JP3500726B2 - Backlight - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight for a panel which illuminates a transmissive or semi-transmissive panel from the back side.

[0002]

2. Description of the Related Art Recently, a liquid crystal display device having a backlight mechanism which is thin and easy to see has been used as a display device for a laptop or book type word processor, a computer or the like. For such a backlight, an edge light system is often used in which a linear light source such as a fluorescent tube is provided at one end of a light-transmitting light guide plate as shown in FIG. In case of such edge light method,
As shown in FIG. 2, it is often arranged such that one wide surface of the light guide plate is partially covered with a light diffusing substance, and the entire surface is covered with a reflection plate.

Particularly in recent years, in order to improve the performance of these word processors and personal computers, further miniaturization and improvement of visibility are desired, and in backlight, it corresponds to the display area of a liquid crystal display panel. We are trying to achieve miniaturization by making the maximum outer shape of the light guide plate smaller than the light emitting area of the backlight.

However, in the case where the area (maximum outer shape) of the light guide plate with respect to the light emitting area of the backlight is made smaller, a position substantially parallel to the end portion of the light guide plate is provided in the vicinity of the end portion where the linear light source of the light guide plate is brought close. There is a problem in that a high-luminance portion (bright line) is generated, and the luminance uniformity in the light emitting region is deteriorated, resulting in poor visibility.

The cause of the bright line is that both ends of the light reflector (5 in the figure) covering the linear light source (4 in the figure) are bonded to the light guide plate as shown in FIG. This is because the adhesive layer (11 in the figure) such as a tape diffuses and reflects a light beam that is incident on the light guide plate and should normally repeat total reflection. or,
Even if you do not use an adhesive layer such as double-sided tape on the light guide plate,
As shown in FIG. 4, if there is a structural gap between the end of the reflector that covers the linear light source and the light guide plate, the light rays reflected by the end of the reflector will be on a surface other than the end face of the light guide plate. The light rays are incident from (the upper surface or the lower surface of the light guide plate) and deviate from the condition of total reflection in the light guide plate, which causes a bright line. Such a bright line was emitted in the highest brightness state from the vicinity of the end of the light guide plate of the light reflector on the light emitting surface side.

In order to solve such a problem, there has been proposed a method of providing a light emitting portion between an end portion of a reflection cover covering a light source and a diffusion plate (see Japanese Utility Model Laid-Open No. 6-2301). ), The light emitted from the light emitting part of the light guide plate is emitted to the outside without passing through the diffuser plate, and thus the light is lost, and since the light guide plate is exposed, dust or the like is mixed on the surface of the light guide plate. There was a problem that it was easy to do and that the surface of the light guide plate was easily scratched.

On the other hand, in order to increase the brightness in the vicinity of the direction of the normal line standing on the light emitting surface of the backlight (increasing the brightness), the prisms or the linear convex portions having linear peaks at fine intervals on the same surface It is particularly often used recently to arrange a sheet made of a light-transmitting material having a large number of ridges in a state where the apexes are substantially parallel to each other on the light exit surface of the light guide plate (Japanese Patent Laid-Open No. 5-12).
7159, Japanese Patent Laid-Open No. 5-119218).

However, when the sheet made of a translucent material having the above-mentioned straight apex is arranged on the light emitting surface of the light guide plate,
There is a problem that the above-mentioned bright lines are remarkably conspicuous as compared with the case where they are not arranged.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a backlight which has high brightness and has a small external dimension with respect to a light emitting region and has good visibility.

[0010]

Means for Solving the Problems The present inventors have conducted various studies on the structure of the light guide plate near the end where the linear light sources are close to each other and the luminance distribution of the light exit surface of the light guide plate. Type backlight, a sheet made of a translucent material having a straight top edge and an end portion of the light guide plate of the light reflector that covers the linear light source, and a light diffusion sheet. It has been found that by devising the relationship (distance) of (1), a backlight having high brightness, an external dimension as small as possible with respect to an effective light emitting area, and good visibility can be obtained.

That is, according to the present invention, a linear light source which is made of a light-transmitting material and has a function of emitting light from a wide surface, is provided at the end of at least one side surface of the light guide plate, and a light reflection for covering the linear light source. At least 1 on the light emitting surface side of the container and the light guide plate.
A plurality of prisms having linear vertexes or convex portions having linear vertexes at minute intervals on the same surface as at least one light diffusion sheet are provided in a state where the vertexes are substantially parallel to each other. In a backlight in which a sheet made of a translucent material is arranged, at least the light diffusion sheet and the sheet made of a translucent material having a straight top edge are provided at least at the light source side end portion of the light guide plate. The present invention relates to a backlight that is laminated in a state where parts thereof do not overlap.

Next, the present invention will be described in more detail with reference to the drawings.

FIG. 5 is a sectional view of one embodiment of the present invention. In the figure, reference numeral 1 denotes a light guide plate, which may be made of a substance that allows light to efficiently pass therethrough, and quartz, glass, translucent natural or synthetic resin such as acrylic resin is used.

One wide surface of the light guide plate 1 is provided with a function of diffusing light entering the light guide plate, and this diffusion function is provided by forming a light diffusing element on the same surface. The light diffusing element (illustrated as 6 in the figure) formed on the surface of the light guide plate is, for example, TiO ₂ , BaSO ₄ , or SiO _2.
It is formed by applying a light-scattering substance, such as a paint, printing ink, etc., that contains a pigment with a large diffuse reflectance to the light guide plate surface in a dot or line pattern by a method such as screen printing. It is done by printing on a letter. In addition, the surface of the light guide plate may be roughened, small holes may be formed, or small protrusions may be provided to impart light diffusing property to the surface of the light guide plate itself. These light diffusing elements are formed in a dot shape or a line shape so that the light diffusing property per unit area of the light guide plate gradually increases as the distance from the light source increases in the light guide plate. Further, light diffusivity may be imparted to the inside of the light guide plate itself by making a large number of fine particles having different refractive indexes exist in the light guide plate.

Reference numeral 4 denotes a linear light source (rod-shaped light source), which is arranged in the vicinity of at least one end surface around the light guide plate, and in a preferred mode, a line is provided so that light enters the end portion of the light guide plate. The linear light source is arranged so that its central axis is substantially parallel to the same end face, and the surface of the linear light source other than the face facing the end portion of the light guide plate is arranged in a state of being covered with the light reflector 5. That is. The linear light source 4 may be a fluorescent tube, a tungsten incandescent tube, an optical rod, an LED array, or the like, but a fluorescent tube is preferable, and an electrode is preferable in terms of uniformity of luminance distribution of an effective light emitting area and power saving. It is preferable that the length of the uniform light emitting portion excluding the portion is substantially equal to the length of the end portion of the light guide plate adjacent thereto.

The light reflector 5 has only to have a property that the surface facing the linear light source reflects light. When the reflection surface is a specular reflection plate or sheet, silver, aluminum, platinum, A material made of nickel, chromium, or the like, preferably a plastic film base material such as polyester or a metal plate on which silver, aluminum or the like is surface-coated by vapor deposition or sputtering. When the reflecting surface is a light diffusing reflector or sheet, a resin such as polyester is used as a light diffusing substance (for example, TiO ₂ , BaSO ₄ , Si).
O _{2 and the} like), a resin such as polyester foamed to impart light diffusivity, and a plate such as an Al plate coated with the light diffusing substance. The material is not particularly limited as long as it has a property of diffuse reflection. The end portion of the light reflector that covers the linear light source efficiently reflects the light beam from the linear light source and makes it incident on the end surface of the light guide plate, as shown in FIG. Usually, it is laminated and arranged on a portion opposite to the surface side.

A light diffusion sheet 2 scatters the light emitted from the light guide plate surface and allows it to pass through. The material of the light diffusion sheet is not particularly limited as long as it has a property of transmitting light, but may be a polymer material such as polyester or polycarbonate or an inorganic material such as glass. Further, the action of scattering the light of the light diffusing sheet imparts the action of diffusing the light by making the surface of the light diffusing sheet rough, etc. It may be applied by coating a certain substance, or by providing a state in which a large number of fine particles having different refractive indices exist inside the light diffusion sheet. In the present invention, one or more sheets of this light diffusion sheet are used.

Reference numeral 7 denotes a sheet made of a light-transmissive material (hereinafter, simply referred to as a sheet having a straight apex), which are straight lines parallel to each other at a fine interval on the same plane as shown in FIG. It has a large number of ridges (8 in the figure) or convex ridges as shown in FIG. 7 (the cross section perpendicular to the central axis is mountain-shaped or sine wave-shaped). It is arranged so that the top ridge surface is on the outside (the side opposite to the surface facing the light guide plate). By arranging the sheets in this way, it is possible to change the directivity of the light emitted from the light exit surface of the light guide plate, and to enhance the directivity in the vicinity of the normal direction dropped on the light exit surface. Therefore, the brightness in the vicinity of the normal direction of the backlight can be increased (about 1.2 to 1.6 times). In the present invention, one or more sheets are used.

The arrangement relationship between the light diffusing sheet and the sheet having a straight top edge, which is a feature of the present invention, is that the light diffusing sheet is provided between the light guide plate and the sheet having a straight top edge. As shown in FIG. 5 showing a preferred embodiment arranged between them, the light guide plates have portions that do not overlap each other at the light source side end. To explain this in another way, the distance from the end of the light reflector to the end of the sheet having a straight apex is the distance from the end of the light reflector to the end of the light diffusion sheet. Is to be larger than the distance. Further, at this time, the end of the sheet having the straight apex is located far from the light source.
By setting such a state, many light beams are provided in the oblique direction (45 degrees or more with respect to the normal direction) from the vicinity of the end of the light reflector as shown in FIG. 8 with respect to the normal direction of the light exit surface of the light guide plate. The light ray that causes the emitted bright line is not refracted to an angle closer to the normal direction of the light exit surface of the light guide plate by the action of the sheet having the straight apex ridge, thus achieving high brightness, Moreover, since the light diffusion sheet is arranged between the sheet having the straight apexes and the end of the light reflector, the surface of the light guide plate is protected, and the light ray causing the bright line is also formed. Is reflected by the surface of the light diffusion sheet (surface reflection), is backscattered, and is returned to the light guide plate to effectively utilize the light, so that higher brightness can be achieved.

It should be noted that the above-mentioned difference between the two sheets is a large part, particularly the whole, corresponding to the part actually used as the planar light emitting part at the end of the light guide plate where the end of the light reflector faces. Although it is the most preferable state to reduce all the bright lines in that portion, it is sufficient if at least a portion thereof satisfies the conditions limited by the present invention.

A sheath having a straight apex from the end of the light reflector.
To further elaborate the relationship between the distance (A) from the reflector to the light diffusion sheet (B) from the end of the reflector, in order to surely reduce the bright line, Distance (B)
Difference, that is, the value of (A)-(B) is 1.5 mm or more, more preferably 2 mm or more, but a sheet having a straight apex actually exists in the optical window of the display device. The difference can be extended to the corresponding part.

By arranging the light diffusion sheet between the sheet having a straight top edge and the light guide plate, the surface of the light guide plate is protected, and the light ray which causes the bright line is diffused. -It is a preferable mode in which Fresnel reflection (surface reflection) is performed on the surface and backscattering is performed, and the light is effectively returned by returning to the light guide plate. Of course, another light diffusing sheet is arranged outside the sheet having the linear apex (the side not facing the light guide plate) to protect the sheet having the linear apex. It may be in the form.

It is also possible to dispose the light diffusion sheet and the light guide plate with an air layer in between, or to get out of the light guide plate and emit abnormal light (bright line).
This is a particularly preferable mode in order to prevent the light rays that cause the above from being emitted by totally reflecting at the interface between the surface of the light guide plate and the air layer. In order to make the relationship between the light diffusion sheet and the light guide plate mechanically stable, the vicinity of the end of the light guide plate that is not used as a planar light emitting area (for example, a portion having a width of 2 to 3 mm from the end). Even if the light-diffusing sheet and the light-diffusing sheet corresponding to that portion are adhered by a double-sided tape or the like, most of the light-emitting surface of the light guide plate used as the planar light-emitting area and the light-diffusing sheet are air layers It goes without saying that the effects of the present invention can be sufficiently obtained if they are arranged through.

By arranging the light diffusion sheet and the sheet having the linear apex via the air layer, the effect of improving the above-mentioned brightness of the sheet having the linear apex is further enhanced. This is the preferred mode for the purpose.

A sheath having a straight apex from the end of the light reflector
It is preferable to place a light-absorbing substance such as a dark black tape between the top and the bottom to absorb the light rays that cause the slightly leaking bright lines and prevent them from leaking to the outside. If a light-reflecting substance used as a reflector or sheet for a backlight, which will be described later, is arranged between the end of the light guide plate on the light-exiting surface side and the sheet having a straight apex, a slight leak will occur. It is preferable not only to prevent the light rays that cause the bright lines from leaking to the outside and also to return the light rays to the inside of the light guide plate to effectively use the light.

By setting the light diffusing sheet substantially in contact with the end of the light reflector on the light emitting surface of the light guide plate,
Fresnel rays (surface reflection) on the surface of the light diffusing sheet are backscattered as well as returning to the light guide plate to effectively use the light rays that cause the bright lines emitted from the vicinity of the end of the light reflector. In particular, it is particularly preferable in that it can prevent problems such as mixing of dust and scratches on the surface of the light guide plate.

When an exposed portion of the light guide plate is generated between the light diffusion sheet and the end of the light reflector, the light emitted from the exposed portion does not pass through the light diffusion sheet to the outside. Since the light is emitted, it causes a loss of light. Since the light guide plate is exposed, dust and the like are easily mixed on the surface of the light guide plate, and the surface of the light guide plate is easily scratched.

The light guide plate portion opposite to the light guide plate light exit surface side end portion of the light reflector opposite to the light guide plate light exit surface side is covered with a light diffusion reflection plate or sheet through an air layer. Is preferred. With such a configuration, it is possible to prevent the generation of a light ray that causes a bright line emitted from the surface opposite to the light exit surface of the light guide plate.

The main part of the present invention has such a structure and is used as a backlight of a panel, particularly a liquid crystal panel. In the present invention, it is preferable to have the following configuration.

The light reflecting plate or sheet 3 is arranged so as to cover almost the entire surface of the light guide plate facing the light exit surface of the light guide plate. The reflection plate or sheet may be any one as long as it reflects light. When the reflection plate or sheet is a specular reflection plate or sheet, the material is silver, aluminum, platinum, nickel, chromium or the like, preferably polyester or the like. It is a plastic film substrate or a metal plate with a surface coating of silver, aluminum or the like by vapor deposition or sputtering. When the reflection plate or sheet is a light diffusion reflection plate or sheet, a resin such as polyester is used as a light diffusion substance (for example, TiO ₂ ,
BaSO ₄ , SiO ₂ etc.), a resin such as polyester foamed to impart light diffusivity, or a plate such as an Al plate coated with the light diffusing substance. The material is not particularly limited as long as it has the property of diffusing and reflecting the generated light rays.

[0031]

INDUSTRIAL APPLICABILITY The present invention can be used for an optical display or the like as a backlight which is small in size, has a small outer dimension with respect to an effective light emitting area, has a high luminance, and has a good visibility.

[0032]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. A rectangular acrylic plate with a thickness of 4 mm (2
A cold-cathode fluorescent tube (made by Harrison Electric Co., Ltd.) with a diameter of 3 mm and a length of 180 mm is arranged at the short end of 05 mm × 160 mm, Delaglass made by Asahi Kasei Co. A), and on the back surface of the light guide plate. An ink containing a light-scattering substance (titania) was screen-printed with a circular dot pattern at a pitch of 1 mm, and a screen printing plate was prepared using CAD under the following conditions.
The light diffusing substance coverage is 20% at the minimum point (just below the cold cathode fluorescent tube side of the sheet having a linear prism described later near the cold cathode fluorescent tube), and the maximum point (the light source farthest from the light guide plate). (Part) was 95%, and in the middle, the ratio was sequentially increased from the point where the coverage was the minimum, and the plot was made.

White light diffuse reflection sheet made of polyester having a thickness of 0.13 mm (Melinex 329 manufactured by ICI)
Was arranged so as to cover the entire surface of the light guide plate coated with the light-scattering material with an air layer in between. The outer circumference of the cold cathode fluorescent tube is PET
(Polyester) film with silver deposited thickness: 0.05
mm silver film (manufactured by Reiko Co., Ltd.), and the end of the light guide plate of the silver film on the light emitting surface side has a width of 2.5 mm and a thickness of 0.16.
mm double-sided adhesive tape (Teraoka Seisakusho Co., Ltd. WPT-No750F
) To the light exit surface of the light guide plate, and the end of the silver film on the side opposite to the light exit surface side of the light guide plate is attached to the surface of the light diffusive reflection sheet not facing the light guide plate. -I glued it with a push.

A light diffusion sheet (8B36 manufactured by GE) made of polycarbonate having a thickness of 0.18 mm is arranged so that the rough surface side is opposite to the light guide plate side and the light exit surface of the light guide plate is It was placed with an air layer in between so as to cover almost the entire surface.

Further, on the rough surface side of the above-mentioned light diffusion sheet, as shown in FIG. 6, a commercially available polycarbonate made apex angles (9 in the figure) of 90 degrees and parallel to each other are provided. A sheet having a thickness of 0.23 mm, which is provided with a large number of linear prisms at intervals of 0.05 mm (P in the figure), is arranged so that the linear prisms are on the outside. At this time, the distance from the edge of the silver film of the light source reflector to the sheet having the linear prism is 2 mm.
The distance from the edge of the silver film to the light diffusion sheet was shifted so that it was 0.5 mm.

The surface luminance when a cold cathode tube was driven at a constant current (tube current 6 mA) by applying an alternating voltage of 30 KHz from the inverter, was measured by a luminance meter (Topcon BM-8) using a normal line of the light guide plate. Measured from the direction. 99 in the effective light emitting surface at this time (the portion corresponding to the portion of the light guide plate on which the light scattering material is applied in FIG. 5)
The average luminance at points (equal division) was 1500 cd / m ² . The abnormal light emitting portion (bright line) near the end of the light guide plate where the cold cathode tube was brought close to was not noticeably observed.
The method of observing the bright line was visually observed from the direction normal to the light emitting surface of the backlight. When the luminance of the bright line portion was measured by a luminance meter (Topcon BM-8) from the direction normal to the light guide plate, the maximum luminance in the bright line portion was 1700 cd / m ² (Example 1).

Next, the average luminance measured under the same apparatus and conditions as in Example 1 was 1500 except that the distance from the end of the silver film to the sheet having the linear prism was 2.5 mm.
It was cd / m ² . Further, the abnormal light emitting portion (bright line) near the end of the light guide plate where the cold cathode tube was brought close to was less observable than in the case of Example 1. The maximum brightness in the bright line part is 1650
It was cd / m ² . Similar results were obtained even when the distance from the edge of the silver film to the sheet having the linear prism was 3 mm, and the maximum brightness in the bright line portion was 1600 cd / m ² (Example 2).

Next, except that the distance from the edge of the silver film to the light diffusion sheet is set to 2 mm (that is, the sheet having the light diffusion sheet linear prisms is overlapped on the light source side). The average luminance measured under the same apparatus and conditions as in Example 1 is 140
It was 0 cd / m ² . An abnormal light emitting portion (bright line) near the end of the light guide plate where the cold cathode tube was brought closer was observed more than in Example 1, and the maximum brightness in the bright line portion was 1750 cd / m ² . In addition, since the part between the end of the silver film on the light exiting side of the light guide plate and the light diffusion sheet was exposed, dust was invaded and the light guide plate surface was easily scratched (comparison). Example).

Next, the average luminance measured under the same conditions and conditions as in Example 1 was 1300 cd / m, except that the light diffusing sheet was arranged outside the sheet having a linear prism (light emitting surface side). ²
Met. An abnormal light emitting part (bright line) near the end of the light guide plate where the cold cathode tube was brought close to was observed more than in Example 1, and the maximum brightness in the bright line portion was 1600 cd / m ² (Example 3).

Next, the measurement was carried out under the same apparatus and conditions as in Example 1 except that one sheet of light diffusing sheet was also arranged outside the sheet made of a translucent material having a linear prism. The average brightness was 1300 cd / m ² . An abnormal light emitting portion (bright line) in the vicinity of the end of the light guide plate where the cold cathode tube was brought close to was not observed so much as in Example 1 (Example 4).

Next, Example 1 was adopted except that the air layer between the light diffusing sheet and the light guide plate was eliminated by a double-sided adhesive tape.
The average brightness measured with the same equipment and conditions as 1500 cd / m
^Although it was ² , the brightness distribution in the effective light emitting surface is extremely non-uniform (the cold cathode tube side of the light guide plate has extremely high brightness, and the part far from the cold cathode tube of the light guide plate has extremely low brightness). It was An abnormal light emitting portion (bright line) near the end of the cold cathode tube of the light guide plate was observed more prominently than in Example 1, and the maximum brightness in the bright line portion was 3000 cd / m ² (Example 5). ).

Next, the average brightness measured under the same apparatus and conditions as in Example 1 except that the air layer between the light diffusion sheet and the sheet having the linear prism was eliminated was 1100 cd / m ^2. Met. The abnormal light emitting portion (bright line) in the vicinity of the end portion of the light guide plate where the cold cathode tube was brought close to was equivalent to that in Example 1 (Example 6).

Next, the average brightness measured under the same conditions and conditions as in Example 1 except that a dark black tape was placed between the end of the silver film and the sheet having the linear prism. It was 1500 cd / m ² . No abnormal light emitting part (bright line) was observed in the vicinity of the end of the light guide plate where the cold cathode tubes were brought close to each other. The average luminance measured under the same conditions and conditions as in Example 1 was 1650 cd / m ² except that a silver film was arranged with the reflecting surface facing the light guide plate instead of the dark black tape. The abnormal light emitting portion (bright line) in the vicinity of the end of the cold guide tube of the light guide plate was not observed as in Example 1, and the maximum brightness in the bright line portion was 1550 cd / m ² (Example 7). .

Next, the end of the silver film and the end of the light diffusion sheet are in contact with each other so that the distance between the end of the silver film and the light diffusion sheet is substantially 0 mm. The average luminance measured under the same conditions and conditions as in Example 1 was 1600 cd / m ² . The abnormal light emitting portion (bright line) in the vicinity of the end of the light guide plate where the cold cathode tube was brought close to was the same as that in Example 1 (Example 8).

Next, the surface of the light reflector opposite to the light exit surface of the light guide plate facing the light exit surface side of the light guide plate is covered with a specular reflection sheet through an air layer, as shown in FIG. Example 1 except that the end portion of the light guide plate of the silver film opposite to the light exit surface side is bonded to the surface of the light diffusive reflection sheet facing the light guide plate by a double-sided tape as shown in FIG. The average luminance measured by the same apparatus and conditions as above was 1500 cd / m ² . An abnormal light emitting portion (bright line) near the end of the light guide plate where the cold cathode tube was brought closer was observed more than in Example 1, and the maximum brightness in the bright line portion was 1900.
It was cd / m ² (Example 9).

[Brief description of drawings]

FIG. 1 is a perspective view of a backlight according to a conventional embodiment.

FIG. 2 is a sectional view of a conventional backlight according to an embodiment.

FIG. 3 is a cross-sectional view near a light source of a backlight according to a conventional embodiment.

FIG. 4 is a sectional view around a light source of a backlight according to a conventional embodiment.

FIG. 5 is a sectional view of a backlight according to an embodiment of the present invention.

FIG. 6 is a cross-sectional view of one embodiment of a sheet having a linear prism.

FIG. 7 is a cross-sectional view of one embodiment of a sheet having a linear convex portion.

FIG. 8 is a diagram explaining a cause of increase in bright lines.

FIG. 9 is a sectional view of a backlight according to an embodiment of the present invention.

[Explanation of symbols]

1: Light guide plate 2: Light diffusion sheet 3: Reflector or sheet 4: Linear light source 5: Reflector 6: Light diffusion element 7: Sheet having a straight top edge 8: Straight ridge 9: Vertical angle 10: Light rays that cause bright lines 11: Adhesive layer

Claims (7)

(57) [Claims] 1. A light guide plate made of a plate-shaped light-transmitting material and having a function of emitting light from one wide surface, and a linear light source provided on at least one side surface of the light guide plate in proximity to the light guide plate. And a specular reflector or a specular reflector that covers the linear light source.
A sheet or a light diffusing reflector or a light diffusing reflecting sheet.
That the light reflector (hereinafter referred to as "optical reflector"), said laminated on the light exit surface side of the light guide plate is provided, the light diffusing sheet of at least one - and DOO, at least one finely same surface A sheet made of a translucent material in which a large number of prisms having linear apexes or convex portions having linear apexes at various intervals are formed in a state in which the apexes are substantially parallel (hereinafter referred to as “linear form”). Sheer with a ridge
In a state in which at least a part of the end portion of the light diffusion sheet on the side of the linear light source does not overlap with the sheet having the linear vertex,
A backlight in which the light diffusion sheet and the sheet having a straight top edge are stacked. 2. A light diffusing sheet and a sheet having a straight top edge are arranged along the end of the light guide plate on the light source side so as not to overlap with each other at an interval of at least 1.5 mm. The backlight according to claim 1. 3. The backlight according to claim 1, wherein the light diffusion sheet is arranged between the sheet having a straight top edge and the light guide plate. 4. The backlight according to claim 3, wherein the light diffusion sheet and the light guide plate are arranged with an air layer in between. 5. The backlight according to claim 1, wherein the light diffusing sheet and the sheet having a straight top edge are arranged with an air layer in between. 6. The backlight according to claim 1, wherein a light absorbing substance is arranged at least between an end of the light reflector on the light emitting surface side of the light guide plate and a sheet having the straight apex. . 7. A light diffuse reflection plate or light diffuse reflection through an air layer at a portion opposite to the light guide plate light emitting surface of the light guide plate light emitting surface side end portion facing the light reflector end portion. The backlight according to claim 1, further comprising a sheet.