JP2003031016A - Planar lighting device and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar lighting device using a point light source and a light guide plate, which is capable of uniform planar light emission, with bright-line and brightness unevenness suppressed, as well as a narrow-architraved trimming making total surface area smaller, and further, is capable of forming the light guide plate thin which occupies a large area with respect to the entire body. SOLUTION: The planar lighting device includes a light guide plate 1, a point light source 2, a linear light guide body 3 with the point light source 2 located at the side face 33 and changing light path of light from the point light source and emitting it from a light-emitting face 31 as though it is a point light source light, and a reflecting member 4 for guiding the light from the linear light guide body 3 to an incident end face 11 of the light guide plate 1. The linear light guide body 3 is arranged overlapped to the light guide plate 1, and the thickness of the latter is to be less than that of the former.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar illumination device and an image display device using the planar illumination device.

[0002]

2. Description of the Related Art With the widespread use of mobile phones and PDAs (Personal Digital Assistants) today, it is desired to provide an image display device with low power consumption and high display quality. There is a liquid crystal display element as a display element used for these, and as its type, a transmissive type, a semi-transmissive type, a reflective type and the like are known. Auxiliary light source (backlight) for transmissive and semi-transmissive LCDs
On the other hand, the reflection type liquid crystal display element uses external light as illumination light in a bright place, but in a dark place to improve visibility, an auxiliary light source (front light) for illuminating from the element observation surface side. Is required.

As for the front light and the back light, a side light system in which a linear light source is arranged on a light incident end face of a light guide plate which is a surface light emitting member is mainly used.

As such a linear light source, a cold cathode tube has been conventionally used as a bright light source, but it has been pointed out that an inverter circuit is required, power consumption is high, and life is short. For this reason, a light source for illumination of a small liquid crystal display element (for example, a liquid crystal display element of a mobile phone) requires low power consumption, requires no inverter circuit, and has a long-life light emitting diode.

However, for a light source of a planar illuminating device for an image display device of a display device (for example, an electronic book) having a screen larger than the above-mentioned small liquid crystal display element, sufficient brightness can be obtained with a small number of light emitting diodes. However, since a compact linear light source using many light emitting diodes cannot be found, cold cathode tubes are still used.

[0006]

Although the present situation is as described above, in the future, from the viewpoint of power saving, space saving, etc., especially when a display element or device is upsized, a light emitting diode (LED) is used. It is considered that a device using a point light source as a light source and capable of illuminating a wide area will be indispensable.

In that case, a means for converting a point light source into a linear light source is required in order to suppress the occurrence of local bright lines and to suppress the uneven brightness. As one of such means, there can be mentioned a method in which light from a point light source is once incident on a linear light guide, the light is made uniform into light like a linear light source, and the light is incident on a light guide plate. However, in order to make the light as uniform as possible, as shown in FIG. 6, if the distance between the lateral side surface of the linear light guide Q and the light emitting surface is increased, and the lateral light guide distance is increased. However, a large dead space DS is created in the surface where the light guide plate P is present, which increases the overall planar area including the light guide plate P and the lighting device portion LS ′, and thus can meet the so-called narrow frame requirement. become unable. In addition, in FIG. 6, LT is a point light source.

Further, since it is desirable that the light emitting surface of the linear light guide Q coincides with the light incident end face P1 of the light guide plate P as much as possible from the viewpoint of suppressing the light loss, the linear light guide surface is guided according to the size of the light source LT. If the optical body Q is thickened, the thickness Q of the linear light guide Q is increased.
As a result, the thickness of the light guide plate P also increases with the increase of t, and the overall size of the lighting device increases and the weight increases due to the increase in the thickness of the linear light guide Q having a large area.

Therefore, the present invention is a planar illuminating device using a point light source and a light guide plate, which enables uniform surface emission while suppressing bright lines and luminance unevenness, and reduces the overall planar area. An object of the present invention is to provide a planar illuminating device capable of narrowing a frame and further forming a thin light guide plate occupying a large area in the whole.

Another object of the present invention is to provide a new and useful image display device provided with such a surface illumination device.

[0011]

In order to solve the above-mentioned problems, the present invention provides a point light source and a point light source arranged on a side surface, and the light emitted from the point light source is converted into an optical path to cross the side surface. A linear light guide that emits light like a linear light source from a surface, a light guide plate that changes the optical path of the light incident from the light incident end surface to emit light from the light exit surface, and the light emission of the linear light guide. A reflecting member that guides light from a surface to the light incident end surface of the light guide plate,
The linear light guide is arranged on the light guide plate on the light exit surface side of the light guide plate or on the back side of the light exit surface, and the light guide plate thickness is equal to or less than the linear light guide thickness. Provided is a characteristic planar lighting device.

According to this planar illuminating device, the linear light guide is performed by making the light from the point light source enter the linear light guide from the side surface of the linear light guide, although the point light source is used. It is possible to change the optical path in the body and uniformly emit the light from the light emitting surface of the linear light guide like the light from the linear light source. That is, the linear light guide acts as a member that converts a point light source into a linear light source.

In particular, the linear light guides are arranged on the light exit surface side of the light guide plate or on the back side (opposite side) of the light exit surface so as to be superposed on the light guide plate, thus achieving a narrow frame of the illuminating device. At the same time, the light guide distance (the length of the linear light guide in the direction in which the light is emitted from the linear light guide) can be increased, and the light can be uniformly emitted in a state in which bright lines and uneven brightness are suppressed.

The linear light source-like light emitted from the light emitting surface of the linear light guide is reflected by the reflecting member, is guided to the light incident end surface of the light guide plate, and the optical path is changed in the light guide plate to be emitted from the light guide plate. The light is emitted from the surface and a surface emitting state is obtained.

Furthermore, since the linear light guide is arranged on the light exit surface side of the light guide plate or on the back side (opposite side) of the light exit surface so as to be superposed on the light guide plate and the reflection member is employed, the light guide plate is thin. Even if it is formed, it is possible to guide the light from the linear light guide to the light guide plate, and the linear light source-like light emitted from the light exit surface of the linear light guide is reflected by the reflecting member to form the linear light guide. It is guided to the light incident end face of the light guide plate having a thickness equal to or less than the thickness of the optical body with a low loss in a concentrated manner, the light path is changed in the light guide plate, and the light is uniformly emitted from the light exit face of the light guide plate to obtain a uniform surface emission state. .

Further, since the thickness of the light guide plate is set to be equal to or smaller than the thickness of the linear light guide, it is possible to prevent the entire illuminating device from becoming thicker, which is advantageous in reducing the thickness and weight of the illuminating device. Coupled with the achievement, the degree of freedom of arrangement in various devices such as mobile phones will increase.

The linear light guide and the light guide plate may be arranged in contact with each other, but there may be a gap between them. Although not limited thereto, it is preferable that the light emitting surface of the linear light guide and the light incident end surface of the light guide plate are arranged in the same plane, and the reflecting member is provided over both surfaces.

The point light sources may be arranged only on one side surface of the linear light guide, or may be arranged on both side surfaces. The number of point light sources arranged on one side surface may be one or more. In any case, a light emitting diode can be mentioned as a typical example of the point light source. A light emitting diode (LED) can achieve power saving, light weight, space saving, and long life as compared with a conventional cold cathode fluorescent lamp, and since it does not use a fluorescent agent like the cold cathode fluorescent lamp, it has less adverse effect on the environment.

As the reflecting member, various members such as a plate-like reflecting member, a member that reflects on the surface of a concave curved surface, a member that reflects on the inner surface of a prism, etc. can be adopted. The following can be illustrated. (1) A reflecting member including a light-reflecting concave curved surface (eg, paraboloid).

By making the light reflecting surface of the reflecting member a concave curved surface, the light from the linear light guide can be efficiently incident on the light guide plate. (2) A member including a light reflecting mirror surface.

By forming the light reflecting surface of the reflecting member as a mirror surface, the loss at the time of reflection is less than that in the case where a light diffusing surface is used as the light reflecting surface.

A plurality of mirror surfaces may be combined. (3) Prism.

By making the reflecting member a prism,
The structure is simplified and the holding stability is increased. (4) A prism integrally formed with the linear light guide.

The productivity is improved by integrating the prism and the linear light guide. Further, it is not necessary to fix the reflecting member separately from the linear light guide, and the entire structure is stabilized accordingly.

In any case, the reflecting member may have a bent portion which faces the light emitting surface of the linear light guide and the light incident end surface of the light guide plate (in the "bent portion"). Is
The top of the curved surface of the member including the concave curved surface is also included. ). In the member including the light reflecting mirror surface, the prism, and the prism formed integrally with the linear light guide, the bending angle of the bent portion can be 90 ° from the viewpoint of improving the light guiding efficiency.

The above-described planar lighting device can be used as a backlight for an image display device (such as a liquid crystal display device) or as a front light, and can be widely used in fields where a planar lighting device is generally required.

For example, it is possible to obtain a compact image display device by disposing an image display element between the linear light guide and the light guide plate in any one of the above-mentioned planar lighting devices.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1A is a perspective view of an example of a planar lighting device, FIG. 1B is a side view of the device, and FIG. 1C is an enlarged view of a part of a light guide plate in the device. A side view and FIG. 1D are enlarged plan views of a part of the linear light guide in the same device.

This illuminating device is composed of a flat light guide plate 1 and a light source unit LS provided at one end thereof. The light source unit LS makes the point light source 2, the linear light guide 3 for converting the point light source 2 into a linear light source, and the light emitted from the linear light guide 3 incident on the light incident end face 11 of the light guide plate 1. The reflecting member 4 for

The light guide plate 1 has, at one end, the above-mentioned light incident end face 11
And the lower surface 12 is a light emitting surface and the opposite surface (upper surface) 13 is formed into an uneven surface (see FIG. 1 (C)). An optical path conversion mechanism that guides a part of the light traveling while being totally reflected inside to the light emitting surface 12 and emits the light is provided.

One point light source 2 is provided on each of both side surfaces 33 of the linear light guide 3 which are orthogonal to the light emitting surface 31. Each point light source 2 is a light emitting diode. Although not shown, in order to eliminate external loss, the outside of the point light source 2, the linear light guide 3 and the reflecting member 4 may be entirely covered with a reflecting material such as a white diffusing surface or a mirror-like reflecting sheet. preferable.

The linear light guide 3 is a light incident end face 11 of the light guide plate 1.
The surface 32 on the opposite side of the light emitting surface 31 extends along the outer surface of the linear light guide body by providing V-shaped grooves at predetermined intervals as shown in FIG. 1D. The uneven surface 32 is formed on the surface and provides an optical path conversion mechanism that guides a part of the light traveling while being totally reflected in the linear light guide 3 to the light emitting surface 31.

The linear light guide 3 is arranged so as to face the light exit surface 12 of the light guide plate 1 and to overlap the light guide plate 1. The length S of the linear light guide 3 in the light emission direction (the light guide distance in the light emission direction) is defined by a uniform line of light from the entire light emission surface 31 in which bright lines and uneven brightness are suppressed. It is made long so that it can be emitted like light from a light source. Even though the light guide distance S is long as described above, the linear light guide 3 is arranged on the light guide plate 1 so that a dead space that increases the planar size of the entire illumination device is not formed. So-called narrow frames have been achieved.

The light emitting surface 31 of the linear light guide 3 is arranged on the same plane as the light incident end surface 11 of the light guide plate 1.

Here, the relationship between the thickness of the light guide plate 1 and the linear light guide 3 is the relationship of the thickness of the light guide plate 1 <the thickness of the linear light guide 3 in this example.

Since the light guide plate 1 is formed thin as described above, the entire lighting device is made thinner and lighter.

The reflecting member 4 is a prism arranged across the light emitting surface 31 of the linear light guide body and the light incident end surface 11 of the light guide plate, and the corner portions (bent portions) facing each other on both sides thereof. It is a 90-degree prism.

According to the illumination device described above, the light emitted from each point light source 2 is guided into the linear light guide 3 from the side surface of the linear light guide 3. Light source 2 introduced into linear light guide 3
Light is spread uniformly while repeating total reflection on the inner surface of the linear light guide 3, and at the same time, the inner surface 32 with the V groove is formed.
The light ray that hits is redirected to the light emitting surface 31 and is emitted. The light beam emitted from the linear light guide 3 is reflected by the reflection member 4 to change its course, and is guided to the light incident end face 11 of the light guide plate 1 having a thickness smaller than the thickness of the linear light guide 3 in a concentrated manner with low loss. Then, the light enters the light guide plate 1 and spreads evenly in a plane while repeating total reflection in the light guide plate 1. In addition, a part of the light ray that travels inside the light guide plate 1 is directed to the light exit surface 12 by the optical path conversion mechanism surface 13, whereby the light exit surface 12 of the light guide plate 1 is formed.
A more uniform and uniform illumination light (surface emission) is obtained and emitted to an illuminated object (not shown).

Thus, according to the above-mentioned lighting device, it is possible to achieve uniform surface emission in the state where bright lines and luminance unevenness are suppressed, and to narrow the frame to reduce the overall plane area. The light guide plate occupying a large area can be formed thin.

FIG. 2 is a side view of a part of another example of the planar lighting device. This illuminating device is obtained by replacing the reflecting member 4 in the illuminating device shown in FIG. The other points are similar to those of the apparatus shown in FIG.
The same parts and portions as those of the device (A) are designated by the same reference numerals.

The reflection member 5 is a reflection member including a light reflection concave curved surface (here, a parabolic surface) 51 which is a mirror surface. With this reflecting member, the light from the linear light guide 3 can be efficiently guided by the light guide plate 1.
Can be incident on.

FIG. 3 is a side view of a part of still another example of the planar lighting device. In this lighting device, the reflecting member 4 in the lighting device shown in FIG. 1A is replaced with a reflecting member 6, and two point light sources 2 are arranged on each side surface 31 of the linear light guide 3. The other points are the same as those of the apparatus of FIG. 1A, and the same parts and portions as those of the apparatus of FIG. 1A are denoted by the same reference numerals.

The reflecting member 6 includes two mirror surfaces 61 which are combined so that the butted corner portions (bent portions) 62 are 90 degrees. Further, by having four point light sources 2, the lighting device has high brightness.

FIG. 4 is a side view of a part of still another example of the planar lighting device. In this lighting device, the reflecting member 4 in the lighting device shown in FIG. The other points are the same as those of the apparatus of FIG. 1A, and the same parts and portions as those of the apparatus of FIG. 1A are denoted by the same reference numerals.

The reflecting member 7 is a prism having a corner portion (bent portion) of 90 degrees and is formed integrally with the linear light guide 3. By thus forming the prism 7 and the linear light guide 3 into a negative body, the productivity is improved. Further, it is not necessary to fix the reflecting member 7 separately from the linear light guide 3, and the entire structure is stabilized accordingly. Also, the number of parts is reduced, and the productivity of the lighting device is improved.

5A and 5B, a gap is provided between the linear light guide 3 and the light guide plate 1 in the illuminating device shown in FIG. 1A, and a reflective liquid crystal display element 8 is arranged therein, and the illuminating device part is provided. It is an image display device having a compact structure that uses a light source as a front light. The image of the element 8 can be observed from the upper side of the light guide plate 1 in the drawing (direction OV in the drawing). The same parts and parts as those of the device shown in FIG.
The same reference numerals as in (A) are attached.

An air layer may be provided between the light guide plate 1 and the display element 8, and a transparent filler, an adhesive, or an adhesive sheet having a refractive index n2 lower than the refractive index n1 of the light guide plate 1 may be provided.

The linear light guide 3 and the prism 4 are adhered to both of them by a transparent adhesive having a refractive index close to each other. The light guide plate 1 and the prism 4 may be bonded with the same adhesive.

The light guide plate 1 in the apparatus shown in FIG.
Of the light incident end face 11 of the linear light guide 3 and the prism 4 and the light incident end face 11 of the light guide plate 1 and the prism 7 of the device of FIG. This can be done by using the adhesive.

Each of the lighting devices described above can be used as a backlight by attaching the light guide plate 1 upside down.

In each of the above lighting devices, the light source section LS including the linear light guide 3 may be arranged on both end surfaces of the light guide plate 1 facing each other to increase the light quantity.

[0053]

As described above, according to the present invention, a surface illumination device using a point light source and a light guide plate is capable of uniform surface emission while suppressing bright lines and uneven brightness. It is possible to provide a planar illuminating device capable of narrowing the frame area by reducing the plane area of the above, and further forming a thin light guide plate occupying a large area in the whole.

Further, according to the present invention, it is possible to provide a new and useful image display device provided with such a surface illumination device.

[Brief description of drawings]

1A is a perspective view of an example of a planar lighting device, FIG. 1B is a side view of the device, and FIG. 1C is an enlarged side view of a part of a light guide plate in the device. FIG. 1 (D) is an enlarged plan view of a part of the linear light guide in the same device.

FIG. 2 is an enlarged side view of a part of another example of the planar lighting device.

FIG. 3 is an enlarged side view of a part of still another example of the planar lighting device.

FIG. 4 is an enlarged side view of a part of still another example of the planar lighting device.

FIG. 5 is a side view of an example of an image display device.

FIG. 6 is a diagram showing a dead space in the planar lighting device.

[Explanation of symbols]

1 Light guide plate 11 Light incident end face 12 Light emitting surface 13 Optical path changing mechanism surface LS light source 2 point light source 3 Linear light guide 31 Light exit surface 32 Optical path conversion mechanism surface 33 side S light guide distance 4 Reflective member 5, 6, 7 Reflective member 8 Liquid crystal display element

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09F 9/00 336 G09F 9/00 336B // F21Y 101: 02 F21Y 101: 02 (72) Inventor Yoshie Shimizu 2-3-13 Azuchi-cho, Chuo-ku, Osaka F-term in Minolta Co., Ltd., Osaka International Building (reference) 2H038 AA52 AA55 BA06 2H091 FA16Z FA21Z FA23Z FA41Z FD06 LA11 5G435 AA18 BB12 BB16 DD13 EE22 FF03 FF06 FF08 GG23

Claims (5)

[Claims] 1. A point light source, and a linear conductor that is disposed on a side surface, converts light from the point light source into an optical path, and emits the linear light source light from a light emission surface that intersects the side surface. An optical body, a light guide plate for converting the light path of light incident from the light incident end surface into surface emission from the light exit surface, and guiding light from the light exit surface of the linear light guide to the light incident end surface of the light guide plate. A reflecting member, wherein the linear light guide is arranged on the light guide plate on the light exit surface side of the light guide plate or on the rear surface side of the light exit surface, and the light guide plate thickness is the linear light guide thickness. A planar lighting device characterized in that 2. The planar lighting device according to claim 1, wherein the reflecting member is a member that reflects light on its surface. 3. The planar lighting device according to claim 1, wherein the reflecting member is a prism. 4. The planar lighting device according to claim 1, wherein the reflecting member has a bent portion facing the light emitting surface of the linear light guide and the light incident end surface of the light guide plate. 5. An image display device in which an image display element is arranged between the linear light guide and the light guide plate in the planar lighting device according to any one of claims 1 to 4.