JP2003272428A - Light guide plate, surface illumination device, and display device - Google Patents

Abstract

(57) [Problem] To provide a surface illumination device, a light guide plate, and a display device capable of obtaining high luminance and uniform luminance even in a very thin surface illumination device. SOLUTION: A light source 102 and a light guide plate 101 in which light from the light source 102 enters from a light incident area 104 on a side surface, propagates inside, and exits from a light exit surface 105 which is one main surface to the outside. In the surface illumination device 1, at least one main surface 105 of the light guide plate 101 is provided with a step surface 114 a substantially perpendicular to the light exit surface, and the step surface 114 a faces the light incident area 104 and
01 is provided so as to be thicker on the light incident region 104 side, and the first surface which reflects light toward the light incident region 104 side on the step surface 114a.
The light-reflecting structure 123 is formed, and the light-emitting surface 105 of the thinned portion from the step surface 114a of the light guide plate 101 forms a light-emitting region 113 for emitting light to the outside.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a surface illuminating device such as a backlight for illuminating a display portion of a mobile phone, a mobile terminal or the like, a light guide plate used for the same, and a display device using the same.

[0002]

2. Description of the Related Art In a display section of a mobile phone, a mobile terminal or the like, a display device having a liquid crystal display element (liquid crystal panel) and a thin backlight (surface illumination device) as main components is used. FIG. 18 shows a sectional structure of this type of display device. 18, in this display device, a liquid crystal panel 110 having polarizing films 111a and 111b attached to both surfaces thereof is configured to be illuminated by a backlight unit 109 located on the lower side.

The backlight unit 109 mainly comprises a light guide plate 101 and a light source 102 such as an LED (light emitting diode). The light output from the light source 102 is the light guide plate 1
01 is introduced into the light guide plate 101 from the light incident side surface 104 and propagates while being repeatedly reflected on the upper and lower surfaces of the light guide plate 101. Then, when it hits the diffusion pattern 103 formed on the lower surface (diffusion surface) 106, the light is diffused in various directions,
A part of the diffused light is extracted as output light from the upper surface (light emission surface: main surface opposite to diffusion surface 106) 105. As the material of the light guide plate 101, a resin material such as polycarbonate or a material of a transparent medium having a large refractive index such as glass is used. In addition, the backlight unit 109
In addition to the light guide plate 101 and the light source 102, the light guide plate 101 and the light source 102 may include a reflection sheet 107 for returning the light leaking downward from the diffusion surface 106 to the inside of the light guide plate 101 again. Further, a diffusion sheet 108 for equalizing the directivity of the light emitted from the light emitting surface 105 may be provided, or conversely, a lens sheet or a prism sheet for further increasing the directivity is further added. Sometimes.

A backlight unit 109 as shown in FIG.
Has a feature that the light source 102 can be thinned because the light source 102 is provided on the side surface of the light guide plate 101 rather than the lower side thereof. Further, when light propagates in the light guide plate 101, the amount of propagating light is large in a portion near the light source 102, and the light source 1
Although the amount of propagating light decreases with increasing distance from 02, it is possible to obtain relatively uniform output light over the entire light exit surface by optimally designing the arrangement density of the diffusion patterns 103. Further, it is possible to control the directivity of the output light by optimizing the shape and arrangement direction of the diffusion pattern 103.

Now, in a display device such as a mobile phone or a mobile terminal, it is very thin (in some cases, 1 to 2 mm thick,
A backlight (or less) is required. Although the backlight of FIG. 18 is certainly suitable for thinning,
As shown in FIG. 19A, it is extremely difficult to make the thickness of the light guide plate 101 itself smaller than the size of the light emitting region 102a of the light source 102 (here, the light source 102 is a fluorescent tube due to the relation of the reference document described later). The size of the light emitting region 102a corresponds to the diameter of the fluorescent tube. By doing so, the light from the light source 102 is not effectively introduced into the light guide plate 101, and the brightness in the light emitting area 113 of the light emitting surface 105 (corresponding to an area that actually contributes to the display, which may be called a display area). Is reduced.

Therefore, a structure for overcoming this problem has been devised, which is disclosed in Japanese Patent Laid-Open No. 174938/1994. The specific structure is shown in FIG. 1 of this document, and its schematic structure is shown in FIG. 19 (b) of the present application. In FIG. 19B, the thickness of the light guide plate 101 in the light emission area 113 of the light emission surface 105 is smaller than the size of the light emission area 102 a of the light source 102, but the light guide plate 101 in the vicinity 101 a of the light incident side surface 104. Is equal to or larger than the size of the light emitting region 102a of the light source 102. And, these are connected by a tapered portion 112. By doing so, it is possible to reduce the thickness of the light guide plate 101 in the light emitting region 113 and to effectively introduce the light from the light source 102 into the light guide plate 101.

In a display device such as a mobile phone or a mobile terminal, an LED is mainly used as a light source as described above. The reason is that it is smaller and consumes less power than fluorescent tubes or cold cathode tubes. At this time, since it is not possible to obtain sufficient brightness with only one LED, it is common to use two or more LEDs. As an example using two LEDs, WO
98/19105 (International application number PCT / JP97 / 0
3892, Japanese Patent No. 3151830) shown in FIG. 27.

In this display device, the two light sources are not concentrated in one place but are dispersed in two places, but the heat generated by the light sources is effectively dispersed in this. This means that the temperature rise is suppressed and the deterioration of the light guide plate is prevented.

[0009]

As described above, FIG.
When the configuration having the taper portion 112 as shown in FIG. 19B is used, the light introduction efficiency at the light incident side surface 104 is improved as compared with the case of a light guide plate having a substantially uniform thickness as shown in FIG. You can However, as a result of detailed analysis,
It has been found that in the structure of 9 (b), part of the light once introduced into the light guide plate 101 escapes to the outside of the light guide plate again, and the light is not effectively propagated deeper than the tapered portion 112. That is, it was revealed that the light utilization efficiency was not improved as much as expected.

In addition, in the structure in which a plurality of LEDs are arranged, when the light emitting area 113 is observed, a portion where the brightness of the output light is particularly large occurs near the LED installation position, resulting in uneven brightness. There has occurred. this is,
This is because the fluorescent tube is a linear light source, while the LED is substantially a point light source. The brightness unevenness was too small to be corrected by correcting the arrangement density of the diffusion patterns on the light guide plate.

The present invention solves the above two problems at the same time, and even in a very thin surface illuminator, the light utilization efficiency is improved to obtain high brightness, and the uneven brightness generated near the LED installation position is eliminated to obtain a uniform brightness. It is an object of the present invention to provide a surface lighting device, a light guide plate, and a display device capable of obtaining the above.

[0012]

In order to solve the above-mentioned problems, the inventor of the present invention firstly causes the light, once introduced into the light guide plate, generated in the structure of FIG. 19B to escape to the outside again. I examined the cause of the problem. This will be explained below.

FIG. 20 shows the light incident side surface 10 of FIG.
4 is an enlarged view of the vicinity of 4 and the tapered portion 112. FIG. Now, let us consider a case where a ray such as R1 in this drawing enters from a point A on the light incident side surface 104. When the angle between the light ray R1 and the normal line of the light incident side surface 104 is θA, the angle θA is the light incident side surface (the interface between the medium forming the light guide plate 101 and the medium (air) around the light guide plate 101). The output angle of the light beam incident on the light guide plate 101 into the light guide plate 101 is shown.
Hereinafter, this angle θA will be referred to as an introduction angle. The light ray R1 is incident at a point B on the bottom surface of the light guide plate 101 at an angle of θB = 90 ° −θA, where θB is the critical angle θo (= sin ⁻¹ (1 / η); η of the medium forming the light guide plate 101. Is the light guide plate 10
1 or more (relative refractive index with respect to the outside world (medium around the light guide plate) of the medium constituting 1) (that is, the introduction angle θA is 90
° -θo or less). If the light guide plate 101 has the same thickness in any part and the upper and lower surfaces of the light guide plate are parallel to each other, the incident angle remains θB no matter how many times the light ray R1 is repeatedly reflected on the upper and lower surfaces, and the total reflection condition θB. Since the light propagates in the light guide plate while maintaining ≧ θo, it does not escape to the outside of the light guide plate 101 unless it hits the diffusion pattern. However, in the case where the tapered portion 112 is present as shown in FIG. 20, if the light ray R1 enters the tapered portion 112 (point C), the incident angle θC at that time becomes smaller than θB, and in some cases, θC becomes a critical value. If the angle is smaller than the angle θo, the total reflection condition is not satisfied, and a part of the total reflection condition is lost to the outside of the light guide plate 101.

There is also a case where the light ray R2 is incident from the point D on the light incident side surface 104. That is, since the introduction angle θD of the light ray R2 is equal to or smaller than the introduction angle θA, unless the tapered portion 112 exists, the light ray R2 does not escape to the outside of the light guide plate 101 unless it hits the diffusion pattern. But,
Here, since the ray R2 is incident on the taper portion 112 at the point E, even if the incident angle θE at this time is the critical angle θ
Even if it is greater than or equal to o, the incident angle θF at the time of next incident on the lower surface 106 of the light guide plate 101 (point F) becomes smaller than θE, and in some cases θF falls below the critical angle θo, which also satisfies the total reflection condition. Otherwise, some light will escape to the outside of the light guide plate.

In addition, although the initial incident angle is sufficiently large, the incident angle becomes gradually smaller as reflection is repeated many times between the tapered portion 112 and the lower surface of the light guide plate, and eventually falls below θo to the outside. There are, of course, rays of light that escape.

From the above, it can be understood that in the structure having the tapered portion 112, the light once introduced into the light guide plate 101 escapes to the outside again.

Therefore, in the surface lighting device according to the present invention, the light source and the light from the light source are incident from the light incident region on the side surface, propagate inside, and are emitted to the outside from the light emitting surface which is one main surface. In a surface illuminating device including a light guide plate, a step surface that is substantially perpendicular to the light exit surface is provided on at least one main surface of the light guide plate, and the step surface faces the light incident region and the light guide area. A light plate is provided so as to be thicker on the side of the light incident region, and a first light reflection structure for reflecting light to the side of the light incident region is formed on the step surface, and is thin at the step surface of the light guide plate. The light emitting surface of the portion forming the light emitting area forms a light emitting area for emitting light to the outside (claim 1).
With such a configuration, since the light ray incident on the step surface is almost entirely reflected by the first light reflecting structure, it is almost prevented that the light ray goes out from the step surface to the outside. In addition, since the step surface is provided almost perpendicular to the light exit surface, it is possible to prevent light rays that enter the light guide plate and are reflected by the step surface from striking the upper and lower surfaces of the light guide plate at an angle smaller than the critical angle and escaping to the outside. To be done. As a result, the light utilization efficiency is improved, and the brightness in the light emitting region is improved.

Further, the first light reflecting structure may be a light reflecting film formed on the step surface (claims 2 and 8). With this configuration, the first light reflecting structure can be easily configured.

Further, the first light reflecting structure may be a light reflecting member arranged along the step surface (claims 3 and 11). Even with such a configuration, the first light reflecting structure can be easily configured.

The relative refractive index of the medium around the light guide plate may be √2 or more (claim 4).
With such a configuration, the light rays incident on the light guide plate satisfy the condition of total reflection on the upper and lower parallel surfaces of the light guide plate,
Light loss is reduced.

The light incident area of the light guide plate may be substantially perpendicular to the light emitting surface (claim 5). With such a configuration, the light rays that enter the light guide plate can easily satisfy the conditions for total reflection on the upper and lower parallel surfaces of the light guide plate.

Further, a light reflecting member for reflecting light to the light guide plate side may be provided on both main surfaces of a portion extending from the light incident area of the light guide plate to the stepped surface (claim). 6). With such a configuration, light loss can be reduced.

Further, the light source is a point light source, and the first light reflecting structure is incident from a light incident position which is a position closest to the point light source in the light incident region and is directed toward the step surface. Most of the propagating incident light may be reflected toward a portion of the light incident area other than the light incident position (claim 7). With such a configuration, by forming the light reflecting structure between the point light sources, it is possible to make the brightness in the light emitting region of the light guide plate uniform.

Further, even if the maximum directivity direction of the incident light and the normal direction in the portion of the step surface where the incident light reaches are not parallel to each other when projected onto a plane parallel to the light emitting surface. Good (Claim 9).

The stepped surface may have a sawtooth shape or a curved shape when projected onto a plane parallel to the light emitting surface (claim 10). With such a configuration, the first light reflecting structure can be easily realized.

Further, when the maximum directivity direction of the incident light, the normal direction of the step surface, and the normal direction of the reflecting surface of the light reflecting member are projected on a plane parallel to the light emitting surface, all of them are It may not be parallel (claim 12).

The stepped surface or the reflecting surface of the light reflecting member may have a sawtooth shape or a curved shape when projected onto a plane parallel to the light emitting surface (claim 13). With such a configuration, the first light reflecting structure can be easily realized.

A diffractive optical element may be formed on the step surface (claim 14).

A Fresnel lens may be formed on the stepped surface (claim 15).

Further, the stepped surface may satisfy a total reflection condition for a ray of the incident light in the maximum directing direction (claim 16). With this configuration, the first light reflecting structure can be realized without providing a light reflecting film or a light reflecting member.

In the light incident area, the first
A second light reflecting structure for reflecting the reflected light again toward the maximum directivity direction of the incident light may be formed at a portion where the reflected light from the light reflecting structure of (1) reaches. . With such a configuration, it is possible to make the brightness uniform in the light emitting region of the light guide plate.

Further, the second light reflecting structure may be a light reflecting film formed in the light incident region (claim 18). With this configuration, the second light reflecting structure can be easily realized.

Further, it is assumed that the maximum directivity direction of the incident light and the normal direction of the portion where the reflected light reaches in the light incident area are not parallel to each other when projected on a plane parallel to the light emitting surface. (Claim 19)

The second light reflecting structure may be a light reflecting member arranged along the light incident region (claim 20).

Further, the maximum directivity direction of the incident light, the normal direction of the portion where the reflected light reaches in the light incident area, and the light reflection member of the portion where the reflected light reaches in the light incident area. When the normal direction of the reflecting surface is projected on a plane parallel to the light emitting surface, it may not be all parallel (claim 21).

Further, a diffractive optical element may be formed in a portion of the light incident area where the reflected light reaches (claim 22).

A Fresnel lens may be formed in a portion of the light incident area where the reflected light reaches (claim 23).

Further, a portion of the light incident area where the reflected light reaches may satisfy a total reflection condition for a ray of the reflected light in a maximum directing direction (claim 2).
4).

Further, a light diffusing and reflecting member may be provided in a portion of the light incident area where the reflected light reaches (claim 25), and the light radiation directivity characteristic of the light source is the above-mentioned. The reflection directivity of the light diffusing and reflecting member may be substantially the same (claim 26). With such a configuration, it is possible to make the brightness in the light emitting region of the light guide plate more uniform.

A plurality of the light sources and the light incident positions may be provided (claim 27).

Further, a directional diffusion pattern is formed on the surface of the light guide plate opposite to the light emission surface, and the longitudinal direction of the diffusion pattern is within the light emission region with respect to the maximum directivity direction of the incident light. May be substantially vertical (claim 2
8).

Further, the light guide plate according to the present invention is a light guide plate in which light incident from a light incident area on a side surface propagates inside and is emitted to the outside from a light emission surface which is one main surface. Surface is provided with a step surface substantially perpendicular to the light emitting surface, the step surface is provided so as to face the light incident area and increase in thickness on the light incident area side, and the step surface has the light First to reflect light to the incident area side
The light-reflecting structure is formed, and the light-emitting surface of the thinned portion of the light guide plate with the step surface as a boundary forms a light-emitting region for emitting light to the outside (claim 29). With such a configuration, the brightness can be improved even if it is very thin.

The first light reflecting structure may be a light reflecting film formed on the step surface (claim 3).
0, 32).

In addition, most of the incident light which is incident from the light incident position set in the light incident area and propagates toward the step surface by the first light reflecting structure is the light in the light incident area. The light may be reflected toward a portion other than the incident position (claim 31).

In the light incident area, the first
A second light reflecting structure for reflecting the reflected light again toward the maximum directivity direction of the incident light may be formed in a portion where the reflected light from the light reflecting structure of 1 reaches (claim 33). . With this configuration, it is possible to make the brightness in the light emission region uniform.

Further, the second light reflecting structure may be a light reflecting film formed in the light incident region (claim 34). The light guide plate according to item 3.

Further, the display device according to the present invention comprises:
The surface illuminating device according to claim 1, and a display element that two-dimensionally modulates the light emitted from the surface illuminating device (claim 35).

Further, the display device according to the present invention comprises:
The surface illumination device according to claim 1 and a display element that two-dimensionally modulates light emitted from the surface illumination device (claim 36).

Further, the display device according to the present invention comprises:
The surface illuminating device according to claim 7 and a display element that two-dimensionally modulates light emitted from the surface illuminating device (claim 37).

A mobile phone according to the present invention includes the display device according to claim 35, 36, or 37 as a display section (claim 38).

A portable terminal device according to the present invention comprises the display device according to claim 35, 36 or 37 as a display section (claim 39).

[0052]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is a sectional view schematically showing a configuration of a surface lighting device according to Embodiment 1 of the present invention.

As shown in FIG. 1, the surface lighting device 1 according to the present embodiment has a light guide plate 101. Light guide plate 10
1 is a flat lower surface 1 having a rectangular plane shape here.
06, and the upper surface 105 in which the step portion 114 is formed in parallel with the lower surface 106. The step portion 114 is a characteristic configuration of the present invention, and is parallel to the light incident side surface 104 in the vicinity of the light incident side surface (light incident area) 104, which is one of the four side surfaces (end surfaces) of the light guide plate 101. And the light guide plate 101
The thickness of a portion (hereinafter referred to as a light introducing portion) 121 of the stepped portion 114 located on the light incident side surface side is equal to the thickness of the light guide plate 101.
Is provided so as to be thicker than the thickness of a portion (hereinafter, referred to as a light output portion) 122 located on the side opposite to the light incident side surface side of the stepped portion 114. Step surface 114 of step portion 114
a is formed substantially perpendicular to the lower surface 106 of the light guide plate 101. A reflective film 123 is formed on the step surface 114a. Here, the reflection film 123 is composed of a metal reflection film formed by vapor deposition, sputtering, CVD (chemical vapor deposition method), plating, spin coating, or the like.
It is desirable that the metal reflection film has a high reflectance such as Ag and Al. A diffusion pattern (not shown) is formed on the lower surface 106 of the light guide plate 101 of the light output unit 122,
Therefore, the upper surface 105 of the light guide plate 101 of the light output portion 122 forms the light output region 113. This light emitting area 11
A diffusion sheet 108 is disposed above the sheet 3. Then, adjacent to the incident side surface 104 of the light guide plate 101, the light sources 102 composed of a plurality of (here, four) LEDs are arranged at substantially equal intervals. An upper surface reflection sheet 115 as a light reflection member is provided so as to cover the light source 102 and the upper surface 105 of the light guide plate 101 of the light introduction portion 121.
Further, a reflection sheet 106 is arranged so as to cover the lower part of the light source 102 and the lower surface 106 of the light guide plate 101.

Next, the operation of the surface lighting device 1 configured as described above will be described.

In FIG. 1, the light emitted from the light source 102 is guided from the light incident side surface 104 of the light guide plate 101 to the light guide plate 10.
1, is diffused by the diffusion pattern of the lower surface 106 of the light output portion 122 while propagating in the light guide plate 101, emitted from the light output area 113 of the upper surface 105, and diffused by the diffusion sheet 108.

Next, the function of introducing light into the light guide plate 101, which is a feature of the present invention, will be described in detail. FIG. 2 is a cross-sectional view schematically showing the action of introducing light into the light guide plate.

Referring to FIG. 2, first, a light ray R1 emitted from a light source 102 (not shown in FIG. 2) is directed downward from a point A located in the lower half of the light incident side surface 104 into the light guide plate. Think about the case. Angle of introduction of ray R1 θ
It is assumed that A satisfies the condition of 90 ° −θo or less. The light ray R1 is incident on the point B on the lower surface 106 of the light guide plate 101 at an angle of θB = 90 ° −θA. However, since θB is equal to or greater than the critical angle θo under the above conditions, it is totally reflected and there is no problem. It reaches deeper than the step portion 114. Then, after that, total reflection is repeatedly performed on the upper and lower surfaces of the light guide plate 101 while always maintaining the incident angle θB, and the light propagates in the light guide plate 101 until it reaches a diffusion pattern.

Next, a light ray R incident upwardly into the light guide plate 101 from a point D located substantially in the center of the light incident side surface 104.
Consider a case like 2. Lead angle R2 of ray R2
Satisfies the condition of 90 ° −θo or less. In this case, the light ray R2 is first transmitted to the step surface 114a.
It is incident on the upper point E at an angle θD. Since the metal reflection film is formed on the step surface 114a, almost all incident light rays are reflected at the reflection angle of θD regardless of the incident angle.
The reflected light ray R2 is now incident on the point F on the upper surface 105 of the light guide plate 101, and the incident angle at this time is θF =
90 ° -θD. Under the above conditions, θF is the critical angle θ
Since it is greater than or equal to o, the ray R2 is totally reflected. Next, the ray R2 reaches the point G on the light incident side surface 104, and the incident angle here is 90 ° −θF = θD. Since the total reflection condition is not always satisfied here, a part R2 ′ of the light ray R2 is emitted from the light incident side surface 104 to the outside of the light guide plate and the rest (R
2 ″) propagates again in the light guide plate 101.

On the other hand, the light ray R2 'emitted to the outside of the light guide plate 101 strikes the light source 102, or, when a substantial point light source such as an LED is arranged, either the light source 102 or the gap portion thereof. Hit Generally, the light source 10
The light emitting area of 2 often has diffuse reflection characteristics,
In addition, since a member having a diffuse reflection characteristic is often arranged also in the gap portion of the light source 102, the light ray R2 ′ is diffused and reflected here and is again introduced into the light guide plate 101 from the light incident side surface 104 (hereinafter, this Is called re-incident). Further, the light ray R2 ″ that is reflected at the point G and propagates again in the light guide plate is also equivalent to the light ray that first enters from the light incident side surface 104. Therefore, the light that reaches the point G is emitted to the outside. Whether it is reflected or not, it returns to the drawing board,
The path like the ray R1 or the ray R2 is traced again.

By the way, in the above, for the light rays R1 and R2, the total reflection on the upper and lower surfaces of the light guide plate 101 between the light incident side surface 104 and the step surface 114a is only once (reflection at the point B or the point F). Although the case has been described as an example, of course, other than this, there may be a ray that is totally reflected on the upper and lower surfaces many times, and conversely, a ray that does not hit the upper and lower surfaces even once. However, the step surface 114
The behavior of reflection at a and reflection or re-incidence at the light incident side surface 104 is exactly the same as that described above.
Apart from the total number of total reflections on the upper and lower surfaces, the light guide plate 10
The paths of the light rays that are incident in 1 are summarized in the pattern of either the light rays R1 or R2 described above.

According to the above, even if the light beam R2 hits the step surface 114a and returns to the light incident side surface 104, it will eventually become a pattern of the light beam R1 after repeating the reciprocation several times. As a result, the light will reach a portion deeper than the portion 114, and eventually the light emitting region 113 will have almost no loss.
It will result in reaching up to.

In the above description, the light incident side surface 10
The angle formed by the light ray immediately after incidence from No. 4 with respect to the normal to the light incident side surface 104, that is, the introduction angle θA or θD is 90
It is assumed that it is equal to or less than ° -θo. Consider when this is met.

FIG. 3 is a cross-sectional view schematically showing how the light emitted from the light source 102 enters the inside of the light guide plate 101. As shown in FIG. 3, when the incident angle of the light ray on the light incident side surface 104 is θA0 and the angle after passing through the light incident side surface 104 is θA, sin (θA) / si lies between them.
There is a relationship of n (θA0) = 1 / η (Snell's law).
However, η is a relative refractive index with respect to the medium around the light guide plate 101. According to this equation, θA becomes maximum when the light beam emitted from the light source is incident on the light incident side surface 104 in a gradual manner, that is, when θA0 = 90 °, and θA at that time is θA = It is calculated as sin-1 (1 / η). 90 ° -for this maximum angle θA
The condition that θo is less than or equal to θo is that the critical angle is θo = sin−
Considering that it is expressed as 1 (1 / η), it is expressed as the following expression (1).

[0064]

[Equation 1]

From the equation (1), the condition 1 / η ≦ √2 / 2, that is, η ≧ √2 is obtained. Therefore, if the condition of η ≧ √2 is satisfied, all the light rays emitted from the light source 102 and entering the light incident side surface 104 (and the light ray re-incident from the light incident side surface 104) are totally reflected on the upper and lower surfaces of the light guide plate. Is satisfied, and after repeating a number of round trips, it always reaches the back of the stepped portion 114, and there is almost no loss.

In the above description, the light incident side surface 1
Although 04 is assumed to be substantially perpendicular to the light emitting surface 105, it is desirable to satisfy this condition. This is because the incident angle of the light ray R2 "in FIG.
Since the light ray R2 "is not as large as the light ray R2 'in terms of intensity, the light arrival rate beyond the step portion 114 does not extremely decrease even if this condition is not satisfied, and the efficiency is improved to some extent. The effect can be expected.

By the way, in the present embodiment, as shown in FIG. 1, a top reflecting sheet 115 which is a light reflecting member is provided. As shown in FIG. 4, the upper surface reflection sheet 115 is a light ray R3 emitted from the light source 102 and going upward through the gap between the light source 102 and the light incident side surface 104.
Can be reflected to enter the light guide plate 101.
As a result, the light utilization efficiency can be improved. The reflection sheet 107 is also formed on the lower surface 106 of the light guide plate 101.
Is arranged so as to cover not only the lower surface 106 but also the lower portion of the light source 102, and thus the light ray R4 emitted from the light source 102 and trying to escape downward through the gap between the light source 102 and the light incident side surface 104. Can be reflected and made incident on the inside of the light guide plate 101, whereby the light utilization efficiency can be further enhanced.

In the above structure, the reflection film 123 formed on the step surface 114a is made of a metal reflection film, but it may be made of a dielectric multilayer film. Any material may be used as long as it can obtain a sufficient light reflectance.

Next, a modified example of this embodiment will be described.

FIG. 5 is a sectional view showing a first modification of this embodiment, FIG. 6A is a sectional view showing a second modification of this embodiment, and FIG. 6B is this embodiment. It is sectional drawing which shows the 3rd modification of the form of this.

As shown in FIG. 5, in the first modification, instead of forming the reflection film on the step surface 114a, the light reflecting member 116 such as a reflection sheet is arranged along the step surface 114a. . Even with such a configuration, the same effect as that of the configuration of FIG. 1 can be obtained.

Further, in the configuration of FIG. 1, the step portion 114 is formed on the upper surface 105 of the light guide plate 101.
It may be formed on the lower surface 106 of the light guide plate 101 as in the second modification shown in FIG. 6A, or both surfaces of the light guide plate 101 as in the third modification shown in FIG. 6B. 105,
You may form in 106. Even with such a configuration, of course, the same effect as that of the configuration of FIG. 1 can be obtained. In the second and third modified examples, the light guide plate 101 of the light output section 122.
The reflection sheet 107 is disposed so as to cover the lower surface 106 of the light guide plate 101, and the reflection sheet 117 is disposed separately so as to cover the lower surface 106 of the light guide plate 101 of the light introducing portion 121. Of course, the reflection sheet 107 may be extended to this point. It should be noted that comparing the configuration of FIG. 1 with the second modification of FIG. 6A and the third modification of FIG. 6B, FIG.
This configuration has an advantage that a display element such as a liquid crystal panel can be easily placed on the light emitting area 113. In particular, the step portion 11
4 can be used for positioning the liquid crystal panel. Further, in the third modified example of FIG. 6B, since the light beam having the highest directivity that is vertically incident on the light incident side surface 104 from the light source 102 reaches the inner side without hitting the stepped portion 114, the above three types of The highest efficiency is obtained in the configuration. Embodiment 2 FIG. 7 is a perspective view showing a configuration of a light guide plate used in a surface lighting device according to Embodiment 2 of the present invention. 7, the same reference numerals as those in FIG. 1 indicate the same or corresponding portions. As shown in FIG. 7, in the present embodiment, the upper surface 10 of the light guide plate 101 is
5 is formed in a sawtooth shape (a zigzag shape) in plan view, and the side corresponding to the step portion 114 of the diffusion sheet 108 and the reflection sheet 115 shown in FIG. It is formed in a sawtooth shape corresponding to the shape. Other points are the same as those in the first embodiment.

Next, the function of introducing light into the light guide plate of the surface lighting device configured as described above will be described. 8A and 8B are diagrams showing the action of introducing light into the light guide plate of FIG. 7, where FIG. 8A is a plan view and FIG. 8B is a side view.

In FIG. 8, the ray R1 is the light incident side surface 1
04 light incident position (a portion on the light incident side surface 104 that is in contact with or closest to the light source. As a guide, the light source 102
It is one of the light rays propagating in the light guide plate 101 starting from the point A on the light incident side surface 104), and a step like the light ray R1 in FIG. It is a light beam that propagates toward the back of the light guide plate 101 without hitting the portion 114. On the other hand, ray R2 is also point A
Is a light ray that propagates in the light guide plate 101 from
This corresponds to the light ray R2 in FIG. 2 and is a light ray reflected by the step portion 114. As is clear from FIG. 8 (b),
This ray R2 follows a path substantially the same as the ray R2 (and R2 ″) in FIG. 2. As described above, the action of introducing light in the surface lighting device of the present embodiment is the same as that of the first embodiment in a side view. It is completely equivalent to (FIG. 2), and therefore, it can be seen that the light utilization efficiency can be increased by the same principle as in the first embodiment.

Next, let us look at this ray R2 in the plan view of FIG. When the light ray R2 enters the light guide plate 101, the light ray R2 first propagates to the step portion 114 at an angle nearly perpendicular to the light incident side surface 104 (section between point A and point B), but the step portion 114 has a sawtooth shape. Therefore, the light is reflected in an oblique direction at the point B and propagates toward a portion (point C) other than the light incident position (point A) on the light incident side surface 104. Point C
Then, the light ray R2 is reflected or re-incident and propagates toward the inner side of the light guide plate 101 again. If the position where the light ray strikes at the step portion 114 is on the opposite side of the point B (for example, the point B ′) with the apex T of the sawtooth shape in between, the reflected light propagates toward the vicinity of the point C ′. The vicinity of the point C ′ also corresponds to a portion other than the light incident position on the light incident side surface 104. Of the incident light propagating from the light incident position on the light incident side surface 104 toward the stepped portion 114, the direction with the highest directivity (hereinafter referred to as the maximum directivity direction) is the normal direction of the light incident side surface 104, and Light board 10
It is considered that the directional characteristic of the incident light on 1 has a distribution having a peak in this direction. Therefore, most of the incident light on the light guide plate 101 hits the vicinity of the vertex T, and as a result, most of the light is reflected toward the point C or the point C ′. With such characteristics, not only the effect of improving the light utilization efficiency described in the first embodiment, but also the effect that the uneven brightness generated in the portion near the LED installation position in the light emission region is averaged and the brightness becomes uniform. Is obtained. Hereinafter, this point will be described in more detail.

FIG. 9 is a graph showing the distribution of the amount of light propagating through the light guide plate. FIG. 9A shows the distribution of the amount of propagation light along the line IXa-IXa of FIG. 8A, and FIG. It is a figure which shows the propagation light amount distribution in the cross section corresponding to the IXa-IXa cross section of the light guide plate of 1. As described in the first embodiment, the surface lighting device of FIG. 1 also has four LEDs as the light source 102, similarly to the surface lighting device plate of FIG. 7.

In FIGS. 9 (a) and 9 (b), reference numerals L1, L2, and L3 respectively represent the distribution of the amount of propagating light rays not hitting the step portion, the distribution of the amount of propagating light rays hitting the step portion at least once. And a curve showing the total propagation light amount distribution.

First, consider the light guide plate of FIG. As for a light ray such as the light ray R1 shown in FIG. 2, which does not hit the step portion 114, the amount of propagation light is naturally large in the portion close to the LED light source 102 and is small in the intermediate portion. Therefore, the distribution of the amount of propagation light is as shown by the curve L1 in FIG. On the other hand, for a light ray that strikes the step portion 114 at least once like the light ray R2 in FIG. 2, the propagation distance is slightly increased by the round trip between the light incident side surface 104 and the step portion 114, and the difference in brightness between light and dark is slightly alleviated. However, there is no great difference from the curve L1, and the distribution of the amount of propagation light is as shown by the curve L2. Then, a curve L3 is obtained as the total amount of propagation light obtained by adding the curves L1 and L2. In this way, the total amount of propagation light has a very large difference in brightness.

Next, the light guide plate of FIG. 7 will be considered. The propagation light amount distribution of a light ray that does not hit the step portion 114 like the light ray R1 in FIG. 8B is the same as that in the light guide plate in FIG. 1 and can be expressed as a curve L4 in FIG. 9B. However, as for the light ray that hits the step portion 114 at least once, as described above, the light incident side surface 104 of FIG.
Since the light is intensively returned to a portion other than the light incident position (point A) (for example, near the point C or the point C ′), the light that is re-injected into the light guide plate 101 from there is like the point C or the point C ′. The distribution has a maximum at each position. Therefore, FIG.
A distribution of the amount of propagating light as represented by the curve L5 in (b) is obtained. Then, a curve L having light and dark distributions opposite to each other
4 and the curve L5 are complementarily added, and a very smooth curve L6 is obtained as the total propagation light amount. Then, a cross section (IX-IX) at the starting end of the light output portion 122 of the light guide plate 101.
Since such a smooth distribution of the amount of propagating light is obtained in the cross section, it is possible to obtain a very uniform brightness in the entire light emitting region 113 as well.

To summarize the configuration for obtaining the above-mentioned effect, "from the light incident position on the light incident side surface 104 to the step portion 11
Most of the incident light propagating toward 4 is the light incident side surface 1.
It is said that the stepped portion 114 is formed with a light reflection structure that is reflected toward a portion other than the light incident position 04. Instead of "most of the incident light",
It may be said that "a light ray propagating in the maximum directivity direction of incident light".

In the case of the light guide plate of FIG. 7, as can be seen from FIG. 8A, the maximum directing direction of the incident light (light incident side surface 10
4) and the normal direction of the step surface 114a in the portion where the incident light reaches are not parallel to each other when projected onto a plane parallel to the light exit surface 105 (in plan view). By doing so, the above-mentioned light reflection structure is realized.

In the above configuration, the stepped portion 114 has a sawtooth shape, but various other shapes are conceivable. FIG. 10 shows some specific examples. These are all steps 114 in the light guide plate 101.
3 shows a shape when is projected onto a plane parallel to the light emitting surface 105. FIG. 10A shows an example in which the sawtooth-shaped peaks and valleys of the step portion 114 are opposite to those in the case of FIG. 7. FIG. 10B also shows an example of a sawtooth shape in which only a part of the step portion 114 is made non-parallel to the light incident side surface 104. FIG. 10C shows an example of yet another sawtooth pattern. 10 (d) to (f),
The example in which the step portion 114 is formed in various curved shapes (including a circular arc, a parabolic shape, a hyperbolic shape, a sine wave shape, and various other curved shapes) is shown. With any of the above, a uniform luminance distribution can be obtained.

Also in this embodiment, as in the first modification of the first embodiment, instead of forming a metal reflection film or a dielectric reflection film on the step portion 114, the step portion 114 is formed. The light reflecting member 116 can be arranged along the line. In side view, the structure is similar to that of FIG. FIG. 11 shows a specific example thereof. FIG. 11A shows an example in which the saw-toothed step portion 114 and the planar light reflecting member 116 are combined. FIG. 11B shows a flat step portion 1.
An example in which 14 and a saw-tooth-shaped light reflecting member 116 (having a shape like a folding screen) is combined is shown. FIG. 11C shows an example in which the saw-toothed step portion 114 and the sawtooth-shaped light reflecting member 116 are combined. With such a configuration, in the maximum directivity direction of the incident light propagating from the light incident position A toward the step portion 114, in the case of FIG. 11A, the light ray is transmitted through the step portion 114 and refracted. In the case of FIG. 11B, the light is reflected by the light reflecting member 116, and in FIG. 11C, due to both of these effects, the light is reflected toward the portion other than the light incident position A of the light incident side surface 104. It Therefore, the effect that the luminance distribution can be made uniform is obtained.

The light reflecting structures shown in FIGS. 11A to 11C are common to the maximum directing direction of incident light, the normal direction of the stepped portion 114 (correctly, the stepped surface), and the light reflecting member 116. That is, when the normal direction of the reflecting surface is projected onto a plane parallel to the light emitting surface, all are not parallel (at least one is different from the others). It can be said that this is a condition for causing the reflected light to propagate toward a portion other than the light incident position on the light incident side surface 104 by the light reflection structure.

In this case, as the shape of the stepped portion 114 or the reflecting surface of the light reflecting member 116, various shapes such as the sawtooth shape and the curved shape shown in FIG. 10 can be adopted.

Further, for example, a Fresnel lens 118 is formed on the step portion 114 as shown in FIG. 12A, or a diffractive optical element 119 such as a hologram is formed on the step portion 114 as shown in FIG. 12B. You may do it. With such a configuration as well, the light ray in the maximum directivity direction of the incident light can be reflected toward a portion other than the light incident position A on the light incident side surface 104, thereby obtaining the effect of uniforming the luminance. In the case of the diffractive optical element 119, diffraction is more appropriate than reflection, but
This is also included in the reflection in a broad sense.

In addition, for example, FIG. 10C and FIG.
In the step portion 114 having a relatively fine structure as shown in (a), the inclination of the portion of the step surface that is inclined with respect to the light incident side surface 104 is increased, and total reflection is performed on the ray of the incident light in the maximum directing direction. If the conditions are satisfied, the incident light can be reflected in a desired direction without providing a reflection film or a light reflection member. By using this method, the number of parts and the number of manufacturing steps can be reduced, which leads to cost reduction. Embodiment 3 FIG. 13 is a plan view showing the configuration of a light guide plate used in a surface lighting device according to Embodiment 3 of the present invention. 13, the same reference numerals as those in FIG. 7 indicate the same or corresponding portions.

As shown in FIG. 13, in the present embodiment,
A portion of the light incident surface 104 of the light guide plate 101 other than the portion in the vicinity of the light incident position A is inclined in a plan view, and a reflection film (metal reflection film, dielectric multilayer film, or the like) is formed on that portion. It is substantially parallel to the step surface 114a facing the inclined portion. The other points are similar to those of the second embodiment.

In this structure, the ray R2 in FIG.
Considering the optical path of the ray R7 which once hits the stepped portion 114 as described above, the following is obtained. First, from the incident position A to the light guide plate 1
The light ray R7 that has entered inside 01 is reflected at the point B on the stepped portion 114, and at a point C other than the light incident position A on the light incident side surface 104.
Is reflected again. At this time, since the light incident side surface 104 and the step surface 114a are almost parallel to each other, the optical path of the light ray R7 from the point A to the point B and the optical path after the point B are projected on a plane parallel to the light emitting surface 105. When they do, they are almost parallel. On the other hand, it is assumed that the re-incident light ray from the point G in FIG. 2 in the first embodiment and the re-incident light ray from the point C in FIG. 8 in the second embodiment have a medium having diffuse reflection characteristics behind them. Therefore, the propagation direction is the light guide plate 10.
It was a direction independent of that of the first incident light on 1.
Therefore, the directional characteristic of the re-incident light is not related to that of the incident light, and reflects the reflective directional characteristic of the diffuse reflective material behind. On the other hand, in the re-reflected light in the present embodiment, since the propagation direction of the first incident light to the light guide plate 101 is preserved as it is, the directional characteristic is also the initial directional characteristic of the incident light. Will be saved. Therefore, in the PQ section of the light guide plate of FIG. 13, as shown in FIG. 9A, a light ray that does not hit the step portion 114 (its propagation light amount distribution L4) and a light ray that hits the step portion at least once (that propagation light quantity). When considering the propagation of light separately from the distribution L5), not only do they have a complementary relationship in the amount of propagating light, but also their directional characteristics are substantially the same. On the other hand, in the case of the second embodiment, the two are complementary in the amount of propagating light, but the directional characteristics do not always match.
Therefore, the total propagated light which is the sum of the two (its propagated light quantity distribution L
In 6), the amount of propagation light is uniform and the directional characteristics are also uniform. As a result, more uniform brightness on the light output surface can be obtained than in the second embodiment. In particular, it is possible to greatly improve the uniformity when the surface lighting device is viewed obliquely.

Such an effect can be obtained such that the reflected light is reflected again toward the maximum directing direction of the first incident light on the light guide plate 101 at the portion of the light incident side surface 104 where the reflected light reaches. It can be said that this is because a transparent light reflecting structure is formed.

In the case of the surface illuminating device of FIG. 13, the normal direction of the portion where the reflected light reaches on the light incident side surface 104 and the maximum directing direction of the initial incident light are not parallel to each other. A light reflecting structure has been realized.

As the shape of the portion of the light incident side surface 104 where the reflected light reaches, in addition to the shape shown in FIG. 13, various shapes shown as the shape of the step portion 114 in FIG. 10 may be adopted. It is possible.

Similar to the step portion 114 of FIG. 11, instead of forming a reflection film on the light incident side surface 104 where the reflected light reaches, a light reflecting member is arranged along the light incident side surface 104. Good. Also in this case, the maximum directivity direction of the incident light, the normal direction of the portion of the light incident side surface 104 where the reflected light reaches, and the normal direction of the reflective surface of the light reflecting member provided behind the light incident side surface 104 are defined as follows. When projected onto a plane parallel to the light emitting surface 105, all are not parallel (at least one is different from the others), whereby a desired light reflecting structure can be formed.

Further, similarly to the step portion 114 of FIG. 12, a portion where the reflected light reaches on the light incident side surface 104,
A Fresnel lens may be formed, or a diffractive optical element may be formed.

Further, in the step portion 114 of FIGS. 10C and 12A, the inclination of the inclined portion is increased so that the total reflection condition is satisfied with respect to the ray of the incident light in the maximum directing direction. It is of course possible to apply the same idea as that of forming the reflecting structure to the portion of the light incident side surface 104 where the reflected light reaches. That is, a light reflection structure is formed in this portion so as to satisfy the condition of total reflection with respect to the rays of light reflected from the step portion in the maximum directing direction. Fourth Embodiment In the fourth embodiment of the present invention, as in the case of the second embodiment, in the IXa-IXa cross section, the light rays not hitting the step portion 114 and the light rays hitting the step portion at least once have different directional characteristics. It provides another configuration that solves the problem. 7 and 8 of the second embodiment.
The light guide plate 101 shown in FIG. 2 is used, and a light diffusing / reflecting member is provided in a portion of the light incident side surface 104 where the reflected light from the step portion 114 reaches. It is almost the same as. With such a configuration, it is possible to make the directional characteristics of the light ray that does not hit the step portion 114 and the ray that hits the step portion at least once, and obtain a higher uniformity in the brightness of the light emitting region 113. Light incident side surface 1 as shown in FIG.
In comparison with the method of tilting 04, the light incident side surface 104
Since it is not necessary to perform processing for such inclination, cost reduction can be expected. However, in some cases, it may be necessary to purposely use an expensive light diffusing / reflecting member in order to match the directional characteristics of the light source, and each has advantages and disadvantages. Fifth Embodiment A fifth embodiment of the present invention is one in which the present invention is applied to a light guide plate. That is, in the first to fourth embodiments, examples of application to the surface lighting device of the present invention, specifically, the backlight have been shown. However, the present invention may obtain desired effects not only as a surface lighting device but also as a light guide plate alone. For example, the surface lighting device of FIG. 1 described in the first embodiment, the surface lighting device of FIG. 7 described in the second embodiment, or the third embodiment.
In the surface illuminating device of FIG. 13 described above, when a light reflection film such as a metal reflection film or a dielectric multilayer film is formed on the step portion 114, these light reflection layers are substantially integrated with the light guide plate. These light guide plates alone can provide effects such as improvement of light utilization efficiency and uniformity of brightness. Sixth Embodiment A sixth embodiment of the present invention is one in which the present invention is applied to a display device. Specifically, in FIG. 18, the surface illumination device of the first to fourth embodiments is used instead of the backlight unit 109. That is, a liquid crystal display device is configured by combining the liquid crystal panel 110 as a display element with the surface illumination device of the first to fourth embodiments as a backlight. In this liquid crystal display device, the light output from the surface illumination device is incident on the liquid crystal panel 110, and the transmittance of the incident light in the liquid crystal panel 110 is controlled in accordance with the image signal, so that display is performed. Therefore, even with such a configuration, the light utilization efficiency is improved, that is, the brightness is improved and the liquid crystal panel 110 is displayed as described in the first, second, third, or fourth embodiment. It is possible to obtain effects such as uniform brightness in the area.

As the display element, in addition to the liquid crystal panel, a spatial light modulator of the optical writing type (for example, Japanese Patent Laid-Open No. 07-
306418) and the like) can be adopted. Further, the display element does not necessarily have to use liquid crystal. For example, an electro-optic crystal such as BSO (bismuth silicon oxide) may be used. Alternatively, it may be an electrochromic material. Alternatively, DMD (Deformable Mirror D)
A display element using an electronic device) may be used. Embodiment 7 Embodiment 7 of the present invention applies the present invention to a mobile phone and a mobile terminal device.

15A and 15B are views showing the outer appearance of the mobile phone and the mobile terminal device according to the present embodiment, wherein FIG. 15A is a perspective view showing the mobile phone, and FIG. 15B is a perspective view showing the mobile terminal device. is there.

As shown in FIG. 15A, the mobile phone 301 according to the present embodiment uses the liquid crystal display device according to the sixth embodiment as the display unit 120. Also, FIG.
As shown in FIG. 5B, the mobile terminal device 302 according to the present embodiment is the same as the liquid crystal display device according to the sixth embodiment.
It is used as 0.

Even with such a structure, in the display section 120, the effects of improving and uniforming the brightness as described in the first to fourth embodiments can be obtained.

In addition, the display device of the sixth embodiment can be used as a display unit of a liquid crystal television, a liquid crystal monitor, a liquid crystal monitor for a notebook personal computer, a car navigation device, or the like. [Supplement on Light Source] In the second and third embodiments described above, a plurality of point light sources are used. This is because, as described in the section of the prior art, when using a small LED light source with low power consumption, sufficient brightness cannot be obtained with only one light source. The reason why the plurality of light sources are not concentrated in one place but dispersed in several places is to prevent deterioration of the light guide plate due to heat. But,
If the plurality of point light sources are arranged in a dispersed manner in the present invention (that is, if there are a plurality of light incident positions on the light incident side surface), in addition to the effect of preventing deterioration due to heat, the uniformity of brightness is further improved. The effect of being effectively improved is also obtained.
For example, when four LEDs are used, it is equivalent to the presence of a light source at points C and C ′ in FIG. 8A in the present invention, and substantially eight or nine LEDs are made uniform. Equivalent to those arranged in. From the viewpoint of the uniformity of light emission, such a uniform LED arrangement is at a level that can be considered to be almost equivalent to a linear light source such as between fluorescent tubes and cold cathodes. This indicates that substantially the same uniformity as in the case of using a linear light source such as a fluorescent tube can be obtained in the light emitting region while using an LED that is substantially a point light source.

In the present specification, the case where the number of light sources is four has been mainly described, but the number of light sources is not limited to this and any number of light sources may be used. From the viewpoint of uniformity, the larger the number, the more desirable. [Supplementary Notes on Arrangement of Diffusion Pattern] By the way, WO98 / 19105 (International Application No. PCT / JP97 / 03892, Patent No. 315183) described in the section of Related Art.
In FIG. 27 of No. 0), the diffusion patterns were arranged in concentric circles centered on the respective light sources. However, in the second embodiment and the third embodiment of the present invention (though the first embodiment may be used, of course), the amount of light propagating in the light guide plate 101 is substantially uniform. It does not have to be concentric. That is, the parallel pattern as shown in FIG. 14 may be set. In particular, if the longitudinal direction of the diffusion pattern 103 is arranged so as to be substantially perpendicular to the maximum directivity direction of the incident light over the entire light emission region 113, high directivity can be obtained in the front direction (for this reason). For details of the above, refer to the above-mentioned document WO98 / 19105), and moreover, the diffusion directivity characteristics thereof are uniform over the entire light emitting region 113, and therefore the uniformity when the surface lighting device is viewed obliquely is also improved.

The arrangement of the diffusion pattern 103 is shown in FIG.
There is no need to be random like. For example, they may be arranged in a matrix or staggered order. Also, a long diffusion pattern may be arranged so as to extend over the entire width of the light emitting region 113. [Supplementary Notes on Permissible Range of Vertical Conditions] In the above description, the step surface that is “substantially perpendicular” to the light emitting surface or the light incident side surface of the light guide plate is “substantially perpendicular” to the light emitting surface. I have used expressions such as. The term “substantially vertical” as used herein means that a certain degree of deviation is allowed even if it is not strictly vertical. The degree of this allowable range will be considered below.

FIG. 16 shows the step surface 114a and the light emitting surface 105.
FIG. 6A is a cross-sectional view of the light guide plate when the angle formed by the light guide plate is slightly deviated from a right angle, and FIG.
The figure which shows the case where the angle which 4a makes becomes an obtuse angle, (b)
On the contrary, it is a figure which shows the case where it becomes an acute angle. In each figure, the angle of deviation from the right angle is α.

In FIG. 16, a light ray corresponding to the maximum directing direction, that is, a light ray R perpendicular to the light incident side surface 104.
Consider a case where 8 hits the step surface 114a. Step surface 11
If 4a is strictly perpendicular to the light emitting surface 105, the path of this light ray returns in the opposite direction, but as shown in FIG. 16A, the step surface 114a forms an obtuse angle with respect to the light emitting surface 105. In this case, the light ray R8 is reflected slightly downward by the step surface 114a and is incident on the lower surface 106 of the light guide plate 101 at an angle of 90 ° -2α. Also, FIG.
As shown in FIG. 6 (b), the step surface 11 is
When 4a forms an acute angle, the light ray R8 reflected by the step surface 114a is incident on the upper surface 105 of the light guide plate 101 at an angle of 90 ° -2α. Here, this angle is the critical angle θo for the ray R8 to propagate effectively.
It must be above. That is, this condition is shown in FIG.
In both cases (a) and (b), 90 ° -2α ≧ θo,
Therefore, it is expressed as α ≦ 45 ° −θo / 2. Now, assuming that polycarbonate is used as the medium of the light guide plate 101, for example, the relative refractive index with respect to air is η = 1.59, and the critical angle is found to be θo = sin−1 (1 / 1.59) ≈39 °. Therefore, the condition of α ≦ 25.5 ° is obtained. That is, the allowable range of deviation from the vertical is ± 25.5.
It should be considered within °.

The above is the condition when the light beam in the maximum pointing direction is used as a representative, but if considered more strictly, the light beam entering the upper and lower surfaces of the light guide plate at the smallest angle among the light beams incident from the light incident side surface. Must satisfy the condition for total reflection. FIG. 17 shows a light beam in such a case. As described in the description with reference to FIG. 3, the angle of the incident light from the light incident side surface 104 that deviates most from the normal direction is equal to the critical angle θo. Therefore, when the angle formed by the light emitting surface 105 and the step surface 114a is an obtuse angle, the ray R that follows the path as shown in FIG.
When the angle formed by the light emitting surface 105 and the step surface 114a is an acute angle, the light ray R10 that follows the path as shown in FIG. 17B is reflected by the step surface 114a and then the light guide plate 10 is reflected.
It is incident on the upper and lower surfaces of No. 1 at the smallest angle. In either case, the angle is calculated as 90 ° -θo-2α. The total reflection condition for this incident angle is 90 ° -θo-2α ≧ θ
o, that is, α ≦ 45 ° −θo. Refractive index η
Using a critical angle θo = 39 ° for = 1.59, α
The condition of ≦ 6 ° is obtained. That is, the allowable range of deviation from the vertical must be considered within ± 6 °.

As described above, the more lenient condition (α ≦ 25.5 °)
Then, the more severe condition (α ≦ 6 °) was considered, but there is no particular problem if the former is adopted for the determination. [Other Supplementary Matters] Some supplementary matters regarding each embodiment of the present invention will be described below.

First, an example of a specific size in the surface lighting device of the present invention will be described. In the present invention, for example, when the height of the light emitting area of the LED light source is 0.7 mm even though it is desired to reduce the thickness in the light emitting area of the light guiding plate to 0.5 mm, for example, the The thickness may be set to 0.8 mm to cover the light emitting region, and a step having a height of 0.3 mm may be provided. In addition, it is desirable that the distance from the light incident side surface to the step portion is small for miniaturization. For example, in a light guide plate having a light emission area of 45 mm × 34 mm, this distance is 0.2 to 20 mm, preferably 1
It is good to set it to about 5 mm.

In the light guide plate used in each of the embodiments,
In the light emitting region 113, the upper surface and the lower surface do not necessarily have to be parallel to each other, and may be a wedge shape that becomes thinner toward the inner side of the light guide plate (away from the light source).

The light guide plate has been described on the assumption that the light incident side surface is provided on only one side, but of course, a plurality of sides (two opposite sides, or all four sides of the rectangular light guide plate). The present invention can be applied to the case where there is a light incident side surface.

Although the backlight type is assumed as the surface illumination device in the present specification, the present invention can be applied to a front light type surface illumination device. Further, in that case, the above-described effects can be obtained also in a display device that is set with a reflective liquid crystal panel.

The present invention can be applied to a structure in which a substrate used for a display element such as a liquid crystal panel also serves as a light guide plate.

Although an LED was mainly assumed as the point light emitting light source, the same effect can be obtained by using an organic or inorganic electroluminescent light source or a laser light source. Further, the first embodiment can be applied not only to the case where there are a plurality of point light sources but also to a linear light source such as a fluorescent tube or a cold cathode tube.
A light utilization efficiency improving effect can be obtained.

[0113]

The present invention is embodied in the form as described above, and in a very thin surface lighting device, high light utilization efficiency can be obtained and therefore high brightness can be obtained. At the same time, display uniformity can be improved. Furthermore, since the loss of power consumption can be reduced by improving the light utilization efficiency, it is possible to save energy and obtain an effect of being friendly to the global environment and space environment.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a configuration of a surface lighting device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing the action of introducing light into the light guide plate of FIG.

FIG. 3 is a cross-sectional view schematically showing how light emitted from a light source enters the inside of a light guide plate.

FIG. 4 is a cross-sectional view schematically showing a light leakage preventing action of the reflection sheet of FIG.

FIG. 5 is a sectional view showing a first modification of the first embodiment of the present invention.

6A and 6B are views showing a modified example of the first embodiment of the present invention, in which FIG. 6A is a sectional view showing a second modified example, and FIG.
It is sectional drawing which shows the modification.

FIG. 7 is a perspective view showing a configuration of a light guide plate used in the surface lighting device according to the second embodiment of the present invention.

8A and 8B are diagrams showing the action of introducing light into the light guide plate of FIG. 7, wherein FIG. 8A is a plan view and FIG. 8B is a side view.

9A and 9B are diagrams showing the amount of propagation light in a specific cross section of the light guide plate, wherein FIG. 9A is a diagram showing the distribution of the amount of propagation light in the cross section IXa-IXa of FIG. 8A, and FIG. 9B is the light guide plate of FIG. IXa-IXa
It is a figure which shows the propagation light amount distribution in the cross section corresponding to a cross section.

FIG. 10 is a plan view showing a shape of a stepped portion of the light guide plate, and FIGS. 10A to 10F are views showing specific examples.

FIG. 11 is a plan view showing the shape of the step portion of the light guide plate and the light reflecting member, and FIGS. 11A to 11C are views showing specific examples.

12A and 12B are plan views showing another configuration example of the step portion of the light guide plate, FIG. 12A is a diagram showing a configuration in which a Fresnel lens is formed in the step portion, and FIG. 12B is a diffractive optical element in the step portion. It is a figure which shows the structure in which was formed.

FIG. 13 is a plan view showing a configuration of a light guide plate used in the surface lighting device according to the third embodiment of the present invention.

FIG. 14 is a plan view showing an example of a diffusion pattern in a light guide plate according to embodiments 2 and 3 of the present invention.

15A and 15B are diagrams showing appearances of a mobile phone and a mobile terminal device according to a seventh embodiment of the present invention, in which FIG. 15A is a perspective view showing the mobile phone, and FIG. 15B is a perspective view showing the mobile terminal device. Is.

FIG. 16 is a cross-sectional view of the light guide plate when the angle formed by the step surface and the light emitting surface is slightly deviated from a right angle, and FIG. 16 (a) shows that the angle formed by the light emitting surface and the step surface is an obtuse angle. FIG. 4B is a diagram showing a case where the angle is large, and FIG.

FIG. 17 is a cross-sectional view of the light guide plate when the angle formed by the step surface and the light exit surface is slightly deviated from a right angle and light under severe conditions is incident, and FIG. FIG. 3B is a diagram showing a case where the angle formed by is an obtuse angle, and FIG.

FIG. 18 is a cross-sectional view showing the structure of a conventional liquid crystal display device.

19A and 19B are cross-sectional views schematically showing a configuration in which the light guide plate is thinner than the size of the light emitting area of the light source, FIG. 19A is a diagram showing a virtual configuration, and FIG. 19B is a diagram showing a configuration of a conventional example. Is.

FIG. 20 is an enlarged view of the vicinity of the light incident side surface and the tapered portion of FIG. 19B.

[Explanation of symbols]

One-side lighting device 101 light guide plate 102 light source 103 diffusion pattern 104 Light incident side 105 Top surface (light emission surface) 106 Lower surface (diffusing surface) 107 reflective sheet 108 Diffusion sheet 109 Backlight part 110 LCD panel 111a, 111b Polarizing film 112 taper 113 Light emission area 114 step 114a step surface 115 Top reflective sheet 116 Light reflection member 117 Bottom reflection sheet 118 funnel lens 119 Diffractive optical element 120 display 121 Light introduction part 122 Light output unit 123 Light reflection film 301 mobile phone 302 mobile terminal device L1 to L6 Propagation light amount R1, R2, R2 ', R2 ", R3 to R10 rays

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02B 6/00 331 G02B 6/00 331 G02F 1/13357 G02F 1/13357 // F21Y 101: 02 F21Y 101: 02 (72) Masanori Kimura, 1006 Kadoma, Kadoma City, Osaka Prefecture, Matsushita Electric Industrial Co., Ltd. (72) Ichiro Sato, 1006, Kadoma, Kadoma City, Osaka Prefecture, F Term (reference) 2H038 AA55 BA06 2H091 FA14Z FA19Z FA23Z FA27Z FA32X FA45Z FB02 FD04 FD23 KA01 LA11 LA18 MA10

Claims (39)

[Claims] 1. A surface illuminator including a light source and a light guide plate in which light from the light source is incident from a side light incident area, propagates inside, and is emitted to the outside from a light emitting surface that is one main surface. In, at least one main surface of the light guide plate is provided with a step surface that is substantially perpendicular to the light exit surface, the step surface faces the light incident area, and the light guide plate is thick on the light incident area side. And a first light reflection structure that reflects light toward the light incident region side is formed on the step surface, and the light exit surface of the portion of the light guide plate that is thin at the step surface is a boundary. A surface illuminating device characterized in that a light emitting region for emitting light to the outside is formed. 2. The surface lighting device according to claim 1, wherein the first light reflecting structure is a light reflecting film formed on the step surface. 3. The surface lighting device according to claim 1, wherein the first light reflecting structure is a light reflecting member arranged along the step surface. 4. The surface lighting device according to claim 1, wherein a relative refractive index with respect to a medium around the light guide plate is √2 or more. 5. The surface lighting device according to claim 4, wherein the light incident area of the light guide plate is substantially perpendicular to the light exit surface. 6. The light reflecting member for reflecting light to the light guide plate side is arranged on both main surfaces of a portion extending from the light incident region of the light guide plate to the step surface. Surface lighting device. 7. The light source is a point light source, and the first light reflection structure is incident from a light incident position which is a position closest to the point light source in the light incident region, and is directed toward the step surface. The surface illumination device according to claim 1, wherein most of the propagating incident light is reflected toward a portion other than the light incident position in the light incident region. 8. The surface lighting device according to claim 7, wherein the first light reflecting structure is a light reflecting film formed on the step surface. 9. A maximum directivity direction of the incident light and a normal direction of a portion of the step surface where the incident light reaches,
The surface lighting device according to claim 8, wherein the surface lighting devices are not parallel to each other when projected onto a plane parallel to the light exit surface. 10. The stepped surface has a sawtooth shape or a curved shape when projected onto a plane parallel to the light emitting surface.
The surface lighting device according to claim 9. 11. The surface lighting device according to claim 7, wherein the first light reflecting structure is a light reflecting member arranged along the step surface. 12. The maximum directivity of the incident light, the normal direction of the step surface, and the normal direction of the reflecting surface of the light reflecting member are all projected onto a plane parallel to the light emitting surface. The surface lighting device according to claim 11, which is not parallel. 13. The surface lighting device according to claim 12, wherein the stepped surface or the reflecting surface of the light reflecting member has a sawtooth shape or a curved shape when projected onto a plane parallel to the light emitting surface. 14. The surface illumination device according to claim 7, wherein a diffractive optical element is formed on the step surface. 15. The surface lighting device according to claim 7, wherein a Fresnel lens is formed on the step surface. 16. The surface lighting device according to claim 7, wherein the stepped surface satisfies a condition of total reflection for a ray of the incident light in the maximum directivity direction. 17. A second light reflection unit that reflects the reflected light again toward a maximum directing direction of the incident light at a portion of the light incident region where the reflected light from the first light reflecting structure reaches. The surface lighting device according to claim 7, wherein a structure is formed. 18. The surface lighting device according to claim 17, wherein the second light reflecting structure is a light reflecting film formed in the light incident region. 19. The maximum directivity direction of the incident light and the normal direction of a portion of the light incident area where the reflected light reaches are not parallel to each other when projected onto a plane parallel to the light exit surface, The surface lighting device according to claim 18. 20. The second light reflecting structure is a light reflecting member arranged along the light incident region.
The surface lighting device according to. 21. A maximum directivity direction of the incident light, a normal direction of a portion of the light incident area where the reflected light reaches, and a direction of the light reflecting member in a portion of the light incident area where the reflected light reaches. The surface illumination device according to claim 20, wherein when the normal direction of the reflecting surface is projected on a plane parallel to the light emitting surface, all are not parallel. 22. A diffractive optical element is formed in a portion of the light incident area where the reflected light reaches.
The surface lighting device according to. 23. A Fresnel lens is formed in a portion of the light incident area where the reflected light reaches.
7. The surface lighting device according to 7. 24. The surface lighting device according to claim 17, wherein a portion of the light incident area where the reflected light reaches meets a total reflection condition for a ray of the reflected light in a maximum directing direction. 25. The surface lighting device according to claim 17, wherein a light diffusing and reflecting member is disposed in a portion of the light incident region where the reflected light reaches. 26. The light emission directivity characteristic of the light source is substantially the same as the reflection directivity characteristic of the light diffusing and reflecting member.
5. The surface lighting device according to item 5. 27. The surface lighting device according to claim 7, comprising a plurality of the light sources and the light incident positions. 28. A diffusion pattern having directivity is formed on a surface of the light guide plate opposite to the light emission surface, and the longitudinal direction of the diffusion pattern is within the light emission region with respect to the maximum directivity direction of incident light. 27. The surface lighting device according to claim 7, wherein the surface lighting device is substantially vertical. 29. A light guide plate in which light incident from a side light incident region propagates inside and is emitted to the outside from a light emitting surface which is one main surface, and at least one of the main surfaces has substantially the light emitting surface. A vertical step surface is provided, the step surface is provided so as to face the light incident area and has a thickness that becomes thicker on the light incident area side, and reflects light to the light incident area side on the step surface. The first light reflection structure is formed, and the light emitting surface of the thinned portion of the light guide plate with the step surface as a boundary forms a light emitting area for emitting light to the outside. Light board. 30. The light guide plate according to claim 29, wherein the first light reflection structure is a light reflection film formed on the step surface. 31. Most of the incident light that is incident from the light incident position set in the light incident region and propagates toward the step surface is the light in the light incident region. The light is reflected toward a portion other than the incident position.
9. The light guide plate according to item 9. 32. The light guide plate according to claim 31, wherein the first light reflection structure is a light reflection film formed on the step surface. 33. Second light reflection for reflecting the reflected light again in the maximum directivity direction of the incident light to a portion of the light incident region where the reflected light from the first light reflecting structure reaches. The light guide plate according to claim 31, wherein a structure is formed. 34. The light guide plate according to claim 33, wherein the second light reflection structure is a light reflection film formed in the light incident region. 35. A display device comprising: the surface lighting device according to claim 1; and a display element that two-dimensionally modulates light emitted from the surface lighting device. 36. A display device comprising: the surface lighting device according to claim 7; and a display element that two-dimensionally modulates light emitted from the surface lighting device. 37. A display device comprising: the surface lighting device according to claim 17; and a display element that two-dimensionally modulates light emitted from the surface lighting device. 38. A mobile phone comprising the display device according to claim 35, 36, or 37 as a display unit. 39. A mobile terminal device comprising the display device according to claim 35, 36, or 37 as a display unit.