JP2001281459A - Back light device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a back light device of a liquid crystal panel by which a plurality of viewing angle characteristics are acquired. SOLUTION: The back light device is composed of the first light guide plate 48 with a wedge-shaped cross section, the first light source 34 placed at the rear end side of the first light guide plate 48, the first diffuse reflection layer 36 to diffuse and reflect the light of the first light source 34, the second light guide plate 46 whose cross section is formed in a wedge shape and which is placed under the first light guide plate 34, the second light source 46 placed at the rear end side of the second light guide plate 40, the second diffuse reflection layer 38 to diffuse and reflect the light of the second light source 46, a reflecting sheet 42 placed under the second light guide plate 40, which reflects the light of the second light source 46 and an angle changing member 58 which is placed between the first light guide plate 48 and the liquid crystal panel 50, and adjusts an emission angle of light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device for illuminating a liquid crystal panel, and more particularly to a backlight device capable of switching viewing angle characteristics.

[0002]

2. Description of the Related Art Since a liquid crystal display panel is a non-light emitting element, it is necessary to illuminate it in places where external light conditions are poor. A liquid crystal panel used for an OA terminal or the like often includes a surface light source (so-called backlight) for uniformly illuminating the liquid crystal panel from the rear in order to perform clear display. In particular, a full-color liquid crystal panel such as a portable color television requires a thin, white backlight.

FIG. 4 is a sectional view showing a conventional backlight device. As shown in FIG. 4, a fluorescent tube 12 as a light source is installed at an end of the light guide plate 16, and is covered with a fluorescent tube cover 10. A reflection layer 18 and a reflection sheet 20 are provided below the light guide plate 16. The optical sheets 22, 24 and the liquid crystal panel 26 are arranged above the light guide plate 16. These are covered with a cover 28 of the liquid crystal display device constituting the metal bezel.

[0004] Light is emitted from the fluorescent tube 12 and is emitted from the light guide plate 16.
Propagation to the far inside. The internal propagation light 14 is not emitted toward the liquid crystal panel 26 if the front and back surfaces of the light guide plate 16 are parallel and flat. However, since the light guide plate 16 is provided with the reflective layer 18 having irregularities formed on the back surface, most of the light propagating in the light guide plate 16 is
The light that is scattered by the reflection layer 18 and becomes scattered light, and light that exceeds the critical angle of the light guide plate 16 is emitted as emitted light to the upper liquid crystal panel 26. In addition, the remaining light propagating through the light guide plate 16 becomes light that repeatedly exceeds the critical angle of the light guide plate 16 by repeating internal propagation and exits toward the liquid crystal panel 26 because the light guide plate 16 has a wedge shape. Is done.

As described above, since the reflection layer 18 is formed of irregularities and white dots whose area increases as the distance from the fluorescent tube increases, the propagation light 14 is scattered or deflected and emitted light. And the light is emitted to the liquid crystal panel 26 side. Light emitted to the liquid crystal panel 26 side is reflected by the reflection layer 1.
By adjusting the area of the unevenness and the white halftone dot 8 according to the distance from the fluorescent tube 12, the balance between the above two types of emitted light is adjusted to a desired emission angle.

[0006]

The characteristics required for a backlight device of a liquid crystal panel include a thin shape, a small light leakage, a light weight, and a high illuminance. Furthermore, in recent years, a function that can arbitrarily change the viewing angle of a liquid crystal panel has been required. First, users who use the liquid crystal panel are more likely to use the liquid crystal panel in an environment other than the office, so that only the person operating the liquid crystal panel can see the liquid crystal panel without being seen by the surrounding people. This is because there is a request to do so.

Second, contrary to the first requirement, there is a demand to increase the viewing angle so that people around the person operating the liquid crystal panel can view the liquid crystal panel. . In other words, there is a demand for a backlight device that can switch the function of allowing a person around the person operating the liquid crystal panel to see or not see the liquid crystal screen. However, the conventional liquid crystal panel backlight device does not have a function of changing the viewing angle, and thus has a problem in that substantially only one designed viewing angle can be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a backlight of a liquid crystal panel capable of obtaining a plurality of viewing angle characteristics.

[0009]

The above object is achieved by a backlight device for illuminating a liquid crystal panel, wherein a first light guide plate having a wedge-shaped cross section and a first light guide plate disposed at an end of the first light guide plate are provided. A light source, a first diffuse reflection layer on the surface of the first light guide plate for diffusing and reflecting light from the first light source, and a cross section arranged below the first light guide plate. A wedge-shaped second light guide plate, a second light source disposed at an end of the second light guide plate, and a light diffuser for diffusing light from the second light source on the surface of the second light guide plate A second diffuse reflection layer for reflecting light, a reflection sheet laminated on the second light guide plate and reflecting light from the first light guide plate and the second light guide plate, and the first light guide plate And the liquid crystal panel, the light emitted from the first light guide plate and the light emitted from the second light guide plate. Having a bending member for varying the angular light emitted solved by the backlight device according to claim.

In the backlight device according to the first or second aspect, light emitted from one light guide plate has a principal ray angle in a substantially vertical direction, and light emitted from the other light guide plate is emitted from the one light guide plate. Is preferably different from the principal ray angle from the light guide plate. Further, in the backlight device according to claim 1 or 2, the light emitted from one of the light guide plates has a substantially vertical principal ray angle, and the emission angle distribution of the light emitted from the other light guide plate has an angle. On the other hand, the characteristic may have no peak.

Further, in the backlight device according to the first or second aspect, it is preferable that the variable angle member has an uneven shape on a surface facing the first light guide plate. Furthermore, in the backlight device described in claim 1 or claim 2, the plurality of light sources used may have different emission colors. In the present invention, the first light emitted from the first light source is propagated by the first light guide plate, and the first light is scattered by the first diffuse reflection layer and emitted to the liquid crystal panel side. . Further, the second light emitted from the second light source is propagated by the second light guide plate, the second light is scattered by the second diffuse reflection layer, and the liquid crystal is transmitted through the first light guide plate. The light is emitted to the panel side. In this case, the exit angle (principal ray angle) to the liquid crystal panel side can be adjusted by the deflection member.

For example, by making the chief ray angle of light emitted from the first light guide plate to the liquid crystal panel side and the chief ray angle of light emitted from the second light guide plate to the liquid crystal panel different from each other, The viewing angle characteristic can be changed when only the first light source is turned on, when only the second light source is turned on, or when both the first and second light sources are turned on. The angular distribution of light emitted from the first light guide plate toward the liquid crystal panel and the angular distribution of light emitted from the second light guide plate toward the liquid crystal panel may be different from each other. It is good also as a characteristic which has an angle and the other does not have a peak with respect to an angle.

In this manner, by selectively turning on or off the first light source and the second light source, visibility can be improved only for a person in a predetermined direction according to the situation. it can.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a backlight device for a liquid crystal panel according to an embodiment of the present invention. As shown in FIG. 1, a backlight device for a liquid crystal panel according to an embodiment of the present invention first includes a first fluorescent tube cover 32.
A first elongated fluorescent tube 34 covered with
The first light guide plate 48 disposed on a plane parallel to the longitudinal direction of the first light guide plate 4
A first backlight unit 33 including a first light-guiding plate 48 and a first diffuse reflection layer 36 in which irregularities are formed on the lower surface of the first light guide plate 48 is disposed.

An elongated second fluorescent tube 46 covered with a second fluorescent tube cover 44 is provided below the first backlight unit 33 so as to be symmetrical with the first backlight unit 33. A second light guide plate 40 connected to a surface parallel to the longitudinal direction of the second fluorescent tube 46, and a second light guide plate 4;
And a second diffuse reflection layer 38 having irregularities formed on the upper surface of the second backlight unit 35.
Is arranged. Light guide plates 48 and 40 and diffuse reflection layer 3
6 and 38 are made of a transparent acrylic plate,
The unevenness in 6, 38 is formed, for example, by molding an acrylic plate.

A reflection sheet 42 for reflecting light is disposed below the second backlight unit 35. Above the first light guide plate 48, a variable angle member 58 for adjusting the light emission angle is arranged. A prism-shaped unevenness is formed on the lower surface of the variable angle member 58 as described later, and the first fluorescent tube 34 and the second fluorescent tube 46 are formed.
From the liquid crystal panel 50 can be adjusted. In the present embodiment, it is assumed that the prism-shaped irregularities are formed in parallel with the longitudinal direction of the first fluorescent tube 34, but are arranged obliquely with respect to the longitudinal direction of the first fluorescent tube 34. May be formed.

The backlight device according to the embodiment of the present invention has the above-described configuration, and transmits light emitted from the first fluorescent tube 34 and light emitted from the second fluorescent tube 46 to the liquid crystal panel 50. Since the light can be emitted at different emission angles, the viewing angle characteristics can be changed by appropriately turning on or off the fluorescent tubes 34 and 46. The backlight device according to the present embodiment includes a first backlight unit 3
3 and a second backlight unit 35. In a preferred embodiment, the backlight device may be configured by arranging two or more first backlight units 33 and second backlight units 35, respectively.

The color of the light emitted from the first fluorescent tube 34 and the second fluorescent tube 46 is not limited to white, but may be, for example, a combination of red, blue, green, and the like. The light emitted from the first fluorescent tube 34 and the light emitted from the second fluorescent tube 46 may be used differently. Hereinafter, propagation of light emitted from the first backlight unit 33 will be described. The internal propagation light 52 generated by turning on the first fluorescent tube 34 propagates through the first light guide plate 48 and reaches the right end. On the lower side of the first light guide plate 48, there is provided a diffuse reflection layer 36 on which irregularities having a height of several tens of μm are formed. For this reason, a part of the propagation light 52 in the first light guide plate 48 becomes scattered light, and the scattered light exceeding the critical angle of the first light guide plate 48 is emitted radially toward the liquid crystal panel 50. Outgoing light 54 which is the first outgoing light A.

The cross section of the first light guide plate 48 (the cross section in the direction perpendicular to the first fluorescent tube 34) increases as the distance from the first light source 34 increases. (A cross-sectional area in a parallel direction). Therefore, the light that repeats the internal propagation gradually approaches the critical angle, eventually exceeds the critical angle, and is the emission light 55 that is the first emission light B emitted toward the liquid crystal panel 50. Becomes These emitted lights 54 and 55 reach the liquid crystal panel 50 through the variable angle member 58.

On the other hand, light generated by turning on the second fluorescent tube 46 and propagating through the second light guide plate 40 is reflected by, for example, the reflection sheet 42, and is reflected by the second diffuse reflection layer 38 and the first diffusion layer. The light is diffusely reflected by the reflection layer 36, further passes through the first light guide plate 48, and reaches the liquid crystal panel 50 through the variable angle member 58. In FIG. 2, the horizontal axis represents the viewing angle (the vertical direction to the panel surface is 0 °), and the vertical axis represents the brightness. When only one fluorescent tube is turned on (wide viewing angle lighting), the other fluorescent tube is turned on. FIG. 7 is a diagram illustrating emission angle characteristics when only the fluorescent lamps are turned on (narrow viewing angle lighting) and when both fluorescent tubes are turned on (both lightings). As shown in FIG. 2, when only one fluorescent tube is turned on, the emission angle distribution becomes substantially flat (that is, has no peak with respect to the angle), and when only the other fluorescent tube is turned on, The visibility on the right side from the front of the panel increases. Also,
When both fluorescent lamps are turned on, the brightness is increased as a whole, and the visibility is improved as a whole.

The emission angle characteristics can be changed by changing the shape of the light guide plates 40 and 48 and the shape of the variable angle member 58. For example, the light emitted from one light guide plate may have a substantially vertical principal ray angle, and the light emitted from the other light guide plate may be different from the principal ray angle from the one light guide plate. Further, the light emitted from one light guide plate may have a principal ray angle in a substantially vertical direction, and the emission angle distribution of the light emitted from the other light guide plate may have no peak with respect to the angle.

FIG. 3A shows the bending member 58 of the present embodiment.
FIG. 4 is a schematic diagram showing the prism shape of FIG. The variable angle member 58 is the first light guide plate 4
A transparent acrylic plate whose surface is formed in the shape of a prism on the eight side. The prism shape is as shown in FIG.
For example, it is formed with irregularities having angles of θa = 60 ° and θb = 30 °. The outgoing light 55 that has propagated from the first fluorescent tube 34 through the first light guide plate 48 and then entered the prism shape of the deflecting member 58 enters the inclined surface 62 and then exits from the outgoing surface 6.
The light 6 is reflected on the inclined surface 64, is converted into a desired angle, for example, 60 ° with respect to the vertical axis of the liquid crystal panel 50, and is emitted as emission light 70.

In this manner, not only the person who operates the liquid crystal panel 50 but also the person on the left side when viewed from the front of the liquid crystal panel 50 has good visibility characteristics.
Of the person on the right side when viewed from the front can be degraded. In the present embodiment, the direction (principal ray angle) of the emitted light is changed by appropriately setting the prism shape angle of the variable angle member 58. Therefore, the prism shape of the variable angle member 58 is not limited to the above example.

Next, a method for improving the visibility characteristics of a person who operates the liquid crystal panel 50 from the front and persons on the left and right sides thereof will be described. The path of light that propagates from the second fluorescent tube 46 to the liquid crystal panel 50 through the second light guide plate 40 is transmitted from the first fluorescent tube 34 to the liquid crystal panel 50 through the first light guide plate 48. It is different from that emitted to 50.

FIG. 3B is a schematic diagram showing the reflection of light that propagates from the second fluorescent tube 46 through the second light guide plate 40 and exits to the variable angle member 58. The second light guide plate 40 has a wedge-shaped cross section, and on the upper side, as in the case of the first light guide plate 48, unevenness having a height of several tens of μm is formed. Therefore, light propagating through the second light guide plate 40 is reflected by the second diffuse reflection layer 38 toward the reflection sheet 42, and further reflected by the reflection sheet 42 toward the liquid crystal panel 50. Then, as shown in FIG. 3 (b), the out-going light 55 emitted from the opposite direction to the outgoing light 55
8 is incident.

As shown in FIG. 3B, the outgoing light 59 is incident on the inclined surface 64 (inclination angle θ _b = 30 °) of the variable angle member 58, and after passing through the inclined surface 64, the outgoing light 59 66
At the inclined surface 62. That is, with this mechanism, the emitted light emitted from the second fluorescent tube 46 and emitted to the liquid crystal panel 50 cannot be obtained. However, actually, the light that has propagated through the second light guide plate 40 and has been reflected by the reflection sheet 42 is not reflected by the first light guide plate 4.
8, the light is scattered by the uneven shape of the first diffuse reflection layer 36 formed below the first light guide plate 48. Due to the scattering of the light due to the uneven shape, the light is emitted to the variable angle member 58 at an output angle at which the angle of the light is hardly converted by the variable angle member 58 like the output light 57 in FIG.

That is, the light emitted from the second fluorescent tube 46 is not substantially converted in angle by the variable angle member 58, and is emitted to the liquid crystal panel 50 with a predetermined inclination. 57. Therefore, when only the second fluorescent tube 46 is turned on, the liquid crystal panel 50 is viewed from the front,
This can be achieved mainly by improving the visibility characteristics of a person on the right side.

When only the first fluorescent tube 34 is turned on, the emitted light 54 and the liquid crystal panel 50 that improve the visibility characteristics of a person who operates the liquid crystal panel 50 from the front are viewed from the front, and the left side is viewed from the front. Outgoing light 70 with good characteristics is obtained. Therefore, by illuminating both the first fluorescent tube 34 and the second fluorescent tube 46, the emitted light 54, 70, 57 can be obtained. Can have good visual recognition characteristics.

In the present embodiment, as described above, the angle of the prism shape of the deflecting member 58 is changed to change the light emitted from the first fluorescent tube 34 into the liquid crystal panel 5.
The exit angle (principal ray angle) and the exit angle distribution to the 0 side, the exit angle (principal ray angle) of the light emitted from the second fluorescent tube 46 to the liquid crystal panel 50 side, and the exit angle distribution can be set. it can. Thereby, when only the first fluorescent tube 34 is turned on, when only the second fluorescent tube 46 is turned on, and when both the first fluorescent tube 34 and the second fluorescent tube 46 are turned on, they are different from each other. The effect that viewing angle characteristics can be obtained can be obtained.

The present invention may be embodied in various other forms without departing from its spirit or essential characteristics. Therefore, the above-described embodiment is merely an example in all aspects, and should not be interpreted in a limited manner. The scope of the present invention is defined by the claims, and is not limited by the embodiments.

[0031]

As described above, the backlight device of the present invention is composed of the first and second light sources, the first and second light guide plates, and the deflecting member. The viewing angle characteristic changes when only one light source is turned on, when only the second light source is turned on, and when both light sources are turned on. Further, the principal ray angle of the emitted light can be changed according to the shape of the variable angle member. Thus, for example, visibility can be improved only for a person in a desired direction, and visibility for a person in another direction can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a backlight device according to an embodiment of the present invention.

FIG. 2 illustrates a case where only a first light source is turned on (wide viewing angle lighting) and a case where only a second light source is turned on (narrow viewing angle lighting).
FIG. 6 is a diagram illustrating emission angle characteristics when both are lit (both lit).

FIG. 3A is a schematic diagram showing a cross-sectional shape of a prism of a deflecting member and light reflection of a first fluorescent tube, and FIG. FIG. 3 is a schematic diagram showing light reflection of a fluorescent tube.

FIG. 4 is a sectional view showing a conventional backlight device.

[Explanation of symbols]

 Reference Signs List 10 fluorescent tube cover, 12 fluorescent tube, 16 light guide plate, 18 reflective layer, 20, 42 reflective sheet, 22, 24 optical sheet, 26, 50 liquid crystal panel, 28 liquid crystal display device cover, 32 first fluorescent tube cover, 33 first backlight unit, 34 first fluorescent tube, 35 second backlight unit, 36 first diffuse reflection layer, 38 second diffuse reflection layer, 40 second light guide plate, 42 reflection sheet, 44 second fluorescent tube cover, 46 second fluorescent tube, 48 first light guide plate, 26, 52 internal propagating light, 54, 55, 59, 70 outgoing light, 62, 64 inclined surface, 66 outgoing surface.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G09F 9/00 336 F21Y 103: 00 // F21Y 103: 00 G02F 1/1335 530 F term (reference) 2H038 AA55 BA06 2H091 FA14Z FA16Z FA23Z FA31Z FA42Z GA11 LA19 5G435 AA01 BB12 EE27 FF03 FF06 FF08 GG24 GG26

Claims (4)

[Claims] 1. A backlight device for illuminating a liquid crystal panel, comprising: a first light guide plate having a wedge-shaped cross section; a first light source disposed at an end of the first light guide plate; A first diffuse reflection layer on the surface of the light guide plate for diffusing and reflecting light from the first light source; a second light guide plate having a wedge-shaped cross section disposed below the first light guide plate; A second light source disposed at an end of the second light guide plate, and a second diffuse reflection layer on the surface of the second light guide plate for diffusing and reflecting light from the second light source; A reflection sheet laminated on the second light guide plate to reflect light from the first light guide plate and the second light guide plate; and a reflection sheet disposed between the first light guide plate and the liquid crystal panel. And
A backlight device, comprising: a deflecting member that deflects light emitted from the first light guide plate and light emitted from the second light guide plate. 2. A first backlight unit including the first light source, the first light guide plate, and the first diffuse reflection layer, the second light source, the second light guide plate, The backlight device according to claim 1, comprising at least one or more second backlight units each including the second diffuse reflection layer. 3. A principal ray angle of light emitted from one of the first light guide plate and the second light guide plate and a principal ray angle of light emitted from the other light guide plate are different from each other. The backlight device according to claim 1 or 2, wherein 4. An emission angle distribution of light emitted from one of the first light guide plate and the second light guide plate, and
The backlight device according to claim 1, wherein an emission angle distribution from the other light guide plate is different.