JP2005268098A - Cold-cathode type fluorescent lamp and backlight unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold-cathode type fluorescent lamp which can be housed in a limited housing space of a backlight unit, and in which light emission efficiency is unlikely to be reduced, even if lamp electric current is made to be increased. <P>SOLUTION: The cold-cathode type fluorescent lamp 100, having a glass bulb 10 and a pair of electrodes 4a, 4b arranged and installed at both end parts in this glass bulb 10, and in a positive column light-emitting part 10a of the glass bulb 10, has a flat shape for the cross-sectional face of a light take-out part 10d. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a backlight unit used in a cold cathode fluorescent lamp and an LCD (liquid crystal display) device.

The backlight unit is attached to the back surface of the LCD panel and used as a light source of the LCD device.
There are roughly two types of backlight unit systems: an edge light system and a direct system (see, for example, Patent Document 1).
Among these, the direct type backlight unit has an envelope composed of a bottom plate and a side plate surrounding the bottom plate, and the opening of the envelope is covered with a diffusion plate, a diffusion sheet, etc. A plurality of fluorescent lamps are arranged in the vicinity of the bottom plate. The direct-type backlight unit is relatively easy to increase the brightness on the surface (hereinafter referred to as “light-emitting surface”), and thus is employed in LCD devices such as large-sized liquid crystal televisions such as 32 inches.

In such a backlight unit, in order to improve the image quality of the LCD device, the luminance on the light emitting surface is required to be high and uniform, and it is thin in order to realize space saving. It is requested to be.
For this reason, the inner surfaces of the bottom plate and the side plate are covered with a material having a high light reflectivity, and the light emitted from the fluorescent lamp to the back is reflected forward (in the direction of the light emitting surface) and emitted from the lamp. The effective use efficiency of the luminous flux (the proportion of the luminous flux emitted from the lamp, emitted from the light emitting surface) is increased, and the diffuser plate and diffusion sheet forward the direct light and reflected light from the fluorescent lamp forward. Is diffused and the brightness is uniform over the entire light emitting surface.

Furthermore, a cold cathode fluorescent lamp is used as the fluorescent lamp. This is because the cold cathode fluorescent lamp does not have a filament coil, so that it is easy to reduce the diameter of the lamp and meet the demand for a thinner backlight unit.
Such a backlight unit is required to have higher luminance in order to improve the image quality of the LCD device.
JP 2000-310778 A

  As a method of realizing high brightness of the backlight unit, a method of operating by simply increasing the lamp current of each cold cathode fluorescent lamp (hereinafter simply referred to as “lamp”) can be considered. However, although the luminous flux of the lamp is increased to some extent, the coldest spot temperature excessively increases due to an increase in the lamp current and deviates from the optimum range, whereby the luminous efficiency of the lamp (hereinafter referred to as “lamp efficiency”). There is a problem that decreases.

  If the heat dissipation is improved by using a lamp with a larger tube diameter as the lamp current increases, the above-mentioned excessive rise in the coldest spot temperature can be suppressed. However, if the tube inner diameter is increased, the inside of the tube from the center of the positive column plasma space is increased. Since the distance to the wall is increased, the luminous efficiency is lowered, and there is a problem that an increase in luminous flux corresponding to the expected increase in lamp current cannot be obtained. In addition to this, in the case where the storage space of the lamp is limited, such as a backlight unit, if a lamp having a larger tube diameter than before is used, the distance between the lamp and the light emitting surface will be shorter, and the lamp on the light emitting surface will be reduced. There is a disadvantage that luminance unevenness (wave-like luminance unevenness) occurs in which the luminance is increased only in a portion where the distance to is short. This can be solved by increasing the thickness direction of the storage space and disposing the lamp backward from the light emitting surface. However, as described above, the backlight unit is required to be particularly thin. Therefore, it is not practical to take such a method.

  The present invention has been made in view of the above problems, and can be stored in a limited storage space of the backlight unit, and the cold cathode fluorescent lamp is less likely to have lower luminous efficiency even when the lamp current is increased, and An object of the present invention is to provide a backlight unit using the same.

In order to achieve the above object, a cold cathode fluorescent lamp according to the present invention is a cold cathode fluorescent lamp having a glass bulb and a pair of electrodes disposed at both ends of the glass bulb, Of the positive column light emitting part of the glass bulb, the light extraction part has a flat cross-sectional shape.
Further, the electrode has a cylindrical shape, and the glass bulb has a substantially circular cross-sectional shape at least in a portion from the both ends to the tip of the electrode disposed at the location.

Further characterized in that the value obtained by dividing the power consumed by the positive column discharge in the outer peripheral surface area of the positive column light emitting portion is set in the range of 45 mW / cm ² or more 90 mW / cm ² or less.
Furthermore, the short inner diameter of the flat cross-section is in the range of 1.0 mm to 3.0 mm.

Further, the short inner diameter of the flat cross section is in the range of 1.0 mm to 2.5 mm.
In the backlight unit according to the present invention, a plurality of the cold cathode fluorescent lamps are arranged in parallel at a predetermined interval in an envelope having a reflector and a side plate surrounding the reflector. The cold cathode fluorescent lamp is characterized in that the long axis of the flat cross section is arranged so as to be substantially parallel to the main surface of the reflector.

  The cold cathode fluorescent lamp according to the present invention is a cold cathode fluorescent lamp having a glass bulb and a pair of electrodes disposed at both ends of the glass bulb, the positive column light emitting portion of the glass bulb. Among them, since the shape of the cross section of the light extraction portion is flat, the outer peripheral surface area is increased compared to the conventional straight tube lamp having the same outer diameter as the short outer diameter of the flat cross section. An excessive rise in the coldest spot temperature can be suppressed, and the flat inner short diameter is shorter than a conventional straight tube lamp having a tube inner diameter comparable to the long inner diameter. The distance from the center to the inner wall of the pipe can be effectively kept short. For this reason, even if the lamp current is increased as compared with the prior art, it is possible to make it difficult to reduce the light emission efficiency. For example, when the cold cathode fluorescent lamp is used in a backlight unit, it can be stored without increasing the thickness direction of the limited storage space of the backlight unit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Configuration of cold cathode fluorescent lamp)
FIG. 1A is a cross-sectional view showing the configuration of a cold cathode fluorescent lamp (hereinafter referred to as “lamp”) 100 according to the present embodiment, and FIG. FIG. 4C is a cross-sectional view taken along line -B, (c) is a cross-sectional view taken along line CC, and (d) is a cross-sectional view taken along line DD. In FIGS. 1B and 1D, only the cross sections of the glass bulb 10 and the phosphor 6 are shown in order to avoid complicated drawings.

As shown in FIG. 1A, the lamp 100 includes a glass bulb 10 made of borosilicate glass and a pair of electrodes 4a and 4b disposed at both ends of the glass bulb 10.
Both ends of the glass bulb 10 are sealed with bead glasses 2a and 2b. Through the bead glasses 2a and 2b, lead wires 8a and 8b made of tungsten are introduced from both ends of the glass bulb, and the lead wires 8a and 8b hold electrodes 4a and 4b made of niobium having a bottomed cylindrical shape. doing.

  The electrodes 4a and 4b are hollow-type electrodes, the electrode length in the longitudinal direction is 5.0 mm, and the wall thickness is 0.1 mm. Further, the gap between the outer periphery of the electrodes 4a and 4b and the inner periphery of the glass bulb 10 is set to be as narrow as 0.2 mm or less. By setting the interval narrow in this way, it is possible to prevent discharge from leaking into the gap, thereby suppressing mercury consumption due to sputtering (for details, see JP-A-2002-289138).

The glass bulb 10 is filled with approximately 2.0 mg of mercury (not shown) and neon / argon mixed gas (Ne 95% -Ar 5%) at a pressure of 8.0 kPa at room temperature.
The inner surface of the glass bulb 10 emits red (Y ₂ O ₃ : Eu), green (LaPO ₄ : Ce ₃ , Tb ₃ ) and blue (BaMg ₂ Al ₁₆ O ₂₇ : Eu ₂ , Mn) colors. The rare earth phosphor 6 mixed with the phosphor to be coated is applied.

Hereinafter, the respective portions from the both ends of the glass bulb 10 to the tips of the electrodes 4a and 4b disposed at the corresponding portions are referred to as electrode portions 10b and 10c. Further, a portion excluding the electrode portions 10b and 10c and corresponding to a region where a positive column is substantially generated when the lamp 100 is turned on is referred to as a positive column light emitting unit 10a.
Further, a portion of the positive column light emitting portion 10a of the glass bulb 10 that contributes to light emission for the purpose in the illumination device in which the lamp 100 is used is referred to as a light extraction portion 10d. For example, when the lamp 100 is used in a liquid crystal backlight unit, the portion that contributes to light emission on the effective display surface of the liquid crystal panel that the unit emits light is the light extraction portion 10 d of the glass bulb 10. In the present embodiment, the ranges of the positive column light emitting unit 10a and the light extraction unit 10d are substantially the same.

As shown in FIGS. 1B to 1D, in the glass bulb 10, the shape of the cross section of the positive column light emitting part 10a (light extraction part 10d) is substantially elliptical, and the electrode parts 10b and 10c The cross-sectional shape is substantially circular.
Here, each dimension of the lamp 100 will be described. The total length L of the lamp 100 is 705 mm, the length Da of the positive column light emitting section 10a (light extraction section 10d) in the tube axis 9 direction is about 680 mm, and the lengths Db and Dc of the electrode sections 10b and 10c in the tube axis 9 direction are respectively. About 12 mm, the outer peripheral surface area of the positive column light emitting part 10 a is about 105 cm ² . Further, the short outer diameter ao of the substantially elliptical shape is 4.0 mm, the short inner diameter ai is 3.0 mm, the long outer diameter bo is 5.8 mm, and the long inner diameter bi is 4.8 mm. The substantially circular tube outer diameter ro is 5.0 mm, and the tube inner diameter ri is 4.0 mm.

The reason why the lamp 100 according to the present embodiment has such a shape is as follows.
As described above, the conventional lamp has a problem that the lamp efficiency is lowered when the lamp current is increased. For example, in a lamp having a total length of 705 mm and a tube outer diameter of 4.0 mm / tube inner diameter of 3.0 mm, when the lamp current is increased from the rated current of 5.5 mA to 8.5 mA, the lamp efficiency is about 60 (lm / W). It decreases to about 83% from 50 to 50 (lm / W).

  The reason why the lamp efficiency is reduced in this way is that the coldest spot temperature of the glass bulb is excessively increased due to the increase of the lamp current. In general, it is known that a lamp having a tube inner diameter of 1.2 to 4.0 mm can obtain optimum lamp efficiency when the coldest spot temperature is in a range of 60 to 65 ° C. (“backlight fluorescence The latest trends in lamps ", Masataka Takagi, 2002.7 Bulb Industry Bulletin No. 449, page 40), the cold spot temperature was excessively increased outside the optimum range, and the lamp efficiency was lowered.

Therefore, if the lamp current is increased and a lamp having a larger tube inner diameter and larger tube outer diameter is used (for example, a tube outer diameter of 5 mm instead of a lamp having a tube outer diameter of 4.0 mm / tube inner diameter of 3.0 mm). A lamp having a diameter of 0.0 mm / tube inner diameter of 4.0 mm is used.) Since the heat radiation area is increased by increasing the outer peripheral surface area of the glass bulb, it is possible to suppress an excessive increase in the coldest spot temperature.
However, in particular, when the inner diameter of the tube is increased, the distance from the center of the positive column plasma space to the inner wall of the tube is increased, so that the problem that lamp efficiency is lowered becomes apparent. In detail, in the positive column plasma space, ultraviolet rays emitted when mercury atoms return from an excited state to a lower energy state are absorbed by another mercury, and the energy state of the mercury transitions to a higher energy state. Let As described above, the ultraviolet rays do not directly reach the phosphor in the glass bulb, but propagate through the mercury atoms. That is, when the tube inner diameter is increased, the probability that ultraviolet rays generated in the positive column plasma space reach the tube wall is lowered, so that the lamp efficiency is lowered.

In addition, when a lamp having a large tube outer diameter is used for a backlight unit, it may be an obstacle to making the unit thinner.
On the other hand, in the present embodiment, the shape of the positive column light emitting part 10a (light extraction part 10d) is substantially elliptical, so that the outer peripheral surface area is increased and the coldest spot temperature is excessively increased. While suppressing the distance from the center of the positive column plasma space to the inner wall of the tube, it is possible to effectively keep the distance short, and even if the lamp current is increased, a decrease in lamp efficiency can be suppressed.

More specifically, as will be described later, the glass bulb 10 is a straight tubular lamp having a tube outer diameter of 5.0 mm / tube inner diameter of 4.0 mm (hereinafter, a lamp having such a tube diameter is referred to as “straight tube lamp A”). ) Is formed into a flat shape, the outer peripheral surface area of the positive column light emitting portion is substantially the same as that of the straight tube lamp A, and is a straight tube lamp (hereinafter referred to as a tube outer diameter 4.0 mm / tube inner diameter 3.0 mm). The lamp having such a tube diameter is referred to as “straight tube lamp B”). In addition, since the short inner diameter ai of the elliptical cross section in the positive column light emitting section 10a is 3.0 mm and the long inner diameter bi is 4.8 mm, the short inner diameter ai is particularly short. The distance from the center of the positive column plasma space to the inner wall of the tube is not far away.
(About positive column load)
Normally, when the lamp 100 is turned on, the electrode portions 10b and 10c are relatively hot, and the coldest spot temperature is located near the center of the positive column light emitting portion 10a in the tube axis direction.

  According to the inventor's study, the coldest spot temperature is a value obtained by dividing the power Wp consumed by the positive column discharge (positive column input power Wp) by the outer peripheral surface area Sp of the positive column light emitting section 10a (hereinafter, It was found that this value depends on "positive column load"). This is because the heat loss in the positive column input power Wp in the lamp power W is diffused from the outer peripheral surface of the positive column light emitter 10a by thermal radiation and heat conduction.

Further, by setting the positive column load 45 mW / cm ² or more 90 mW / cm ² or less in the range, the cold spot temperature is found not to deviate from the optimum range. Where coldest point temperature as described above is optimally 60 ℃ ~65 ℃, 45mW / cm 2 less than the coldest point temperature is substantially below the 50 ° C. and optimum temperature, and greater than 90 mW / cm ² This is because it has been confirmed through experiments that the coldest spot temperature rises excessively to 75 ° C.

The positive column input Wp is obtained by subtracting the electrode loss We from the lamp power W, and Wp = W−We. The electrode loss We is determined by a known tube length changing method. The outer peripheral surface area Sp is calculated from Sp = π (ao + bo) Lp / 2. In the lamp 100, the positive column input Wp is 7.8 W (lamp current 8.5 mA) and the outer peripheral surface area is 105 cm ² , so the positive column load is 74 mW / cm ² .
(Glass bulb molding method)
FIG. 2 schematically shows a method for forming the glass bulb 10 of the lamp 100.

  First, (a) a glass bulb 21 made of straight tubular borosilicate glass (softening point 765 ° C.) is prepared [FIG. 2 (a)], (b) the cross-sectional shape of the glass bulb 21 is flattened. The planned portion is installed so as to be sandwiched between two forming jig plates 22a and 22b made of stainless steel [FIG. 2 (b)]. (C) Then, the glass bulb 21 is heated to a tube wall temperature (for example, 620 to 700 ° C.) lower than the softening point by a heating furnace (not shown), and due to the weight of the forming jig plate 22a [FIG. 2 (c)]. (D) The glass bulb 21 having a desired shape can be obtained by processing the cross section from a circular shape to a substantially elliptical shape (FIG. 2 (d)).

The glass bulb forming method is not limited to such a method.
The glass bulb 10 according to the present embodiment is obtained by molding the completed straight tube lamp A through the steps (b) to (d). As a result, the straight tube lamp A has a tube outer diameter of 5.0 mm and a substantially elliptical short outer diameter of 4.0 mm and a long outer diameter of 5.8 mm, and a tube inner diameter of 4.0 mm is substantially elliptical. The short inner diameter is 3.0 mm and the long inner diameter is 4.8 mm. When the straight tube lamp A having a tube outer diameter of 5.0 mm is flattened by the above molding method, the long outer diameter bo is set to 6.6 mm and the short outer diameter ao is set to 3.0 mm at the maximum ( The flatness in this case is preferably ao / bo≈0.45.) This is because if the tube is excessively flattened, the thickness of the tube may change significantly, leading to a decrease in yield.
(Backlight unit)
FIG. 3 is a schematic perspective view showing a configuration of a backlight unit 1000 for a liquid crystal television of 32 inches (aspect ratio 16: 9) according to the present embodiment. In the drawing, the diffusion plate 140, the diffusion sheet 142, and the lens sheet 144 are partly cut away so that the internal structure can be easily understood. FIG. 4 is a partial enlarged view of the backlight unit 1000 of FIG. 3 when the central portion in the X-axis direction is cut in the Y-axis direction. In the figure, the lamp 100 shows only its outer diameter. A circle indicated by a two-dot chain line indicates the tube outer diameter of the conventional straight tube lamp B having a tube outer diameter of 4.0 mm / tube inner diameter of 3.0 mm. For convenience of explanation, the second straight line from the top in the figure is shown. The center of the tube lamp B coincides with the center of the lamp 100.

In a direct-type backlight unit 1000, 14 lamps 100 are arranged in parallel in an envelope 120 having a rectangular bottom plate 122 and a side plate 124 surrounding it. The lamp 100 is arranged such that the long axis 19 of the flat cross section is substantially parallel to the main surface of the reflector 122. Details will be described later.
The envelope 120 is made of, for example, polyethylene terephthalate (PET) resin, and a reflective surface is formed by depositing a metal such as silver on the inner surface (inside the bottom plate 122 and the side plate 124). The inner dimensions of the envelope 120 are set to be thin, with a horizontal direction (X-axis direction) of 728 mm, a vertical direction (Y-axis direction) of 408 mm, and an outer depth of 19 mm. The main surface (inner surface) of the bottom plate (reflecting plate) 122 is separated from the inner surface of the front panel 145 by about 14 mm, and the lamp 100 is located at a position close to the reflecting plate 122 between the lamp axes (between adjacent lamp tube axes). distance) are arranged at a P _1.

The front opening of the envelope 120 is covered with a translucent front panel 145 formed by laminating a diffusion plate 140, a diffusion sheet 142, and a lens sheet 144. It is hermetically sealed so that the lamp 100 and the like are not damaged.
The diffusing plate 140 and the diffusing sheet 142 in the front panel 145 scatter and diffuse the light emitted from the lamp 100, and the lens sheet 144 collects light in a direction normal to the sheet 144. Thus, the light emitted from the lamp 100 is configured to irradiate the front uniformly over the entire surface (light emitting surface) of the front panel 145.

As described above, since the envelope 120 has a sealed structure, the temperature of the coldest spot is likely to rise excessively, and by using the lamp 100 according to the present invention, the coldest spot temperature is excessive. The increase can be suppressed particularly effectively, and an increase in luminous flux commensurate with the increase in lamp current can be obtained.
In the present embodiment, the lamp 100 is arranged such that the long axis 19 of the flat cross section is substantially parallel to the main surface of the reflecting plate 122. Thereby, the following effects are obtained.

First, since the short outer diameter ao (4.0 mm) of the lamp 100 is equivalent to the tube outer diameter of the straight tube lamp B, even if it is housed in the envelope 120 for the straight tube lamp B, the wavy luminance unevenness described above. Can be suppressed.
In addition, even if the distance between the lamp and the reflector is too close, luminance unevenness may occur, but the distance between the lamp 100 and the reflector 122 is the same as when the straight tube lamp B is used. In this respect, it can be said that the thickness of the envelope 120 can be kept thin.

Moreover, since the length of the substantially oval long outer diameter bo is 5.8 mm and is longer than the straight tube lamp B having a tube outer diameter of 4.0 mm, even if the lamp interval is made larger than the conventional lamp interval P ₀ , Luminance unevenness in which the luminance decreases at a position corresponding to between the lamp 100 and the lamp 100 on the light emitting surface is less likely to occur. That is, the lamp interval P ₁ can be made larger than the conventional lamp interval P ₀ when the horizontal direction and the vertical direction of the light emitting surface are arranged in the envelope 120 of the same size. The number of lamps (number) can be reduced, which is advantageous in terms of cost.

Furthermore, as indicated by a solid arrow in the third lamp 100 from the top in FIG. 4, in the lamp 100, the short axis is closer to the long axis 19 than the long axis 19 is far from the center of the positive column light emitting unit. More light is emitted in 18 directions. For this reason, if it arrange | positions so that the long axis 19 and the reflecting plate 122 may become substantially parallel as mentioned above, the light from a lamp | ramp can be directed to the front (light emitting surface direction) and back (direction of the reflecting plate 122). . Therefore, the effective utilization efficiency of the light flux emitted from the lamp 100 can be increased, and the luminance on the light emitting surface can be further improved.
(Measurement tests such as lamp efficiency and backlight brightness)
Next, in the case where the conventional straight tube lamp and the lamp 100 according to the present embodiment are arranged in the envelope 120 of the backlight unit 1000, the lamp efficiency and the light emitting surface of the backlight unit 1000 at the central portion of the light emitting surface. A test for measuring brightness was conducted. Table 1 below shows the measurement results of the above test. In the table, the tube inner diameter / tube outer diameter of the lamp 100 are described in the order of a short inner diameter, a long inner diameter, a short outer diameter, and a long outer diameter each having a substantially elliptical cross section.

(Straight tube lamp B)
First, in the envelope 120, the 16 straight tube lamps B have a lamp interval of 25.7 mm (in the 16 lamps, the distance between the uppermost lamp and the side plate 124, the lowermost lamp, When the backlight unit 1000 is operated with the lamp current value flowing through each lamp set to 5.5 mA, the distance from the side plate 124 is approximately half of the lamp interval. The lamp efficiency of the lamp located near the center of the reflector vertical direction (Y-axis direction) was measured. The lamp efficiency at this time was about 60 (lm / W). The luminance at the center of the front panel surface 145 was about 8000 (cd / m ² ).

(Straight tube lamp A)
Next, 15 straight tube lamps A were arranged in the envelope 120 with a lamp interval of 27.2 mm, and a lamp current value of each lamp was set to 8.5 mA. The lamp efficiency at this time was about 55 (lm / W). Further, the luminance was about 9500 (cd / m ² ), and although the luminance was improved as compared with that using the straight tube lamp B, a wavy luminance unevenness with a variation rate of about 6% was observed.

(Lamp 100)
Next, 14 lamps 100 according to the present embodiment are arranged in the envelope 120 with a lamp interval of 29.0 mm, and a lamp current value of each lamp is set to 8.5 mA. It was. The lamp efficiency at this time was about 65 (lm / W). This is about 8% higher than the straight tube lamp B (current value 5.5 mA) and about 18% higher than the straight tube lamp A. In addition, a high luminance of about 11400 (cd / m ² ) was obtained at the center of the front panel surface.

In addition, no wavy luminance unevenness was observed. Furthermore, the lamp interval was expanded from 25.7 mm when using the straight tube lamp B to 29.0 mm, and the number of lamps was reduced from 16 to 14 lamps by 2 lamps. In this case, the luminance unevenness in which the luminance is reduced at a position corresponding to the period of no.
(Modification 1)
In order to suppress an excessive temperature rise of the coldest spot temperature and to substantially shorten the distance from the center of the positive column plasma space to the tube wall, the entire region of the positive column light emitting unit 10a as in the above embodiment. It is preferable that the cross-sectional shape is substantially elliptical. However, even if the cross section of the most part of the positive column light emitting part is substantially elliptical and the cross section of the remaining part is substantially circular, a certain degree of effect can be obtained.

FIG. 5 is a diagram showing such a modification.
As shown in the figure, the cross-sectional shape of the light extraction portion 10d in the positive column light emitting portion 10a is substantially elliptical, and the remaining portion and the electrode portion deviated from the light extraction portion 10d of the positive column light emission portion 10a. The cross-sectional shapes of 10b and 10c are substantially circular.
The glass bulb 10 of the lamp 101 shown in the figure has a total length L of 405 mm, lengths Db and Dc of the electrode portions 10b and 10c (see FIG. 1) of about 12 mm, and a length Da of the positive column light emitting portion 10a of about 12 mm. The length Dd of the light extraction portion 10d having a cross section of approximately 380 mm in the positive column light emitting portion 10a is approximately 340 mm, and the cross sections of both ends of the positive column light emission portion 10a from the light extraction portion are substantially the same. Each of the circular portions has a length of about 20 mm.

Thus, the lamp 101 has a light extraction portion 10d that is narrower than the positive column light emitting portion 10a. For example, when the lamp 101 is used in a backlight unit, the lamp longitudinal direction of the liquid crystal panel from the light emitting surface of the unit. This is because the effective display surface is substantially narrow, and the light at both ends of the lamp is not so required for light emission on the display surface.
In order to improve the lamp efficiency by substantially reducing the distance from the center of the positive column plasma space to the tube wall, the length of the light extraction portion 10d having a substantially elliptical cross section is substantially circular. It has been confirmed by experiments that the electrode portions 10b and 10c having the cross-sections and the length of the remaining portion removed from the light extraction portion 10d of the positive column light emitting portion 10a may be longer (de <Dd> Df may be sufficient). Yes. In addition, since the coldest spot temperature is formed at a central portion in the direction of the tube axis 9 of the positive column light emitting portion 10a, it is desirable that at least the cross section of this portion be flat.
(Modification 2)
In the above embodiment, the shape of the cross section of the positive column light emitting portion is substantially elliptical. However, the shape is not limited to substantially elliptical, and may be other shapes as long as it is flat. .

FIG. 6 is a diagram showing such a modification.
As shown in the figure, the cross section of the positive column light emitter 10a has a substantially rectangular shape (race shape) having straight portions in the major axis bi and bo directions.
Thus, even when the cross section is substantially rectangular, the same effects as those of the above-described embodiment can be obtained.
(Other)
1. In the above embodiment, a hollow electrode is used as an electrode, but a rod-shaped electrode may be used. Moreover, although the cross section of the electrode part is substantially circular, the cross section of the electrode part may be flat and may be flat over the entire length of the glass bulb. In this case, the shape of the electrode may be flat according to the cross section.

  However, especially in the case of a hollow electrode, it is possible to flatten both the electrode portion of the glass bulb and the hollow electrode and to set the gap between the inner circumference of the glass bulb and the outer circumference of the electrode with high accuracy (for example, 0.2 mm or less). , Manufacturing costs increase. On the other hand, if the cross sections of the electrode portion of the glass bulb and the hollow electrode are both substantially circular, the gap can be set by adjusting the diameters of both, which is preferable in terms of manufacturing.

  2. It is preferable that the short inner diameter of the flat cross section is defined within a range of 3.0 mm or less. Experiments have confirmed that when the short inner diameter is larger than 3.0 mm with a boundary of 3.0 mm, the distance from the center of the positive column plasma space to the tube wall increases and the lamp efficiency rapidly decreases. Because. Furthermore, it is more preferable that the short inner diameter is defined in a range of 2.5 mm or less. This is because the lamp has a lamp current of 8.5 mA having a configuration similar to that shown in FIG. 1 and defined as a short inner diameter ai 2.5 mm, a short outer diameter ao 3.5 mm, a long inner diameter bi 5.4 mm, and a long outer diameter bo 6.4 mm. This is because it has been found that the efficiency is about 10% higher than that when the current value of the straight tube lamp B is 5.5 mA.

  In addition, since it is difficult to manufacture the short inner diameter below 1.0 mm, the lower limit of the short inner diameter is 1.0 mm.

  Since the cold-cathode fluorescent lamp according to the present invention can increase the luminous flux corresponding to the increase in lamp current, it can be applied to applications such as a backlight unit.

It is sectional drawing which shows the structure of the cold cathode type fluorescent lamp which concerns on embodiment. It is a schematic diagram which shows the shaping | molding method of a glass bulb. It is the schematic which shows the structure of the backlight unit which concerns on embodiment. FIG. 4 is a partially enlarged view of the backlight unit of FIG. 3 when a central portion in the X-axis direction is cut in the Y-axis direction. It is a figure which shows the modification which concerns on embodiment. It is a figure which shows the modification which concerns on embodiment.

Explanation of symbols

4a, 4b electrode 10 glass bulb 10a positive column light emitting part 10b, 10c electrode part 10d light extraction part 100, 101 cold cathode fluorescent lamp 120 envelope 122 reflector 1000 backlight unit

Claims (6)

A cold cathode fluorescent lamp having a glass bulb and a pair of electrodes disposed at both ends in the glass bulb,
A cold-cathode fluorescent lamp characterized in that the cross-sectional shape of the light extraction portion of the positive column light emitting portion of the glass bulb is flat. The electrode has a cylindrical shape,
The cold-cathode fluorescent lamp according to claim 1, wherein the glass bulb has a substantially circular cross-sectional shape at least in a portion from the both ends to the tip of the electrode disposed at the location. Claim, characterized in that the values obtained the power consumed by the positive column discharge was divided by the outer circumferential surface area of the positive column light emitting portion is set in the range of 45 mW / cm ² or more 90 mW / cm ² or less 1 Or the cold cathode fluorescent lamp according to 2.   The cold cathode fluorescent lamp according to any one of claims 1 to 3, wherein a short inner diameter of the flat cross section is in a range of 1.0 mm to 3.0 mm.   5. The cold cathode fluorescent lamp according to claim 4, wherein a short inner diameter of the flat cross section is in a range of 1.0 mm to 2.5 mm. A plurality of cold cathode fluorescent lamps according to any one of claims 1 to 5 are arranged in parallel at a predetermined interval in an envelope having a reflector and a side plate surrounding the reflector.
Each of the cold cathode fluorescent lamps is disposed so that the long axis of the flat cross section is substantially parallel to the main surface of the reflector.

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