JP4454361B2 - Surface emitting device - Google Patents

Description

  The present invention relates to a surface light emitting device used in a direct type backlight for a liquid crystal display device, for example.

  2. Description of the Related Art Conventionally, liquid crystal display devices or the like are equipped with a direct type backlight that is a kind of surface light emitting device. The direct type backlight is based on a configuration in which a light source accommodated in a lower frame is disposed behind (directly below) a diffusion plate as a planar diffusing member serving as a light emitting surface, and such a configuration is adopted. Therefore, as compared with the side light type in which the light source is arranged not on the light emitting surface but on the side, the light loss is small, and a large number of lamps can be used. In addition, the direct type backlight has an advantage that the inner space has a hollow structure, so that it is lightweight even if it is enlarged. For this reason, the direct type backlight is particularly suitable as a large surface light-emitting device exceeding 15 inches.

  In such a direct type backlight, in order to improve luminance, the same or similar reflecting sheet, reflecting plate, etc. are provided on the bottom surface, which is the inner wall surface of the lower frame, on each side surface standing from the bottom surface. The reflection member is laid (see, for example, Patent Document 1).

JP 2001-202814 A (page 2)

  As the reflection member, a metallic luster regular reflection sheet, a white diffuse reflection sheet, and the like are often used. Since the metallic gloss regular reflection sheet reflects light regularly, it has an advantage of easily improving luminance. However, because of regular reflection, it is difficult to eliminate the lamp image, and it is necessary to increase the distance between the lamp and the planar diffusing member, which makes it difficult to meet the demand for downsizing the direct type backlight. Have. In addition, for the metallic gloss specular reflection sheet itself, if the electrical conductivity of the sheet surface is not reduced by coating the metal surface with a transparent resin, etc., when laid on the lower frame, the lamp will leak due to the leakage current from the lamp. There are also disadvantages that problems such as short life, low brightness, and high power consumption are likely to occur. Furthermore, since the metallic gloss regular reflection sheet usually has a multi-layer structure, there is a drawback that the cost is likely to increase.

  On the other hand, since the white diffuse reflection sheet is diffuse reflection, it has the advantages that it is excellent in eliminating the lamp image, has good light emission quality, and is inexpensive. In addition, the provision of a light-resistant layer on the surface has an advantage that there is almost no deterioration due to ultraviolet rays. For this reason, as a reflective sheet laid on the inner wall surface of the lower frame, a white diffuse reflection sheet is increasingly used rather than a metallic luster regular reflection sheet.

However, with the recent demand for high light emission quality of direct type backlights, white diffuse reflection sheets are becoming insufficient. That is, in the white diffuse reflection sheet, the luminance on the light emitting surface near the side surface of the lower frame is considerably lower than the luminance on the light emitting surface on the center side, and the light emitting surface near the side surface of the lower frame is dark. (Sumoku phenomenon). And if such a corner black phenomenon is seen, it cannot be said that it fully responded to a user's request. For this reason, there is a strong demand for the development of a technique for making the luminance distribution of the light emitting surface of the direct type backlight more uniform than ever.
The present invention has been made in view of such circumstances. In particular, the present invention provides a surface emitting device with high light emission quality in which the occurrence of corner black phenomenon is effectively suppressed and the luminance distribution of the light emitting surface is uniformized. Objective.

  The inventor has intensively studied to develop a surface light emitting device that realizes a high light emission quality by making the luminance distribution of the light emitting surface uniform. In that process, in the conventional surface light emitting device, paying attention to the fact that the entire inner wall of the lower frame is formed of the same or similar reflecting surface, light is emitted by making the reflecting surface completely different from the bottom surface and the side surface of the lower frame. We thought that we could improve the uniformity of luminance distribution on the surface, and conducted various experimental studies. As a result, it was found that if the bottom surface of the lower frame is formed as a diffuse reflection surface and the regular reflection surface is included in the side surface of the lower frame, the luminance distribution on the light emitting surface can be made more uniform than before, and the present invention is completed. did.

That is, the surface light-emitting device of the present invention is erected in such a way that one surface is open, the bottom surface is located opposite to the opening, and the opening is inclined from the bottom surface toward the opening side so that the opening is wider than the bottom surface. A lower frame having a side surface, a planar diffusion member disposed on the opening side of the lower frame, and a linear light source disposed behind the diffusion member,
The bottom surface of the lower frame is formed as a diffuse reflection surface, and the surface parallel to the long light emitting portion of the linear light source is formed as a regular reflection surface among the side surfaces of the lower frame,
The difference between the reflectance of the specular surface reflectance of the diffuse reflection surface, Ri Contact set within 5%,
An inclination angle formed between a surface parallel to the long light emitting portion of the linear light source among the side surfaces of the lower frame and a surface obtained by extending the bottom surface of the lower frame straight toward the outside of the lower frame, The shortest distance from the surface parallel to the long light emitting part of the linear light source to the linear light source among the side surfaces of the lower frame that is set within a range of 60 ° to 75 ° is the linear shape. It is characterized in that it is set within a range of ¼ to ½ of the distance L between the light sources .

  According to the above configuration, on the inner wall surface of the lower frame, the bottom surface is formed as a diffuse reflection surface, and at least a part of the side surfaces is formed as a regular reflection surface, so that it is effective to generate a lamp image. It is possible to distribute a large amount of light to a region near the side surface side of the lower frame that tends to be dark. For this reason, it is possible to effectively suppress the occurrence of the corner black phenomenon and make the luminance distribution on the light emitting surface more uniform than before. That is, the surface light-emitting device of the present invention selects each surface of the inner wall of the lower frame as a diffuse reflection surface or a regular reflection surface according to the light source, thereby effectively utilizing each advantage and improving the light emission quality. It is what.

  Further, in the above surface light emitting device, the light source is a linear light source having a linear long light emitting portion, and a surface parallel to the long light emitting portion of the linear light source among the side surfaces of the lower frame is regularly reflected. It is preferably formed on the surface. In this case, since a large amount of light can be spread in the vicinity of the surface parallel to the long light emitting portion of the linear light source on the side surface of the lower frame, the occurrence of corner black phenomenon is effectively suppressed and the luminance of the light emitting surface is reduced. The distribution can be made more uniform than before.

Furthermore, in the surface light emitting device, it is preferable that a side surface on the end side of the linear light source is formed on a diffuse reflection surface. In this case, since light can be distributed to a region near the side surface on the end side of the linear light source that tends to be dark, the luminance distribution on the light emitting surface can be more effectively uniformized .

  In the surface light emitting device, an inclination angle formed between a side surface of the lower frame and a surface obtained by extending the bottom surface of the lower frame straightly toward the outer side of the lower frame is in a range of 60 ° to 75 °. It is preferable that the shortest distance from the light source to the side surface of the lower frame is set within a range of ¼ to ½ of the distance L between the light sources. In this case, the luminance distribution on the light emitting surface can be made even more effective.

  According to the present invention, on the inner wall surface of the lower frame, the bottom surface is formed as a diffuse reflection surface, and the side surface formed on the regular reflection surface is formed as a regular reflection surface that is parallel to the light emitting portion of the linear light source. Therefore, it is possible to provide a surface light emitting device with high light emission quality in which the occurrence of corner black phenomenon is effectively suppressed and the luminance distribution on the light emitting surface is made uniform.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partially exploded cross-sectional view schematically showing the structure of a direct type backlight according to an embodiment of a surface light emitting device of the present invention. The direct type backlight 10 according to the present embodiment is disposed and used on the back side of a liquid crystal display device, for example, as a lower frame 11 having an opening on one side, and a planar diffusing member disposed so as to close the opening. A diffusion plate 12, a light source 13 disposed behind (directly below) the diffusion plate 12, and an upper frame 14 disposed on the diffusion plate 12 via a plurality of optical sheets (not shown). Configured.

The upper frame 14 is formed of various metal materials and resin materials, and has an upper surface having a window portion 14b for emitting light to the outside and a side surface extending from the upper surface to the opening side. It is formed in a shape that can be put on the lower frame 11. As shown by the broken line in FIG. 1, the window portion 14b has a larger area than the bottom surface 11a of the lower frame 11, and is formed with a large opening so that the side surfaces 11b, 11c, 11d, and 11e of the lower frame 11 can be seen. . And the opening area | region of this window part 14b becomes a light emission surface.
The diffusion plate 12 is a white or milky white plate-like body such as polycarbonate or acrylic, and is disposed so as to close the opening of the lower frame 11, and diffuses and transmits light from the light source 13 disposed behind. It is something that can be done. Specifically, a resin composition in which light diffusing fine particles are blended into a resin material such as polycarbonate or acrylic is formed into a plate shape. With such a diffusion plate 12, the light from the light source 13 can be made uniform and emitted from the surface of the diffusion plate 12.

  Referring also to FIG. 2, the light source 13 is a linear light source having a long linear light emitting portion 13 a 1 and is accommodated in an internal space formed by the lower frame 11 and the diffusion plate 12. Specifically, the light source 13 includes, for example, six cold cathode tubes 13a each having a U-shaped elongated tubular body having a diameter of about several millimeters, each of which is attached to the holder 13b and made of white resin (polycarbonate or the like). Are supported by a lamp support (not shown). Each U-shaped cold-cathode tube 13a has a linear long light-emitting portion 13a1 and a short light-emitting portion 13a2, and the light-emitting portions 13a1 are arranged in parallel so as to be equidistant and parallel to each other. The light source 13 is connected to a known electrical component such as an inverter (not shown) so that it can be turned on and off.

  The lower frame 11 is formed of various metal materials or resin materials, and has a rectangular bottom surface 11a and side surfaces 11b, 11c, and 11d that are erected so as to spread from the bottom surface 11a toward the opening side. 11e, and one surface (upper surface in FIG. 2) is formed in a shape having a large opening. Here, among the side surfaces, the side surfaces 11 d and 11 e are surfaces parallel to the long light-emitting portion 13 a 1 of the light source 13.

  The bottom surface 11a of the lower frame 11 is formed on a diffuse reflection surface by laying a known white diffuse reflection sheet that diffuses and reflects light from the light source 13. Such a diffuse reflection surface can diffuse the light from the light source 13, so that the lamp image can be effectively eliminated, and the distance to the light source 13 can be reduced, so that the direct-type backlight 10 can be downsized. It also contributes. Needless to say, a white reflection coating may be used instead of the white diffuse reflection sheet.

  Further, the side surfaces 11d and 11e of the lower frame 11 are formed on regular reflection surfaces by laying a known metallic gloss regular reflection sheet or the like that regularly reflects light from the light source 13. Since the regular reflection surface has a higher reflectance than the diffuse reflection surface, the luminance can be improved. Of course, instead of the metallic glossy reflection sheet, a highly reflective metal film may be directly formed to form a regular reflection surface.

  The difference between the reflectance of the bottom surface (diffuse reflection surface) 11a of the lower frame 11 and the reflectance of the side surfaces (regular reflection surfaces) 11d and 11e of the lower frame 11 is preferably set within 5%. This is because if the difference in reflectance is too large, the luminance distribution on the light emitting surface cannot be made uniform. Specifically, the direct type backlight 10 of the present embodiment improves the uniformity of the luminance distribution on the light emitting surface by making the side surfaces 11d and 11e of the lower frame 11 a regular reflection surface having a higher luminance than the diffuse reflection surface. However, if the reflectance of the side surfaces 11d and 11e that are regular reflection surfaces is too large, the light emitting surface in the vicinity of the side surfaces 11d and 11e becomes too brighter than the light emitting surface in the central region, and the luminance distribution is made uniform. This is because it tends to be impossible to plan.

  Referring to FIG. 3, the side surface 11 d (11 e) of the lower frame 11 is inclined with respect to a surface K obtained by extending the bottom surface 11 a of the lower frame 11 straight toward the outside of the lower frame 11. Is inclined so as to be in the range of 60 ° to 75 °. Further, the distance D from the side surface 11d (11e) of the lower frame 11 to the light emitting portion 13a1 of the light source 13 is within a range of ¼ to ½ of the distance L between the light emitting portions 13a1 of the light source 13. Is formed. By forming in this way, the lamp image reflected on the side surface 11d (11e) can be improved, and the luminance distribution on the light emitting surface can be more effectively uniformed.

Returning to FIG. 2, the side surface 11 b of the lower frame 11 has a tendency to hardly spread the light from the light source 13, and thus is formed on a diffuse reflection surface. On the other hand, the side surface 11c of the lower frame 11 is formed as a regular reflection surface because the short light emitting portion 13a2 of the U-shaped cold cathode tube 13a exists in the vicinity thereof. By thus forming the side surface 11c on the regular reflection surface, it is possible to improve the uniformity of the luminance distribution on the light emitting surface.
In the present embodiment, the type in which the holder 13b and the light emitting unit 13a2 are exposed in the internal space of the lower frame 11 is described, but a type in which the holder 13b and the light emitting unit 13a2 are not exposed may be used. In this case, the side surfaces 11b and 11c are formed on regular reflection surfaces because the same level of light as the side surfaces 11d and 11e is supplied. Here, for the side surfaces 11b and 11c, a diffuse reflection surface or a regular reflection surface is selected according to the amount of light supplied from the light source 13. The selection is based on the difference between the luminance in the vicinity of the side surface and the luminance in the central area. That is, when the luminance near the side surface is 80% or less of the luminance of the central region, the side surface is formed on the diffuse reflection surface, and conversely, when the luminance near the side surface is larger than 80% of the luminance of the central region, The side surface is formed as a regular reflection surface. However, when the luminance in the vicinity of the side surface is much larger than the luminance in the central region, the side surface is preferably formed on the diffuse reflection surface.

  The direct type backlight 10 according to the present embodiment configured as described above has a bottom surface 11a of the lower frame 11 formed on a diffuse reflection surface by laying a white diffuse reflection sheet or the like, and a side surface 11d of the lower frame 11; 11e is formed on the specular reflection surface by laying a metallic luster specular reflection sheet or the like, so that it is possible to eliminate the lamp image and suppress a decrease in luminance on the light emitting surface in the vicinity of the side surfaces 11d and 11e of the lower frame 11. The distribution can be made uniform. For this reason, it becomes a direct type backlight having a high light emission quality as compared with a regular reflection surface alone or a diffuse reflection surface alone. Moreover, since the inner wall surface of the lower frame 11 should just be formed in a different reflective surface, light emission quality can be improved simply. Further, since the luminance distribution on the light emitting surface can be made uniform without increasing the number of the light sources 13, it is possible to meet the demand for cost reduction. Further, since a decrease in luminance on the light emitting surface near the side surfaces 11d and 11e of the lower frame 11 can be suppressed, the opening area of the window portion 14a of the upper frame 14 is made larger than the area of the bottom surface 11a as shown in FIG. be able to. That is, the opening area of the window portion 14a of the conventional upper frame 14 is substantially the same as the area of the bottom surface 11a of the lower frame 11, and there are many cases where each side surface of the lower frame 11 is visible or invisible. Since the luminance on the light emitting surface near the side surface can be improved by combining the regular reflection surface with the regular reflection surface, the opening area can be enlarged. In other words, a narrow frame of the upper frame 14 can be realized. Therefore, the direct type backlight 10 of the present embodiment is suitable as a large-sized surface light emitting device.

  Hereinafter, the verification test conducted by the present inventor will be described. First, as shown in FIG. 4 and FIG. 5, a lower frame 31 having a bottom surface 31a and side surfaces 31b, 31c, 31d, 31e that are inclined and extended so as to spread from the bottom surface 31a toward the opening side, A 2 mm thick acrylic resin diffuser plate 32 (see FIG. 5) disposed on the opening side of the lower frame 31 and a U-shaped cold cathode tube having a diameter of 3 mm disposed behind (directly below) the diffuser plate 32. A measurement unit 30 provided with two 33 was prepared. In this measuring unit 30, the bottom surface 31a and the side surfaces 31b, 31c, 31e are diffusive reflecting surfaces having a reflectance of 92% by laying E60V made by Toray Industries, and the side surface 31d is a 150 W05 made by Reiko (on a polyethylene terephthalate film). A regular reflection surface (silver reflection surface) having a reflectance of 93% was formed by laying a reflection sheet having a total thickness of about 155 μm on which a silver vapor deposition film was formed. Further, the distance D2 between the bottom surface 31a and the diffusing plate 32 was 16.3 mm, and the distance D3 between the bottom surface 31a and the U-shaped lamp 33 was 4.0 mm. Then, using this measurement unit 30, the inclination angle θ of the side surface 31d is changed to 45 °, 60 °, and 75 °, the distance D1 is set to 0, and the light emission portion distance L of the cold cathode tube 33 is ¼. The luminance on the diffusion plate 32 serving as the light emitting surface was measured by changing the distance L to ½ of the distance L between the light emitting portions and the distance L between the light emitting portions. The results are shown in FIGS.

  6 to 8 are diagrams viewed from above the diffusion plate 32 that is a light emitting surface of the measurement unit 30, respectively, and changes in luminance measured along points A1 to A2 on the diffusion plate 32 (A line). And a change in luminance (indicated by a B line) measured along points B1 to B2 on the diffusion plate 32. FIG. In each figure, the brightness of the A line is higher as it goes to the right side of the figure, and the brightness of the B line is higher as it goes to the upper side of the figure.

Here, FIGS. 6A to 6D all show the results when the inclination angle θ of the side surface 31d is 45 °, where (a) is 0 for the distance D1, and (b) is L / 4 for the distance D1. (C) is the result of setting the distance D1 to L / 2, and (d) is the result of setting the distance D1 to L.
7A to 7D all show the results when the inclination angle θ of the side surface 31d is 60 °. FIG. 7A shows the distance D1 being 0, and FIG. 7B shows the distance D1 being L / 4. (C) is the result of setting the distance D1 to L / 2, and (d) is the result of setting the distance D1 to L.
8A to 8D all show the results when the inclination angle θ of the side surface 31d is set to 75 °. FIG. 8A shows the distance D1 being 0, and FIG. 8B shows the distance D1 being L / 4. (C) is the result of setting the distance D1 to L / 2, and (d) is the result of setting the distance D1 to L.

6 to 8, the luminance change (line B) measured along points B1 to B2 on the diffusion plate 32 is high and uniform in the central region, but is a region near the side surfaces 31b and 31c. It was confirmed that a decrease in luminance was observed.
On the other hand, the following was confirmed from the change in luminance (A line) measured along points A1 to A2 on the diffusion plate 32.
That is, according to FIGS. 6A to 6D, in the region in the vicinity of the side surface 31d side which is a regular reflection surface, as apparent from the portion surrounded by the broken line, although there is some improvement effect of the luminance reduction, It was confirmed that the effect of suppressing the black phenomenon was small.

  Further, according to FIG. 7A, in the region near the side surface 31d, which is a regular reflection surface, there is a portion where the luminance is excessively high, as is apparent from the portion surrounded by the broken line. confirmed. In addition, according to FIG. 7D, in the region in the vicinity of the side surface 31d which is a regular reflection surface, as apparent from the portion surrounded by the broken line, although there is some improvement effect of luminance reduction, the corner black phenomenon is suppressed. It was confirmed that the effect to do was small. On the other hand, according to FIGS. 7B and 7C, in the region in the vicinity of the side surface 31d, which is a regular reflection surface, no significant reduction in luminance is seen up to a portion that is almost close to the side surface 31d. It was confirmed that the effect of sufficiently uniforming the luminance distribution was observed.

  Further, according to FIG. 8A, in the region near the side surface 31d, which is a regular reflection surface, there is a portion where the luminance is excessively high, as is apparent from the portion surrounded by the broken line. confirmed. Further, according to FIG. 8 (d), in the region near the side surface 31d, which is a regular reflection surface, as is apparent from the portion surrounded by the broken line, the effect of reducing the luminance is somewhat improved, but the corner black phenomenon is suppressed. It was confirmed that the effect to do was small. On the other hand, according to FIG. 8B and FIG. 8C, in the region in the vicinity of the side surface 31d side which is a regular reflection surface, no significant decrease in luminance is observed up to a portion almost close to the side surface 31d. It was confirmed that the effect of sufficiently uniforming the luminance distribution on the surface was observed.

  As described above, when the surface parallel to the light emitting part of the light source on the side surface of the lower frame is a regular reflection surface, the inclination angle θ of the surface is set to 60 ° to 75 °, and the surface and the linear light source When the distance D1 is set to ¼ or more and ½ or less of the distance L between the light emitting portions, it has been proved that the light can be brightened to the corner and the luminance distribution on the light emitting surface can be more effectively improved. In particular, when the tilt angle θ is 75 ° and the distance D1 is set to L / 4 (see FIG. 8B), the uniformity of the luminance distribution on the light emitting surface can be improved more effectively, and high light emission quality can be achieved. It has been demonstrated that it can be done.

The present invention is not limited to the above embodiment. For example, the light source is not limited to the U-shaped cold cathode tube, and a rod-like cold cathode tube may be used, and the number thereof may be changed as appropriate according to the size of the direct type backlight. Further, the diffusion plate 12 as the diffusion member is not necessarily sandwiched between the lower frame 11 and the upper frame 14, and may be disposed on the upper side of the upper frame 14. Further, the bottom surface 11a of the lower frame 11 does not have to be flat, and may have a corrugated shape.
The surface light-emitting device of the present invention is not limited to the direct type backlight used on the back side of the liquid crystal display device, but is used as a shaw casten for viewing X-ray photographs, a signboard that requires back light, a one for viewing photographic negatives, and the like. Can be used.

1 is an exploded sectional view showing a direct type backlight according to an embodiment of the present invention. It is a top view which shows the direct type | mold backlight which remove | eliminated the upper frame and the diffusion plate. It is an expanded sectional view for explaining the side of a lower frame. It is a top view which shows the measurement unit which removed the upper frame and the diffusion plate. It is a fragmentary sectional view showing a measurement unit. It is explanatory drawing which shows the diffusion plate (light emission surface) of a measurement unit, and the measurement result of a brightness | luminance. It is explanatory drawing which shows the diffusion plate (light emission surface) of a measurement unit, and the measurement result of a brightness | luminance. It is explanatory drawing which shows the diffusion plate (light emission surface) of a measurement unit, and the measurement result of a brightness | luminance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Direct type backlight 11 Lower frame 11a Bottom surface 11b, 11c Side surface 11d, 11e Side surface 12 Diffusion plate 13 Light source 14 Upper frame

Claims (2)

A lower frame having a bottom surface facing one side of the opening, a bottom surface positioned opposite to the opening, and a side surface erected so that the opening is wider than the bottom surface from the bottom surface toward the opening side; comprising a planar diffusing member disposed on the opening side of the frame, and a linear light source disposed behind the diffusing member,
The bottom surface of the lower frame is formed as a diffuse reflection surface, and the surface parallel to the long light emitting portion of the linear light source is formed as a regular reflection surface among the side surfaces of the lower frame,
The difference between the reflectance of the specular surface reflectance of the diffuse reflection surface, Ri Contact set within 5%,
An inclination angle formed between a surface parallel to the long light emitting portion of the linear light source among the side surfaces of the lower frame and a surface obtained by extending the bottom surface of the lower frame straight toward the outside of the lower frame, The shortest distance from the surface parallel to the long light emitting part of the linear light source to the linear light source among the side surfaces of the lower frame that is set within a range of 60 ° to 75 ° is the linear shape. The surface emitting device is set within a range of [1/4] to [1/2] of the distance L between the light sources . The surface light-emitting device according to claim 1, wherein a side surface disposed on an end side of the linear light source among side surfaces of the lower frame is formed on a diffuse reflection surface.

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