JPH09318818A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device whose light utilization efficiency is high enough, and whose luminance irregularity can be reduced enough inside a surface. SOLUTION: A light guide plate 101 includes plural projections 141 arranged on the one main surface 131 of the plate 101, so that light from a light source transmitted inside the plate 101 is emitted from one main surface 131 side of the plate 101, and diffusing boards 800 and 900 guide the peak of the light from the light source emitted from the one main surface 131 side of the plate 101 to the normal with respect to the one main surface 131.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an edge light type surface light source device.

[0002]

2. Description of the Related Art A display device represented by a liquid crystal display device is:
It has come to be used as various display devices for televisions, computers, car navigation systems, etc. by taking advantage of its features such as thinness, light weight, and low power consumption.

For example, a light transmission type liquid crystal display device includes a liquid crystal panel having a liquid crystal layer held between a pair of electrode substrates,
The liquid crystal panel includes a surface light source device which is disposed on one main surface and guides light source light to the liquid crystal panel.

In such a display device, in order to further reduce the thickness and size of the device, it is necessary to reduce the thickness of the surface light source device, and the surface light source device of the backlight type to the edge light type is used. It has become possible to be.

The edge light type surface light source device is a
As disclosed in Japanese Patent Publication No. 63-24529 and the like, a tubular light source and a thin plate-shaped light guide plate such as acrylic resin having a milky white scattering pattern printed on the back side are included, and the tubular light source has one end surface of the light guide plate. Are placed close together. Then, the light source light from the tubular light source propagates through the light guide plate, is scattered by the scattering pattern on the back surface of the light guide plate, and is emitted to the main surface of the light guide plate.

According to the above-mentioned edge light type surface light source device, although the device can be made thin, there is light loss due to the scattering pattern, and it is necessary to print the scattering pattern separately. And the improvement of productivity were respectively desired.

As a solution to the above problems, there are known edge light type surface light source devices disclosed in, for example, JP-A-5-313163 and JP-A-6-75123. This is because a plurality of protrusions are arranged on the main surface side of the light guide plate facing the display panel side, and the emission direction from the light guide plate is controlled by the protrusions, which makes it possible to eliminate the conventional scattering pattern. The light utilization efficiency can be improved.

Similarly, the present applicant arranges a plurality of projections on the main surface side of the light guide plate facing the display panel, and controls the light emitted from the light guide plate by these projections. Are proposed, and a surface light source device with improved light use efficiency is proposed.

[0009]

The above-described surface light source device will be described with reference to FIG. This surface light source device (1001)
Is a rectangular light guide plate (1101) made of acrylic and a light guide plate.
One end surface (1121a) of (1101) is used as a light incident surface, and this end surface (1121a)
The tubular light source (1501) arranged close to (a) and the light guide plate (110
1) A light collecting sheet (1901) arranged on the top. The light guide plate (1101) includes a plurality of comb tooth-shaped prism projection rows (1141) substantially parallel to the tube length direction of the tubular light source (1501).

The prism projection row (1141) is provided with a tubular light source (1).
501) a first slope (1143) that is inclined close to the pipe length direction;
A second slope (1145) intersecting with the first slope (1143),
The first slope (1143) intersects the main surface (1131) of the light guide plate (1101) at an angle (θ1), and the second slope (1145) intersects the light guide plate (1101).
It intersects the main surface of 1) at an angle (θ2).

[0011] The light source light emitted from the tubular light source (1501) is based on the difference in refractive index between the air and the acrylic resin.
(1101) becomes a light having a condensing angle (Ω1) of about 42 °, and the angle (θ1) is set to a condition for totally reflecting the light source light propagating in the light guide plate (1101), for example, 27 °, The angle (θ2) depends on the light guide plate (11
The condition for emitting the light source light propagating in 01) is set to, for example, 88 °.

Thus, the first of the rows of prism projections (1141)
When the light source light is incident on the slope (1143), the light source light is emitted on the first slope.
The light is totally reflected by (1143) and is guided to the second slope (1145) which is the emission surface, and passes through the second slope (1145) and then the main surface of the light guide plate (1101).
The light is condensed at a converging angle (Ω2) of about 90 ° with respect to (1131) and is emitted as outgoing light having directivity.

Further, the light-condensing sheet (190) is provided so as to have a luminance peak in a direction substantially normal to the main surface (1131) of the light guide plate (1101).
It is emitted via 1). According to such a surface light source device, a sufficiently condensed light source light can be obtained substantially only by reflection and refraction, so that the light utilization efficiency is significantly improved.

However, as a result of further research conducted by the present inventor, it has been found that there are the following problems. That is, in manufacturing the light guide plate, extremely fine burrs and the like occur at the corners of the light incident surface. Since such a light guide plate substantially utilizes only reflection and refraction, it is affected by the undesired light source light incident from the flash portion and has a stripe-like uneven brightness in the surface. Occurs.

When such a surface light source device is used in a liquid crystal display device or the like, moire may occur due to interference between the pitch of the prism protrusions of the light guide plate, the prism pitch of the light collecting sheet and the pixel pitch of the display device.

Further, since the light source light emitted from the surface light source device has an extremely high condensing property, there is a problem that the viewing angle characteristic is impaired when used in a liquid crystal display device or the like. The present invention has been made in response to the above technical problem, and an object thereof is to provide a surface light source device in which light utilization efficiency is sufficiently high and luminance unevenness in the surface is sufficiently reduced. .

It is another object of the present invention to provide a surface light source device in which moire can be easily controlled even when used in a display device. Another object of the present invention is to provide a surface light source device whose light-collecting property can be easily controlled in response to the demand of a display device.

[0018]

According to a first aspect of the present invention, there is provided a tubular light source, and a light guide plate including a light introducing surface disposed near the tubular light source for introducing light source light from the tubular light source. In a surface light source device including a diffuser plate arranged in proximity to one main surface of the light guide plate, the light guide plate transmits the light source light propagating in the light guide plate from the one main surface side of the light guide plate. A plurality of protrusions disposed on the one main surface of the light guide plate so as to emit light, wherein the diffusion plate measures a peak of a light source light emitted from the one main surface side of the light guide plate with respect to the one main surface. The surface light source device is characterized by being guided by a line method.

The diffusing plate makes it impossible to visually recognize the streak-like luminance unevenness caused by the flash on the light incident surface. Further, it is possible to prevent moire between the prism protrusions of the light guide plate and the prisms of the light condensing sheet, and moire between the prism protrusions of the light guide plate and the pixel pitch.

The invention according to claim 2 is characterized in that the diffusion plate controls the angle formed by the luminance peak of the emitted light source light and the normal to the main surface within 30 °. 1 is a surface light source device.

Since the luminance peak is oriented in the direction of use of the surface light source device, the driving voltage to the tubular light source can be lowered, leading to low power consumption of the surface light source device. The invention described in claim 3 is the surface light source device according to claim 1, wherein the diffusing plate has a condensing property of 2 or more.

Since the diffusing plate having the light converging property of 2 or more is used, the light source light emitted obliquely to the main surface can be directed more in the normal direction of the main surface, and the light utilization efficiency can be improved. You can

When the light collecting property is less than 2, it becomes difficult to direct the light emitted obliquely from the main surface of the light guide plate in the normal direction. The invention described in claim 4 is the surface light source device according to claim 1, wherein the diffusion plate has a haze of 70% or more.

Since the haze is 70% or more, the viewing angle characteristics are improved by the appropriate diffusion action of the diffusion plate. Claim 5
The invention according to claim 1 is the surface light source device according to claim 1, wherein the diffusion plate includes a first diffusion plate and a second diffusion plate.

By using the second diffusing plate, the direction of the luminance peak of the light emitted from the first diffusing plate can be oriented more in the normal direction, and the light utilization efficiency can be improved. The invention according to claim 6 is the surface light source device according to claim 1, characterized in that a condensing sheet for condensing the light emitted from the diffusion plate is disposed on the diffusion plate.

By eliminating the moire and uneven brightness and improving the light utilization efficiency, it is possible to increase the luminance in the normal direction by mounting a light-condensing sheet, and thus the light utilization efficiency can be improved. The invention according to claim 7 is the surface light source device according to claim 6, wherein the light-condensing sheet includes a plurality of prism rows that are substantially aligned with an arrangement direction of the protrusions of the light guide plate. .

By aligning the prism array of the light-condensing sheet with the projection array direction of the light guide plate, a surface light source device having high luminance in the normal direction and excellent viewing angle characteristics in the horizontal direction of the screen can be obtained.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION A surface light source device according to an embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the surface light source device (1) is a molded body made of acrylic resin, and is a substantially rectangular light guide plate having an effective light emitting area (111) having a diagonal size of 10.4 inches. (101), one long end surface of the light guide plate (101) is a light introduction surface (121a)
And the tubular light source (5
01), the light source light from the tubular light source (501) is efficiently guided (10
Reflective film (601) leading to 1), one main surface (1) of the light guide plate (101)
31) First and second diffusion plates 700, 800 arranged on the top of the second diffusion plate 800, and a condensing sheet 900 arranged on the second diffusion plate 800.

This light guide plate (101) has a wall thickness (t) of the light introducing surface (121a) as shown in FIG. 2 in order to achieve a thin device.
1) is 3 mm, the thickness of the end face (121b) opposite to the light introduction face (121a)
(t2) is composed of 1mm wedge type. Also, the light guide plate (101)
On one main surface (131), a plurality of comb-tooth-shaped prism projection rows (141) substantially parallel to the tube length direction of the tubular light source (501) are included. The prism protrusion row (141) includes a first slope (143) that is inclined in the vicinity of the tubular light source (501) and a second slope (145) that intersects with the first slope (143). The slope (143) is the light guide plate (10
Intersects the main surface (131) of 1) at an angle (θ1), and
The slope (145) forms an angle (θ) with respect to the main surface (131) of the light guide plate (101).
Encounter at 2). Further, the pitch of the prism projection array (141) is formed to be gradually smaller as the distance from the tubular light source (501) is increased in order to make the brightness uniform.

The first slope (143) and the main surface (13) of the light guide plate (101).
The angle (θ1) formed with 1) is set to 27 ° in this embodiment, and the second slope (145) and the main surface (1) of the light guide plate (101) are set.
The angle (θ2) formed with 31) is set to 88 ° in this embodiment. Here, the angle (θ1) is set to 27 °, but the angle (θ1) is not limited to this, and the light source light that enters from the light introduction surface (121a) and propagates in the light guide plate (101). May be set so as to be reflected and guided to the second inclined surface (145) of the prism protrusion row (141). However, if the angle (θ1) is too small, it is not possible to arrange a large number of protrusion rows (141), which may lead to uneven brightness.Therefore, set the angle (θ1) in the range of 20 to 40 °. Is desirable. Although the angle (θ2) is set to about 90 ° here, it is preferably 80 ° or more in order to reduce the spread of the emitted light, and may be an obtuse angle exceeding 90 °.

The first and second diffusing plates (700) and (800) are, for example, diffusing plates having a total light transmittance of 80%, a haze of 90% and a condensing property of 2.5.
(DF-100: made by Fuji Photo Film Co., Ltd.).
Incidentally, the condensing property of the diffuser plate here means that when a uniform diffused light is irradiated, the angle formed with the normal direction of the main plane is within the range of -80 ° to + 80 °, and the peak luminance (Q1) The ratio (Q1 / Q2) to the minimum brightness (Q2).

The condensing sheet (900) is composed of a prism sheet (BEFII: manufactured by Sumitomo 3M Ltd.) in which isosceles prism rows with a vertical angle of 90 ° are arranged, and prism projections of the light guide plate (101) in the prism row direction. It is arranged so as to substantially coincide with the direction of the row (141). When the prism array direction of the light collecting sheet (900) is used for a liquid crystal display device or the like, in consideration of interference with the display device, for example, a light guide plate ( It may be arranged so as to have an inclination of several degrees with respect to the prism projection row (141) direction of 101).

Next, the operation of the surface light source device (1) will be described. The light source light emitted from the tubular light source (501) has a converging angle (Ω1) of about 42 ° in the light guide plate (101) due to the difference in refractive index between air and acrylic resin. Propagated as light.

Here, when the light source light propagating in the light guide plate (101) is guided to, for example, the first inclined surface (143) of the prism projection array (141), the light source light is totally reflected by the first inclined surface (143). The light is reflected and guided to the second inclined surface (145) which is the exit surface, and passes through the second inclined surface (145), and the light collecting angle (about 90 ° with respect to one main surface (131) of the light guide plate (101) ( Ω2) and is emitted from the light guide plate (101) as emitted light having directivity. Similarly, when the light source light propagating in the light guide plate (101) is guided to, for example, the second inclined surface (145) of the prism protrusion row (141), it also passes through the second inclined surface (145) and then the light guide plate ( Convergence angle of about 90 ° to the main surface (131) of 101)
The light guide plate (10
Emitted from 1).

In FIG. 4, the light source light emitted from the light guide plate (101) is plotted along the horizontal axis at the center of one main surface (131) of the light guide plate (101) in the normal direction and the measuring direction (the tubular light source (501)). (Direction orthogonal to)
FIG. 6 is a diagram showing an angle formed by and the luminance (cd / m ² ) on the vertical axis. From this figure, it is understood that the light guide plate (101) emits highly efficient and sufficiently condensed light source light.

In this way, the light source light emitted from the light guide plate (101) with directivity is first diffused by the first diffusion plate (700), and the luminance peak is one of the light guide plate (101). It is shifted in the direction normal to the main surface (131).

FIG. 5 shows the angle formed by the light source light emitted from the first diffusion plate (700) between the normal direction and the measurement direction at the center of one main surface (131) of the light guide plate (101) on the horizontal axis. , The vertical axis represents the brightness (c
d / m ² ), the curve (a) in the figure is in the direction orthogonal to the tubular light source (501), and the curve (b) in the figure is the direction parallel to the tubular light source (501). . As can be seen from this figure, the light from the light source is maintained by the first diffuser plate (700) while maintaining its light-collecting property.
The light guide plate (101) is shifted in the direction of the normal to the main surface (131).

Further, the light source light emitted from the first diffusing plate (700) is diffused by the second diffusing plate (800) and has a luminance peak with respect to one main surface (131) of the light guide plate (101). Is further shifted in the normal direction.

FIG. 6 shows the angle formed by the light source light emitted from the first diffusion plate (700) between the normal direction and the measurement direction at the center of one main surface (131) of the light guide plate (101) on the horizontal axis. , The vertical axis represents the brightness (c
d / m2), the curve (a) in the figure shows a direction orthogonal to the tubular light source (501), and the curve (b) in the figure shows a case parallel to the tubular light source (501). As can be seen from this figure, the brightness peak of the light source light is caused by the second diffusion plate (800).
1) It is controlled within about 30 ° with respect to the normal direction to the one main surface (131).

Further, the light source light emitted from the second diffusing plate (800) is condensed by the condensing sheet (900), and the luminance peak is on the main surface (131) of the light guide plate (101). It is further shifted in the normal direction.

FIG. 7 shows an angle formed by the light source light emitted from the light-condensing sheet (900) between the normal direction and the measuring direction at the center of one main surface (131) of the light guide plate (101) on the horizontal axis, Brightness (c
d / m2), the curve (a) in the figure shows a direction orthogonal to the tubular light source (501), and the curve (b) in the figure shows a case parallel to the tubular light source (501). As can be seen from this figure, the light from the light source is condensed by the condensing sheet (900), and the luminance peak substantially coincides with the normal direction to the one main surface (131) of the light guide plate (101).

As described above, according to the surface light source device (1) of this embodiment, the light guide plate (101) is substantially reflective,
Since only refraction is used, the light utilization efficiency of the light source light from the tubular light source (501) is extremely high. Therefore, for example, in a surface light source device in which the same diffusion sheet and condensing sheet as described above are combined on the main surface of the light guide plate having the scattering pattern printed on the back side, even if the number of diffusion sheets is reduced to one, The peak of the central brightness from the surface light source device is 1100 (cd / m ² ).
On the other hand, in this embodiment, the value is set as high as 1300 (cd / m ² ), as can be seen from FIG. 7.

Further, in this embodiment, as described above, the light emitted from the light guide plate (101) immediately passes through the first and second diffusion plates (700) and (800) and then the condensing sheet ( 900). Therefore, even if burrs or the like are generated at the ends of the light introduction surface (121a) of the light guide plate (101) and undesired light source light is introduced into the light guide plate (101), the light is emitted from the light guide plate (101). Since the emitted light is immediately diffused through the first and second diffusion plates (700) and (800), the uneven brightness is sufficiently eliminated. For example, as a surface light source device,
Light guide plate (101), light collecting sheet (900), first and second diffuser plates (7)
When the layers are arranged in the order of 00) and (800), the stripe-shaped uneven brightness was visually recognized, but according to this embodiment, it was not visible at all.

Further, even when such a surface light source device (1) is used in a liquid crystal display device or the like, the diffusion plates (700) and (800) are inserted between the liquid crystal display device and the light guide plate (101). Light guide plate (10
Moire does not occur due to the interference between the prism protrusion row (141) pitch of 1) and the pixel pitch of the display device.

Further, as can be seen from FIG. 7, the surface light source device
Since the light source light emitted from (1) is appropriately condensed, the viewing angle characteristics are not impaired when used in a liquid crystal display device.

In the embodiment described above, the first and second
Diffusion plates (DF-100: manufactured by Fuji Photo Film Co., Ltd.) were used as the diffusion plates (700) and (800).
(Manufactured by Tsujimoto Electric Co., Ltd.) is preferably used. It is desirable that these diffusers have a high total light transmittance, for example, 80% or more, in order not to impair the utilization efficiency of the light from the light source. Further, it is desirable that these diffusion plates have an appropriate diffusion effect in order to reduce uneven brightness, and haze is desirably 70% or more. Furthermore, it is desirable that these diffusers have an appropriate light condensing effect, and that the light condensing property is 2 or more.

Further, in this embodiment, the first and second diffusion plates (700), (800) are used in combination, but the brightness peak of the light emitted from the light guide plate is the same as that of the light guide plate (101). It does not matter if the angle formed by the normal to the one main surface (131) is controlled within 30 °.

Further, in this embodiment, the light collecting sheet is used.
(900) was used prism sheet (BEFII: Sumitomo 3M Co., Ltd.) in which isosceles prism rows with an apex angle of 90 ° are arranged, but in accordance with the required directivity, a prism sheet (V7 : Dainippon Printing Co., Ltd.), a prism sheet (H210: Mitsubishi Rayon Co., Ltd.), a wave sheet (W518: Sekisui Chemical Co., Ltd.), etc. are appropriately used.

Furthermore, in this embodiment, the light guide plate (10
Although acrylic resin is used as 1), other materials may be used. In this case, since the light collection angle of the light source light incident from the light introduction surface (121a) is slightly different, the angle formed by each projection row may be appropriately changed in consideration of the above-mentioned circumstances.

In this embodiment, the light guide plate (10
Although one end surface (121a) of (1) was used as the light introducing surface, the light guide plate (101) was provided with a groove or a through hole including the light introducing surface to form a tubular light source (5
You may arrange 01).

[0052]

According to the invention described in claim 1, a tubular light source, a light guide plate including a light introducing surface for introducing light source light from the tubular light source and arranged in the vicinity of the tubular light source, and the light guide plate. In a surface light source device including a diffuser plate disposed adjacent to one main surface of a light plate, the light guide plate emits the light source light propagating in the light guide plate from one main surface side of the light guide plate. A plurality of protrusions arranged on the one main surface of the light guide plate, the diffusion plate is a method of normalizing the peak of the light source light emitted from the one main surface side of the light guide plate to the one main surface. Led to.

The diffusing plate makes it impossible to visually recognize the stripe-shaped luminance unevenness caused by the flash on the light incident surface. Further, it is possible to prevent moire between the prism protrusions of the light guide plate and the prisms of the light condensing sheet, and moire between the prism protrusions of the light guide plate and the pixel pitch.

According to the second aspect of the invention, the angle formed by the luminance peak of the light source emitted from the diffuser plate of the first aspect and the normal to the main surface is controlled within 30 °. By doing so, the luminance peak is oriented in the direction of use of the surface light source device, so that the driving voltage to the tubular light source can be lowered, leading to low power consumption of the surface light source device.

According to the invention described in claim 3, since the light-gathering property of the diffusion plate of the invention described in claim 1 is 2 or more, the light source light emitted obliquely to the main surface is generated. The light can be directed more in the direction of the main surface normal, and the light utilization efficiency can be improved.

If the light-collecting property is less than 2, it becomes difficult to direct the light emitted obliquely from the main surface of the light guide plate in the normal direction. According to the invention described in claim 4, since the haze of the diffuser plate of the invention of claim 1 is 70% or more, a proper diffusing action of the diffuser plate improves the viewing angle characteristics.

According to the invention described in claim 5, the diffusion plate of the invention described in claim 1 includes the first and second diffusion plates, so that the brightness peak of the light emitted from the first diffusion plate is obtained. Can be directed more toward the normal direction, and the light utilization efficiency can be improved.

According to the invention described in claim 6, since the condensing sheet for condensing the light emitted from the diffusion plate according to claim 1 is arranged on the diffusion plate, the moire and the brightness are reduced. By eliminating the unevenness and improving the light utilization efficiency, it is possible to increase the brightness in the normal direction by mounting the light-condensing sheet, and thus it is possible to improve the light utilization efficiency.

According to the invention described in claim 7, the light-condensing sheet of the invention described in claim 6 includes a plurality of prism rows which are substantially aligned with the arrangement direction of the projections of the light guide plate. It is possible to obtain a surface light source device having high luminance in the line direction and excellent viewing angle characteristics in the horizontal direction of the screen.

[Brief description of drawings]

FIG. 1 is a schematic front view of a surface light source device according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional perspective view of the surface light source device taken along line AA ′ in FIG.

FIG. 3 is a diagram for explaining the operation of the surface light source device of FIG.

FIG. 4 shows the light source light emitted from the light guide plate of the surface light source device of FIG. 1 with the horizontal axis representing the angle between the normal direction and the measuring direction at the center of one main surface of the light guide plate and the vertical axis representing the luminance. It is the figure shown.

5 is a diagram showing the light source light emitted from the first diffusion plate of the surface light source device shown in FIG. It is the figure which has shown.

6 is a diagram showing the light source light emitted from the second diffuser plate of the surface light source device of FIG. 1, the horizontal axis representing the angle between the normal direction at the center of one main surface of the light guide plate and the measuring direction, and the vertical axis representing the luminance. It is the figure which has shown.

7 shows the light source light emitted from the light-condensing sheet of the surface light source device of FIG. 1, the horizontal axis representing the angle between the normal direction and the measuring direction at the center of one main surface of the light guide plate, and the vertical axis representing the luminance. It is the figure which has shown.

FIG. 8 is a schematic configuration diagram of a conventional surface light source device.

[Explanation of symbols]

 (1) Surface light source device (101) Light guide plate (700) 1st diffuser plate (800) 2nd diffuser plate (900) Condenser sheet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichiro Saito 7-1 Nisshin-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Toshiba Electronics Engineering Co., Ltd.

Claims (7)

[Claims] 1. A tubular light source, a light guide plate including a light-introducing surface for introducing light from the tubular light source into the tubular light source, and a light guide plate disposed adjacent to one main surface of the light guide plate. A light guide plate disposed on the one main surface of the light guide plate such that the light source light propagating in the light guide plate is emitted from one main surface side of the light guide plate. A planar light source device, wherein the diffusion plate guides a peak of light source light emitted from the one main surface side of the light guide plate in a direction normal to the one main surface. 2. The surface light source device according to claim 1, wherein the diffuser plate controls an angle between a luminance peak of the emitted light source light and a normal to the main surface to be within 30 °. 3. The surface light source device according to claim 1, wherein the diffusion plate has a light condensing property of 2 or more. 4. The surface light source device according to claim 1, wherein the diffusion plate has a haze of 70% or more. 5. The surface light source device according to claim 1, wherein the diffusion plate includes first and second diffusion plates. 6. The surface light source device according to claim 1, wherein a condensing sheet for condensing light emitted from the diffusion plate is arranged on the diffusion plate. 7. The surface light source device according to claim 6, wherein the light-condensing sheet includes a plurality of prism rows that are substantially aligned with an arrangement direction of the protrusions of the light guide plate.