JP3249896B2 - Backlight structure of liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens sheet having a large number of prisms protruding from one side thereof interposed between a liquid crystal panel and a light guide plate, so that light is incident from the side end face of the light guide plate. The present invention relates to a backlight structure of a liquid crystal display device in which the directivity of light from a light source toward a liquid crystal panel is enhanced to improve brightness, and particularly to an improvement in a lens sheet thereof.

[0002]

2. Description of the Related Art In a liquid crystal display device using a lens sheet of this kind as a component of a backlight, a light source is disposed at a position facing a side end face of a light guide plate, and the light emitted from the light source passes through the light guide plate and passes through the liquid crystal. By refracting the light rays going to the panel by the prism part whose outer surface is an inclined surface, the directivity of the light emitted from the back side to the liquid crystal panel is strengthened and the irradiation light is concentrated within the desired viewing angle range Thus, the brightness of the backlight is improved, and is widely used in color liquid crystal display devices and the like.

FIG. 7 is an explanatory view showing a backlight of a conventional liquid crystal display device having such a lens sheet. A lens sheet 2 is mounted on a transparent light guide plate 1 made of acrylic resin or the like. The lower surface of the light guide plate 1 is covered with a reflection sheet 4 for reflecting light upward. Also,
A light source 5 such as a cold cathode fluorescent lamp (CCFL) is arranged at a position facing one side end surface of the light guide plate 1.
Light entering the light guide plate 1 through the lens sheet 2 is applied to the rear side of the liquid crystal panel (not shown). The lens sheet 2 is a transparent sheet in which one surface is a prism surface and the other surface is a flat surface, and a triangular prism having a cross-sectional shape of an isosceles triangle is laid on the prism surface which is a surface facing the liquid crystal panel. Prism part 3
A large number of parallel inclined surfaces 3a and 3b are provided in parallel with each other, and the outer surfaces of the prism portions 3 have the same inclination and are opposed to each other.
Is formed.

Accordingly, when the light from the light source 5 is incident on the lens sheet 2 via the light guide plate 1, the light is
When the liquid crystal panel crosses the inclined surface 3a or 3b toward the upper liquid crystal panel in the figure, the light is refracted inward by a lens effect, so that light illuminating the liquid crystal panel is required within a specific viewing angle range, for example, for a display screen. It can be concentrated within a range of about ± 20 °, and the brightness of the backlight can be increased within this viewing angle range.

In this type of liquid crystal display device, the longitudinal direction of the light source 5 disposed along the side end face of the light guide plate 1 and the longitudinal direction of the triangular prism portion 3 are set to be parallel. Therefore, in each of the prism portions 3, the light incident surface of one of the inclined surfaces 3a (farther from the light source) faces the light source 5 side.

There is also known a liquid crystal display device in which light sources are arranged in an L-shape along two adjacent side end faces of a light guide plate in order to further improve the brightness of the backlight.

[0007]

By the way, in the above-mentioned backlight of the conventional liquid crystal display device, the light from the light source 5 is reflected by the reflection sheet 4 or the like, so that the light guide plate 1 is formed.
Although the light emitting direction from the lens sheet 2 to the lens sheet 2 is not deviated, actually, of the two inclined surfaces 3a and 3b of each prism portion 3 of the lens sheet 2, the light incident surface is the light source. The other inclined surface 3b is attached to the inclined surface 3a facing the fifth side.
Slightly more light is incident. For this reason, the display screen of such a conventional liquid crystal display device is slightly brighter when viewed obliquely from above the light source 5 (arrow B) than when viewed obliquely from above the light source 5 (arrow B). There were many users who saw it and were worried about the imbalance.

When the light sources are arranged in an L-shape along two adjacent side end faces of the light guide plate, for example, the prism portion 3 of the lens sheet 2 is formed into a quadrangular pyramid shape as shown in FIG. For example, the light emitted from the light source 5 is effectively used by the lens effect of the opposed inclined surfaces 3a and 3b, and the light emitted from the light source 6 is effectively used by the opposed inclined surfaces 3c and 3d. It is necessary to effectively use the lens effect from the viewpoint of improving the brightness, but in this case, there is a problem that the display screen looks dark when viewed along the arrow E direction in FIG. That is, in this case, the inclined surface 3
Due to the difference in the amount of light incident on the surfaces a and 3b, not only does the line of sight look slightly brighter in the direction of arrow A than in the direction of arrow B, but also the line of sight changes due to the difference in the amount of light incident on the inclined surfaces 3c and 3d. Although it looks slightly brighter in the direction of C than in the direction of arrow D, in particular, the line of sight is
In the case of the direction, only the light emitted from the inclined surfaces 3b and 3d with a relatively small amount of incident light is emitted at a large exit angle, so that the darkness of the display screen is conspicuous and display quality is impaired. Will be lost.

In order to correct such a problem that the display screen becomes dark when viewed from a specific direction, a diffusion sheet may be interposed between the lens sheet and the liquid crystal panel. When a diffusion sheet is added, the irradiation light is weakened, the luminance is reduced, and the number of components is increased.

Therefore, an object of the present invention is to improve the brightness and to make the brightness not vary from any direction, which is suitable especially when the light source is arranged in an L-shape.
An object of the present invention is to provide a backlight structure of a liquid crystal display device.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lens sheet having a plurality of prism parts having an inclined outer surface protruding from one side of a transparent sheet. The liquid crystal panel is interposed between the liquid crystal panel and the light guide plate in a state where the liquid crystal panel is opposed to the liquid crystal panel, and the light of the light source disposed opposite to the side end surface of the light guide plate is interposed between the light guide plate and the lens sheet. In the backlight structure of the liquid crystal display device that irradiates the light from the back side, of the inclined surfaces of the prism portion, the inclination of the inclined surface with the light incident surface facing the light source side is another inclined surface facing the inclined surface. to be gentler than the inclination of the surface, and the inclination angle of the inclined surface directing light incident surface to the light source side 25 ° to 45 °, the inclination angle of the other inclined surface facing the said inclined surface 35 It is set to ° ~55 °
Is achieved by

For example, a light source is arranged in an L shape along two adjacent side end surfaces of a light guide plate, and an upright quadrangular pyramid-shaped prism portion is formed on a lens sheet vertically and horizontally along the L shape. When a large number of projections are provided, of the four inclined surfaces forming the outer surface of each prism portion, the inclination of the first inclined surface whose light incident surface is directed to the light source side extending in the vertical direction is opposed to the first inclined surface. While making it more gradual than the inclination of the second inclined surface,
The inclination of the third inclined surface with the light incident surface facing the light source extending in the lateral direction may be made gentler than the inclination of the fourth inclined surface facing the third inclined surface.

[0013]

As described above, among the inclined surfaces forming the outer surface of each prism portion, the first inclined surface (or the third inclined surface) receiving a large amount of light because the light incident surface faces the light source side. )
Of the second inclined surface (or the fourth inclined surface) opposed to the inclined surface and having a relatively small amount of incident light , and the light incident surface on the light source side. Turn
Facing the inclined surface at an angle of inclination of 25 ° to 45 °
If the inclination angle of another inclined surface is set to 35 ° to 55 °, the light emitted from the first inclined surface can be dispersed over a wider range, so that within a predetermined viewing angle range, There is no significant difference in brightness between the case where only the light emitted from the first inclined surface is visually observed and the case where only the light emitted from the second inclined surface is visually observed.

Therefore, when the light sources are arranged in an L-shape, the outer surface of each prism portion is formed by four inclined surfaces to improve the luminance, and the light incident surface is formed on the light source side extending in the vertical direction. The inclination of the inclined surface directed is gentler than the inclination of the inclined surface facing the inclined surface, and the inclination of the inclined surface facing the light incident surface toward the light source extending in the lateral direction is gentler than the inclined surface facing the inclined surface. By doing so, the inconvenience that the display screen becomes dark when viewed from a specific direction can be resolved.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view for explaining a basic configuration of a liquid crystal display device according to the present embodiment, FIG. 2 is an explanatory view of a main part of a backlight of the embodiment, FIG. 3 is a schematic plan view of the backlight, Numeral 4 is an explanatory view showing the shape of the prism portion of the lens sheet constituting the backlight, and the portions corresponding to those in FIGS. 7 and 8 used in the description of the prior art are denoted by the same reference numerals. FIG. 5 is a characteristic diagram showing a change in light intensity when the viewing direction is changed along the long side of the lens sheet. FIG. 6 is a graph showing the change in the intensity of the emitted light while changing the inclination angle of the opposing inclined surfaces of the prism portion. This is experimental data obtained by examining the intensity and the viewing angle. However, the horizontal axis in FIG. 5 indicates the angle between the line of sight (reference line) and the viewing direction when the lens sheet is viewed from directly in front. The viewing angle indicates how much the viewing direction at which 75% of the light intensity is measured with respect to the peak value of the light intensity measured when the lens sheet is viewed from directly in front is inclined from the reference line. Angle.

In the liquid crystal display device shown in FIG. 1, the backlight has a transparent light guide plate 1 made of acrylic resin or the like,
A lens sheet 2 described below mounted on the upper surface of the light guide plate 1
And a reflection sheet 4 covering the lower surface of the light guide plate 1, and a light source 7 such as a cold-cathode tube arranged in an L-shape along two adjacent side end surfaces of the light guide plate 1. The liquid crystal panel 8 provided on the lens sheet 2 is irradiated with light from the back side. That is, as shown in FIG. 3, the light source 7 is a vertical light source 5 facing the left end face of the light guide plate 1.
And an L-shaped tube made up of a horizontal light source 6 facing the lower end surface of the light guide plate 1, and the light guide plate 1 is arranged around the light sources 7 (5, 6) as shown in FIG. A reflector 9 is provided for efficiently making light incident on the opposite side end surfaces of the reflectors. A reflection tape (not shown) for preventing light leakage is attached to a right end surface and an upper end surface of the four side end surfaces of the light guide plate 1 that are not opposed to the vertical light source 5 or the horizontal light source 6. is there.

The lens sheet 2 is a transparent sheet having a prism surface on one side and a flat surface on the other side, and an upright quadrangular pyramid-shaped prism portion on the prism surface facing the liquid crystal panel 8. It is made by protruding many 3
Four inclined surfaces 3a to 3d forming the outer surface of each prism portion 3
Are not equal, the inclined surface 3a has a gentler inclination than the inclined surface 3b opposed thereto, and the inclined surface 3c has a gentler inclination than the inclined surface 3d opposed thereto.
Specifically, while the inclination angle β of the inclined surfaces 3b and 3d is 45 °, the inclination angle α of the inclined surfaces 3a and 3c is 35 °.
Is set to When light from the light source 7 (5, 6) is incident on the lens sheet 2 through the light guide plate 1, the light crosses the inclined surfaces 3a to 3d of the prism portion 3 and the liquid crystal panel 8
Since the light is refracted inward by the lens effect when heading toward the lens, the directivity is enhanced, whereby the light irradiated on the liquid crystal panel 8 can be concentrated within a specific viewing angle range. Each prism portion 3 of the lens sheet 2 has a light incident surface of the inclined surface 3a facing the vertical light source 5 side and the inclined surface 3a.
The light sources 7 are arranged vertically and horizontally along the L-shape of the light source 7 so that the light incident surface faces the side of the horizontal light source 6.

In the above-described liquid crystal display device, since the light source 7 is arranged in an L shape along the light guide plate 1 and each prism portion 3 of the lens sheet 2 is formed in a quadrangular pyramid shape, Inclined surface 3 facing the light emitted from 5
Not only can the lens effects a and 3b be used effectively, but also the light emitted from the lateral light source 6 faces the inclined surfaces 3c and 3d facing each other.
The lens effect can be used effectively, so that there is little wasteful irradiation light and it is very advantageous for improving the brightness.
Since there is no need to worry about increased costs because it is a single-light type that uses an L-shaped tube.

Moreover, of the inclined surfaces forming the outer surface of each prism portion 3, the inclination of the inclined surfaces 3a and 3c whose light incident surface faces the light source side and the incident light amount is relatively large, Since the inclinations of the inclined surfaces 3b and 3d facing the light source side are set to be gentler and the light emitted from the former inclined surfaces 3a and 3c is dispersed over a wider range, the display screen can be displayed even if the viewing direction is different. There is no big difference in brightness. That is, in FIG. 2, the light emitted from the inclined surface 3a having a relatively large amount of incident light is dispersed in a wider range than the light emitted from the inclined surface 3b, and accordingly, the amount of light directed toward a predetermined viewing angle range. Is slightly smaller, so that the line of sight looks only at the light emitted from the inclined surface 3a in the direction of arrow A, and the line of sight looks only at the light emitted from the inclined surface 3b in the direction of arrow B. The difference in light intensity hardly occurs. Similarly, when the light emitted from the inclined surface 3c having a relatively large amount of incident light is dispersed in a wider range than the light emitted from the inclined surface 3d, only the light emitted from the inclined surface 3c is visually observed. There is almost no difference in light intensity between the case where the light is emitted from the inclined surface 3d and the case where only the light emitted from the inclined surface 3d is visually observed. As a result, there is no inconvenience that the display screen is particularly dark when viewed from a specific direction, and good display quality can always be expected.

As described above, in this embodiment, the brightness of the display screen is hardly different between when viewed from the light source side and when viewed from the opposite light source side.
Can be confirmed in the characteristic diagram of FIG. That is, the graph shown in the figure is obtained by measuring the light intensity when the viewing direction is changed along the long side of the lens sheet 2, and the line of sight when the lens sheet 2 is viewed from directly in front is set as the reference line, The abscissa indicates the angle when viewed from the position inclined to the light source 5 side and the angle when viewed from the position inclined to the opposite side with a value of +, but when the viewing angle range is within ± 30 °, the standard is used. If the angle between the line and the viewing direction is the same, it can be seen that the light intensity is the same from either side.

Next, with respect to the inclined surfaces 3a and 3b of the prism portions 3 of the lens sheet 2 facing each other, the intensity and the viewing angle of the emitted light were measured while changing the inclination angles α and β (α <β). However, as shown in FIG. 6, it can be seen that as the inclination angles α and β increase and the inclination increases, the light intensity increases but the viewing angle decreases. For example, α> 45
When β> 55 ° in °, the viewing angle becomes too narrow to be less than ± 17 °, and when β <35 ° in α <25 °, the decrease in light intensity cannot be ignored. Therefore, as the inclination angles α and β, α is 25 ° to 45 °.
And β is preferably set in the range of 35 ° to 55 °. Then, as in the present embodiment, α
Is set to 35 ° and β is set to 45 °, most of the light emitted from the inclined surfaces 3a and 3b of each prism portion 3 is concentrated within a viewing angle range of ± 20 ° required for the display screen. You can see that it is done.

[0022]

[0023]

As described above, in the backlight structure of the liquid crystal display device according to the present invention, of the inclined surfaces forming the outer surfaces of the prism portions of the lens sheet, the light incident surface faces the light source side. The inclination is gentler than the inclination of another inclined surface facing the inclined surface , and the light incident surface is set to the light source side.
The inclination angle of the inclined surface to be turned to 25 ° to 45 °,
By setting the inclination angle of another inclined surface opposite to the above to 35 ° to 55 ° , the light intensity balance is maintained within a predetermined viewing angle range, and in particular, the light intensity is arranged in an L shape. When the outer surface of the prism is formed with four inclined surfaces to improve the brightness of the backlight by effectively utilizing the light from the light source, there is a large difference in the brightness of the display screen from any direction. Does not occur, and an excellent effect that good display quality can always be expected can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view for explaining a basic configuration of a liquid crystal display device according to an embodiment.

FIG. 2 is an explanatory diagram of a main part of the backlight of the embodiment.

FIG. 3 is a schematic plan view of the backlight.

FIG. 4 is an explanatory diagram showing a shape of a prism portion of a lens sheet constituting the backlight.

FIG. 5 is a characteristic diagram showing a change in light intensity when a viewing direction is changed along a long side of the lens sheet.

FIG. 6 shows experimental data obtained by examining the intensity and the viewing angle of emitted light while changing the inclination angle of the opposing inclined surfaces of the prism section.

FIG. 7 is an explanatory diagram showing a backlight of a conventional liquid crystal display device.

FIG. 8 is an explanatory diagram of a liquid crystal display device provided with a quadrangular pyramid-shaped prism portion corresponding to an L-shaped light source.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light guide plate 2 Lens sheet 3 Prism part 3a, 3b, 3c, 3d Inclined surface 4 Reflection sheet 5 Vertical light source 6 Horizontal light source 7 Light source (L-shaped tube) 8 Liquid crystal panel α, β Tilt angle

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/00 331 F21V 8/00 601 G02F 1/13357

Claims (3)

(57) [Claims] 1. A lens sheet comprising a plurality of prism portions having an inclined outer surface protruding from one side of a transparent sheet, and a lens sheet and a liquid crystal panel with the prism portions opposed to the liquid crystal panel. A liquid crystal display device which is interposed between the light guide plate and irradiates light from a light source disposed opposite to a side end surface of the light guide plate to the liquid crystal panel from the back side through the light guide plate and the lens sheet. Of the inclined surfaces of the prism portion, the inclination of the inclined surface with the light incident surface facing the light source side,
An inclined surface with a light incident surface facing the light source side so as to be gentler than another inclined surface facing the inclined surface.
Is set to 25 ° to 45 °, and
A backlight structure for a liquid crystal display device, wherein an inclination angle of another opposed inclined surface is set to 35 ° to 55 ° . 2. A method according to claim, characterized in that the light source is along two side end surfaces adjacent the light guide plate is disposed in an L-shape 1
The backlight structure of the liquid crystal display device described in the above . 3. A process according to claim, characterized in that the record Nzushito is allowed to protrude a number of prism portions of the force standing the quadrangular pyramid
3. The backlight structure of the liquid crystal display device according to 2 .