JP2007294163A - Direct backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct backlight having high uniformity ratio. <P>SOLUTION: In the direct backlight including a plurality of tubular fluorescent lamps 2 arranged in a housing 1 having an opening part 1b1, a bottom part 1b2 and a side part 1b3, the fluorescent lamp 2 includes a first luminance area La generating low brightness along the tube axis of the lamp by thickening the thickness of a phosphor layer 25, and a second luminance area Lb generating high brightness by thinning the thickness of the phosphor layer 25, wherein the fluorescent lamps 2 are arranged to face to the side of the opening part 1b1 of the first luminance area La. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a direct type backlight used for a liquid crystal television or the like.

  There are various backlight lighting methods used for liquid crystal televisions, such as a light guide plate method using a light guide plate, a hollow method, and a direct type, and the direct type is mainly used for large display devices.

  As a structure of the direct type backlight, a plurality of lamps are arranged inside the casing as described in Japanese Utility Model Laid-Open No. 6-54038 (hereinafter referred to as Patent Document 1), and at the opening of the casing. In general, a diffusion plate is disposed, and an optical sheet such as a diffusion sheet is generally disposed on the diffusion plate as desired.

Japanese Utility Model Publication No. 6-54038

However, the direct type backlight has a problem that luminance unevenness is likely to occur on the light emitting surface because the portion directly above the lamps is particularly bright and the space between the lamps tends to be darker than the portion directly above the lamps. (Similar problems are described in Japanese Patent Application Laid-Open Nos. 2004-354533 and 2000-10094)
In view of the above problems, as a result of tests conducted by the present inventors, it has been found that the problem can be solved by using a fluorescent lamp in which the luminance distribution is changed by the fluorescent substance by paying attention to the fluorescent substance of the lamp. So I came up with a proposal.

  Accordingly, an object of the present invention is to provide a direct type backlight having a high degree of uniformity.

  In order to achieve the above object, a direct type backlight according to the present invention is a direct type backlight in which a plurality of tubular fluorescent lamps are arranged inside a casing having an opening, a bottom, and a side part. And a first light emitting region that generates low luminance along a tube axis direction of the lamp, and a second light emitting region that generates high luminance, and the first light emitting region is directed toward the opening. A fluorescent lamp is arranged.

  According to the present invention, a direct type backlight having a high degree of uniformity can be realized.

(First embodiment)
Hereinafter, a direct backlight according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall view of a direct type backlight according to the first embodiment, and FIG. 2 is a cross-sectional view of the direct type backlight according to the first embodiment.

  A casing 1 constituting an envelope of a direct type backlight includes a front frame 1a and a back frame 1b. The back frame 1b is a flat housing having an opening 1b1, a bottom 1b2, and a side 1b3. A reflective surface having a high reflection efficiency is attached to the inner surfaces of the bottom 1b2 and the side 1b3, for example, a reflective sheet. It is formed by. In the back frame 1b, a plurality of tubular fluorescent lamps 2 are arranged so that their tube axes are substantially parallel to each other.

  FIG. 3 is a sectional view in the tube axis direction of the fluorescent lamp of the first embodiment, and FIG. 4 is a sectional view in the circumferential direction.

  The fluorescent lamp 2 is composed of a glass tube 21 made of soft glass, has a circular cross section, and has a straight tube shape elongated in the tube axis direction. Stems 22a and 22b are fixed to both ends of the glass tube 21, and lead wires 23a and 23b communicate with the inside and outside of the lamp. A pair of electrodes 24a and 24b made of a tungsten coil coated with a thermionic emission material mainly composed of BaO, CaO and SrO are provided at the leading ends of the lead wires 23a and 23b on the lamp inner side. The glass tube 21 is filled with mercury and 1.3 kPa argon gas. A phosphor layer 25 formed by blending RGB phosphors is formed on the inner surface of the glass tube 21.

  The phosphor layer 25 is formed so as to have a first light emitting region La that generates low luminance and a second light emitting region Lb that generates high luminance along the tube axis direction of the lamp. In this embodiment mode, the light emitting region is formed depending on the film thickness. Specifically, as shown in FIG. 4, a first phosphor region 25 a having a large film thickness is formed as the first light emitting region La, and the film thickness gradually decreases from the portion along the inner wall of the glass tube 21. Thus, the second phosphor region 25b having a small thickness is formed as the second light emitting region Lb. The first phosphor region 25a has the thickest portion (0 °), and the second phosphor region 25b has the thinnest portion (180 °). Yes.

  FIG. 5 is a characteristic diagram of the fluorescent lamp according to the first embodiment, where (a) is a relative luminance distribution diagram in the outer surface circumferential direction of the lamp, and (b) is a light distribution characteristic diagram of the lamp. In the figure, A indicates the characteristics of the lamp of the present invention, and B indicates the characteristics of the conventional lamp.

  As can be seen from FIG. 5 (a), in the conventional fluorescent lamp with uniform film thickness and phosphor particle size, the intensity of the light emitted from the outer surface of the glass tube is the same 360 °, so (b The light distribution characteristic of a substantially perfect circle is obtained as shown in FIG. On the other hand, in the fluorescent lamp used in the present invention, the luminance is low in the first phosphor region 25a having a large film thickness, and the luminance is high in the second phosphor region 25b having a small film thickness. The luminance emitted from the outer surface of the light has a wave-like characteristic, and the light distribution characteristic is egg-shaped. Since the fluorescent lamp 2 used in the present invention is configured to change the luminance only by the film thickness of the phosphor layer 25, the light loss is small compared to the case where a light shielding film is used, and the total luminous flux There is an advantage that it is almost the same as a fluorescent lamp. The lamp that can be used in the present invention has a typical light distribution characteristic as shown in (b), but is not limited to such a characteristic.

  Here, an example of the formation method of the fluorescent substance layer of the fluorescent lamp of this invention is demonstrated with reference to FIG.

  First, a thin phosphor layer 25 is formed on the entire inner surface of the glass tube 21 as shown in FIG. Then, a phosphor layer is partially formed at a portion where the film thickness is to be increased as shown in FIG. By repeating the step (b), the phosphor layer 25 of the present embodiment as shown in (c) can be formed. Alternatively, the phosphor layer 25 can be formed on the entire inner surface, a part of the phosphor layer 25 can be removed, and the entire formation and partial removal steps can be repeated.

  As another method, a sheet-like phosphor layer in which a phosphor layer having a desired film thickness is formed on a sheet via a water-soluble and adhesive adhesive is prepared, and the sheet-like phosphor is formed in water. After the body layer is disposed on the glass tube 21 and the adhesive is dissolved, the body layer is taken out from the water, only the sheet is peeled off from the sheet-like phosphor layer, and the remaining phosphor layer is formed on the inner wall of the glass tube 21. Similarly, it is possible to produce a fluorescent lamp having a desired thickness as in the present invention. Further, in this method, after the sheet-like phosphor layer formed with a uniform film thickness is similarly disposed in the glass tube 21 in water, the sheet is peeled off to form the phosphor layer on the inner wall. The fluorescent lamp 2 having a changed film thickness can also be obtained by forming the phosphor layers so that a part of the film thickness is increased.

  The fluorescent lamp 2 as described above is disposed with the phosphor layer 25 having the thick film portion facing the opening 1b1 side of the back frame 1b and the thin film portion facing the bottom portion 1b2.

  In the opening 1b1 of the back frame 1b, a diffusion plate 31 is disposed as the optical surface material 3, and a diffusion sheet 32 is disposed on the diffusion plate 31. Here, as the optical surface material 3, a transparent plate may be used instead of the diffusion plate 31, or a sheet such as a prism sheet or a polarizing sheet may be used as desired.

  One specification of this embodiment is shown below.

Backlight: Size = 32 inches (about 700 mm × about 400 mm), thickness D = 25 mm,
Fluorescent lamp 2: hot cathode fluorescent lamp, number of lamps used = 6 lamps, distance D1 = 6.0 mm with diffusion plate 3, distance D2 = 6.0 mm with reflecting surface, lamp pitch P = 67 mm
Glass tube 21: inner diameter = 7.0 mm, outer diameter R = 8.0 mm, lamp length = 730 mm,
Phosphor layer 25: film thickness T1 = 60 μm at the thickest part, film thickness T2 = 10 μm at the thinnest part, average median particle diameter = 3 μm
Optical surface material 3: diffusion plate, power per diffusion sheet lamp = 18 W, lamp current = 70 mA
FIG. 7 is a diagram showing the relative luminance distribution of the backlight of FIG. 2, in which A indicates the relative luminance distribution of the lamp of the present invention, and B indicates the relative luminance distribution of the conventional lamp.

  As can be seen from the figure, the relative luminance distribution is almost uniform. In other words, conventionally, the luminance is high directly above the lamps, the luminance is low between the lamps, and the luminance distribution is wavy. However, in the present invention, the portion with high luminance is suppressed in the conventional luminance distribution and the luminance is weak. The result was improved because the part was improved.

  Furthermore, in the present invention, adjusting the relative positional relationship of the fluorescent lamp 2 with respect to the backlight in accordance with the luminance generated in the first and second phosphor regions 25a and 25b makes the luminance distribution uniform. More desirable above. That is, when the luminance obtained by the first phosphor region 25a is too low (T1 is too thick), the distance D1 to the diffusion plate 3 is shortened and the luminance obtained by the second phosphor region 25b is too low. When (T2 is too thin), the fineness can be further increased by finely adjusting the distance D2 to the reflecting surface to be long. Regarding the lamp pitch, if the brightness between the lamps is low, the uniformity can be further increased by adjusting the lamp pitch P narrowly. In the best mode in the present embodiment, when the ratio of the thicknesses of the phosphor layers is T1: T2 = 3: 1, the relationship in the thickness direction of the backlight is D1: R: D2 = 1: 1. : 1.5 and the relationship in the width direction is about R: P = 1: 8.

  Here, the invention of the fluorescent lamp formed so that the film thicknesses of the phosphor layers are partially different is described in Japanese Utility Model Laid-Open No. 54-173584. The present invention is an invention of a fluorescent lamp aimed at obtaining a high brightness locally by directing a thinly formed phosphor layer portion toward an irradiation side. On the other hand, the present invention aims to obtain a uniform luminance on the light emitting surface by directing the thick phosphor layer portion toward the irradiation side, and therefore the fluorescent lamp as described in the above patent document. It is not an invention that is simply used in a normal usage form.

  When a fluorescent lamp 2 having a conventional phosphor structure having a diameter R of 8.0 mm as in the present embodiment is used as a light source, and a backlight with high uniformity is to be realized, the thickness of the backlight D is about 60 mm. On the other hand, since the present invention has a configuration in which the distance from the diffusing plate 3 can be shortened, a backlight with high uniformity can be realized with a thickness of about D = 25 mm. That is, according to the present invention, even when a large-diameter fluorescent lamp capable of obtaining a high total luminous flux is used, a backlight can be realized with a thickness of about 1/3 of the conventional one. In the present invention, when a backlight is configured using a cold cathode fluorescent lamp having a diameter R of 3.0 mm, which is the mainstream light source of the current direct type backlight, a conventional lamp having a uniform luminance in the circumferential direction is sufficient. In order to obtain a high degree of uniformity, about D = 25 mm is required, but in the lamp of the present invention, a backlight with a high degree of uniformity is realized with a thickness of about 1/3, which is about 8 mm. Can do.

  Therefore, in the first embodiment, the first phosphor region 25a having a thick film thickness of the fluorescent lamp 2 formed so that the film thickness of the phosphor layer 25 is changed is arranged facing the light emitting surface side. By configuring the direct type backlight, the luminance can be suppressed immediately above the lamps, and the luminance can be improved between the lamps. Therefore, the uniformity on the light emitting surface can be increased.

  Further, since the distance D1 to the diffusion plate 3 can be shortened, the direct type backlight can be thinned.

(Second Embodiment)
FIG. 8 is a cross-sectional view of a fluorescent lamp used in the direct type backlight according to the second embodiment of the present invention. About each part of this 2nd Embodiment, the part same as each part of the fluorescent lamp used for the direct type | mold backlight of 1st Embodiment shown in FIG. 4 is shown with the same code | symbol, and the description is abbreviate | omitted.

  In the second embodiment, the thickness of the phosphor layer 25 of the fluorescent lamp 2 is constant, and only the particle diameter of the phosphor is changed. Specifically, the first phosphor region 25a disposed toward the diffusion plate 3 has a small particle size, and the second phosphor region 25b disposed toward the reflecting surface has a large particle size. (For example, the average median particle size of the first phosphor region 25a is 1.5 μm, and the average median particle size of the second phosphor region 25b is 4.0 μm). When the phosphor layer 25 is formed by changing the particle size of the phosphor as described above, the first phosphor region 25a has a small particle size and thus has low light transmittance, while the second phosphor region 25b has a particle size. Since the diameter is large, the light transmittance is high, so that the luminance can be suppressed immediately above the lamps and the luminance can be improved between the lamps as in the first embodiment.

  Therefore, in the second embodiment, the first phosphor region 25a having a small particle size of the fluorescent lamp 2 formed so that the particle size of the phosphor constituting the phosphor layer 25 is changed is changed to the light emitting surface side. By arranging the direct-type backlight so as to face the screen, the same effects as those of the first embodiment can be obtained.

(Third embodiment)
FIG. 9 is a cross-sectional view of a fluorescent lamp used in the direct type backlight according to the third embodiment of the present invention. About each part of this 2nd Embodiment, the part same as each part of the fluorescent lamp used for the direct type | mold backlight of 1st Embodiment shown in FIG. 4 is shown with the same code | symbol, and the description is abbreviate | omitted.

  In the third embodiment, the thickness of the phosphor layer 25 of the fluorescent lamp 2 is constant, and only the density of the phosphor is changed. Specifically, the phosphor density of the first phosphor region 25a disposed toward the diffusion plate 3 is high, and the phosphor density of the second phosphor region 25b disposed toward the side is low. (For example, the phosphor density of the first phosphor region 25a is high, and the phosphor density of the second phosphor region 25b is low). When the phosphor layer 25 is formed by changing the phosphor density in this way, the transmittance can be changed as in the second embodiment, so that the luminance can be suppressed immediately above the lamps, and between the lamps. The brightness can be improved.

  Therefore, in the third embodiment, the first phosphor region 25a having a high phosphor density of the fluorescent lamp 2 formed so that the density of the phosphor constituting the phosphor layer 25 is changed is changed to the light emitting surface side. By arranging the direct-type backlight so as to face the screen, the same effects as those of the first embodiment can be obtained.

  In addition, embodiment is not necessarily restricted above, For example, you may change as follows.

  In addition to the hot cathode fluorescent lamp used in the embodiment of the present invention, the fluorescent lamp 2 can be any type of lamp such as a cold cathode fluorescent lamp or an outer electrode fluorescent lamp. In addition to the straight pipe, lamps having various shapes such as a U shape and a W shape can be used.

  Regarding the first embodiment in which the film thickness of the phosphor layer 25 is changed, not only when the film thickness is gradually changing as shown in FIG. 4, but also when it is changing stepwise as shown in FIG. Is also acceptable. This is because the lamp of FIG. 10 can obtain substantially the same characteristics as the embodiment of FIG. 4, and the uniformity is improved when the backlight is configured. That is, as long as the phosphor layer 25 has a substantially egg-shaped light distribution characteristic as shown in FIG. 5B, a fluorescent lamp having any configuration can be used.

  For the fluorescent lamp 2 adjacent to the side portion 1b3 in FIG. 2, the phosphor layer 25b may be formed so as to form the second light emitting region Lb that generates high luminance also on the side portion 1b3 side. In this case, the brightness near the frame portion of the backlight, the brightness of which tends to be low, can be brought close to the brightness of the other portions, so that the brightness on the light emitting surface can be made more uniform.

1 is an overall view of a direct type backlight according to a first embodiment. FIG. Sectional drawing of the direct type | mold backlight of 1st Embodiment. Sectional drawing of the tube-axis direction of the fluorescent lamp of 1st Embodiment. Sectional drawing of the circumferential direction of the fluorescent lamp of 1st Embodiment. The brightness | luminance characteristic of the fluorescent lamp of 1st Embodiment. Explanatory drawing of the formation method of the fluorescent substance layer of the fluorescent lamp of 1st Embodiment. FIG. 3 is a relative luminance distribution diagram of the backlight of FIG. 2. Sectional drawing of the fluorescent lamp used for the direct type | mold backlight of the 2nd Embodiment of this invention. Sectional drawing of the fluorescent lamp used for the direct type | mold backlight of the 3rd Embodiment of this invention. The other modification of the fluorescent lamp of 1st Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Case 1a Front frame 1b Back frame 1b1 Opening part 1b2 Bottom part 2 Fluorescent lamp 21 Glass tube 25 Phosphor layer 25a First phosphor area 25b Second phosphor area 3 Optical surface material 31 Diffusion plate 32 Diffusion sheet La First 1 light emitting region Lb second light emitting region

Claims (4)

In a direct type backlight in which a plurality of tubular fluorescent lamps are arranged inside a housing having an opening, a bottom and sides,
The fluorescent lamp has a first light emitting region that generates low luminance along a tube axis direction of the lamp and a second light emitting region that generates high luminance, and the first light emitting region is located on the opening side. A direct type backlight characterized in that the fluorescent lamp is arranged toward the front.   2. The fluorescent lamp according to claim 1, wherein the first phosphor region is formed with a thick phosphor layer and the second phosphor region is formed with a thin phosphor layer. Direct type backlight.   2. The direct type according to claim 1, wherein the fluorescent lamp has a first phosphor region having a small particle size of the phosphor and a second phosphor region having a large particle size of the phosphor. Backlight. 2. The direct type backlight according to claim 1, wherein in the fluorescent lamp, the first phosphor region is formed with a dense phosphor density, and the second phosphor region is formed with a sparse phosphor density.

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