JP2003121656A - Light guide plate and plane illumination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light guide plate which can easily control the intensity and directivity of projection light emitted from an arbitrary position of a light projection surface part, and to provide a plane illumination device using the light guide plate. SOLUTION: The plane illumination device is equipped with the light projection surface part 16 for projecting the light, a reverse-surface part which is positioned on the opposite side from the light projection surface part 16, flank parts 13a to 13d which cross the light projection surface part 16 at right angles, an incidence end part 14 which is formed at the flank parts 13a and 13b and where light from a light source 15 is made incident, a light guide plate 12 having a plurality of light deflecting elements 19 which are projected at the reverse- surface part and have ridges 20 extended radially from the incidence end part 14 so that the heights of the ridges 20 from the reverse-surface part gradually increase toward the incidence end part 14 and sectional shapes perpendicular to the ridges 20 are triangular, and a light reflecting sheet 17 which covers the light guide plate 12 except the incidence end part 14 and light projection surface part 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate for emitting light introduced from an incident end portion from a light emitting surface portion intersecting the incident end portion, and a flat lighting device using the light guide plate, and more particularly to a light source. Is suitable for small area illumination using at least one light emitting diode.

[0002]

2. Description of the Related Art A flat lighting device used as a backlight light source of a transmissive liquid crystal display is a cold cathode fluorescent lamp (FC).
L) or a light source such as a light emitting diode (LED) array is guided to an incident end face which is a side end face of a transparent light guide plate, and total reflection of the light inside the light guide plate is used to guide the light. The light is emitted substantially uniformly from the entire area of the light emitting surface that is the surface of the.

In such a conventional light guide plate and flat illuminating device, in order to make the amount of light emitted from the light emitting surface portion uniform, the light emitting surface portion and the opposite side thereof are irrespective of the size of the liquid crystal display device. The distribution state of the light control elements such as minute concave portions and convex portions randomly provided on the back surface is increased as the distance from the light incident end surface is increased. Also,
The size of these light control elements is partially changed to adjust the brightness distribution of the emitted light according to the requirements of the flat illumination device.

[0004]

In the conventional light guide plate and flat illumination device, regardless of the size of the liquid crystal display device, minute concave portions or convex portions randomly provided on the light emitting surface portion or the back surface portion on the opposite side thereof. The intensity of the emitted light is increased according to the requirements of the flat lighting device because the distribution state of the light control elements such as is increased as the distance from the light incident end face increases, and the amount of light emitted from the light emitting face is made uniform. It is difficult to arbitrarily adjust the directional characteristics, such as the brightness distribution of the emitted light in a specific direction.

In the method of adjusting the brightness distribution of the emitted light by partially changing the size of the light control element, the size and shape of the light control element are not stepless, but are changed stepwise, so that The change also becomes gradual, and there is a drawback that unevenness in brightness occurs and the final appearance is deteriorated. Also in this method, the directional characteristics of the light emitted from the light emitting surface portion,
That is, it is difficult to freely adjust the diffusion state of light.

Particularly in a small liquid crystal display device used in a mobile phone or the like, it is necessary to suppress the power consumption of the illumination light source as much as possible, and therefore, the cold cathode fluorescent lamp (FCL) is used.
It can be said that the LED array is more preferable as the light source than the LED array. However, there is no known flat illumination device that can emit high-luminance illumination light uniformly using only one LED, although it has a small area.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light guide plate capable of easily controlling the intensity and directional characteristics of outgoing light emitted from an arbitrary position on a light exit surface portion, and a flat lighting device using this light guide plate. It is in.

[0008]

The first aspect of the present invention is as follows.
A light emitting surface portion for emitting light, a back surface portion opposite to the light emitting surface portion, a side surface portion orthogonal to the light emitting surface portion, and a light source formed on a part of the side surface portion from a light source. Of the incident light and the ridge line protruding from the back surface portion so as to extend radially from the light incident end portion, and the height of these ridge lines from the back surface portion gradually decreases toward the light incident end portion side. Then, the light guide plate is provided with a plurality of light deflection elements each having a triangular sectional shape perpendicular to the ridgeline.

In the present invention, the light from the light source that has entered the light guide plate from the incident end portion travels over the entire area of the light guide plate while repeating total reflection. Some of them are suppressed from diffusing along the arrangement direction by the light deflecting elements radially provided on the back surface, and the other part is broken from the light emitting surface to the outside of the light guide plate by violating the condition of total reflection. Emit to. In this case, the light emission surface closer to the incident end side emits light with a wider diffusion angle and weaker directivity, and conversely, the light emission surface closer to the incident end side emits light with a narrower diffusion angle and stronger directivity. To do. The light amount itself tends to be stronger toward the incident end side.

A second aspect of the present invention is a light guide plate according to the first aspect of the present invention, a light source for projecting illumination light toward the incident end portion of the light guide plate, and the incident end of the light guide plate. And a light reflection sheet that covers a portion other than the light emitting surface portion.

In the present invention, the illumination light emitted from the light source enters the light guide plate from the incident end of the light guide plate, and travels over the entire area of the light guide plate while repeating total reflection. Some of them are prevented from diffusing along the array direction by the light deflecting elements provided on the back surface, and the other part of the light is reflected from the back surface and the light emitting surface of the light guide plate by violating the condition of total reflection. The light is emitted outside. The light emitted from the back surface or the side surface to the outside of the light guide plate is re-entered into the light guide plate by the light reflection sheet, but the light deflection element suppresses diffusion along these arrangement directions, and finally All the light is emitted from the light emitting surface. In this case, the light emission surface closer to the incident end side emits light with a wider diffusion angle and weaker directivity, and conversely, the light emission surface closer to the incident end side emits light with a narrower diffusion angle and stronger directivity. To do. The light amount itself tends to be stronger toward the incident end side.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the light guide plate according to the first aspect of the present invention, the light deflection element having the maximum length of the ridgeline may have an isosceles triangle in cross-section perpendicular to the ridgeline. In this case, the two light deflection elements, which are separated from each other by the same number in the opposite direction from the light deflection element having the maximum ridge length, have the maximum ridge length in a cross-sectional shape perpendicular to these ridge lines. It can be formed symmetrically with respect to the light deflection element. Further, as the light deflecting element is farther from the light deflecting element having the maximum length of the ridge, the inclination angle of at least one of the pair of slopes forming the light deflecting element can be gradually decreased or gradually increased.

It is possible to provide two side portions which are adjacent to each other in a state of intersecting with each other, and an incidence end portion can be formed in an intersection region of these two side portions.

The incident end may be a plane orthogonal to the light emitting surface or a concave cylindrical surface whose axis is perpendicular to the light emitting surface.

The back surface portion may have a wedge-shaped flat surface portion which is formed between the adjacent light deflection elements and is parallel to the light emitting surface portion. Alternatively, the slopes forming the adjacent light deflection elements may be continuous.

A plurality of light control elements may be further provided which are disposed on the light emitting surface portion and control the emission state of light from the light emitting surface portion. In this case, it is preferable that the light control elements have a predetermined distribution with respect to the light emitting surface portion.

In the flat lighting device according to the second aspect of the present invention, the light source may have at least one light emitting diode. In this case, it is preferable that the light guide plate has a rectangular plate shape, and the optical axis of the light emitting diode is on a diagonal line of the light guide plate.

It is possible to further include a light diffusing sheet which is arranged on the light guide plate and which adjusts the directionality of the light emitted from the emission surface portion.

[0019]

Embodiments of the flat lighting device according to the present invention will be described in detail with reference to FIGS. 1 to 8. However, the present invention is not limited to these embodiments and may be further combined or claimed. Any changes and modifications included in the concept of the present invention described in the scope of the above can be made, and thus can be naturally applied to other techniques belonging to the spirit of the present invention.

FIG. 1 shows an external view of a flat illumination device according to an embodiment of the present invention in a disassembled state, its warped surface shape is shown in FIG. 2 in a partially cutaway state, and its III-III arrow sectional structure is shown in FIG. FIG. 4 shows the schematic shape of one light deflection element in this embodiment by extracting and enlarging it in FIG. That is, the flat lighting device 11 according to the present embodiment includes a transparent light guide plate 12 having a rectangular plate shape.
And two adjacent side surface portions 13a, 1 of the light guide plate 12.
3b intersecting area, that is, the light source 15 arranged at the incident end portion 14, the incident end portion 14 of the light guide plate 12, and the light emitting surface portion 1
A light reflection sheet 17 for covering a portion other than 6; and a light diffusion sheet 18 for adjusting the directionality of light emitted from the light emitting surface portion 16 of the light guide plate 12, which is superposed on the light emitting surface portion 16. As the light diffusion sheet 18, for example, a milky white plate or a prism sheet can be adopted.

The light source 15 composed of a single LED or semiconductor laser is surrounded by a reflector (not shown) having a concave reflecting surface, and the light from the light source 15 is guided together with the reflected light from the reflector. Incident end 14 of light plate 12
To enter the light guide plate 12. This reflector is made of a sheet-shaped material in which a white insulating material or a metal such as aluminum is vapor-deposited, and surrounds the incident end portion 14 of the light guide plate 12 and the light source 15, respectively.
Care is taken to prevent light from leaking from other than the incident end portion 14 of the light guide plate 12.

The light reflection sheet 17 covers the four side surface portions 13a to 13d and the back surface portion around the light guide plate 12 and reflects the light emitted from the outside of the light guide plate 12 into the light guide plate 12 again. It is for finally emitting all the light from the light emitting surface portion 16 of the light guide plate 12, and is a non-conductive film or the like on which a metal such as aluminum is vapor-deposited or a metal film is attached, or barium titanate. It is possible to use a resin or the like mixed with or coated with, and it is preferable that the surface of the film or resin is subjected to fine unevenness.

The light guide plate 12 in this embodiment has a refractive index n.
Is formed of a transparent acrylic resin (PMMA) of 1.49, and the incident end portion 14 for introducing light from the light source 15
And four side surface portions 13a to 13d (hereinafter, these may be collectively abbreviated as 13), and these incident end portions 1
4 and a side surface portion 13 and a light emitting surface portion 16 for emitting the light incident from the incident end portion 14 and a back surface portion on the opposite side. On the back surface, the incident end 14
A plurality of light deflecting elements 19 extending in a radial pattern centering on the center are provided in a protruding manner. Each of the light deflection elements 19 has an isosceles triangular shape in a cross section orthogonal to the extending direction thereof, and the individual ridge lines 20 extend radially around the incident end portion 14 and the rear surface portions of these ridge lines 20. A pair of slopes 21 whose height from the ridge 20 gradually increases along the ridge line 20, and the light guide plate 12
And a side surface portion 13c to 13d and an end face 22 of an isosceles triangular shape on the same plane. In these light deflection elements 19, the height of the ridge line 20 gradually decreases linearly as the distance from the incident end 14 increases, and the slopes 21 of the adjacent light deflection elements 19 are continuously formed.

One light deflection element 19 is schematically shown in FIG. The diagonal lines in the figure are portions that are integrally joined to the back surface portion, and the light mainly entering the light deflection element 19a from the diagonally shaded region is 0 ° to 4 ° with respect to the diagonal line of the light guide plate 12.
It has a refraction angle in an arbitrary direction within a range of 2 °, and propagates toward the end face 22 side while repeating total reflection on the slope 21. In this case, since the pair of slopes 21 forming the light deflection element 19 are inclined with respect to each other and also with respect to the back surface portion (light emission surface portion 16), the total reflection condition is broken and one of these light rays is lost. The part exits the light guide plate 12 from the slope 21. In order to reduce the amount of light emitted from the slopes 21, it is desirable to set the apex angle α of the pair of slopes 21 of the light deflection element 19 in the cross section perpendicular to the diagonal line of the light guide plate 12 as follows.

That is, the light deflection element 1 according to the present embodiment.
9 is schematically shown in FIG. 5, which shows points A, B, C, D, E, F.
It is represented by the line segment connecting The pair of slopes 21 has points A, B,
It is represented by a line segment connecting D and E and a line segment connecting points A, C, D, and F. When the incident area of the incident light with respect to the point A of the light deflection element 19 is represented by a surface connected by A, E, and F, and the midpoint of the line segment EF is G, the incident angle γ of ∠DAG Maximum value,
That is, the critical angle for total reflection is about 42 ° in the case of PMMA described above. ∠The incident angle range β expressed by EAF and ∠
The relationship with the apex angle α of the light deflection element 19 represented by BAC is tan (β / 2) = (α / 2) / (segment AG) (1). Here, if the height of the line segment DG is represented by h, there is a relation of line segment AG = h / sinγ, so by substituting this into the formula (1), the formula (1) is transformed as follows. can do. β = 2 tan ^-1 (αsinγ / 2h) = 2tan ^-1 {tan (α / 2) ・ sinγ} ・ ・ ・ (2)

On the other hand, the value of β / 2 is smaller than the total reflection critical angle of 42 °, so that β≈
By assuming this as 90 and substituting this into the above equation (2) together with γ = 42, the apex angle α of the light deflection element 19 is approximately 11
It will be understood that it will be 2 °. That is, the light deflection element 1
By setting the apex angle α of 9 to 112 ° or more, the light emitted from the inclined surface 21 to the outside of the light guide plate 12 can be reduced as much as possible.

In any case, there is less light leakage toward the end face 22 side of the light deflection element 19, and more light leakage toward the incident end 14 side opposite to this. As a result, the light emitted from the light emitting surface portion 16 located immediately above the end face 22 side of the light deflection element 19 has a stronger directivity, that is, the diffusion angle of the light is narrower and the light amount tends to be small, whereas The light emitted from the light emitting surface portion 16 located immediately above the end portion 14 side has weaker directivity, that is, the light diffusion angle is wider, and the light amount tends to be larger. In this case, the pair of slopes 2 forming the light deflection element 19
Due to the light condensing effect of 1, the diffusion of the emitted light along the arrangement direction of the light deflection elements 19 is simultaneously suppressed, and the diffusion angle thereof tends to be narrowed.

In the above-described embodiment, the height of the ridgeline 20 of the light deflection element 19 from the rear surface portion is changed linearly, but it may be changed into a curved line if necessary. In this case, the back surface may be convex or concave. When it is changed to a convex shape, the directional characteristics of the emitted light can be abruptly changed on the incident end 14 side, and conversely, when it is changed to a concave shape, it can be abruptly changed on the end surface 22 side of the light deflection element 19. . In this way, by adjusting the change in the height of the ridge line 20 of the light deflection element 29 from the back surface portion, the diffusion angle of the light emitted from the light emitting surface portion 16 can be adjusted according to the size of the light guide plate 12, the purpose of use, and the like. The adjustment range can be expanded to some extent. Further, in this embodiment, the light guide plate 12
Although acrylic resin was used as the material, other optically transparent materials such as polycarbonate (P
It is of course possible to adopt C) or the like.

In the above-mentioned embodiment, the cross-sectional shape of the light deflection element 19 perpendicular to the ridge line 20 is set to be an isosceles triangle, but the length of the ridge line 20 on the diagonal line of the light guide plate 12 is set. Only the maximum light deflection element 19 or two light deflection elements 19 having the maximum length of the ridge lines 20 adjacent to each other across the diagonal line of the light guide plate 12 have an isosceles triangle in cross section perpendicular to the ridge line 20. , The lengths of these ridges 20 are the same number in the opposite direction from the light deflection element 19 where the length is the maximum, that is, 2 apart from the two side surface portions 13a, 13b.
It is also effective to form the two light deflection elements 19 symmetrically with respect to the light deflection element 19 in which the cross-sectional shape perpendicular to the ridge lines 20 is the maximum length of the ridge lines 20.

For example, light deflection equidistant from the light source 15
A cross-sectional shape perpendicular to each ridge line 20 of the element 19 is schematically
6 is shown on the diagonal line of the light guide plate 12 as shown in FIG.
Light deflection element 19 having the longest ridge 20_COnly that edge
Make the cross-section perpendicular to the line 20 an isosceles triangle,
The light deflection element 19 in which the length of these ridges 20 is maximum_CFrom
An equal number of opposite directions, that is, two side surface portions 13a, 1
The two light deflection elements 19 which are apart from each other on the 3b side are formed by these ridge lines.
The cross-sectional shape perpendicular to each of 20 is the length of the ridge line 20.
Light deflection element 19 that maximizes_CForming symmetrically with respect to
There is. In this embodiment, the optical polarization that maximizes the length of the ridgeline 20 is used.
Orientation element 19_CAway from, that is, the side surfaces 13a, 13b
The closer the light deflection element 19 is to the side, the more the light deflection element 19 is configured.
Light deflection that maximizes the length of the ridgeline 20 of the pair of slopes
Element 19_CSlope 21 facing to the side_iInclination angle of_iGradually increase
With the slope 21 facing the side surface portions 13a and 13b_oThe slope of
Angle θ _oIs gradually reduced.

As a result, the light entering the light guide plate 12 from the back surface side tends to be emitted in a converged or collimated state from the light emitting surface portion 16 due to the pseudo Fresnel lens effect of the light deflection element 19, so that the directivity is maintained. It is possible to obtain high brightness light having a relatively high luminance. This means that although the light source 15 employs a single point light source, the visibility of the liquid crystal display of the mobile phone can be sufficiently secured even in the bright outdoors in the daytime.

Conversely, the farther the light deflection element 19 _C from which the length of the ridge line 20 becomes maximum, the longer the length of the ridge line 20 of the pair of slopes forming the light deflection element 19 becomes. The inclination angle θ _{i of the} slope 21 _i facing the light deflection element 19 _C side
It is easy to understand that when the inclination angle θ _o of the slope 21 _o facing the side surface portions 13a and 13b is gradually increased, diffused light with low directivity can be emitted from the light emission surface portion 16. .

In the above-described embodiment, the slopes 21 of the adjacent light deflection elements 19 are formed so as to be continuous, but a wedge-shaped flat surface parallel to the light emitting surface 16 is formed between them. Good.

FIG. 7 shows the appearance of another embodiment of such a light guide plate according to the present invention, and FIG. 8 shows the end face shape corresponding to the portion VIII in the arrow view. Elements having the same functions as those of the previous embodiment are shown. The same reference numerals as those in FIG. That is, in the present embodiment, between the adjacent light deflection elements 19, a wedge-shaped flat surface portion 23 radially extending around the incident end portion 14 is formed in parallel with the light emission surface portion 16, and the light deflection element 19 is formed. 19 and the flat surface portion 23 are arranged in a fan shape alternately. In this way, by forming the flat surface portion 23 parallel to the light emitting surface portion 16 on the back surface portion, the proportion of light propagating in the light guide plate 12 in the total reflection state is increased, and the light from the back surface portion to the outside of the light guide plate 12 is increased. Since the ratio of the emitted light can be reduced, it is possible to reliably propagate the light that has entered the light guide plate 12 from the incident end portion 14 to the light emitting surface portion 16 that is located away from the incident end portion 14. Is. As a result, it becomes possible to emit light of more uniform brightness from the entire area of the light emitting surface portion 16.

Further, in the light emitting surface portion 16 in the present embodiment, the light control elements 24 are randomly arranged with the incident end portion 14 as the center and the distribution becoming denser as the distance from the incident end portion 14 increases.
Each light control element 24 is formed by a hemispherical convex surface having a radius of curvature of 50 μm, and the projection height from the light emitting surface portion 16 is set to, for example, 1 μm. The area of each light control element 24 in the light emitting surface portion 16 is 7 × 10 ⁻⁸ cm ^2.
The above is required, and the light control element 2 is more than this.
When the area of 4 becomes small, the light emitting surface portion 16 becomes in a state like a satin finish, and diffuse reflection by the light control element 24 becomes large, so that it is difficult to emit high-intensity light having strong directivity from the light emitting surface portion 16. Becomes

When the radius of curvature of the light control element 24 is set to, for example, 25 μm, the projection height from the light emitting surface portion 16 is set to about 2 μm in order to make the area 7 × 10 ⁻⁸ cm ² or more. There is a need. However, the light emitting surface portion 1
When the protrusion height of the light control element 24 with respect to 6 exceeds 2 μm, the inclination of the light control section 21 with respect to the light emission surface section 16 becomes large, and the diffusion angle of the light emitted from this tends to be small. The protruding height of the light control element 24 from the emission surface portion 16 is preferably 2 μm or less.

As described above, by arranging these light control elements 24 in a higher density as the distance from the incident end portion 14 increases, the amount of emitted light in these regions where the amount of emitted light tends to be relatively small increases. It is possible to emit a uniform amount of emitted light over the entire area of the light emitting surface portion 16.

Although the light control element 24 is made to project from the light emitting surface portion 16 of the light guide plate 12 in the above-mentioned embodiment,
It is also possible to form a hemispherical concave surface, a columnar shape, or a conical shape, and have a circular shape, an elliptical shape, or a polygonal shape to form the light emitting surface portion 16. Further, the rear surface portion 19 on which the light deflection element 19 is not formed. The light control element 24 may be formed on the flat portion 23 of the.

[0039]

According to the light guide plate of the present invention, the ridge lines extend radially from the incident end portion, and the heights of these ridge lines from the back surface portion gradually decrease toward the incident end portion, and are perpendicular to the ridge line. Since a plurality of light-deflecting elements each having a triangular cross-section are provided on the back surface, the diffusion angle of the light emitted from the light-emitting surface is narrowed along the arrangement direction of the light-deflecting elements, and at the same time,
The intensity and directivity of the emitted light can be continuously changed along the extending direction of the ridgeline of the light deflection element, and the light source is L
Even with a point light source such as an ED, it is possible to emit light of uniform brightness from the entire area of the light emitting surface.

The light deflection element having the maximum ridge length has a cross-sectional shape perpendicular to the ridges of two light deflection elements which are separated from each other by the same number in the opposite direction from the light deflection element having the maximum ridge length. When formed symmetrically with respect to, the light deflection element farther from the light deflection element having the maximum length of the ridgeline,
When the inclination angle of at least one of the pair of slopes forming the light deflection element is gradually decreased or gradually increased, it is possible to control the directivity and the brightness distribution of the light emitted from the light emitting surface portion in a wider range.

When the two side surfaces are adjacent to each other in an intersecting state and the incident end portion is formed in the intersecting region of these two side surfaces, even if the light guide plate is rectangular, light is emitted by a single light source. Light having a uniform distribution can be emitted from the emission surface portion.

When the incident end portion is a plane orthogonal to the light emitting surface portion or has a concave cylindrical surface whose axis is perpendicular to the light emitting surface portion, the light from the light source incident on the light guide plate from the incident end portion is emitted. Light can be efficiently propagated in the light guide plate. In particular, when the incident end face is a concave cylindrical surface, the light from the light source is diffused in the light guide plate due to the concave lens effect, and it becomes possible to emit light of more uniform brightness from the entire area of the light emitting face. .

When a wedge-shaped flat surface portion parallel to the light emitting surface portion is formed between the adjacent light deflection elements, the proportion of the light emitted from the back surface portion to the outside of the light guide plate can be reduced, and the incident end portion can be reduced. It is possible to reliably propagate the light that has entered the light guide plate from the portion to the light emission end surface portion apart from the incident end portion. As a result, light with more uniform brightness can be emitted from the entire area of the light emitting surface portion.

When a wedge-shaped flat surface portion parallel to the light emitting surface portion is formed between the adjacent light deflection elements, the proportion of the light emitted from the back surface portion to the outside of the light guide plate can be reduced, and the incident end can be reduced. It is possible to reliably propagate the light that has entered the light guide plate from the portion to the light emission end surface portion apart from the incident end portion. As a result, light with more uniform brightness can be emitted from the entire area of the light emitting surface portion.

When the slopes forming the adjacent light deflecting elements are continuously formed, the light incident from the light guide plate is promptly emitted to the back surface side, and the leaked light is again introduced from the back surface part into the light guide plate. It is possible to more easily control the directionality of light when the light is made incident on and emitted from the light emitting surface portion.

According to the flat lighting device of the present invention, the ridge lines extend radially from the incident end portion, the heights of the ridge lines from the back surface portion gradually decrease toward the incident end portion, and the cross section perpendicular to the ridge line. Since a plurality of light deflection elements each having a triangular shape are projected on the back surface of the light guide plate, the diffusion angle of the light emitted from the light exit surface is narrowed along the arrangement direction of the light deflection elements, and at the same time, the light deflection elements are formed. The intensity and directional characteristics of the emitted light can be continuously changed along the extending direction of the ridgeline, and even if the light source is a point light source such as an LED, light of uniform brightness is emitted from the entire area of the light emission surface. It is possible to emit the light, and it is possible to reduce the power consumption of the flat lighting device and at the same time make it compact.

When the light source has at least one light emitting diode, it is possible to realize a compact flat lighting device with reduced power consumption.

When the light guide plate has a rectangular plate shape and the optical axis of the light emitting diode is on the diagonal line of the light guide plate, the light emitting surface portion which is farthest from the incident end portion can surely emit light of high brightness. Can be emitted, and the uneven brightness of light emitted from the light emitting surface can be reduced.

When a light diffusing sheet for adjusting the directionality of the light emitted from the light emitting surface is arranged on the light guide plate, the variation in the brightness distribution is further eliminated and a uniform brightness with a wide viewing angle is obtained. It is possible to obtain a flat illuminating device.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of an embodiment of a flat lighting device according to the present invention.

2 is a partially cutaway plan view of the embodiment shown in FIG. 1. FIG.

3 is a sectional view taken along the line III-III in FIG.

FIG. 4 is an extracted perspective view showing an appearance of a light deflection element in the embodiment shown in FIG.

FIG. 5 is a schematic diagram geometrically showing a propagation state of light with respect to the light deflection element shown in FIG.

FIG. 6 is a cross-sectional view schematically showing a shape of a light guide plate according to another embodiment of the present invention along an arrangement direction of light deflection elements.

FIG. 7 is a perspective view showing an appearance of another embodiment of the light guide plate according to the present invention.

8 is an end view corresponding to arrow VIII in FIG. 7. FIG.

[Explanation of symbols]

11 Planar Illuminator 12 Light Guide Plates 13a to 13d Side Surface 14 Incident End 15 Light Source 16 Light Emitting Surface 17 Light Reflecting Sheet 18 Light Diffusing Sheet 19 Light Deflection Element 19 _C Longest Light Deflection Element 20 Ridge Line 21 Slope 21 _i Ridge Line Is the longest slope 21 facing the side of the light deflection element _{o A} slope 22 facing the side surface side 22 End face 23 Plane 24 Light control element α Apex angle β of a pair of slopes forming the light deflection element γ Incident angle γ Incident angle of light h Height of the ridge from the back surface θ _i Angle of inclination of the slope facing the light deflection element side where the length of the ridge is maximum θ _o Angle of slope of the side facing the side

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Claims (14)

[Claims] 1. A light emitting surface portion for emitting light, a back surface portion located on the opposite side of the light emitting surface portion, a side surface portion orthogonal to the light emitting surface portion, and a part of the side surface portion. An incident end portion formed to introduce light from a light source, and a ridge line protruding from the back surface portion and extending radially from the incident end portion, and a height of these ridge lines from the back surface portion to the incident side. A light guide plate, comprising: a plurality of light deflecting elements each having a triangular cross-sectional shape that is gradually reduced toward the end and is perpendicular to the ridge. 2. The light guide plate according to claim 1, wherein the light deflection element having the maximum length of the ridgeline has an isosceles triangular cross-sectional shape perpendicular to the ridgeline. 3. The two light deflection elements, which are separated from each other by an equal number in the opposite direction from the light deflection element having the maximum length of the ridge, have a cross-sectional shape perpendicular to these ridges in the length of the ridge. The light guide plate according to claim 2, wherein the light guide plate is formed symmetrically with respect to the light deflection element having the maximum length. 4. The light deflection element farther from the light deflection element having the maximum length of the ridge line, the inclination angle of at least one of a pair of slopes constituting the light deflection element is gradually decreased or gradually increased. Claim 2 or Claim 3 characterized by
The light guide plate described in. 5. The method according to claim 1, further comprising two side portions adjacent to each other in an intersecting state, wherein the incident end portion is formed in an intersection region of the two side portions. The light guide plate according to any one of 4 above. 6. The incident end portion has a flat surface orthogonal to the light emitting surface portion or a concave cylindrical surface whose axis is perpendicular to the light emitting surface portion.
6. The light guide plate according to claim 5. 7. The back surface portion has a wedge-shaped flat surface portion that is formed between the adjacent light deflection elements and is parallel to the light emitting surface portion. The light guide plate of Crab. 8. The light guide plate according to claim 1, wherein the slopes forming the adjacent light deflection elements are continuous. 9. The light control device according to claim 1, further comprising a plurality of light control elements arranged on the light emitting surface portion for controlling a light emitting state from the light emitting surface portion. The light guide plate according to any one of claims. 10. The light guide plate according to claim 9, wherein the light control element has a predetermined distribution with respect to the light emitting surface portion. 11. The light guide plate according to claim 1, a light source that projects illumination light toward the incident end portion of the light guide plate, the incident end portion of the light guide plate, and A flat illumination device comprising: a light reflection sheet that covers a portion other than the light emitting surface portion. 12. The flat lighting device according to claim 11, wherein the light source includes at least one light emitting diode. 13. The flat lighting device according to claim 12, wherein the light guide plate has a rectangular plate shape, and an optical axis of the light emitting diode is on a diagonal line of the light guide plate. 14. The light diffusion sheet according to claim 11, further comprising a light diffusing sheet that is arranged on the light guide plate and adjusts the directionality of light emitted from the emission surface portion. The flat lighting device according to claim 1.