JP2004319122A - Light emitting device, and lamp image relaxation method in light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new technical means for relaxing a lamp image while preventing luminance degradation. <P>SOLUTION: This light emitting device 1 composed by installing a lamp 3 behind its light emitting surface is equipped with: diffusion films 11 and 13 used as blurring parts for blurring the lamp image by diffusing light from the lamp 3 to a level leaving the lamp image; and lens parts 12b and 14 for increasing the number of the blurred lamp images in the surface direction by lenses. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light emitting device such as a direct type backlight for a liquid crystal display device and a method for relaxing a lamp image in the light emitting device.
[0002]
[Prior art]
The basic structure of a conventional direct-type backlight for a liquid crystal display device is that a plurality of cold-cathode tube lamps are arranged behind a white diffusion plate formed by mixing a diffusing agent to a thickness of about several mm. The light from the cold-cathode tube lamp is diffused in the diffusion plate to obtain a planar light-emitting surface.
When the light from the lamp passes through the diffuser, the light is diffused by the diffusing agent present inside the diffuser. In addition, the diffusion plate usually has a thickness of several millimeters, and when light passes through the thick diffusion plate, the diffusion effect of the diffusion agent is increased, and the lamp image can be effectively reduced. In addition, the conventional diffuser has a relatively low light transmittance, and reflects or absorbs the light from the lamp at the diffuser, thereby suppressing brightness at a position immediately above the lamp and achieving a high diffusion effect. In combination, relatively good luminous quality is obtained.
As described above, in the conventional direct-type backlight, a diffusion plate is indispensable to obtain a planar light-emitting surface from a cold-cathode tube lamp as a linear light source.
In addition, when it is difficult to eliminate a lamp image using only a diffusion plate, as in Patent Document 1, light uniformity may be obtained on a light emitting surface by blocking light at a position immediately above a lamp by a lighting curtain. Also, in this case, a diffusion plate is necessary.
[0003]
[Patent Document 1]
JP, 2002-313103, A
[Problems to be solved by the invention]
The provision of the diffusion plate is indispensable for obtaining a desired luminous quality, but has a drawback of lowering the luminous efficiency. That is, since the diffuser reflects or absorbs light from the lamp with good light emission quality at the diffuser, the luminance is reduced and the luminous efficiency is poor. In particular, light absorption by the diffusing agent in the diffusion plate causes a decrease in luminous efficiency. It is also conceivable to increase the number of lamps to increase the brightness and reduce the distance between adjacent lamps to increase the brightness and ease the lamp image. However, an increase in the number of lamps causes an increase in power consumption, which is not preferable. .
[0005]
Therefore, an object of the present invention is to provide a new technical means for alleviating a lamp image while preventing a decrease in luminance.
[0006]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a light emitting device in which a lamp is arranged behind a light emitting surface, wherein a light from the lamp is scattered to an extent that a lamp image remains so as to blur the lamp image, and a blurred lamp. And a lens unit for increasing the number of images in the surface direction by using a lens.
[0007]
In the present invention, although the lamp image remains, the light from the lamp is appropriately scattered by the blurring portion made of a diffusion film or the like, thereby changing the brightness of the lamp image. Then, when the number of lamp images whose brightness is blurred increases in a plane direction by a lens such as a lens film, a larger number of lamp images than the actual number of lamps appear on the light emitting surface. Therefore, an effect of eliminating a lamp image as in the case where the number of lamps is increased is obtained. In addition, since the lamp image is divided into a plurality of parts while the boundary between light and dark is blurred by the other part, the light emitting surface is easily made uniform.
[0008]
Note that the conventional lens film is used for condensing light on the diffusion plate, not for increasing the number of lamp images as described above. Under the combination of the diffuser and the lens film, the light from the lamp enters the lens film in a state where the diffuser has sufficiently diffused the lamp image. At this time, although the diffusion plate eliminates the lamp image, since the light is diffused in all directions, the front luminance when the light emitting surface is viewed from the front is low. The lens film focuses the diffused light in the front direction to increase the front luminance.
[0009]
On the other hand, a lens film can be used as the lens of the present invention, but the light entering the lens film as the lens of the present invention is such that the lamp image is blurred, and the linearity of the light from the lamp is maintained. It has been found that when such light passes through a lens film, the lamp image appears to be divided into a plurality.
[0010]
According to a second aspect of the present invention, in the light-emitting device in which a linear light source is disposed behind the light-emitting surface structure, the light-emitting surface structure includes a first diffusion film through which direct light from the linear light source can enter. A first lens surface portion having a plurality of ridges arranged so as to pass light from the first diffusion film side and extending substantially parallel to the linear light source; And a second diffusion film arranged to allow light to pass therethrough.
[0011]
Since the first diffusion film is in a film state and is thin, unlike a diffusion plate having a thickness of several mm, the lamp image is only blurred and does not eliminate the lamp image. When the light emitted from the first diffusion film passes through the first lens surface, the lamp image is divided by a lens action in a direction orthogonal to the longitudinal direction of the linear light source. The lamp images blurred by the first diffusion film are increased, the interval between the lamp images is reduced, and the uniformity of the light emitting surface is improved as in the case where the number of lamps is increased. Further, the uniformity of light is further improved by blurring the light again by the second diffusion film. It is difficult to eliminate the lamp image with only two diffusion films stacked without a diffusion plate, but by interposing a lens surface between the two diffusion films, the light from the lamp (without the diffusion plate) Thus, the lamp image can be eliminated even if the light is directly incident on the first diffusion film.
[0012]
In the case where the resolution of the lamp image is not sufficient or the light emission quality is to be further improved, the light from the second diffusion film side is disposed so as to pass therethrough, and the protrusions of the first lens surface portion are provided. It is preferable to further include a second lens surface having a plurality of ridges extending substantially in parallel. The second lens surface further increases the number of lamp images in the direction orthogonal to the linear light source, and improves the uniformity of the light emitting surface as in the case where the number of lamps is very large. As described above, by repeating the blurring and the increase of the number of lamp images a plurality of times, the luminous quality can be further improved.
[0013]
According to a third aspect of the present invention, in the light emitting device in which the linear light source is disposed behind the light emitting surface structure, the light emitting surface structure is configured by stacking a plurality of planar members. A blur portion for scattering the light from the linear light source to such an extent that the lamp image remains, and for blurring the lamp image, disposed so that light from the blur portion side passes therethrough, and substantially parallel to the linear light source. A lens surface portion having a plurality of protrusions formed so as to extend to the lens surface, wherein the lens surface portion is formed of a plate-shaped transparent material, which is the thickest among the planar members and ensures rigidity in the light emitting surface structure. Has been characterized. In this case, the light emission quality can be improved by the blurring by the blurring portion and the increase in the number of lamp images by the lens surface portion. Conventionally, the light-emitting surface was rigidized by a diffusion plate having a thickness of several mm, so that the loss of light due to the diffusing agent was large. However, since the rigid member was transparent, it was as thick as several mm. Even though, there is almost no loss due to light absorption, and the luminous efficiency is good.
In addition, it is preferable to employ | adopt a diffusion film as said blurring part.
[0014]
A fourth aspect of the present invention is a lamp image mitigation method in a light emitting device in which a lamp is disposed behind a light emitting surface, wherein light from the lamp is scattered to such an extent that the lamp image remains, and the lamp image is blurred. By increasing the number of lamp images in the plane direction by a lens, the number of lamp images on the light emitting surface is reduced. The light emission quality of the light emitting surface can be improved by increasing the blur and the number of lamp images.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a light emitting device 1 used as a direct type backlight for a liquid crystal display device. The light emitting device 1 is configured such that a lamp 3 is provided in a casing 2 having an opening in which a light emitting surface is formed, and a light emitting surface structure 4 is arranged in the opening. Light emitted from the light emitting surface structure is applied to a liquid crystal panel (not shown).
Note that, for a direct-type backlight for a liquid crystal display device, a reduction in thickness and an increase in luminance are required.
[0016]
The casing 2 is formed in a box shape with an upper opening, with side surfaces 2b standing from each side of a rectangular bottom surface 2a. A reflection film 5 is laid on the inner surface of the casing 2, and a reflection surface for reflecting light from the lamp 3 toward the light emitting surface structure 4 is formed.
The lamp 3 is configured as a linear light source, specifically, a cold cathode tube lamp. A plurality of lamps 3 are arranged in the casing 2, and the lamps 3 are arranged in parallel with each other. In FIG. 1, the longitudinal direction of the lamp 3 is a direction orthogonal to the paper surface.
[0017]
The light emitting surface structure 4 is configured by stacking a plurality of planar members 11, 12, 13, and 14. The transparent plate 12 is provided as the thickest member among the planar members. The thickness of the transparent plate 12 is about 1 to 3 mm, preferably about 2 mm. The planar members 11, 13, and 14 other than the transparent plate 12 are all in the form of a film, and specifically have a thickness of 0.25 mm or less. Although the film-like planar members 11, 13, and 14 do not have such rigidity that the light-emitting surface structure 4 located at the opening of the casing 2 can be prevented from being bent, the thickest transparent plate 12 is similar to the conventional diffuser plate. It is responsible for securing rigidity for preventing bending as a light emitting surface. The transparent plate 12 is preferably made of a resin having high transparency and maintaining a stable shape under high temperature (about 80 ° C.), such as acrylic, polycarbonate, or cycloolefin polymer (commercial surface: manufactured by Zeonor Nippon Zeon Co., Ltd.). . Further, the transparent plate 12 may be made of glass.
[0018]
The transparent plate 12 has a certain thickness, but since it is transparent, there is almost no loss of light even when light passes through the inside. On the other hand, the diffusion plate, which has conventionally been responsible for securing rigidity, is milky white and has a large loss due to light absorption of a diffusing agent or the like. Loss can be prevented.
[0019]
The transparent plate 12 has a first lens portion formed on a light exit surface 12b opposite to the light entrance surface 12a on the lamp 3 side. In the first lens portion 12b, a plurality of protrusions having a triangular or semicircular cross section are formed substantially parallel to the longitudinal direction of the lamp 3 on the light emitting surface. As described above, the transparent plate 12 is configured as a lens surface that is a planar member having a lens. FIG. 1 illustrates a triangular shape (prism) as the cross-sectional shape of the ridge. The first lens portion 12b may be formed integrally with the transparent plate 12, or a lens portion (lens film) separately formed on the transparent plate 12 having no lens may be joined by a UV curing resin or the like. .
[0020]
The lens unit 12b divides the lamp image on the light emitting surface into a plurality in the surface direction. The lamp image is divided in a direction D orthogonal to the longitudinal direction of the ridge of the lens portion 12b. Since the protrusions of the first lens portion 12b are oriented in the same direction as the longitudinal direction of the linear lamp 3, the linear lamp images corresponding to the respective lamps 3 are two in the direction D orthogonal to the lamp longitudinal direction. Split. Therefore, similarly to the case where the number of the lamps 3 is doubled to reduce the distance L1 between the lamps, the number is doubled and the distance between the lamp images is reduced.
[0021]
FIG. 3 illustrates the principle (estimated) of increasing the number of lamp images together with FIG. At the position B in FIG. 2 (directly above the lamp), as shown in FIG. 3B, the light that directly reaches the lens portion 12b from the lamp 3 is substantially orthogonal to the surface of the lens portion 12b. Such light is difficult to emit due to double reflection by a ridge (prism). On the other hand, at positions A and C which are displaced in the direction D from the position B directly above the lamp, as shown in FIGS. 3 (a) and 3 (c), the light is raised in the front direction by refraction by a ridge (prism) and emits light. As a result, a lamp image appears at the positions A and C, and light from one lamp 3 appears as two lamp images. Further, since the lamp images are separated, the brightness of each lamp image is reduced, and the difference in brightness on the light emitting surface is reduced.
[0022]
In a conventional direct-type backlight, a lens film is sometimes used as a lens.However, a lens film in a conventional direct-type backlight is also called a brightness enhancement film, and light diffused by a diffusion plate is directed to the front. It is used to increase the luminance in the front direction by condensing light in the direction (normal direction of the diffusion plate), but not to separate the lamp images. That is, conventionally, before the light enters the lens film, the light is made uniform by diffusion by a diffusion plate or the like. For this reason, diffused light is generated not only at the positions A, B, and C in FIG. 2 but also over the entire light emitting surface. In the lens film, the light diffused in all directions was condensed in the front direction by the refraction of the lens film (refraction in FIGS. 3A and 3B). For this reason, although the lens film has a light collecting function, it did not function to separate the lamp images. On the other hand, in the direct backlight of the present embodiment, the lamp image remains and light enters the lens portion 12b while the linearity of the light from the lamp 3 is maintained. Therefore, the lens portion 12b separates the lamp image. It is thought to work.
[0023]
The first diffusion film 11 is disposed on the light incident surface 12a side of the transparent plate 12. The first diffusion film 11 is one in which the light from the lamp 3 enters first among the planar members 11, 12, 13, 14 constituting the light emitting surface structure 4, and is disposed closest to the lamp 3. ing. In the first diffusion film 11, the direct light from the lamp 3 is diffused and scattered to some extent, and the brightness of the lamp image is blurred. That is, the first diffusion film 11 functions as a blurring portion. However, the diffusion film does not have a strong diffusion action enough to eliminate the lamp image like a thick diffusion plate because the diffusion film is very thin, and the lamp image remains.
The first diffusion film 11 preferably has a high haze value, and more specifically, has a haze value of 80% or more. Examples of such a diffusion film 11 include BS-04 manufactured by Keiwa Co., Ltd., # 100-KBS2 manufactured by the company, 100GM2 manufactured by Kimoto Corporation, 188GM2 manufactured by the company, D117UEY manufactured by Tsujiden Co., Ltd., or The company's D120 etc. can be adopted.
[0024]
Further, in order to reinforce the blur caused by the first diffusion film 11, fine irregularities (grain) are formed on the light incident surface 12a of the transparent plate 12, and the lamp image is also blurred by the irregularities. The texture of the transparent plate 12 can be formed by forming fine irregularities by sandblasting or the like in a range corresponding to the light incident surface 12a of the molding die that forms the transparent plate 12. In addition, as the blurring portion provided on the transparent plate 12, in addition to the unevenness, printing of white dots on the light incident surface 12a, application of diffusion beads, adhesion of a member having a diffusion action, and the like can be adopted. In addition, only the one provided on the light entrance surface 12a of the transparent plate 12 may be adopted as the blurring part, and the first diffusion film may be omitted.
[0025]
Light enters the first lens unit 12b in a state where the difference in brightness of the lamp image is blurred by the blurring unit. The first lens unit 12b simply divides the lamp image into a plurality of blurred lamp images. The light emitting surface can be made more uniform than by separating.
In addition, a transparent layer of the transparent plate 12 is interposed between the blurring portion 11 and the first lens portion 12b, and light scattered by the blurring portion 11 reaches the first lens portion 12 due to the presence of this transparent layer. By this time, a positional shift in the plane direction occurs, and the degree of blur can be increased.
[0026]
When the lamp image is weak, such as when the distance between the plurality of lamps 3 is relatively small, or when the distance from the lamp 3 to the light emitting surface structure 4 is relatively large, the first diffusion plate 11 is used. And the transparent plate 12 provide good light emission quality. However, in the present embodiment, while keeping the distance L1 between the lamps 3 relatively large (about 25 mm), the distance L2 between the bottom of the reflecting surface 5 and the light emitting surface structure 4 is made relatively small (about 10 mm). Therefore, since a lamp image appears strongly, a good light emission quality is obtained by the second blurring portion and the second lens portion described later.
[0027]
Specifically, a second diffusion film 13 is disposed on the light exit surface 12b side of the transparent plate 12. Light emitted from the first lens unit 12b enters the second diffusion film 13. Like the first diffusion film 14, the second diffusion film 13 also functions as a portion for blurring the brightness of the lamp image. The provision of the second diffusion film 13 promotes uniform light. The second diffusion film 13 preferably has a high haze value, more specifically, a haze value of 80% or more. Examples of the diffusion film 13 include BS-04 manufactured by Keiwa Co., Ltd., # 100-KBS2 manufactured by the company, 100GM2 manufactured by Kimoto Co., Ltd., 188GM2 manufactured by the company, D117UEY manufactured by Tsujiden Co., Ltd., or The company's D120 etc. can be adopted.
[0028]
On the second diffusion film 13, a lens film (prism film) 14 is further disposed. Light emitted from the second diffusion film 13 enters the lens film 14. In the present embodiment, the second diffusion film 13 is the last one of the light emitting surface structures 4 as a planar member for light uniformity. The lens film 14 is disposed such that the surface on which the lens is formed is the light emitting side (the upper side in FIG. 1). The lens film 14 has a plurality of ridges having a triangular or semicircular cross section formed substantially parallel to the longitudinal direction of the lamp 3 and the ridge of the first lens portion 12b. As described above, the lens film 14 is configured as a second lens surface portion (second lens portion) that is a planar member having a lens. As the lens film 14 as the second lens portion, for example, BEFII90 / 50 manufactured by 3M or BEFII90 / 50 manufactured by the company can be adopted.
[0029]
The second diffusion film 13, which is the second blurring part, and the second lens film 14, which is the second lens part, perform the same functions as the first diffusion film 11 and the first lens part 12b, respectively. In other words, the lamp image is blurred by the second blur unit 13, and the blurred lamp image is divided into a plurality by the second lens unit 14. As a result, the number of lamp images is much larger than the actual number of lamps 3, and a part or all of the individual lamp images overlap with other lamp images, so that uniform brightness is obtained. can get. As described above, by dividing the lamp image by the lens unit a plurality of times, the number of the lamp images can be increased, and the light emission quality can be easily improved. Moreover, simply increasing the number of lamp images leaves a strong difference in brightness, which may require a strong diffusing action such as that of a diffuser.However, it is necessary to divide the lamp image and blur the lamp image. Are combined, the number of lamp images increases in a state where the difference in brightness is reduced, and a uniform light emitting surface can be easily obtained.
[0030]
The above-mentioned planar members 11, 12, 13, and 14 shown in FIG. 1 are for uniformizing light, but as the light emitting surface structure 4, the second lens film 14 (second lens If the film 14 is not provided, another optical film may be included for the purpose of protecting the first lens portion 12b) or widening the viewing angle. For the purpose of protecting the lens, for example, a diffusion sheet having a low haze (for example, PSS-010 manufactured by Keiwa Co., Ltd., # 100-BMU4S manufactured by the company) can be adopted as the protection film. When widening the viewing angle, a diffusion sheet having a higher haze (30% to 50% haze value) than the protective film (for example, # 100-BMU4S from Keiwa Co., Ltd., PBS-060 manufactured by the company, Kimoto Co., Ltd.) 125TL4).
[0031]
【Example】
In the direct-type backlight shown in FIG. 1, the casing 2 is made of aluminum having a thickness of 1.0 mm, the lamp 3 is a cold-cathode tube lamp having a diameter of 3 mm, the reflection film 5 is made of E60V manufactured by Toray, and the first diffusion film 11 is made of Keiwa Corporation. ) BS-04, transparent plate 12 is an acrylic transparent plate having a thickness of 2 mm, light-entering surface 12a of transparent plate 12 is uneven by sandblasting, and light-exiting surface 12b of transparent plate 12 has a vertical angle of 100 ° with a triangular ridge. The prism surface having a width (length of the base of the triangle) of each protrusion of 70 μm, the second diffusion film 13 is BS-04 manufactured by Keiwa Co., Ltd., and the lens film 14 is BEFII 90/50 manufactured by 3M, between lamps. The distance L1 was 25 mm, the distance L2 between the light emitting surface structure 4 (first diffusion film 11) and the reflecting surface 5 was 10 mm, and the light emitting quality of the light emitting surface obtained by the light emitting surface structure 4 was visually observed. Guessed, the luminance was measured.
[0032]
If L2 is reduced to about 10 mm in a direct type backlight using a conventional diffusion plate, it is difficult to eliminate the lamp image, and if L2 is not increased to about 16 mm, good luminous quality cannot be obtained. Good light emission quality was obtained even when L2 was reduced to 10 mm. That is, it was confirmed that the light uniformity was high. In addition, since there was no diffuser plate and no lighting curtain, light loss was small, and since L2 was reduced, a high luminance of 7500 cd / m ² was obtained.
As described above, in this example, a reduction in thickness, good light emission quality, and high luminance were achieved.
[0033]
Note that the present invention is not limited to the above example, and various modifications are possible. For example, when the light emitting surface structure does not require rigidity, a lens film may be used instead of the transparent plate 12. In this case, a light emitting surface structure as thin as about 1 mm can be formed, and a strong light homogenizing action can be exhibited even if it is thin.
Further, the light emitting device of the present invention can be employed not only for a liquid crystal display device but also for a Schaukasten or a light emitting signboard.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a light emitting device according to an embodiment.
FIG. 2 is an explanatory diagram of a light splitting action by a lens.
3A is a diagram illustrating refraction of light at a position A in FIG. 2, FIG. 3B is a diagram illustrating double reflection of light at a position B in FIG. 2, and FIG. FIG. 3 is a diagram showing refraction of light at a position C in FIG.
[Explanation of symbols]
1 light emitting device 3 lamp (linear light source)
4 light emitting surface structure 11 first diffusion film (first blurring part)
12 Transparent plate (first lens surface)
12b first lens unit 13 second diffusion film (second blurring unit)
14 Lens film (second lens part; second lens surface part)

Claims (6)

In a light emitting device in which a lamp is arranged behind a light emitting surface,
A blur section for scattering the light from the lamp to the extent that the lamp image remains to blur the lamp image,
A lens unit for increasing the number of blurred lamp images in the surface direction by a lens,
A light emitting device comprising: In a light emitting device in which a linear light source is arranged behind a light emitting surface structure,
The light emitting surface structure,
A first diffusion film to which direct light from a linear light source can enter;
A first lens surface portion having a plurality of ridges formed so as to pass light from the first diffusion film side and extending substantially parallel to the linear light source;
A second diffusion film disposed so that light from the lens surface passes therethrough. A second lens surface portion having a plurality of ridges arranged so as to pass light from the second diffusion film side and extending substantially parallel to the ridges of the first lens surface portion; The light emitting device according to claim 2, wherein In a light emitting device in which a linear light source is arranged behind a light emitting surface structure,
The light emitting surface structure is configured by stacking a plurality of planar members,
As the planar member,
A blur section for scattering the light from the linear light source so that the lamp image remains to blur the lamp image;
A lens surface portion having a plurality of ridges arranged so that light from the blur portion side passes therethrough and extending substantially parallel to the linear light source,
Including
The lens surface portion is the thickest among the planar members, and is formed of a plate-shaped transparent material that ensures rigidity in the light emitting surface structure.
A light-emitting device characterized by the above-mentioned. The light emitting device according to claim 1, wherein the blurring portion is a diffusion film. A lamp image mitigation method in a light emitting device in which a lamp is disposed behind a light emitting surface,
The light from the lamp is scattered to the extent that the lamp image remains, blurring the lamp image,
A lamp image mitigation method, wherein the number of blurred lamp images is increased in a plane direction by a lens, so as to alleviate the lamp image on the light emitting surface.

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