JP2003151330A - Front light and electronic equipment having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem with impossible uniform lighting all over a front light when introducing a light from a point light source directly to a light guide plate. SOLUTION: This front light comprises the platy light guide plate 1 arranged on the side of a display surface 2a of a liquid crystal 2 and the point light source 3, the light guide plate 1 having first plane surfaces 8 opposed to each other on the side off the display surface 2a thereof, a second surface 6 having a plurality of first prism grooves 7 perpendicular to the direction of the optical axis of the point light source 3 and a third surface 5 for introducing the light therein, wherein a plurality of second prism grooves 9 are formed in a portion deviating from a light distribution range H of the point light source 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device, and more particularly to a so-called front light which is installed on a display surface side of various reflective display devices including reflective liquid crystal to illuminate. .

[0002]

2. Description of the Related Art In recent years, instead of a backlight that illuminates a transmissive liquid crystal from the back side, a front that directly illuminates the display surface of the liquid crystal by being disposed on the display surface side of the reflective liquid crystal. Lights are becoming mainstream. According to the display device including the reflective liquid crystal and the front light, there are advantages that the viewing angle can be increased and the power consumption can be reduced.

As this front light, for example, the configurations disclosed in Japanese Patent No. 2925530, Japanese Patent Laid-Open No. 2001-110223, and Japanese Patent Laid-Open No. 2001-23424 are known.

According to each of the above publications, the surface of the light guide plate facing the liquid crystal is a flat surface, and a semicircular concave or convex portion having a sawtooth or triangular prism-shaped cross section is formed on the opposite surface. However, by totally reflecting the light incident from the end surface of the light guide plate on these prism-shaped surfaces, the light is directed to the liquid crystal to illuminate, and the light is emitted from the light emitting surface to uniformly illuminate the entire surface. Is configured. further,
Japanese Unexamined Patent Publication No. 2000-221501 discloses a configuration in which a liquid crystal is bonded to a liquid crystal via a refractive layer having a refractive index smaller than that of the light guide plate.

According to the front lights proposed in the above publications, for example, Japanese Patent Laid-Open No. 2000-1172 is used.
As disclosed in Japanese Patent Publication No. 3, the point light source is converted into a line (plane) light source, and then the light is introduced into the light guide plate.

[0006]

However, in order to convert a point light source into a linear light source or a planar light source in this way, a conversion member for converting the point light source into a linear or planar shape is required. . Then, when the light passes through the conversion member and is reflected, a light amount loss of 10 to 30% occurs, and an extra installation space for the conversion member is required.

Therefore, it may be considered that the point light source directly introduces light into the light guide plate. However, since the point light source has a substantially elliptical light distribution as is well known, a portion outside the light distribution range of the point light source becomes dark, resulting in a problem that uniform illumination over the entire front light cannot be performed.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to enable uniform illumination over the entire surface.

[0009]

[Means for Solving the Problems]
In order to achieve the object, according to the present invention, there is provided a front light including a plate-shaped light guide plate having a light-transmitting property and a point light source arranged on the display surface side of a display device including a reflective liquid crystal. The light guide plate has a planar first surface that is arranged to face the display surface of the display device, and a plurality of light guide plates that are orthogonal to the optical axis direction from the point light source on the back surface side of the first surface. First
A prism-grooved second surface, and a third surface that is formed so as to be sandwiched between the first surface and the second surface and that introduces the light from the point light source into the inside. And a plurality of second
The prism groove is formed in either one or both of the predetermined portions on the first surface or the second surface outside the light distribution range of the point light source.

Further, the second prism groove has the first prism groove.
It is characterized in that it is formed in parallel with the prism groove.

Further, the point light source is composed of one light emitting diode arranged to face the center of the third surface or a plurality of light emitting diodes arranged to face the third surface. There is.

Further, the first prism groove and the second prism groove are formed so as to have a gradation such that the distance between the first prism groove and the second prism groove decreases as the distance from the point light source increases. The feature is that the light quantity density is made uniform.

Further, the first prism groove and the second prism groove are formed with gradation so that the depth becomes deeper as the distance from the point light source increases, so that the first prism groove and the second prism groove are formed. The feature is that the light quantity density of the surface is made uniform.

Further, an electronic apparatus having a front light is characterized by including the display device illuminated by the front light.

A light guide plate of a front light type liquid crystal display device having a light emitting surface on which a plurality of prism grooves are formed, and from which light from a light source is introduced from a side surface, wherein the plurality of prism grooves are dense and dense. Is changed according to the distribution range of the light from the light source.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 (a)
FIG. 1 is an external perspective view of a front light common to each embodiment described later, and FIG.

Although FIG. 1 shows a case where the electronic device is used for liquid crystal display of the mobile phone 10, other than this, it is also applicable to liquid crystal lighting for palmtop computers and desktop computers. For this purpose, the light quantity of the point light sources may be increased or the number of the point light sources may be increased as necessary.

First, in FIG. 1B, the liquid crystal 2 is, for example, a reflection type TFT liquid crystal, and the light guide plates 1 are arranged so as to face each other with the display surface 2a thereof facing upward. Then, on the second surface 6 which is the light emitting surface of the light guide plate 1,
As shown in the drawing, the plurality of first prism grooves 7 are formed in a gradation shape in which the first prism grooves 7 gradually become denser with distance from the point light source 3. Alternatively, the first prism groove 7 and the second prism groove to be described later are formed with gradation so that the depth becomes deeper as the distance from the point light source 3 increases. Here, the denser the inter-line density of the prism grooves, the brighter the brightness becomes, and the deeper the prism grooves become, the brighter the brightness becomes. Therefore, this ratio is appropriately set.

The light guide plate 1 can be stably manufactured together with a second prism groove, which will be described later, by integrally molding it by injection molding using a transparent or good light transmitting acrylic resin or polycarbonate resin. In addition to this injection molding, it is also possible to heat the final flat plate light guide plate in advance and perform plastic processing to mold it by pressing a female mold with convex prism grooves. is there.

On the other hand, a third surface 5 is provided on the side surface of the light guide plate 1.
Is formed, and one high-intensity light-emitting diode surrounded by the reflection plate 4 serving as the point light source 3 is arranged facing the third surface 5, and with respect to the light guide plate 1. It is configured to directly introduce light.

The light guide plate 1 has a planar first surface 8 arranged on the side of the display surface 2a of the liquid crystal 2 and a first surface 8.
On the back surface side of the above, the plurality of first prism grooves 7 formed so as to be orthogonal to the direction of the optical axis from the point light source 3 and a second prism groove described later are integrally formed.

With the above structure, the first prism groove 7 is directly reflected by the valley on the side of the point light source 3 and a part of the emitted light is captured by the other valley of the first prism groove, and is again The light is guided into the light guide plate 1 so that the contrast of the liquid crystal 2 is not impaired, and the luminance is uniform over the entire surface so that the liquid crystal 2 can be illuminated in a state where the display contrast is high.

Next, FIG. 2A is a diagram showing a light distribution range in the light guide plate of the point light source 3, and FIG. 2B shows a light intensity, which is separated from the point light source 3. It is a figure showing that the intensity of light decreases as it goes.

It is known that the point light source 3 has a spindle-shaped three-dimensional light distribution in the air. By guiding the light in the light guide plate, the point light source 3 has an elliptical shape as shown in FIG. It is confirmed that the light is distributed in the light distribution range H. Also, FIG.
As shown in (b), it has a characteristic that the light intensity decreases in proportion to the distance from the point light source 3 as the distance from the point light source 3 increases.

For this reason, when it is used as it is as a front light for a liquid crystal formed in a rectangular shape as shown in FIG. 1, a portion outside the light distribution range H of the point light source 3 becomes dark, so that the entire front light is covered. The uniform illumination cannot be achieved.

Therefore, as shown in the plan view of the front light in FIG. 3, the second prism groove 9 is formed at a portion outside the light distribution range H of the point light source 3 shown by the broken line. In short, uniform illumination is realized by changing the density of the prism grooves according to the light distribution range. In this case, it is dark to be dense.

In this figure, the components already described are given the same reference numerals and their explanations are omitted, and the first prism groove 7 is formed on the second surface 6 of the light guide plate 1. On the other hand, the second prism grooves 9 are formed at the four corners outside the light distribution range H shown by the broken line. These second
The prism grooves 9 are formed at a pitch smaller than the pitch of the first prism grooves 7, and are configured to increase the amount of light emitted from the four corners outside the light distribution range H.

4A is a sectional view taken along the line XX of FIG. 3, and FIG. 4B is a sectional view taken along the line YY of FIG.
(C) is a sectional view taken along the line YY of FIG. 3 of another embodiment.

First, in FIG. 4A, the light beam incident on the light guide plate 1 from the third surface 5 which is the side surface of the light guide plate 1 at an angle in the illustrated direction is refracted by the resin light guide plate 1 described above. Refraction is repeated at a critical angle obtained from the index and reaches a distance as shown in the figure.

Further, of the light incident on the slope which is the slope on the side of the point light source 3 in the first prism groove 7, the light having an incident angle larger than the critical angle is totally reflected and goes to the liquid crystal. Further, light having an incident angle smaller than the critical angle is refracted and emitted to the outside of the light guide plate 1, but the light emitted in this way is trapped by the slope far from the point light source 3 of the first prism 7, The light is guided again into the light guide plate so that it reaches a long distance, thereby achieving uniform brightness.

Further, as shown in FIG. 4B, a part of a light beam which is incident on the light guide plate 1 from the third surface 5 at an angle in the direction shown in the drawing, and the incident angle of which is larger than the critical angle. Is totally reflected by the second prism groove 9 and directed toward the liquid crystal as shown in the drawing, thereby enabling uniform illumination over the entire surface.
The second prism grooves 9 may be formed not only on the second surface 6 as shown in FIG. 4C but also at the four corners of the first surface.

Finally, FIG. 5 shows the point light source 1 as one for comparison.
It is a top view of the front light which showed the case where two pieces of point light sources 3 were provided, and the case where one piece is provided.

In this figure, the components already described are given the same reference numerals and their description is omitted. First, in FIG. 5A, a point light source is provided at the center of the third surface 5 of the light guide plate 1. 3 are provided, and two second prism grooves 9 are formed at symmetrical positions with respect to the optical axis K of the point light source 3 as a symmetrical axis.

Further, in FIG. 5B, two point light sources 3 are arranged at equal parts where the third surface 5 of the light guide plate 1 is divided into four, and the optical axes of these point light sources 3 are arranged. Six second prism grooves 9 are formed symmetrically with K1 and K2 as the axes of symmetry, and the central second prism groove 9 is formed in common.

With the above configuration, the first surface 6 of the light guide plate 1 is
It has become possible to make the density of light emitted from the entire surface uniform. That is, since the brightness on the light guide plate 1 is predicted in advance from the light distribution characteristics of the point light source 3, the predicted brightness value
Since it is possible to appropriately change the interval and the length of the second prism groove 9 provided on the light guide plate 1, it is possible to brighten a portion that is expected to be dark, and it is expected that it will be too bright. As a result, it is possible to darken the portion to be made dark by reducing the prism groove or the like. As a result, the in-plane luminance deviation of the light guide plate 1 can be reduced, and the luminance in the display surface can be made more stable and uniform. I can do it now.

The present invention is not limited to the above construction,
Needless to say, various configurations are possible, for example, in the case where the shape of the light guide plate 1 is not rectangular, a predetermined portion on the first surface 8 or the second surface 6 outside the light distribution range H of the point light source. Needless to say, the second prism groove 9 may be appropriately formed, and the present invention is also applicable to the case where the point light source 3 whose light distribution range H is not elliptical is used.

Further, although it is particularly useful in the case of a point light source,
The present invention can also be applied to a linear or planar light source.

[0038]

As described above, according to the present invention,
It is possible to realize illumination with uniform brightness over the entire surface of the front light.

[Brief description of drawings]

FIG. 1A is an external perspective view of a front light common to each embodiment, and FIG. 1B is a sectional view taken along line XX of FIG.

2A is a diagram showing a light distribution range in the light guide plate of the point light source 3, and FIG. 2B is a diagram showing light intensity.

FIG. 3 is a plan view of a front light.

4 (a) is a cross-sectional view taken along the line XX of FIG. 3, (b).
3 is a cross-sectional view taken along the line YY of FIG. 3, and (c) is a cross-sectional view taken along the line YY of FIG. 3 of another embodiment.

5A is a plan view of a front light in which one point light source 3 is provided, and FIG. 5B is a plan view of a front light in which two point light sources 3 are provided.

[Explanation of symbols]

1 Light guide plate 2 liquid crystal 3 point light source 5 Third side 6 Second side 7 First prism groove 8 First side 9 Second prism groove H light distribution range

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02B 6/00 331 G02B 6/00 331 G02F 1/1335 520 G02F 1/1335 520 1/13357 1/13357 / / F21Y 101: 00 F21Y 101: 00

Claims (7)

[Claims] 1. A front light comprising: a light guide plate-like light guide plate having a light transmitting property, which is disposed on a display surface side of a display device including a reflective liquid crystal; and a point light source, wherein the light guide plate comprises: A first flat surface arranged to face the display surface of the display device.
Surface, a second surface having a plurality of first prism grooves orthogonal to the optical axis direction from the point light source on the back surface side of the first surface, the first surface and the second surface. A third surface which is formed so as to be sandwiched between the surfaces and which introduces the light from the point light source into the inside;
A plurality of second prism grooves are formed on either one or both of the predetermined parts on the first surface or the second surface outside the light distribution range of the point light source. Front light. 2. The front light according to claim 1, wherein the second prism groove is formed in parallel with the first prism groove. 3. The point light source is composed of one light emitting diode arranged to face the center of the third surface or a plurality of light emitting diodes arranged to face the third surface. The front light according to claim 1. 4. The first prism groove and the second prism groove are formed so as to have a gradation that becomes smaller as the distance from the point light source increases.
The front light according to claim 1 or 2, wherein the light quantity density of the first surface is made uniform. 5. The first prism groove and the second prism groove are formed with gradation so that the depth becomes deeper as the distance from the point light source increases, and thus the first prism groove and the second prism groove are formed. The front light according to claim 1 or 2, wherein the surface has a uniform light amount density. 6. An electronic device having a front light, comprising a display unit illuminated by the front light according to claim 1. Description: 7. A light guide plate of a front light type liquid crystal display device, which has a light emitting surface on which a plurality of prism grooves are formed, and into which light from a light source is introduced from a side surface, wherein Is changed according to the distribution range of the light from the light source.