JP2000003609A - Sidelight type surface light source device and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend the dimming range by laminating plate members having respective light sources, and correcting the directive illuminating light possessed by each plate member to the front directivity of the emitting surface by a light control member. SOLUTION: An illuminating light LA emitted from a light guide plate 7A with a directivity inclined toward a wedge tip is transmitted by a light guide plate 7B, and emitted from an emitting surface 7BO. The emitted illuminating light LA1 is emitted with the same directivity as the emitting surface 7AO of the light guide plate 7A. With respect to the illuminating light LB of the second light guide plate 7B, an illuminating light LB1 is emitted from the emitting surface 7BO with a directivity inclined in the wedge tip direction similarly to the light guide plate 7A. The illuminating lights LA1, LB1 are emitted with the same directivity in the normal direction of the emitting surfaces, when transmitted by a prism sheet 9, by correcting the directivity by its inclined surface. As occasion demands, the fluorescent lamp 11A, 11B of the primary light source 3A, 3B of each light guide plate 7A, 7B is driven to remarkably extend the dimming range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sidelight type surface light source device and a liquid crystal display device, and can be applied to, for example, an in-vehicle liquid crystal display device applied to a car navigation system. According to the present invention, a plate-like member having a light source is laminated, and the directional illumination light from each plate-like member is corrected to a directivity in a front direction of an emission surface by a light control member. We propose a sidelight type surface light source device capable of expanding the dimming range, and a liquid crystal display device using the sidelight type surface light source device.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal display device, a display image is formed by illuminating a liquid crystal display panel with a side light type surface light source device.

That is, this type of sidelight type surface light source device is a transparent plate member made of acrylic or the like (hereinafter referred to as a light guide plate).
A primary light source of a fluorescent lamp is arranged on the side surface of the light source, and illumination light of the fluorescent lamp is incident on the light guide plate. The sidelight type surface light source device propagates this illumination light inside the light guide plate and emits it from the emission surface. Thereby, the sidelight type surface light source device forms a surface light source from the illumination light of the fluorescent lamp which is a bar-shaped light source.

The sidelight type surface light source device is adapted to adjust the driving current of the fluorescent lamp by a dimming circuit, whereby the amount of light emitted to the liquid crystal display panel is adjusted according to, for example, extraneous light, so that the display image can be easily viewed. Can be displayed.

[0005]

Incidentally, some liquid crystal display devices of this type are used in an environment in which the amount of extraneous light varies significantly according to the surrounding conditions, such as a car navigation system. That is, the car navigation system may be used outdoors during the day when the amount of extraneous light is extremely large, and conversely, it may be used at night when there is almost no extraneous light.

[0006] In such a liquid crystal display device as a car navigation system, etc., if the emission light amount of the sidelight type surface light source device can be adjusted so as to correspond to a remarkable change in the amount of extraneous light, it is easy to see in any environment. A display image can be displayed. However, the conventional sidelight type surface light source device has a problem that the amount of emitted light cannot be adjusted within a large range that can cope with such a remarkable change in the amount of external light.

The present invention has been made in view of the above points, and a sidelight type surface light source device capable of greatly expanding the dimming range as compared with the related art, and a sidelight type surface light source device And a liquid crystal display device using the same.

[0008]

According to the first aspect of the present invention, there is provided a side light type surface light source device, wherein a first light emitted from a first primary light source is applied.
And a first plate-shaped member which is incident on the end face, bends the first illumination light and emits it from the emission surface, and is disposed so as to be superimposed on the first plate-shaped member, from the second primary light source. The emitted second illumination light is incident from the end face, and the first illumination light emitted from the first plate-like member is incident from the back surface facing the emission surface, and the first and second illumination lights are emitted. A second plate-shaped member that is emitted from the emission surface, and the emission directions of the first and second illumination lights emitted from the emission surface of the second plate-shaped member are substantially in front of the emission surface of the second plate-shaped member. And a light control member that corrects in the direction.

According to the first aspect of the present invention, the first plate-shaped member has a directional surface light source in the first emission direction, and the second plate-shaped member has a directional surface light source in the second emission direction. The illumination light can be emitted by the light source and the first or second illumination light can be selectively emitted by stopping the supply of the first or second illumination light with a uniform emission light amount distribution and, if necessary, Illumination light with directivity can be emitted. Accordingly, if the light control member corrects the emission directions of the first and second illumination lights in a direction substantially in front of the emission surface of the second plate-like member, the first and second illumination lights are emitted simultaneously. Illumination light with a large amount of emitted light, and the first or second
Can be selectively emitted to reduce the amount of emitted light.

[0010] In the invention according to claim 2, in the structure of claim 1, the first plate-like member has a pair of sloped projections repeatedly formed along the end face on the surface facing the emission surface. You.

According to the second aspect of the present invention, the first illumination light can be efficiently emitted by the projection formed by the pair of slopes.

Further, in the invention according to claim 3, in the structure of claim 1 or 2, the first and second primary light sources are rod-shaped light sources arranged so that their extending directions are substantially parallel. In the light control member, a light control surface for correcting the emission directions of the first and second illumination lights is formed on a surface on the side of the second plate member, and the light control surface is orthogonal to the longitudinal direction of the rod-shaped light source. In this direction, a pair of sloped protrusions are repeatedly formed.

According to the third aspect of the present invention, it is possible to efficiently correct the emission directions of the first and second illumination lights to substantially equal emission directions by the light control surface formed by repeating the pair of slopes.

The invention according to claim 4 is applied to a liquid crystal display device, and is applied to a liquid crystal display device.
The liquid crystal display panel is illuminated by the side light type surface light source device according to the above configuration.

According to a fifth aspect of the present invention, in the configuration of the fourth aspect, emission of the first or second illumination light from the first or second primary light source can be selectively stopped. .

[0016]

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

(1) First Embodiment FIG. 1 is an exploded perspective view showing a sidelight type surface light source device applied to a liquid crystal display device according to a first embodiment of the present invention, and FIG. FIG. 1 is a sectional view of a liquid crystal display device showing the sidelight type surface light source device 1 together with a liquid crystal display panel, a driving circuit and the like.

The liquid crystal display device 2 is applied to, for example, a car navigation system, and drives two primary light sources 3A and 3B built in the sidelight type surface light source device 1 by a driving circuit 4.
(FIG. 2), the illumination light is supplied to the liquid crystal display panel in a wide light control range.

For this reason, the side light type surface light source device 1
Primary light sources 3A and 3B are arranged on the sides of the first and second light guide plates 7A and 7B, respectively, and a reflection sheet 8, a first light guide plate 7A, a second light guide plate 7B, and a prism sheet including a light control member are provided. 9. The light diffusion sheet 10 is formed by sequentially laminating.

Here, the primary light sources 3A and 3B are formed by surrounding the fluorescent lamps 11A and 11B, each of which is a cold-cathode tube, with reflectors 12A and 12B, respectively. The light guide plates 7A and 7B are opened from the opening sides of the reflectors 12A and 12B. Illumination light is incident on end surfaces (hereinafter referred to as incident surfaces) 7AI and 7BI. Here, the reflectors 12A and 12B are reflection members that specularly or irregularly reflect incident light, and are formed of, for example, a sheet material.

The reflection sheet 8 is formed of a sheet-like regular reflection member made of a metal foil or the like, or a sheet-shaped irregular reflection member made of a white PET film or the like, and reflects the illumination light leaking from the light guide plate 7A to reflect the light guide plate. 7A, thereby improving the efficiency of use of illumination light.

The first light guide plate 7A is a plate-like member having a wedge-shaped cross section, for example, polymethyl methacrylate (PMM).
It is formed by uniformly dispersing and mixing translucent fine particles having a different refractive index from the matrix composed of A). The light guide plate 7A has a surface (hereinafter referred to as an emission surface) 7A on the light guide plate 7B side.
O is formed in a rectangular shape, and is formed so that the plate thickness gradually decreases along the long side of the rectangular shape. An end surface of the light guide plate 7A along the short side on the thick side is set as the incident surface 7AI, and the illumination light L of the primary light source 3A is received from the incident surface 7AI.
A is incident. As a result, the light guide plate 7A is
While the illumination light LA incident from the light is scattered by the light-transmitting fine particles, the illumination light LA propagates by being repeatedly reflected between the emission surface 7AO and a surface 7AR opposed to the emission surface 7AO (hereinafter referred to as a back surface). . Further, at the time of this propagation, the illumination light LA incident on the output surface 7AO at an incident angle equal to or smaller than the critical angle is output from the output surface 7AO.

Further, in the light guide plate 7A, a light scattering pattern for promoting the emission of the illumination light LA propagating inside is formed on the emission surface 7AO, thereby making the light quantity distribution of the illumination light LA emitted from the emission surface 7AO uniform. It has been made like that. Note that this light scattering pattern is formed by making the emission surface 7AO partly rough due to a small size (for example, a size of about 80 μm or less) that is difficult to see with the naked eye from the emission surface 7AO side. Is done. Further, the light scattering pattern is formed by irregular arrangement, so that generation of moire fringes due to interference with the liquid crystal display panel can be effectively avoided.

Further, the light guide plate 7A has a pair of slopes 7AE and 7
A protrusion by AF is repeatedly formed along the incident surface 7AI. Here, these projections are formed in a triangular cross section by directly connecting the pair of slopes 7AE and 7AF.
Thus, the light guide plate 7A efficiently emits the illumination light by reducing the incident angle of the illumination light LA incident on the emission surface 7AO, and further increases the directivity of the emission light in an in-plane direction along the incident surface 7AI. When viewed, the illumination light is emitted with a sharp directivity in the normal direction of the emission surface 7AO. As a result, the illumination light emitted from the emission surface 7AO is emitted with a large amount of light in the in-plane direction along the incidence surface 7AI toward the normal direction of the emission surface 7AO.

The second light guide plate 7B is made of the same material as that of the first light guide plate 7A and has substantially the same shape. Further, the light guide plate 7B includes an end face on the wedge-shaped tip side of the first light guide plate 7A,
The light guide plate 7 is formed such that the incident surface 7BI forms substantially the same surface.
A is superposed on the light guide plate A and is arranged on the emission surface side of the light guide plate 7A. As a result, the light guide plate 7B receives the illumination light LB from the primary light source 3B disposed on the incident surface 7BI side, and scatters the illumination light LB with the light-transmitting fine particles while the light guide plate 7B is in contact with the emission surface 7BO and the back surface 7BR. The light is repeatedly reflected between and exits from the exit surface 7BO. Further, the illumination light LA emitted from the light guide plate 7A is incident on the back surface 7BR, passes through the incident illumination light LA, and is emitted from the emission surface 7BO.

Further, in the light guide plate 7B, similarly to the light guide plate 7A, a light scattering pattern is formed on the emission surface 7BO, whereby the light amount distribution of the illumination light propagating through the inside and emitted is made uniform. Further, the light guide plate 7B is formed with a substantially flat mirror surface on the back surface 7BR, as shown in an enlarged manner by reference numeral B.
Thus, the illumination light incident on the back surface 7BR from the light guide plate 7A can be incident on the inside without waste.

The prism sheet 9 corrects the directivity between the illumination light propagating inside the light guide plate 7B and emitted, and the illumination light emitted from the light guide plate 7A and transmitted through the light guide plate 7B. Arranged for. That is, the prism sheet 9 is formed of a translucent sheet material such as polycarbonate, and a prism surface is formed on the surface facing the light guide plate 7B. The prism surface is formed by repeating projections having a triangular cross section directly connecting the pair of slopes 9A and 9B in a direction orthogonal to the extension direction of the incident surface of the light guide plate 7B, as shown in an enlarged manner by reference numeral C. Is done.

The prism sheet 9 has a pair of slopes 9A.
And 9B are set at an angle of 66 degrees, and the pair of slopes 9A and 9B are set at the same inclination.

The light diffusing sheet 10 is made of a sheet material having a light diffusing property. The light diffusing sheet 10 weakly scatters the illumination light so that the brightness of the edge of the light guide plate 7B cannot be perceived through the liquid crystal display panel. To

In the above configuration, the illumination light LA emitted from the fluorescent lamp 11A on the side of the light guide plate 7A (FIG. 2) is reflected directly or after being reflected by the reflector 12A, after which the incident surface 7A is irradiated.
I, the light enters the inside of the light guide plate 7A and is scattered by the light-transmitting fine particles inside the light guide plate 7A.
And the light propagates inside the light guide plate 7A by repeating reflection.
At this time, each time the illumination light LA is reflected by the back surface 7AR, the incident angle with respect to the emission surface 7AO decreases, and a component having a critical angle or less with respect to the emission surface 7AO is emitted from the emission surface 7AO.

Further, at this time, the illumination light LA is emitted from the light guide plate 7A.
The emission is promoted by the light scattering pattern formed on the emission surface 7AO. Thus, the illumination light LA is emitted from the emission surface 7AO.
The light is emitted with a more constant light quantity distribution and with a directivity inclined toward the wedge-shaped tip.

Further, the projection angle of the pair of slopes 7AE and 7AF formed on the back surface 7AR of the illumination light LA reduces the incident angle with respect to the emission surface 7AO when propagating inside. As a result, the emission surface 7A has a smaller number of internal reflections than the case where the back surface 7AR is formed of a flat surface.
The light is emitted from O and is emitted more efficiently. When the directivity is viewed in the in-plane direction along the incident surface 7AI, the light is emitted with a sharp directivity in the normal direction of the emission surface 7AO. As a result, at the peak of the directivity, the light is emitted with a large amount of light. You.

Thus, the illumination light LA emitted with the directivity inclined toward the wedge-shaped tip from the light guide plate 7A.
Is incident on the light guide plate 7B from the back surface 7BR of the light guide plate 7B,
The light passes through the light guide plate 7B and is emitted from the emission surface 7BO of the light guide plate 7B. At this time, since the cross-sectional shape of the light guide plate 7B is formed in a wedge shape, the emission surface 7 of the light guide plate 7B is formed.
The illumination light LA1 emitted from the BO is emitted from the emission surface 7BO of the light guide plate 7B with almost the same directivity as that emitted from the emission surface 7AO of the light guide plate 7A, although the emission direction changes very slightly.

The illumination light LA1 is efficiently incident on the light guide plate 7B and emitted from the emission surface 7BO of the light guide plate 7B because the back surface 7BR of the light guide plate 7B is formed by a substantially flat mirror surface. However, this illumination light LA
1 is scattered and attenuated by the internal fine particles when passing through the light guide plate 7B, and the back surface 7B of the light guide plate 7B efficiently.
Although the light enters from R, the amount of spectral attenuates when the light enters from the back surface 7BR. With respect to such attenuation of the light amount, the illumination light LA1 is incident on the back surface 7BR of the light guide plate 7B with a large amount of light at the peak of directivity due to a pair of slopes formed on the back surface 7AR of the light guide plate 7A. In addition, a decrease in the amount of light due to the light emitted through the light guide plate 7B is prevented.

FIG. 3 shows the first light guide plate 7A as described above.
FIG. 7 is a characteristic curve diagram showing the directivity of the illumination light LA1 emitted from the light emitting device. In this figure, the emission surface 7BO of the light guide plate 7B is shown.
, The longitudinal direction of the light guide plate 7A was set to the Y direction, and the direction along the incident surface 7AI was set to the X direction. According to the measurement result of FIG. 3, it is understood that the illumination light LA1 is emitted with a directivity inclined toward the wedge-shaped tip.
FIG. 3 shows the configuration shown in FIG. 2, in which the prism sheet 9, the light diffusion sheet 10, and the liquid crystal display panel are removed, only the fluorescent lamp 11A is turned on, and the directivity is measured from the emission surface 7BO of the light guide plate 7B. It is.

On the other hand, in the second light guide plate 7B, the illumination light LB emitted from the fluorescent lamp 11B enters the inside of the light guide plate 7B from the incident surface 7BI and is scattered by the light transmitting fine particles inside. While receiving, the reflection is repeated between the back surface 7BR and the emission surface 7BO, and propagates inside the light guide plate 7B. Further, the propagating illumination light LB is emitted from the emission surface 7BO with directivity inclined toward the wedge-shaped tip in the same manner as in the case of the light guide plate 7A.

FIG. 4 shows the second light guide plate 7B
FIG. 9 is a characteristic curve diagram showing the directivity of illumination light LB1 emitted from the light emitting device. In this figure, under the same conditions as in FIG. 3, the measurement was performed with the fluorescent lamp 11A of the primary light source 3A turned off and the fluorescent lamp 11B of the primary light source 3B turned on. According to the measurement result of FIG. 4, it is understood that the illumination light LB1 is emitted in a direction opposite to that of FIG. 3 and with a directivity inclined toward the wedge-shaped tip as in the case of the light guide plate 7A.

Thus, in comparison with FIGS. 3 and 4,
When the directivity of the emitted light is measured by turning on the two fluorescent lamps 11A and 11B together, as shown in FIG.
Directivity peaks are formed in two directions, an emission direction by A1 and an emission direction by illumination light LB1.

Thus, the emission surface 7BO of the light guide plate 7A
When the illumination lights LA1 and LB1 emitted from are transmitted through the prism sheet 9 disposed on the emission surface 7BO side, the directivity is corrected by the slope of the prism sheet 9. That is, as shown in FIG. 6, the illumination light LA1 on the first light guide plate 7A side is incident on the prism sheet 9 from the slope 9B facing the incident surface 7A1 side of the light guide plate 7A, and then reflected on the other slope 9A. Out of the prism sheet 9. The illumination light LB1 on the second light guide plate 7B side enters the prism sheet 9 from the other slope 9A, is reflected by the slope 9B, and is emitted from the prism sheet 9.

In this embodiment, since the light guide plates 7A and 7B are formed in substantially the same shape,
Further, since the pair of slopes 9A and 9B of the prism sheet 9 are set to have the same inclination and the apex angle is set to 66 degrees, the illumination lights LA1 and LB1 reflected by these slopes 9A and 9B are: Light is emitted with almost the same directivity in the normal direction of the emission surface.

FIG. 7 shows a state in which the liquid crystal display panel and the light diffusion sheet 10 are removed from the structure shown in FIG.
FIG. 7 is a characteristic curve diagram in which only the fluorescent lamp 11A is turned on and the directivity of the illumination light LA2 by the first light guide plate 7A is measured.
FIG. 8 shows the second fluorescent lamp 1 in the same state as FIG.
Only 1B is turned on, and the illumination light LB2 from the second light guide plate 7B is turned on.
FIG. 4 is a characteristic curve diagram obtained by measuring the directivity of the image. Further, FIG.
In the same state as FIG. 7, the first and second fluorescent lamps 11A
11B is a characteristic curve diagram in which the directivities of the illumination lights LA2 and LB2 by the first and second light guide plates 7A and 7B are measured by turning on the light guides 11B and 11B. Note that in FIGS. 7 to 9,
The amount of emitted light is shown by reducing the height in the vertical axis direction as compared with FIGS.

In the liquid crystal display device 2, the first and second illumination lights LA2 and LB2 generated as described above are weakly diffused in the subsequent light diffusion sheet 10, and then supplied to the liquid crystal display panel. When viewed from the front of the emission surface, the fluorescent lamps 11A and 11B are both
Is turned on, a bright screen can be displayed by the illumination lights LA2 and LB2, and the fluorescent lamps 11A and 1B can be displayed.
The brightness of the brightly displayed screen can be adjusted by varying the drive current of 1B.

On the other hand, the fluorescent lamp 11A or 11B
When only the light is turned on, the display screen is formed by the illuminating light LA2 or LB2, and the driving current of the fluorescent lamp 11A or 11B is varied in a state where the brightness is reduced to almost half, thereby increasing the brightness of the screen. It can be adjusted.

According to the above arrangement, the light guide plates each having a primary light source are laminated, and the directivity of the illumination light by each light guide plate is corrected in the front direction of the light emission surface and emitted. Obtaining a sidelight type surface light source device capable of driving a primary light source of a light guide plate to greatly expand a dimming range as compared with the related art, and a liquid crystal display device using the sidelight type surface light source device Can be.

By the way, even if the primary light sources are arranged on both end surfaces of the flat light guide plate, the directivity can be switched as in this embodiment by switching the primary light sources and lighting them. However, in this case, the switching of the primary light source significantly changes the light amount distribution of the emitted light. However, if a light source is arranged on each light guide plate as in this embodiment, illumination light can be emitted in each direction with a uniform amount of emitted light, and the directivity can be switched as needed.

In the lower first light guide plate, the projections are repeatedly formed on the back surface, and in the upper second light guide plate, the back surface is formed by a flat surface, so that the first light guide plate is smaller than the first light guide plate. The emitted illumination light can be efficiently emitted, thereby improving the utilization efficiency of the illumination light as a whole.

Further, by arranging the primary light sources so that the fluorescent lamps are substantially parallel to each other, the first and second prism sheets are formed by forming a pair of projections by a pair of slopes repeatedly in a direction orthogonal to the longitudinal direction of the fluorescent lamps. It is possible to efficiently correct the emission directions of the two illumination lights to substantially equal emission directions.

(2) Other Embodiments In the above-described embodiment, the lower first light guide plate has projections formed on the back surface, and the upper second light guide plate has projections formed on the back surface. Although the case of forming with a mirror surface has been described, the present invention is not limited to this, and in the case where practically sufficient characteristics are obtained, in the lower first light guide plate, the emission surface,
Protrusions may be formed on one or both of the back surfaces, and both the emission surface and the back surface may be mirror surfaces. In the upper light guide plate, from the viewpoint of efficiently transmitting and emitting the illumination light emitted from the lower light guide plate, it is desirable that no projection is formed on the emission surface and the back surface, but it is practically sufficient. When such characteristics are obtained, a projection may be formed on one or both of the exit surface and the back surface of the upper light guide plate.

Further, in the above-described embodiment, the case where the light scattering pattern is formed by partially making the light exit surface of the light guide plate a rough surface is described. Various forming techniques can be widely applied, for example, when a light scattering pattern is formed by the partial adhesion of a material.

In the above-described embodiment, the case where the light scattering pattern is formed on the emission surfaces of the first and second light guide plates has been described. However, the present invention is not limited to this. The light-scattering pattern may be omitted if sufficient characteristics can be obtained for practical use.

Further, in the above-described embodiment, the case where the light guide plate is constituted by the transparent member mixed with light-transmitting fine particles has been described. However, the present invention is not limited to this, and various light-scattering fine particles may be used. The light guide plate may be constituted by the mixed transparent member, or the light guide plate may be simply formed by the transparent member without mixing these fine particles.

In the above-described embodiment, the case where the primary light source by one fluorescent lamp is disposed on each of the first and second light guide plates has been described. However, the present invention is not limited to this, and FIG. As shown, a primary light source with various light sources can be widely applied, for example, when a primary light source with two fluorescent lamps is arranged.

Further, in the above-described embodiment, the case where the surface light source device is configured to have directivity in two directions by laminating two light guide plates each having a primary light source has been described. The present invention is not limited to this, and light guide plates each having a primary light source may be stacked in various numbers. Incidentally, as shown in FIG. 11, if the first and second light guide plates and the prism sheet according to the above-described embodiment are unitized and stacked in two sets, the light control range can be further increased.

In the above embodiment, the apex angle 6
Although the case of arranging the prism sheet of 6 degrees has been described, the present invention is not limited to this, and in the prism sheet, the apical angle is appropriately selected within a range of 40 degrees or more to secure the required directivity. Can be.

Further, in the above embodiment, the case where the prism sheet is arranged so that the surface on the light guide plate side becomes the prism surface has been described. However, the present invention is not limited to this, and the required directivity is not limited to this. If obtained, the prism sheet may be arranged such that the surface on the side opposite to the light guide plate side is the prism surface.

Further, in the above-described embodiment, the case has been described where the directivity is corrected in a plane direction orthogonal to the incident surface of the light guide plate by one prism sheet. However, the present invention is not limited to this. A prism sheet may be additionally arranged so that the repeating direction of the protrusions is orthogonal to the above-described prism sheet, and the directivity may be further corrected in an in-plane direction along the incident surface of the light guide plate.

In the above-described embodiment, a case has been described in which a pair of slopes are directly connected to form a projection having a triangular cross section on the light guide plate and the prism sheet. However, the present invention is not limited to this. These projections may be formed by connecting a pair of slopes by a curved surface, or the slope itself may be formed by a curved surface.

Further, in the above-described embodiment, the case where the light diffusion sheet is arranged in addition to the prism sheet on the emission surface side of the upper light guide plate has been described. In addition, a so-called polarization separation sheet that selectively transmits only illumination light of a predetermined polarization plane and reflects illumination light on a polarization plane in a direction orthogonal to the polarization plane may be provided. The light diffusion sheet can be omitted if necessary.

Further, in the above-described embodiment, the case where the present invention is applied to a liquid crystal display device of a car navigation system has been described. For example, the present invention can be widely applied to various liquid crystal display devices used as displays of personal computers and game machines and the like and surface light source devices thereof.

[0060]

As described above, according to the present invention, plate members each having a light source are stacked, and the directional illumination light from each plate member is converted by the light control member into directivity in the front direction of the emission surface. By performing the correction, it is possible to obtain a sidelight type surface light source device capable of greatly expanding the dimming range as compared with the related art, and a liquid crystal display device using the sidelight type surface light source device.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a sidelight type surface light source device applied to a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing the side light type surface light source device of FIG. 1 together with peripheral components.

FIG. 3 is a characteristic curve diagram showing directivity of first illumination light by a first light guide plate with a prism sheet removed.

FIG. 4 is a characteristic curve diagram showing directivity of second illumination light by a second light guide plate after removing a prism sheet.

FIG. 5 is a characteristic curve diagram showing directivities of first and second illumination lights by first and second light guide plates with a prism sheet removed.

FIG. 6 is a cross-sectional view for explaining the operation of the prism sheet with respect to first and second illumination lights.

FIG. 7 is a characteristic curve diagram showing directivity of first illumination light by a first light guide plate.

FIG. 8 is a characteristic curve diagram showing directivity of second illumination light by a second light guide plate.

FIG. 9 is a characteristic curve diagram showing directivity of first and second illumination lights by the first and second light guide plates.

FIG. 10 is a cross-sectional view showing a side light type surface light source device when two fluorescent lamps are arranged for each primary light source.

FIG. 11 is an exploded perspective view showing a sidelight type surface light source device having a configuration in which four light guide plates are stacked.

[Explanation of symbols]

1 ... side light type surface light source device, 2 ... liquid crystal display device, 3A, 3B ... primary light source, 7A, 7B ... light guide plate,
8 ... reflection sheet, 9 ... prism sheet, 11A, 1
1B Fluorescent lamp

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H038 AA41 AA55 2H091 FA21Z FA23Z FA32Z FA42Z FB02 FC17 FD06 LA16 LA17 5G435 AA02 BB12 DD14 EE27 FF02 FF03 FF08 GG03 GG24 GG26 LL17

Claims (5)

[Claims] A first plate-like member that receives first illumination light emitted from a first primary light source from an end face, bends the first illumination light, and emits the first illumination light from an emission surface; The second illumination light emitted from the second primary light source is incident on an end face of the first plate-shaped member, and the first illumination light emitted from the first plate-shaped member.
Illumination light from the back surface facing the emission surface, and the first
And a second plate-like member that emits second illumination light from the emission surface, and sets the emission direction of the first and second illumination light emitted from the emission surface of the second plate-like member to the first A side light type surface light source device, comprising: a light control member for correcting the light emission surface of the plate-shaped member in a substantially frontal direction. 2. The device according to claim 1, wherein the first plate-shaped member has a pair of sloped projections formed repeatedly along the end surface on a surface facing the emission surface. Sidelight type surface light source device. 3. The first and second primary light sources are rod-like light sources arranged so that their extending directions are substantially parallel, and the light control member is a surface on the second plate-like member side. A light control surface for correcting the emission directions of the first and second illumination lights is formed, and the light control surface is formed by repeatedly forming a pair of inclined surfaces in a direction orthogonal to a longitudinal direction of the rod-shaped light source. The side light type surface light source device according to claim 1, wherein the side light type surface light source device is provided. 4. A liquid crystal display device which illuminates a liquid crystal display panel with the sidelight type surface light source device according to claim 1, 2 or 3. 5. The liquid crystal display according to claim 4, wherein emission of said first or second illumination light from said first or second primary light source can be selectively stopped. apparatus.