JPH10221529A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device having little local luminance change by providing a rough surface part on one surface of a light guide plate having a light emitting function part on its other surface. SOLUTION: A rough surface part 41 constituted of a plurality of fine projection parts 40 extending in the direction crossing at right angles with a tubular light source 21 is formed on a reflecting surface 25 of a light guide plate. The light emitted from the tubular light source 21 enters into the light guide plate 22 from an incident surface 26 of the light guide plate 22. When the light advancing in the light guide plate 22 reaches the fine projection parts 40 of the rough surface part 41, it is irregularly reflected and a part of the irregularly reflected light is emitted from a light emitting surface 24 except prism projections 31 of the light guide plate 22 to the outside of the light guide plate 22. The change in the local luminance of the light emitting surface 24 of the light guide plate 22 is reduced by the light emitted from the light emitting surface 24 except the prism projections 31.

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 having a light emitting function on one of a light emitting surface and a reflection surface, a tubular light source disposed adjacent to a side surface of the light guide plate, and a light source. And a light control sheet having an optical structure for guiding the light in a predetermined direction.

[0002]

2. Description of the Related Art Next, a conventional example will be described with reference to the drawings.
FIG. 10 is a configuration diagram illustrating an example of a conventional surface light source device. In the drawing, 1 is a tubular light source, 2 is a reflecting plate for reflecting light emitted from the tubular light source 1 in the right direction in the drawing, and 3 is a light guide plate through which light from the tubular light source 1 travels.

In the light guide plate 3, the surface facing the object is defined as a light emitting surface 4, the surface opposite to the light emitting surface 4 is defined as a reflecting surface 5, and the surface on which light from the tubular light source 1 is incident is defined as an incident surface 6. Note that the light emitting surface 4 and the reflecting surface 5 are mirror-like.

[0004] On the light emitting surface 4 of the light guide plate 3, a prism protrusion 11 is formed as a light emitting function for guiding light traveling inside the light guide plate 3 to the outside. The prism projections 11 are formed so as to be sparse near the tubular light source 1 and densely near the tubular light source 1 so that light is emitted from the light emitting surface 4 uniformly.

A light-collecting sheet 9 as a light control sheet for changing the traveling direction of light by refraction and reflection is provided on the light-emitting surface 4, and a reflection sheet 8 is provided below the reflection surface 5. On the surface of the light-condensing sheet 9 facing the light guide plate 3, in this conventional example, a lenticular 9 a having a triangular cross section as a first optical structure that condenses light in the normal direction of the sheet and increases the luminance of incident light. Are formed at substantially the same pitch. still,
In the present specification, a structure having a periodic structure at a substantially equal pitch, such as a lenticular 9a, is called an optical structure. In addition, a lenticular having a semicircular or semielliptical cross section, a sin curve There is such a structure.

[0006] A liquid crystal panel 10 as an object to be irradiated is arranged on the condensing sheet 9. Next, the operation of the above configuration will be described. Light emitted from the tubular light source 1 enters the light guide plate 3 from the incident surface 6 of the light guide plate 3. Light entering the light guide plate 3 travels while repeating total reflection on the light emitting surface 4 and the reflecting surface 5. When the light enters the prism protrusion 11, the light exits the light guide plate 3.

Light emitted from the prism protrusions 11 is condensed by the light condensing sheet 9 in a direction substantially perpendicular to the light guide plate 3 (front direction), and irradiates the liquid crystal panel 10.

[0008]

However, in the surface light source device having the above-described structure, the emission position of the light emitted from the light emitting surface 4 of the light guide plate 3 is substantially limited to the prism protrusion 11.

For example, as shown in FIG. 11, when the light emitting surface 4 of the light guide plate 3 is observed, a dark portion (a portion on which no prism protrusion is formed with a width of about 29 mm) and a linear bright portion (a prism having a width of about 5 mm) are formed. The projections 11) are mixed.

That is, a high-luminance part and a low-luminance part are mixed, and a local luminance change is large. The present invention has been made in view of the above problems, and an object of the present invention is to provide a surface light source device having a small local luminance change.

[0011]

According to a first aspect of the present invention, there is provided a light guide plate in which a light emitting function is formed on one of a light emitting surface and a reflection surface; A tubular light source disposed adjacent to a side surface; and a light control sheet having a first optical structure on a light emitting surface of the light guide plate, the surface facing the light emitting surface of the light guide plate guiding light rays in a predetermined direction. In the surface light source device, a rough surface portion is provided on the other surface of the light guide plate.

Light emitted from the tubular light source enters the light guide plate. When the light traveling inside the light guide plate reaches the rough surface portion, it is irregularly reflected here, and a part of the irregularly reflected light is emitted outside the light guide plate from the light emitting surface of the light guide plate other than the light emitting portion.

[0013] The light that has reached the light emitting portion is emitted from the light emitting portion to the outside of the light guide plate. The light emitted to the outside of the light guide plate is condensed in a predetermined direction by the first optical structure of the light control sheet, and irradiates the illuminated object.

According to the above configuration, the light emitted from the light guide plate includes, in addition to the light emitted from the light emitting function portion, light that is irregularly reflected on the rough surface portion and emitted from the light emitting surface other than the light emitting function portion. Due to the light emitted from the light emitting surface other than the light emitting function, the brightness of the light emitting surface of the light guide plate where the light emitting function is not formed (dark portion) increases, and the local change in brightness decreases.

In the present invention, the light control sheet may have a second optical structure for guiding light rays in a predetermined direction on the surface opposite to the surface facing the light guide plate. The invention according to claim 2 is
The surface light source device according to claim 1, wherein the rough surface portion has a direction substantially orthogonal to a longitudinal direction of the tubular light source.

By making the rough surface portion have a direction substantially perpendicular to the tubular light source, it is possible to reduce a local luminance change and to maintain the luminance uniformity of the entire light emitting surface. Even if the rough surface portion has an uneven surface with no direction or a direction substantially perpendicular to the longitudinal direction of the tubular light source, local luminance change can be reduced. In this case, since the rough surface portion performs the same function as the light emitting function portion, the luminance of the rough surface portion becomes too high,
Insufficient luminance value in a portion distant from the tubular light source, adversely affecting luminance uniformity of the entire light emitting surface.

According to a third aspect of the present invention, in the first or second aspect, the first optical structure is a lenticular having a ridge line substantially parallel to a longitudinal direction of the tubular light source. It is a light source device.

When light enters the lenticular, which is the optical structure of the light control sheet, the peak direction of the light is directed to the normal direction of the light emitting surface. Therefore, the front luminance is increased and the light use efficiency is improved.

In the present invention, the ridge line refers to a line connecting points at which the inclination changes (inflection point) in a cross section orthogonal to the extending direction of the light emitting function unit. In the present invention,
From the viewpoint of preventing the occurrence of moire, it is desirable that the direction in which the light emitting function portion extends does not coincide with the direction in which the ridgeline of the lenticular extends.

According to a fourth aspect of the present invention, there is provided a light guide plate having a light emitting function portion formed on one of a light emitting surface and a reflection surface; a tubular light source disposed adjacent to a side surface of the light guide plate; At least one diffusion sheet disposed on the light emitting surface of the light guide plate, and one or more light control sheets having a second optical structure on a surface opposite to the surface facing the light guide plate In the surface light source device, a rough surface portion is provided on the other surface of the light guide plate.

Light emitted from the tubular light source enters the light guide plate. When the light traveling inside the light guide plate reaches the rough surface portion, it is irregularly reflected here, and a part of the irregularly reflected light is emitted outside the light guide plate from the light emitting surface of the light guide plate other than the light emitting portion.

Further, the light that has reached the light emitting section is emitted from the light emitting section to the outside of the light guide plate. The light emitted out of the light guide plate is diffused by the diffusion sheet, and, by being diffused, the peak direction of the light approaches the normal direction of the light emitting surface,
The light is condensed in a predetermined direction by the second optical structure of the light control sheet, and irradiates the object to be illuminated.

According to the above arrangement, the light emitted from the light guide plate includes light emitted from the light emitting surface other than the light emitted from the light emitting function, in addition to the light emitted from the light emitting function. By the light emitted from the light emitting surface other than the light emitting surface, the brightness of the light emitting surface of the light guide plate where the light emitting function unit is not formed (dark portion) increases, and the local brightness change of the light emitting surface of the light guide plate increases. Decrease.

In the present invention, the order of laminating the light control sheet and the diffusion sheet is not limited. The light control sheet and the diffusion sheet may be arranged in this order from the light emitting surface of the light guide plate, or the diffusion sheet and the light control sheet may be arranged in the order from the light emitting surface of the light guide plate.

Further, even when there are a plurality of light control sheets and diffusion sheets, the order of stacking them is not limited. According to a fifth aspect of the present invention, there is provided the surface light source device according to any one of the first to fourth aspects, wherein the light emitting function portion of the light guide plate is formed on the light emitting surface.

When the light emitting function portion is formed on the reflecting surface, a reflecting member is required to re-enter the light emitted from the reflecting surface to the light guide plate. Therefore, light absorption loss occurs in the reflection member.

By forming the light emitting function on the reflecting surface, the loss of light absorption by the reflecting member is small, and the front luminance is increased.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) First Embodiment FIG. 1 is a configuration diagram of a surface light source device according to a first embodiment of the present invention, FIG. 2 is a bottom view of a light guide plate when a reflection sheet in FIG. 1 is removed, FIG. 3 is a diagram illustrating a state of irregular reflection of light at a convex portion as a rough surface portion in FIG. 2, and FIG. 4 is a diagram illustrating a state of light reflection at a portion other than the convex portion in FIG.

In FIG. 1, reference numeral 21 denotes a tubular light source, 22 denotes a reflecting plate for reflecting light emitted from the tubular light source 21 in the right direction in the drawing, and 23 denotes a light guide plate through which the light from the tubular light source 21 travels.

In the light guide plate 23, the surface facing the object to be irradiated is the light emitting surface 24, and the surface opposite to the light emitting surface 24 is the reflecting surface 2.
5. The surface on which the light from the tubular light source 21 is incident is defined as an incident surface 26. On the light emitting surface 24 of the light guide plate 23, a prism protrusion 31 as a light emitting function for guiding light traveling inside the light guide plate 23 to the outside is formed substantially parallel to the longitudinal direction of the tubular light source 21. The prism projection 31 of the present embodiment has a triangular cross section and has two slopes 31a and 31b.

The light control sheet 27 is provided on the light emitting surface 24.
However, a reflection sheet 28 is disposed below the reflection surface 25. The surface of the light control sheet 27 facing the light emitting surface 24 of the light guide plate 22 has a ridge line extending in a direction substantially parallel to the tubular light source 21,
A first optical structure 34 includes a plurality of first lenticulars 33 having a triangular cross section.

On the light control sheet 27, a liquid crystal panel as an object to be illuminated is arranged. In FIG. 2 to FIG. 4, on the reflection surface 25 of the light guide plate 22, a rough surface portion 41 composed of a plurality of fine projections 40 extending in a direction substantially orthogonal to the tubular light source 21 is formed.

Next, the operation of the above configuration will be described. Light emitted from the tubular light source 21 enters the light guide plate 23 from the incident surface 26 of the light guide plate 23. When the light traveling inside the light guide plate 23 reaches the minute convex portion 40 of the rough surface portion 41, it is irregularly reflected here (see FIG. 3), and a part of the irregularly reflected light is a light emitting surface other than the prism protrusion 31 of the light guide plate 22. The light exits from the light guide plate 22 to the outside.

The light that has reached the prism projection 31 exits the light guide plate 22 through the slope 31 b of the prism projection 31. The peak direction of the light emitted from the light guide plate 22 is oblique to the light emitting surface 24.

Then, the light passes through the light control sheet 27. At this time, due to the first lenticular 33 of the first optical structure 34 of the light control sheet 27, the peak direction of the light transmitted through the light control sheet 27 is directed to the normal direction of the light emitting surface 24 of the light guide plate 22, and A liquid crystal panel as an object is irradiated.

According to the above configuration, the light emitted from the light guide plate 22 is not only the light emitted from the inclined surface 31 b of the prism projection 31, but also the light that is irregularly reflected by the rough surface portion 41 and emitted from the light emitting surface 24 other than the prism projection 31. There is. The light emitted from the light emitting surface 24 other than the prism protrusion 31 reduces a local luminance change of the light emitting surface 24 of the light guide plate 22.

Further, by making the extending direction of the convex portion 40 of the rough surface portion 41 substantially perpendicular to the tubular light source 21, a local luminance change and a luminance change of the entire light emitting surface are also reduced. Can be.

That is, even if the rough surface portion 41 has a random uneven surface or a direction substantially parallel to the longitudinal direction of the tubular light source 21, local luminance change can be reduced. Compared with the present embodiment which is orthogonal to the present embodiment, since it has many components parallel to the tubular light source 21, the luminance value in a portion close to the tubular light source becomes too high, and the luminance value in a portion far from the tubular light source 21 is increased. Does not rise, and a luminance change occurs on the entire light emitting surface.

As the optical structure of the light control sheet 27,
By providing the first lenticular 33, the peak direction of the light emitted from the light emitting surface 24 of the light guide plate 22 is changed to the light emitting surface 2
4, the front luminance of the surface light source device is increased, and the light use efficiency is improved.

Further, from the viewpoint of preventing the occurrence of moire,
The direction in which the ridge line of the prism protrusion 31 of the light guide plate 22 extends;
It is desirable that the direction of the ridge line of the first lenticular 33 of the light control sheet 27 does not match.

The present invention is not limited to the above embodiment. Although the first lenticular 33 in the above-described embodiment has a prism shape with a triangular cross section, it may have, for example, a semi-elliptical shape or a sin curve. (2) Second Embodiment FIG. 5 is a configuration diagram of a second embodiment of the present invention.
In FIG. 5, the same parts as those in FIGS. 1 to 4 showing the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the figure, reference numeral 60 denotes a second light control sheet disposed on the light control sheet 27. On the surface of the second light control sheet 60 opposite to the surface facing the light emitting surface 24 of the light guide plate 22, a ridge line extends in a direction substantially orthogonal to the longitudinal direction of the tubular light source 21, ie, the first optical structure. The second optical structure 62 extends in a direction substantially perpendicular to the direction in which the first lenticular 33 extends, and has a plurality of second lenticulars 61 having a triangular cross section.

The above operation will be described.
7 and the light peak direction is the light emitting surface 24 of the light guide plate 22.
Is transmitted through the second light control sheet 60 and irradiates the liquid crystal panel which is the object to be illuminated.

According to the above configuration, in addition to the effects of the first embodiment, the second lenticular 61 substantially perpendicular to the first lenticular 33 is provided.
Since the light is condensed even in a plane perpendicular to a, the luminance in the front direction can be increased as compared with the first embodiment.

The present invention is not limited to the above embodiment. In the above embodiment, the first optical structure 34 is provided on the light control sheet 27, and the second optical structure 60 is provided on the light control sheet 27, which is another light control sheet. Although 62 is provided, the first and second optical structures may be formed on the front and back surfaces of one light control sheet. (3) Third Embodiment FIG. 6 is a configuration diagram of a third embodiment of the present invention.
In FIG. 6, the same parts as those in FIGS. 1 to 4 showing the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the figure, reference numeral 70 denotes the light emitting surface 2 of the light guide plate 22.
4 is a diffusion sheet, 71 is a diffusion sheet 70
A second light control sheet placed on the second light control sheet. This second
A ridge line 72 a extends in a direction substantially parallel to the tubular light source 21 on a surface of the light control sheet 71 opposite to the surface facing the light emitting surface 24 of the light guide plate 22, and is constituted by a plurality of lenticulars 72 having a triangular cross section. A second optical structure 73 is provided.

The operation described above will be described. Light emitted from the tubular light source 21 is transmitted from the entrance surface 26 of the light guide plate 23 to the light guide plate 2.
3 Enter inside. When the light traveling inside the light guide plate 23 reaches the minute convex portion 40 of the rough surface portion 41, the light is irregularly reflected here, and a part of the diffusely reflected light is transmitted from the light emitting surface 24 other than the prism protrusion 31 of the light guide plate 22 to the light guide plate 22. Emitted out.

The light that has reached the prism projection 31 exits the light guide plate 22 through the slope 31 b of the prism projection 31. The peak direction of the light emitted from the light guide plate 22 is oblique to the light emitting surface 24.

The light emitted from the light emitting surface 24 passes through the diffusion sheet 70, is diffused, and is diffused, so that the peak direction of the light approaches the normal direction of the light emitting surface 24. Next, the light passes through the light control sheet 71. At this time, due to the second lenticular 72 of the second optical structure 73 of the light control sheet 71, the peak direction of the light transmitted through the light control sheet 71 is directed in the normal direction of the light emitting surface 24 of the light guide plate 22, and According to the above configuration for irradiating the liquid crystal panel as an object,
In addition to the effects of the first embodiment, by providing the diffusion sheet 70 and the second light control sheet 71, the peak direction of light can be closer to the normal direction of the light emitting surface,
The front luminance can be increased.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the diffusion sheet 70 and the light control sheet 71 are provided on the light emitting surface 24 of the light guide plate 22 in this order.
, A light control sheet 71 and a diffusion sheet 70 may be provided in this order.

Further, a plurality of light control sheets and a plurality of diffusion sheets may be provided. In the first to third embodiments, the prism projections 31 serving as the light emitting function of the light guide plate 22 are provided on the light emitting surface 24 side, but may be provided on the reflection surface 25 side. At this time, the rough surface portion is formed on the light emitting surface side.

When the prism projection 31 is provided on the reflection surface 25 side, light emitted from the slope 31 b of the prism projection 31 is reflected by the reflection sheet 28 and reenters the light guide plate 22. Then, the light is emitted from the light emitting surface 24.

In this case, the prism projection 31 is connected to the light emitting surface 24.
Since light absorption loss occurs in the reflection sheet 28 as compared with the case where the light guide plate is formed above, it is desirable that the light emitting function portion of the light guide plate be formed on the light emitting surface.

[0054]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The inventor of the present application measured the luminance distribution of the light control sheet 27 with a surface light source device having a configuration as shown in FIG.

(1) Light guide plate 22 The external dimensions are 217 mm in length parallel to the tubular light source 21, 170 mm in vertical length, 3 mm in height of the incident surface 26, and 3 mm in height of the anti-incident surface.
1mm wedge shape, effective emission area is 210
mm and the short side direction is 160 mm.

Acrylic (Sumipex MG5R, Sumitomo Chemical Co., Ltd.) was selected as a material, and was molded by injection molding.
The die of the light guide plate 22 is formed into a mirror-finished die blank by using an NC lathe. The movement coordinates (XY coordinates) of the cutting tool for cutting the groove and the cut amount (Z coordinate) at the coordinate position were controlled on the order of submicrons.

A vertex angle of 65 ° formed on the light emitting surface 24
The projection area ratio of the prism projections 31 (percentage of the prism projections 31 per unit area) was set as shown in FIG.

Then, based on the projected area ratio, the width and pitch of each prism projection 31 were determined.
1680 prism projections 31 were formed on the light emitting surface 24. The light guide plates 23, 2 on which such prism protrusions 31 are formed.
3 ′, a plurality of fine projections 40 extending in a direction substantially orthogonal to the tubular light source 21 are provided on the reflection surface of one light guide plate 23.
Is formed.

FIG. 7A is a diagram showing the surface roughness of the reflection surface of the light guide plate 23, and FIG. 7B is a diagram showing the surface roughness of the reflection surface of the light guide plate 23 '. (2) Light control sheet 27 The first lenticular 33 has an isosceles triangular cross section and an apex angle of 68 °. ・ Other inverter Harrison Electric Co., Ltd. “HIU-714” (3) Measurement conditions ・ Tube current 5 ( (mArms) ・ Input voltage to inverter circuit 11.00 (V) ・ Measurement distance 50cm ・ Brightness meter Topcon Corporation “BM-7” (Measurement viewing angle 0.2deg) In the above configuration, room temperature 24.0 ± 0.5 ℃, linear light source lighting 30
After one minute, the front luminance distribution of the surface light source device using these two light guide plates 23, 23 'was measured at a pitch of 1 mm. The result is shown in FIG. In the figure, a plot (◇) shows the front luminance distribution when the light guide plate 23 ′ having no rough surface portion on the reflection surface is used, and a plot (□) shows the light guide plate 23 with the rough surface portion formed on the reflection surface 25. 4 shows the front luminance distribution when there is an image.

As can be seen from FIG. 9, the change in luminance at two adjacent points is smaller in the case where the rough surface portion is formed (□) than in the case where the rough surface portion is not formed (◇), and It turns out that the number has decreased.

[0061]

As described above, according to the first aspect of the present invention, the light emitted from the light guide plate is emitted from the light emitting portion because the rough surface is provided on the other surface of the light guide plate. In addition to light, there is light that is irregularly reflected on the rough surface portion and emitted from the light emitting surface other than the light emitting portion. By the light emitted from the light emitting surface other than the light emitting function portion, the brightness of the light emitting surface of the light guide plate where the light emitting function portion is not formed (dark portion) is increased, and the local brightness change of the light emitting surface of the light guide plate is reduced. Can be reduced.

According to the second aspect of the present invention, the rough surface portion of the first aspect of the present invention has a direction substantially perpendicular to the longitudinal direction of the tubular light source, thereby reducing a local luminance change. At the same time, it is possible to maintain the luminance uniformity of the entire light emitting surface.

According to the third aspect of the present invention, the first optical structure in the first or second aspect of the present invention is a lenticular having a ridge line substantially parallel to a longitudinal direction of the tubular light source. Is directed in the direction of the normal to the light emitting surface, the front luminance is increased, and the light use efficiency is improved.

According to the fourth aspect of the present invention, since the roughened surface is provided on the other surface of the light guide plate, the light emitted from the light guide plate is not only the light emitted from the light emitting portion but also the roughened surface. There is light that is diffusely reflected and emitted from the light emitting surface other than the light emitting function unit. By the light emitted from the light emitting surface other than the light emitting function portion, the brightness of the light emitting surface of the light guide plate where the light emitting function portion is not formed (dark portion) is increased, and the local brightness change of the light emitting surface of the light guide plate is reduced. Can be reduced.

According to the fifth aspect of the present invention, the light emitting function portion of the light guide plate according to any one of the first to fourth aspects is formed on the light emitting surface, so that the light emitting function portion is reflected. Light absorption loss is small and the frontal brightness is increased as compared with the case where it is formed on a surface.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a surface light source device according to a first embodiment of the present invention.

FIG. 2 is a bottom view of the light guide plate when the reflection sheet in FIG. 1 is removed.

FIG. 3 is a diagram illustrating a state of irregular reflection of light on a convex portion serving as a rough surface portion in FIG. 2;

FIG. 4 is a diagram illustrating a state of light reflection at a portion other than a convex portion in FIG. 2;

FIG. 5 is a configuration diagram of a surface light source device according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of a surface light source device according to a third embodiment of the present invention.

FIG. 7 is a view showing the surface roughness of the reflection surfaces of the light guide plates 23 and 23 'of the embodiment.

FIG. 8 is a diagram showing a projected area ratio of a projection of the light guide plate of the example.

FIG. 9 is a diagram showing a front luminance distribution of the light guide plate of the example.

FIG. 10 is a configuration diagram illustrating an example of a conventional surface light source device.

FIG. 11 is an enlarged view of a light emitting surface in FIG.

[Explanation of symbols]

 Reference Signs List 22 light guide plate 24 light emitting surface 25 reflecting surface 27 light control sheet 34 optical structure 40 protrusion 41 rough surface portion

Claims (5)

[Claims] 1. A light guide plate having a light emitting function portion formed on one of a light emitting surface and a reflective surface, a tubular light source disposed adjacent to a side surface of the light guide plate, and a light emitting surface of the light guide plate. A light control sheet having a first optical structure having a surface facing a light emitting surface of the light guide plate for guiding light rays in a predetermined direction, wherein a rough surface portion is provided on the other surface of the light guide plate A surface light source device characterized by the above-mentioned. 2. The apparatus according to claim 1, wherein the rough surface has a direction substantially perpendicular to a longitudinal direction of the tubular light source.
The surface light source device as described in the above. 3. The surface light source device according to claim 1, wherein the first optical structure comprises a lenticular having a ridge line substantially parallel to a longitudinal direction of the tubular light source. 4. A light guide plate having a light emitting function portion formed on one of a light emitting surface and a reflective surface, a tubular light source disposed adjacent to a side surface of the light guide plate, and a light emitting surface of the light guide plate. A surface light source device having at least one or more diffusion sheets disposed thereon, and one or more light control sheets having a surface opposite to a surface facing the light guide plate and having a second optical structure; A surface light source device wherein a rough surface portion is provided on the other surface of the light guide plate. 5. The surface light source device according to claim 1, wherein the light emitting function portion of the light guide plate is formed on the light emitting surface.