4, a diffusion sheet 5, and a prism sheet 6.

  In the cold cathode fluorescent lamp 10, both ends of a cylindrical glass tube 11 are sealed, and discharge electrodes 13 and 13 are disposed so as to face each other. At the glass tube end portion 11a, the discharge electrode 13 passes through the sealing portion 16 and one of the electrode support leads 14 is exposed to the outside. What is indicated by reference numeral 15 is a glass bead 18 which is sealed to the electrode support lead 14 and is welded to the glass tube 11 and sealed. A phosphor layer 12 is formed on the inner surface of the glass tube 11. The glass bead 15 is not limited to the spherical shape shown in FIG. 1, and may be a disk-shaped button stem or flare stem.

  Further, in the present invention, the enlarged inner diameter portion 17 is formed in the glass tube 11 in the vicinity of the elongated discharge electrode tip 13a, that is, the periphery of the discharge electrode tip 13a, and the inner wall 11b of the glass tube is the glass tube. 11 is spreading outward.

  The glass tube 11 has a cylindrical shape made of hard glass having an outer diameter of 4.0 mm and a glass tube length of 500 mm, and a phosphor layer 12 that performs wavelength conversion is applied and formed on the inner surface of the glass tube 11 with both ends open. Sealing portions 16 are formed at both ends 11a of the glass tube 11 to hermetically seal the inside of the glass tube 11. In addition, when attaching to the surface light source device 1 to be described later, it is attached so as to be in a predetermined position with the reflecting surface 7 via a cap member (not shown) that covers the sealing portion 16 or a fixing hook (not shown) provided on the housing 3. I do.

  The inner diameter of the glass tube 11 is 1 to 4 mm. In order to realize a small-diameter cold-cathode fluorescent lamp, if it is made smaller than this, it becomes difficult to attach the discharge electrode, and handling properties deteriorate. Further, if the inner diameter is larger than this range, the outer diameter of the glass tube is increased, and it is difficult to reduce the size and the diameter as one of the features of the cold cathode fluorescent lamp. The inner diameter of the glass tube refers to the inner diameter D1 of the central portion of the glass tube length, that is, the discharge light emitting unit 10a described later.

  The sealed internal space 19 is filled with mercury and an inert gas having a predetermined sealing pressure. Mercury emits ultraviolet rays and excites the phosphor layer 12 described above. As the inert gas, argon, a mixed gas of argon and krypton, or a mixture of argon and another inert gas such as neon, krypton, or xenon in a predetermined ratio is used. The mixing ratio of the mixed gas is, for example, 10% for argon and 90% for other inert gases. Further, the gas pressure is reduced to about 5 KPa, for example.

  The discharge electrode 13 includes an electrode support lead 14 and a cylindrical electrode 15. The cylindrical electrode 15 includes a cylindrical portion 15a corresponding to an elongated cup-shaped side surface and a bottom portion 15b, and is opened toward the discharge light emitting portion 10a between the pair of discharge electrodes of the cold cathode fluorescent lamp 10.

  By making the cylindrical electrode 15 elongated, the electrode surface area can be increased to reduce the current density. That is, even when a lamp current of 10 mA or more, for example, 15 mA is input to increase the brightness, an increase in current density can be suppressed and the lamp brightness can be increased. The length L1 of the cylindrical electrode is preferably 1.5 to 6 times the inner diameter of the discharge light emitting part. When the inner diameter of the glass tube is a thin tube suitable for a backlight of 1 to 4 mm, the electrode size must be reduced, and the cup-type electrode needs to be reduced accordingly. However, simply reducing the size of the cup-type electrode (thinning the diameter) increases the current density, which leads to an increase in the temperature and life of the electrode, which is not preferable. Furthermore, in order to maintain a stable discharge, it is preferable to reduce sputtering of the electrode due to the discharge.

Therefore, it is preferable to increase the electrode surface area to reduce the current density. According to the study by the inventors, if the length L1 of the cylindrical electrode is made smaller than 1.5 times D1, the influence of the increase in current density and the temperature increase is large, and the temperature when used in the backlight of a liquid crystal display device is large. The rise causes the behavior of the liquid crystal in the vicinity of the electrode portion to be different, and display unevenness is conspicuous, which is not preferable for practical use. Further, in order to reduce such display unevenness, if the maximum lamp current is lowered by several mA and less than 5 mA, the display unevenness is reduced, but this time, the luminance is low and this is not preferable. On the other hand, if the length L1 of the cylindrical electrode exceeds 6 times D1, the current density can be further reduced, but the length of the cylindrical electrode portion becomes longer. The portion where the cylindrical electrode portion is located is a non-light emitting portion or a low luminance portion and cannot be used as a light emitting portion. For example, in practical use, when used as a backlight light source of a liquid crystal display device, a cylindrical electrode is provided on the outside of the liquid crystal display device, that is, a so-called frame, on the periphery of the liquid crystal display device. Therefore, it is not preferable to lengthen the cylindrical electrode in order to obtain a narrow frame. Accordingly, a length up to 6 times D1 is preferable. In addition, when it is made longer than this range, for example, even if the lamp current is 10 mA, the rate of increase in luminance is lower than the rate of increase in luminance in the range of 1.5 to 6 times the length of D1. Since it is almost saturated, there is no significant difference in the effect of increasing the lamp current in a practical range.
Specifically, the length of the current mainstream cup-type electrode is 5 mm or less, but in the present invention, the length is preferably in the range of 7 to 20 mm.

  As an electrode material of the cylindrical electrode 15, a plate material made of any metal of molybdenum, tungsten, tantalum, niobium, nickel, iron, or an alloy containing these metals as main components is suitable. The cylindrical electrode 15 is not limited to a pure metal or an alloy, but is a laminated plate of two layers or three or more layers, such as a laminated plate of tungsten and molybdenum, or a molybdenum-nickel alloy laminated on a tungsten alloy. There may be. A material obtained by embedding a high melting point metal material powder of molybdenum, tungsten, tantalum, or niobium in nickel, iron, or an alloy thereof may be used.

  The electrode support lead 14 uses a linear member in which the tip portion 14a on the cylindrical electrode 15 side is made of nickel or a nickel alloy, for example, Kovar. In order to reduce the influence due to the difference in thermal expansion coefficient between the glass tube 11 and the electrode support lead 14, the intermediate portion 14 c is made of a material having a thermal expansion coefficient close to that of the glass tube 11, for example, a dimet wire, Alternatively, a high-melting point metal that is difficult to be sputtered and a connection material of a different material such as a material having excellent conductivity on the connection side end 14b exposed to the outside may be used. The tip portion 14a, the intermediate portion 14c, and the connection side end portion 14b may be metal bars made of a metal material having the same composition.

  The electrode support lead tip 14a and the cylindrical electrode bottom 15a are welded. A well-known method such as a resistance welding method or a laser welding method can be employed for fixing both.

  The discharge electrode 13 having the elongated cylindrical electrode 15 with a reduced diameter is manufactured, for example, by the following method (not shown). According to this method, it is preferable to obtain the discharge electrode 13 with a reduced diameter while suppressing cost. Prepare a metal foil (thickness: 0.1 mm) of molybdenum, tungsten, tantalum, or niobium, which is a refractory metal, cut it to a predetermined length, and weld the cut ends to weld a cylindrical tube 15a is formed. One of the openings in the cylinder is narrowed to form a funnel shape. The electrode support lead 14 is inserted from the other opening, and the tip is drawn out from the narrowed funnel-shaped opening. At this time, the outer diameter of the distal end portion 14a of the electrode support lead 14 is enlarged and processed in advance into a T shape with the enlarged portion as an inclined surface, so that a funnel-shaped opening and a T-shaped distal end portion 14a are formed. And fit. Thereafter, the funnel-shaped opening and the T-shaped tip portion 14a are welded to form the bottom portion 15b, and the cylindrical electrode 15 and the electrode support lead 14 are integrated.

  FIG. 3 is an enlarged cross-sectional view illustrating a main part for explaining the process of providing the inner diameter enlarged portion 17. The inner diameter enlarged portion 17 is formed by the following method, for example. First, a glass tube having a predetermined length is prepared. When the cold cathode fluorescent lamp 10 is completed, the glass tube is heated by the burner 20 around the position around the discharge electrode tip 13a. Further, the enlargement jig 21 is inserted from the glass tube end portion 11a. The enlargement jig 21 has a spherical protrusion 21a at the tip. When the glass tube 11 at the position to become the inner diameter enlarged portion 17 is softened, the inner diameter is increased by relatively rotating the projection 21a of the enlargement jig 21 in contact with the inner wall of the glass tube. Thereafter, the glass tube is naturally cooled. As a result, a glass tube having an enlarged inner diameter D2 is formed.

  The enlarged portion inner diameter D2 is set such that the size of (D2-D1) / 2 does not exceed the thickness of the glass tube 11. This is because when the thickness of the glass tube is exceeded, the enlarged portion 17 becomes thin and it becomes easy to form a weak portion in terms of strength. Further, when the gap D3 between the inner wall of the glass tube 11 and the outer surface of the cylindrical electrode 15 is 0.15 mm, that is, when the thickness is the same as the thickness of the cylindrical portion, the discharge is stable, but when D3 becomes narrower than this, The increase in the outside temperature of the glass tube near the discharge electrode 13 was larger than that in the case where the temperature was wider than that. Therefore, D3 is preferably kept at a distance equal to or greater than the thickness of the cylindrical portion 15a.

  In order to make the cylindrical electrode 15 have an elongated shape and to reduce the diameter of the glass tube to achieve high luminance and long life, the electrode surface area is made as large as possible. For this reason, it is preferable to increase the length L1 of the cylindrical electrode 15 and to increase the outer shape of the cylindrical portion as much as possible within the range of the above-described conditions. That is, the distance between the inner wall of the glass tube and the cylindrical electrode is close. In the present embodiment, since the cylindrical electrode 15 has an elongated shape, even when the cylindrical electrode 15 is inclined, the discharge electrode tip 13a has the enlarged portion 17 and thus is difficult to contact the inner wall of the glass tube. Therefore, it is possible to reduce the problem of temperature rise and lifetime due to inclination.

<< Other Embodiments >>
FIG. 4 is a cutaway sectional view showing the discharge electrode 23 having another shape. In the present invention, since the cylindrical electrode 15 has an elongated shape, even if it is slightly tilted, the cylindrical electrode 15 greatly approaches the inner wall of the discharge tube tip 13a. That is, the tilt control and the eccentricity between the electrode support lead 14 and the cylindrical electrode 15 affect the yield. Therefore, in the present embodiment, the bottom portion 15b has a mortar shape in order to make it difficult to produce an inclination.

  The cylindrical electrode 15 includes a cylindrical portion 15a and a bottom portion 15b. The bottom portion 15b has a mortar shape that is recessed toward the discharge light emitting portion, and the electrode support lead 14 is connected to a mortar-shaped concave portion 15c. Reference numeral 18 denotes a glass bead attached to the intermediate portion 14 c of the electrode support lead 14. The recess 15c has a flat surface and is the same as or slightly larger than the tip area of the electrode support lead tip 14a. Furthermore, the tip shape of the electrode support lead tip portion 14a is made flat. In this way, when the electrode support lead 14 is welded to the bottom portion 15a, the tip portion 14a is drawn into the mortar-shaped recess 15c, and the center axis alignment between the electrode support lead 14 and the cylindrical electrode 15 is easy. In addition, the workability can be improved. Moreover, since both are made into the flat surface mutually, inclination control becomes easy and it can improve a yield.

Next, a backlight using the cold cathode fluorescent lamp 10 will be described.
FIG. 5 is an exploded perspective view schematically showing the overall configuration of the surface light source device 1 using the cold cathode fluorescent lamp 10. The surface light source device 1 includes a fluorescent lamp unit 2, a housing 3, a diffusion plate 4, a diffusion sheet 5, and a prism sheet 6.

  The fluorescent lamp unit 2 is formed by arranging a plurality of cold cathode fluorescent lamps 10 in parallel. On the back surface of the fluorescent lamp unit 2, the light irradiated downward and laterally from each fluorescent lamp 10 for each cold cathode fluorescent lamp 10 is reflected to the front surface of the fluorescent lamp unit 2 (upward in the drawing in FIG. 1). A reflecting surface 7 is provided.

  On the front side (upper side) of the fluorescent lamp unit 2, a diffusion plate 4 and a diffusion sheet 5 for sequentially diffusing light rays such as direct light from each cold cathode fluorescent lamp 10 and reflected light reflected by the reflection surface 7 are sequentially provided. An arranged diffusion surface 9 is provided. The diffusion plate 4 is made of a milky white acrylic resin plate and covers a space in which the fluorescent lamp unit 2 is disposed. The diffusion sheet 5 is made of a transparent resin in which a minute inorganic diffusion material is dispersed. By making both have different diffusion characteristics, the uniformity of the entire surface light source device 1 is improved. The diffusion surface 9 can be formed by a single diffusion member without using a plurality of diffusion plates 4 and diffusion sheets 5.

  Further, on the upper surface side of the diffusion sheet 5, a prism sheet 6 that controls the direction in which the diffused light from the diffusion sheet 5 travels is disposed. In the prism sheet 6, a plurality of continuous surfaces each having a 90 ° apex angle are formed on the surface opposite to the surface facing the diffusion sheet 5 of the cut surface cut by the surface perpendicular to the axial direction of the cold cathode fluorescent lamp 10. It has a triangular prism shape. The prism sheet 6 collects diffused light incident from the diffusion surface 9 side upward to increase the front luminance of the surface light source device 1 and uses the surface light source device as a direct type backlight of the liquid crystal display device. In this case, the front visibility of a liquid crystal display device (not shown) can be improved.

  On the back side of the fluorescent lamp unit 2, there is provided a reflection surface 7 designed to efficiently reflect the light directed from the cold cathode fluorescent lamps 10 toward the back side and the side to the front side. The reflective surface 7 is provided with a plate-like housing 3 so as to cover the back side along the axial direction of each cold cathode fluorescent lamp 10, and the reflective surface is provided on at least the surface of the housing 3 facing the fluorescent lamp portion 2. 7 is formed. The housing 3 is made of a resin or a metal material, and is formed so that the reflection surface has a predetermined reflection light distribution characteristic.

  A large number of cold cathode fluorescent lamps 10 are arranged in a space covered with the reflecting surface 7 and the diffusing surface 9. In addition, the cold cathode fluorescent lamp is often used in a state where it does not coincide with the center of gravity direction, compared to the case where the tube axis direction and the center of gravity direction coincide with each other. For example, in the case of a personal computer panel or the like, it has a horizontally long shape, and a cold cathode fluorescent lamp is often provided in the horizontal direction. Therefore, in the case of a cold cathode fluorescent lamp in which the discharge electrode 13 is elongated and has a small diameter tube, the tip 13a tends to approach the glass tube 11 by being inclined due to its own weight, such as when vibration is applied. In such a case, since the inner diameter enlarged portion 17 is provided in the present embodiment, it is possible to provide a surface light source device that reduces the occurrence of problems caused by inclination.

In this way, according to the present invention, it is possible to obtain a cold cathode fluorescent lamp and a surface light source device with improved reliability with a simple configuration.
The present invention is not limited to the embodiment described above. For example, the cylindrical portion of the cylindrical electrode may be provided with unevenness to increase the surface area. Further, a high electron-emitting material such as barium tungstate, barium titanate, yttrium oxide, barium aluminate, or lanthanum boride may be applied or embedded on the surface of the cylindrical electrode as an emitter.

  The present invention can be applied to devices such as a cold cathode fluorescent lamp and a backlight using the cold cathode fluorescent lamp.

DESCRIPTION OF SYMBOLS 1 Surface light source device 2 Fluorescent lamp part 3 Housing 4 Diffusion plate 5 Diffusion sheet 6 Prism sheet 7 Reflecting surface 8 Joint part 9 Diffusion surface 10 Cold cathode fluorescent lamp 11 Glass tube 12 Phosphor layer 13, 23 Discharge electrode 14 Electrode support lead 15 Cylindrical electrode 16 Sealing portion 17 Inner diameter enlarged portion 18 Glass bead 20 Burner 21 Enlarging jig D1 Glass tube inner diameter L1 Length of cylindrical electrode D2 Inner diameter enlarged portion D3 Gap

Claims (4)

A cylindrical glass tube;
A discharge electrode that is long in the glass tube axial direction sealed at the end of the glass tube;
The discharge / discharge electrode includes an electrode support lead and a cylindrical electrode,
The cold cathode fluorescent lamp, wherein the glass tube has an area close to the tip of the cylindrical electrode that is larger than the inner diameter of the glass tube of the discharge light emitting unit. The glass tube has a discharge light emitting part inner diameter of 1 to 4 mm,
The cold cathode fluorescent lamp according to claim 1, wherein the cylindrical electrode has a length 1.5 to 6 times the inner diameter of the discharge light emitting part.   The discharge electrode has a mortar shape in which a bottom surface of a cylindrical electrode is recessed toward the discharge light-emitting portion, and the electrode support lead is connected to a mortar-shaped recess. Item 3. The cold cathode fluorescent lamp according to Item 2.   A cold-cathode fluorescent lamp portion in which a plurality of the cold-cathode fluorescent lamps according to any one of claims 1 to 3 are arranged in the same direction, a reflective surface provided on a back surface of the cold-cathode fluorescent lamp portion, and the cold cathode A surface light source device having a diffusion surface provided on the front surface of the fluorescent lamp portion, and in which the cylindrical electrode portions on one terminal side of the cold cathode fluorescent lamp are arranged in a line.

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