JP2001083510A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar light source device mainly used as a backlight of a liquid crystal display, which has a high light use efficiency of a light source, can realize a higher luminance, and has a more uniform light. To provide a planar light source device capable of irradiating light. A planar light source device is provided with a prism sheet (1) that emits light incident from the back surface at a substantially vertical emission angle (θ1) from the front surface, and is disposed laterally or behind the prism sheet (1). A linear mirror (3) comprising a linear light source (2) and a long-axis movable mirror (3) for reflecting light emitted from the light source (2) toward the back surface of the prism sheet (1); , The light reflection direction is continuously changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar light source device, and more particularly, to a planar light source device mainly used as a backlight of a liquid crystal display, which has a high light use efficiency of a light source. The present invention relates to a planar light source device which can realize a higher luminance and more uniformly irradiate an object such as a liquid crystal display device with light.

[0002]

2. Description of the Related Art In a transmissive liquid crystal display,
A planar light source device as a backlight disposed on the back side of a liquid crystal display device is indispensable. As a type of the backlight, an edge light method (side light method),
A reflection type or a transmission type may be used. For example,
In the case of a backlight of an edge light type, when a one-side lighting type is used, a reflection sheet, a light guide plate, a diffusion plate (diffusion sheet) and 2
Laminate two lens sheets (lenticular lens)
A light source such as a fluorescent lamp is arranged along the side edge of the light guide plate.

[0003] In the backlight having the above structure, the light of the light source incident on the inside of the light guide plate is guided to the diffusion plate to be diffused in a predetermined angle range, and the directivity given by the light guide plate is corrected by the lens sheet. By doing
Light whose optical axis is substantially perpendicular and spreads at an appropriate viewing angle can be uniformly incident on the entire back surface of the liquid crystal display device. The reflection and transmission backlights also use a prism sheet or a polarizing sheet instead of a lens sheet and have different light paths in the light guide plate, but the light from the light source is evenly distributed by the light guide plate and multiple optical sheets. It is similar in that it is made to be.

[0004]

By the way, a liquid crystal display consumes a large amount of power as compared with a main device such as a personal computer or a television, and it is desired to reduce power consumption in a backlight. In addition, with the active matrix, color, and high pixel count of the liquid crystal display device, a backlight with higher luminance is desired. However,
In the current backlight, a large number of optical members are stacked as described above, and light from the light source is attenuated in proportion to the product of the light transmittance of each optical member. Moreover, it is extremely difficult to dramatically improve the luminance.

The present invention has been made in view of the above circumstances, and has been made as a result of various studies on a novel structure for further reducing the attenuation of light from a light source. It is an object of the present invention to provide a planar light source device capable of realizing a higher and higher luminance and irradiating an object such as a liquid crystal display device with light more uniformly.

[0006]

In order to solve the above-mentioned problems, a planar light source device according to the present invention comprises a prism sheet for emitting light incident from a rear surface from a surface thereof at a substantially vertical exit angle, and a prism sheet for the prism sheet. A linear light source disposed parallel to the prism sheet laterally or rearwardly, and a long-axis movable mirror disposed parallel to the light source and reflecting light emitted from the light source toward the back surface of the prism sheet And characterized by the following.

That is, in the above planar light source device, light emitted from the linear light source at a predetermined width is reflected toward the prism sheet by the long axis type movable mirror.
The light exits from the surface at a substantially perpendicular exit angle via the prism sheet. At that time, the movable mirror continuously changes the light reflection direction by rotating or rotating about the axis. As a result, the prism sheet visually acts as if light is uniformly radiated from the entire surface.

In a preferred embodiment of the present invention, a polygon mirror is used as a movable mirror in order to smoothly change the direction of light reflection on the prism sheet. Further, in another preferred embodiment of the present invention, a galvanometer mirror is used as the movable mirror.

In each of the above embodiments, the prism sheet is formed in a rectangular shape and has a band shape over a set of parallel side edges so that the center of light emitted from the prism sheet is more aligned in the line of sight. The light source and the movable mirror are arranged in parallel and in parallel with the side edges of the prism sheet, and each prism body of the prism sheet has a cross section orthogonal to the longitudinal direction. Is preferably formed into an isosceles triangle, and the apex angle of each prism body is made gradually sharper as the distance from the light source increases in a direction orthogonal to the side edge of the prism sheet.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a planar light source device according to the present invention will be described with reference to the drawings. FIG. 1 is a partially broken schematic side view showing a structure and an application example of a planar light source device according to the present invention. FIG. 2 is a partially broken schematic side view showing another structure and an application example of the planar light source device according to the present invention. FIG. 3 is a longitudinal sectional view schematically showing the structure of the prism sheet. Hereinafter, in the description of the embodiments, the planar light source device is abbreviated as “light source device”.

The light source device of the present invention is a device mainly used as a backlight of a liquid crystal display. The liquid crystal display is, as exemplified in FIG. 1, a liquid crystal device (LCD element) arranged on the front surface of a box-shaped case (6).
It mainly comprises (5) and a light source device housed on the back side of the liquid crystal device (5). As is well known, the liquid crystal device (5) is formed by laminating a liquid crystal layer and a color filter between a pair of polarizing plates provided with a transparent electrode on the inner surface, and by using a light shutter effect by polarized light, from the back side. Is controlled for each pixel, and an image is formed as a set of controlled pixels.

The light source device of the present invention is a device arranged on the back side of the liquid crystal device (5) as described above.
A prism sheet (1) that emits light incident from the rear surface from the surface at a substantially perpendicular exit angle (θ2), and a linear type disposed parallel to the prism sheet (1) on the side or behind the prism sheet (1). Light source (2) and light source (2)
And a long-axis movable mirror (3) that reflects light emitted from the light source (2) toward the back of the prism sheet (1).

The prism sheet (1) is an optical member for changing the direction of light rays, and is usually made of a synthetic resin having excellent transparency. Examples of such a synthetic resin include acrylic resins, polycarbonate resins, fluororesins, vinyl chloride resins, other polyesters, and various thermoplastic resins such as polypropylene. Considering the heat resistance over the above, an acrylic resin or a mixture of a fluororesin and a thermoplastic acrylic resin is preferred. The prism sheet (1) is usually produced by injection molding or press molding using a stamper.

The prism sheet (1) emits light incident at an angle of incidence (θ1) from the back surface at an emission angle (θ2) substantially perpendicular to the sheet surface in order to direct transmitted light more toward the viewing direction. Designed to. The incident angle (θ1) differs substantially between the base point of light irradiation, that is, the part close to the reflection surface of the movable mirror (3) and the part distant from it, but the emission angle (θ2) from the prism sheet (1). Is approximately constant.
It is necessary to preset the apex angle (α) of the angular prism body (10) according to the incident angle (θ1).

Specifically, the prism sheet (1) is formed in a rectangular shape according to, for example, the outer shape of the liquid crystal device (5). Also, as shown in FIG. 3, the prism sheet (1)
Are strip-shaped prisms (1) over a set of parallel side edges.
0) are arranged on the surface (FIG. 3 shows the prism body (10) in a cross section orthogonal to the longitudinal direction). With respect to the prism sheet (1), the light source (2) and the movable mirror (3) are arranged in parallel and in parallel with the side edge of the prism sheet (1). Each prism body (10) has a cross section perpendicular to the longitudinal direction formed into an isosceles triangle, and the apex angle (α) of each prism body (10) is orthogonal to the side edge of the prism sheet (1). As the distance from the light source (2) increases, the sharpness is gradually increased.

The apex angle (prism angle) of the prism body (10)
(Α) can be inversely calculated from the incident angle (θ1), the output angle (θ2), and the refractive index of the material. For example, in the case of a prism sheet (1) formed of an acrylic resin having a refractive index of 1.49, when the incident angle (θ1) of light is 10 °, the base angle (β) of the prism body (10) is 20 °. (Vertical angle (α) is 140
°), the emission angle (θ2) is about 90
°, and when the incident angle of light (θ1) is 50 °,
The base angle (β) of the prism body (10) is 70 ° (vertical angle (α)
Is set to 40 °), the emission angle (θ2) becomes about 90 °. That is, by determining the vertex angle (α) of the prism body (10) based on the refractive index of the prism sheet (1) and the position of the movable mirror (3), the emission angle (θ2) can be set to approximately 90 °.

As the light source (2), a fluorescent lamp which consumes less power is used. However, a straight-tube cold-cathode tube is usually used from the viewpoint of a long life. Further, as the light source (2), a transmission light in which light-emitting bodies are accommodated at both ends of a glass rod can be used. In particular, the light source (2) constituted by the transmission light can obtain high illuminance with low power. Furthermore, the light source (2) leaves a part of the peripheral surface along the longitudinal direction to concentrate the light to be irradiated on the movable mirror (3) as much as possible. ).

The linear light source (2) as described above irradiates light to the side or rear of the prism sheet (1), that is, the rear surface of the prism sheet (1) in cooperation with the movable mirror (3). It is placed in a position where it can be done. More specifically, the light source (2) is arranged, for example, in the vicinity of the side edge of the prism sheet (1) as described above, and in parallel with and parallel to the side edge. Also, behind the prism sheet (1) (back side)
By arranging the light source (2) in the liquid crystal display as described above, the periphery of the liquid crystal surface can be designed to be more compact.

In the present invention, in order to maximize the use efficiency of the light from the light source (2), the light emitted from the light source (2) is converted into a prism sheet (1) by a long-axis movable mirror (3). It is made to reflect to. As the movable mirror (3), for example, a polygon mirror (3a) as shown in FIG. 1 is used. The polygon mirror (3a)
As is well known, it is a rotating mirror formed with a side surface of a polygonal prism as a reflecting mirror.

The polygon mirror (3a) is preferably formed as small as possible in diameter in order to reduce the size of the apparatus. Further, from the viewpoint of reducing the weight and the manufacturing cost, the side surfaces of the resin-formed polygonal column may be formed into a mirror surface by vapor deposition of aluminum or the like. In the case of a polygonal mirror (3a), for example, in the case of a hexagonal prism mirror, a rotation speed of 400 to 1500 rpm (rotation corresponding to a scanning speed on a plane of about 10 ms to 45 ms) is performed by a small motor of a direct drive system attached thereto. number)
To rotate at high speed in one direction.

As the movable mirror (3), a galvano mirror (3b) as shown in FIG. 2 can be used. The galvanometer mirror itself is also a well-known optical member for changing the reflection angle, and has a structure in which a plane mirror is pivotally supported. In the present invention, similarly to the above polygon mirror,
To reduce the size of the device, the galvanomirror (3b)
It is preferable that the surface is formed as short as possible, and from the viewpoint of reducing the weight and manufacturing cost, the surface of the resin-formed flat plate may be formed into a mirror surface by vapor deposition of aluminum or the like. Galvano mirror (3b)
Is configured such that a direct drive type servo motor (galvano motor) rotates a predetermined angular range at high speed in the forward and reverse directions at substantially the same speed as the polygon mirror.

In the present invention, as shown in FIGS. 1 and 2, between the light source (2) and the movable mirror (3), the light emitted from the light source (2) is used more efficiently. Is preferably provided with a condenser lens (4). The condensing lens (4) is a rod-shaped lens whose cross section orthogonal to the longitudinal direction has a shape of a toto lens, and a light source such that the light of the light source (2) is located on the mirror surface of the movable mirror (3) It is arranged parallel to and parallel to (2).

As described above, the light source device of the present invention is disposed on the back side of the liquid crystal device (5), and supplies light to the liquid crystal device (5) via the prism sheet (1). That is, in the light source device of the present invention, light emitted from the linear light source (2) with a predetermined width is reflected toward the prism sheet (1) by the long-axis movable mirror (3), and The light exits from the surface through (1) at a substantially perpendicular emission angle (θ2). At that time, the movable mirror (3) continuously changes the light reflection direction by rotating or rotating at high speed about the axis. As a result, the prism sheet (1) visually acts as if it irradiates light uniformly from the entire surface.

In other words, the light source device of the present invention does not need to transmit light to a large number of optical members such as an optical sheet unlike a conventional backlight, but transmits light to the prism sheet (1) of the light source (2). The light attenuation can be further reduced. In addition, since the planar light having a predetermined width and emitted from the light source (2) is concentrated and reflected on the movable mirror (3), the light from the light source (2) is not dispersed. Therefore, according to the light source device of the present invention, extremely high luminance can be obtained even with a small amount of light, and the liquid crystal display device (5)
Can be more uniformly irradiated with light.

In particular, when the condenser lens (4) is disposed between the light source (2) and the movable mirror (3), the light from the light source (2) is more efficiently transmitted to the movable mirror (3). It can be collected and higher brightness can be obtained.

In the light source device of the present invention, a diffusion plate (diffusion sheet) may be disposed on the front or back of the prism sheet (1). When the diffuser is provided, the amount of light attenuation increases, but the spread of light in the viewing direction can be adjusted more accurately. In addition, the light source device of the present invention can be applied to various display devices and lighting devices that use light, in addition to a liquid crystal display, and can use light more efficiently with less power.

[0027]

According to the planar light source device of the present invention, since the light of the light source is merely transmitted through the prism sheet, the attenuation of the light can be further reduced, and the planar light source having a predetermined width irradiated from the light source can be obtained. Light is concentrated on a movable mirror and reflected, and the light from the light source is not dispersed, so that extremely high brightness can be obtained even with a small amount of light, and it can be applied to an object such as a liquid crystal display device. Light can be more uniformly irradiated.

[Brief description of the drawings]

FIG. 1 is a partially cut-away schematic side view showing a structure and an application example of a planar light source device according to the present invention.

FIG. 2 is a partially broken schematic side view showing another structure and an application example of the planar light source device according to the present invention.

FIG. 3 is a longitudinal sectional view schematically showing the structure of a prism sheet.

[Explanation of symbols]

 1: prism sheet 10: prism body 2: light source 3: movable mirror 3a: polygon mirror 3b: galvano mirror 4: condensing lens 5: liquid crystal device θ1: incident angle θ2: emission angle α: apex angle

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09F 9/00 336 G09F 9/00 336J // F21Y 103: 00 F term (Reference) 2H042 CA13 CA17 2H045 AA01 AB01 CB17 2H091 FA41Z LA18 5G435 AA03 BB12 BB15 EE27 FF05 FF07 FF08 GG03 GG10

Claims (5)

[Claims] 1. A prism sheet (1) for emitting light incident from the back surface at a substantially perpendicular emission angle (θ2) from the front surface;
A linear light source (2) disposed parallel to the prism sheet (1), laterally or behind the prism sheet (1); and light arranged parallel to the light source (2) and emitted from the light source (2). And a long-axis movable mirror (3) for reflecting the light toward the back surface of the prism sheet (1). 2. The moving mirror (3) is a polygon mirror (3).
The planar light source device according to claim 1, which is a). 3. A movable mirror (3) comprising: a galvano mirror (3);
The planar light source device according to claim 1, wherein b) is satisfied. 4. The prism sheet (1) is formed in a rectangular shape and has a structure in which a number of band-like prism bodies (10) are arranged on the surface over a set of parallel side edges, and a light source (2). And the movable mirror (3) is a prism sheet (1)
The prisms (10) of the prism sheet (1) are arranged in parallel and in parallel with the side edges of the prism sheet (1), and the cross section orthogonal to the longitudinal direction is formed in an isosceles triangle, and the prisms (10) The planar light source device according to any one of claims 1 to 3, wherein the apex angle (α) is gradually sharpened as the distance from the light source (2) increases in a direction orthogonal to the side edge of the prism sheet (1). 5. The planar light source device according to claim 1, wherein a condenser lens (4) is arranged between the light source (2) and the movable mirror (3).