JP2001006418A - Lighting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting system not causing degradation in luminance near both ends of a light source, and having highly the uniform luminance on output surface of a light guide plate. SOLUTION: In this lighting system, a rough surface 4 having an Ra (a center line average roughness) of 0.3-5.0 μm is formed in an area of a side surface 1B adjacent to a light incident surface 1A of a light guide plate 1, close to a light source. The rough surface 4 scatters of diffusely reflects light incident from the light incident surface 1A advancing inside the light guide plate 1. Instead of the rough surface 4, a large number of small grooves, slit-like deep grooves or a chamfer part can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device used for lighting a display device, an exhibit, a room, and other various lighting devices, and more particularly to a lighting device suitable as a backlight for a liquid crystal display device. About.

[0002]

2. Description of the Related Art In recent years, as a lighting method for a transmissive or transflective liquid crystal display device, there are a direct type in which a light source such as a fluorescent tube is disposed immediately below a back surface of a liquid crystal display panel, and a light guide plate made of transparent plastic. There is known an edge light type in which a planar light-emitting illumination is manufactured using the light-emitting illumination, and the illumination is disposed on the back surface of a display panel. Since the edge light method has the advantages of being thinner and having a higher degree of uniformity of luminance than the direct light method, the surface light emitting device (backlight device) by this method occupies the mainstream of the illumination method of the liquid crystal display device. It is getting.

In such an edge light type backlight device, a light guide plate for guiding light from a light source to a liquid crystal display panel is used to reflect light from a light source to a liquid crystal display panel in order to improve luminous efficiency and improve luminance and to level luminance. On the surface, that is, the main surface opposite to the main surface on the light emission side where the display panel is arranged, a dot pattern arranged in a grid or the like is printed and formed with white ink mixed with titanium oxide or barium sulfide powder. With this dot pattern, light traveling inside the light guide plate is irregularly reflected or scattered.

In recent years, instead of forming a dot pattern for scattering by printing with white ink, the reflection surface itself of the light guide plate is formed as a rough surface having fine irregularities, thereby forming a dot pattern. By uniformly reflecting or scattering light on a surface, the entire surface is uniformly illuminated.

[0005] The reflection surface of the light guide plate is roughened by roughening the corresponding surface of a molding die by a method such as electric discharge machining, etching, or sandblasting.

[0006]

However, in such an illuminating device, as the size of the liquid crystal display panel becomes larger and the frame becomes narrower, as shown in FIG.
The length of a rod-shaped light source (for example, a cold cathode tube, a hot cathode tube, a halogen lamp, or the like) 12 having the following tendency is equal to or shorter than the length of the light incident side end surface (light incident surface) of the light guide plate 13. It is in. Therefore, both ends of the light entrance surface of the light guide plate 13
Because it faces the electrodes 11 at both ends of the light source 12,
On the main surface (light emitting surface) on the light emitting side, there is a problem that the luminance in a region (indicated by a) close to the electrode 11 of the light source 12 decreases, and the uniformity of the emission luminance deteriorates.

In order to improve such a decrease in the brightness uniformity, it is conceivable to increase the size of the scattering dots provided on the reflection surface of the light guide plate near both ends near the electrodes of the light source. In order to change the dot size in a dot pattern in which the reflection surface itself of the light guide plate is roughened, it is necessary to prepare a new mold for forming the light guide plate, and the processing cost and processing time of the die are required. There was a problem that it took.

The present invention has been made to solve these problems, and does not change the dot pattern for scattering provided on the reflection surface of the light guide plate, and does not reduce the brightness near both ends of the light source. It is an object of the present invention to provide a lighting device having high uniformity of surface luminance.

[0009]

According to the present invention, there is provided a lighting device, comprising: a light guide plate; a rod-shaped light source having electrodes at both ends disposed along at least one side surface of the light guide plate; A reflector disposed so as to reflect light from the light source and condense it on the side surface of the light guide plate, wherein a region of the outer peripheral surface of the light guide plate close to the electrode of the light source is provided. Further, a scattering portion for irregularly reflecting or refracting light traveling inside the light guide plate is formed by directly processing the outer peripheral surface.

In the present invention, a rough surface having fine irregularities on the surface can be used as the scattering portion provided on the outer peripheral surface of the light guide plate in a region close to the electrode of the light source. Such a rough surface can be easily formed by roughening a region near the light source on a side surface connected to the light incident surface of the light guide plate by etching, sand blasting, or the like.

Further, a plurality of shallow narrow grooves or slit-like deep grooves are engraved in an area close to the light source or on a top side on a side surface connected to the light incident surface of the light guide plate, and these narrow grooves are formed. It can be a scattering part. Furthermore, a chamfer formed on the top side between the side surface connected to the light entrance surface of the light guide plate and the light exit surface can also sufficiently enhance the effect as a scattering portion.

In order to form these narrow grooves or chamfers, a method of directly processing the outer peripheral surface of the light guide plate by cutting or the like can be adopted. It is also possible to give the above-mentioned processed shape simultaneously with molding. The latter method is preferable in terms of productivity because the number of processing steps can be reduced as compared with the former method.

In the lighting device of the present invention, the light emitted from the light source is introduced into the light guide plate from the light incident side end surface (light incident surface) of the light guide plate, and is brought into close proximity to the electrode of the light source on the outer peripheral surface of the light guide plate. Since the light is diffusely reflected (scattered) or refracted by the scattering portion such as the rough surface formed in the region where the light is transmitted, the amount of scattered light from this region increases, and the amount of light emitted outside the light guide plate decreases.
Therefore, on the main surface (light emitting surface) on the light emission side of the light guide plate, a decrease in luminance near both ends near the electrode of the light source is prevented, and a lighting device with high uniformity of emission luminance can be obtained.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an exploded perspective view showing a schematic structure of a backlight device of a liquid crystal display device, which is a first embodiment of a lighting device of the present invention.

In this figure, reference numeral 1 denotes a light guide plate made of highly transparent plastic such as acrylic resin, methacrylic resin, polycarbonate resin and the like. A rod-like light source 2 having electrodes at both ends, such as a fluorescent tube (cold cathode tube) or a halogen lamp, is provided near one side surface of the light guide plate 1.
A reflector 3 having a parabolic reflection surface is provided outside the light source 2 so as to cover the light source 2. Here, as the reflector 3, a reflector having a reflective layer formed by depositing a metal having high reflectivity such as silver on the inner surface of a plastic sheet such as polyester is used.

On the reflection surface R (the main surface opposite to the light exit surface) of the light guide plate, a scattering pattern (the surface itself is roughened with a predetermined dot pattern) in order to increase luminous efficiency and improve luminance. (Not shown) is formed. The light guide plate 1 may be a flat plate having a constant thickness at each portion. However, in terms of weight reduction and light emission efficiency, the thickness is reduced from the light source side to the opposite side. It is more desirable to use a plate having a wedge-shaped cross section.

As shown in an enlarged view in FIG. 2, a side surface 1B adjacent to an end surface (light incident surface) 1A of the light guide plate 1 on the light incident side.
The rough surface 4 having fine irregularities on the surface is formed in a region near the light source. The surface roughness of the rough surface 4 is _Ra (center line average roughness) of 0.3 to 5.0 μm, and is formed by a roughening process such as etching and sandblasting.

Further, on the light exit surface S side of the light guide plate 1, a diffusion sheet 5 which has been subjected to a surface treatment such as embossing is provided at a predetermined interval in order to make luminance uniform. A prism sheet 6 having a V-shaped groove or a wavy shape and having a light-condensing effect is provided thereon to improve the luminance.

Further, on the reflection surface R side of the light guide plate 1,
In order to prevent leakage of light, reflective sheets 7 made of white polyester or the like are arranged in an overlapping manner. Here, the light guide plate 1
To prevent light leakage on the three sides other than the light entrance surface,
A reflective tape (not shown) made of white polyester or the like can be attached.

In the illuminating device of the first embodiment configured as described above, the region near the light source on the side surface adjacent to the light incident surface of the light guide plate 1 is a rough surface 4 having fine irregularities. Since the rough surface 4 scatters or irregularly reflects light that enters from the light incident surface and travels inside the light guide plate 1, the rough surface 4 is formed from the region near both ends near the electrode of the light source 2 where the rough surface 4 is formed. The amount of scattered light increases, and the amount of light emitted to the outside decreases.
Therefore, a high light emission luminance with a high degree of uniformity is obtained.

Next, another embodiment of the present invention will be described.

In the second embodiment of the present invention, FIG.
(A) and (b), as shown in a magnified view, a large number of areas are located on a side surface (hereinafter referred to as an adjacent side surface) 1B adjacent to the light incident surface 1A of the light guide plate 1 near the light source. Shallow narrow grooves 8 are formed parallel to each other. Note that these narrow grooves 8 may be provided along the thickness direction of the light guide plate 1 as shown in FIG. 3A, or as shown in FIG.
They may be arranged along a horizontal direction orthogonal to the thickness direction.

In the third and fourth embodiments, as shown in FIG. 4 and FIG. 5, respectively, the top side where the light incident surface 1A of the light guide plate 1 contacts the adjacent side surface 1B or the adjacent side surface 1B A plurality of slit-shaped deep grooves 9 are formed at the top side where the light-emitting surface and the light-exiting surface are in contact with each other so as to be orthogonal to the top side.

Further, in the fifth embodiment, as shown in FIG. 6, the top side between the adjacent side surface of the light guide plate 1 and the light emitting surface is
C-face processing is performed over an appropriate length to form a chamfered portion 10. In the embodiments of the second to fifth embodiments, the other parts are configured in the same manner as the first embodiment, so that the description will be omitted.

In the illuminating devices of the second to fifth embodiments configured as described above, a large number of narrow grooves 8, slit-like deep grooves 9, or chamfers are formed in a region near the light source on the outer peripheral surface of the light guide plate 1. The portion 10 is formed by directly processing the outer peripheral surface of the light guide plate 1.
It scatters or refracts light traveling inside. As a result, the amount of scattered light from the region where the narrow groove 8, the slit-shaped deep groove 9 or the chamfered portion 10 is formed increases, and the amount of light emitted to the outside decreases. Therefore, a high light emission luminance with a high degree of uniformity is obtained.

Next, specific examples of the present invention will be described.

Example First, a light guide plate made of methacrylic resin (MG10; manufactured by Sumitomo Chemical Co., Ltd.) was prepared, and the side surface adjacent to the light incident surface was roughened by etching, sand blasting, or the like to obtain a light source side end. The surface roughness _Ra is 2.2μm over a range of 15mm from the part
Rough surface. Then, using this light guide plate, the lighting device shown in FIG. 1 was manufactured. As a comparative example, a lighting device was manufactured in the same manner as in the example, using the light guide plate as it was without performing the surface roughening treatment.

Next, in the lighting devices obtained in the examples and the comparative examples, the luminance near both ends near the light source electrode on the upper surface of the prism sheet was measured using a luminance meter (BM-7) manufactured by Topcon Corporation. Measured. The measurement results are shown in the graph of FIG. In FIG. 7, the horizontal axis represents the distance from the end face on the light source side, and the vertical axis represents the luminance.

From this figure, it can be seen that the illumination device of the embodiment using the light guide plate having a rough surface formed on the adjacent side surface has a light source of a light source as compared with the comparative example using a light guide plate without such a roughening treatment. It can be seen that the luminance near both ends near the electrode is high, and the uniformity of luminance is improved.

[0031]

As is apparent from the above description, in the illuminating device of the present invention, a rough surface having fine irregularities and a large number of fine surfaces are formed in a region near the light source on the side surface adjacent to the light incident surface of the light guide plate. Scattering portions such as grooves are formed by directly processing the outer peripheral surface of the light guide plate, and these scatter or diffusely reflect light introduced from the light incident surface and traveling inside the light guide plate. The amount of scattered light from the region where the scattering portion is formed increases, and the amount of light emitted to the outside decreases. The amount of scattered light from the region near both ends near the electrode increases. Therefore, a lighting device having a high degree of uniformity and a large emission luminance can be obtained.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a schematic configuration of a backlight device of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is an enlarged perspective view showing a main part of the first embodiment.

FIG. 3 is an enlarged view showing a main part of a second embodiment of the present invention;
(A) is a perspective view showing a mode in which a narrow groove is provided along the thickness direction of the light guide plate. (B) is a narrow groove provided in a direction orthogonal to the thickness direction of the light guide plate. The perspective view which shows an aspect.

FIG. 4 is an enlarged perspective view showing a main part of a third embodiment of the present invention.

FIG. 5 is an enlarged perspective view showing a main part of a fourth embodiment of the present invention.

FIG. 6 is an enlarged perspective view showing a main part of a fifth embodiment of the present invention.

FIG. 7 is a graph showing the measurement results of the luminance of the light exit surface of the light guide plate in the lighting devices obtained in the example and the comparative example.

FIG. 8 is a plan view showing a decrease in luminance in a region near an electrode of a light source in a conventional lighting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light guide plate 2 ... Light source 3 ... Reflector 4 ... Rough surface 7 ... Reflective sheet 8 ... Narrow groove 9 ... Slit-shaped deep groove 10 ... Chamfered part

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor: Manabu Kawada 5-14-25 Ryoke, Kawaguchi City, Saitama Prefecture Toshiba Chemical Corporation Kawaguchi Plant F-term (reference) 2H038 AA55 BA06 2H091 FA14Z FA23Z FA31Z FA41Z FC25 FD01 LA18

Claims (4)

[Claims] 1. A light guide plate, a rod-like light source disposed along at least one side surface of the light guide plate and having electrodes at both ends, covering the light source, and reflecting light from the light source to reflect the light from the light source A reflector disposed on the side surface of the light guide plate so as to condense the light, wherein light traveling inside the light guide plate is located in a region near an electrode of the light source on an outer peripheral surface of the light guide plate. A scattering portion for irregularly reflecting or refracting light by directly processing the outer peripheral surface. 2. The lighting device according to claim 1, wherein the scattering portion is a rough surface having fine irregularities on the surface. 3. The lighting device according to claim 1, wherein the scattering unit is a plurality of narrow grooves arranged in parallel with each other. 4. The illumination according to claim 1, wherein the scattering portion is a chamfered portion formed at a top side between the light incident side end surface and the light emitting side main surface of the light guide plate. apparatus.