JPH0822002A - Backlight - Google Patents

Abstract

PURPOSE:To provide a back light which has enhanced electric power consumption-luminance fluctuation efficiency, is of a thin type and is easy to handle by arranging a sheet consisting of a light transmissive material satisfying specific conditions on the surface of a light transmission plate. CONSTITUTION:The one broad surface of the light transmission plate 1 is provided with the sheet 2 consisting of the light transmissive material. For example, prisms or projecting parts having straight peak ridges or curved peak ridges are formed on the same surface of the sheet 2. The prisms or projecting parts having the length of the peak ridges within the range of the following conditions are used. Namely, the ratio of the width of the bottom of the prisms or the projecting parts and the length of the peak ridges is in a range of 1:2 to 1:200. The sheet having the many prisms or projecting parts existing the same surface is used. The sheet 2 is arranged on the light exit surface side of the light transmission plate 1 in such a manner that the peak ridges exist on the outer side (the side opposite to the surface facing the light transmission plate 1). Additional intensifying of the directivity with the normal direction dropped on the light exit surface is made possible by changing the directivity of the light emitted from the exit surface of the backlight in this arrangement of the sheet 2.

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 the case of this edge light method, as shown in FIG. 2, a light diffusion element is formed in a dot shape or a stripe shape on one surface of the light guide plate, and almost the entire surface is covered with a reflection plate or a sheet to guide the light. Surface opposite to light plate (light emitting surface)
In many cases, it is arranged so as to cover the light diffusion sheet.

Particularly in recent years, since the backlight is driven by a battery, further improvement in power consumption-luminance conversion efficiency is desired, and the light emitting surface of the backlight is parallel to each other at a fine interval on the same surface. A sheet made of a translucent material having a large number of prisms or convex crests with straight rectilinear ridges is arranged to give directivity to the light emitted from the backlight and to improve the brightness in the normal direction of the light emitting surface. It has been proposed to increase the number (Japanese Patent Laid-Open No. 5-323319).

However, since the sheet itself has a low light diffusing property, the performance of concealing the light diffusing element formed on the light guide plate is not sufficient, and the shape of the light diffusing element is seen through the sheet. was there. When the shape of the light diffusing element is seen through in this manner, it is not preferable in that uniform planar light emission is obtained.

In order to solve this problem, it is considered that the sheet itself is coated with a light diffusing substance or the sheet surface is made to be a random rough surface so as to give the light diffusing property. However, such a method has a problem that the property of the sheet that imparts directivity to the light emitted from the light exit surface of the light guide plate is deteriorated, and thus the brightness near the normal line direction of the light exit surface is decreased. Further, there has been proposed a method in which the sheet and a plurality of light diffusing sheets other than the sheet are laminated and used, but in such a form, a backlight is formed by the thickness of the light diffusing sheet itself. In addition to the fact that the requirement for thinning the backlight is not satisfied, it is not always preferable in terms of the brightness of the light emitting surface.

On the other hand, a sheet made of a translucent material having a large number of prisms or convex peaks having linear peaks parallel to each other on the same surface at minute intervals is geometrically shaped. Because of its regularity, slight scratches caused by external force during handling are optically different in shape from other parts, and the scratched part shines as a bright spot, resulting in uniform planar light emission of the backlight. There was a problem that deteriorated the state of.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a backlight which has high power consumption-luminance conversion efficiency, is thin, and is relatively easy to handle.

[0008]

Means for Solving the Problems As a result of various studies on the above points, the present inventors have arranged a sheet made of a translucent material satisfying a certain condition on the surface of a light guide plate, thereby The directivity becomes stronger, the power consumption-luminance conversion efficiency is high in the vicinity of the direction of the normal line substantially dropped on the light output surface, and the concealment effect for the light diffusion element formed on the light guide plate surface is large, and The present invention has been completed by finding that it can be used as a thin backlight.

That is, the present invention provides a backlight for a panel having a linear light source in the vicinity of at least one side end of a light guide plate made of a translucent material and having a light diffusion function,
On the light emitting surface side of the light guide plate, there are a large number of prisms or convex portions having straight or curved apexes on the same surface, and the bottom width and apex edge in the direction orthogonal to the apex of the prisms or convex portions. The present invention relates to a backlight for a panel in which one or more sheets made of a translucent material having a ratio of the length to the length of 1: 2 to 1: 200 are arranged.

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

FIG. 1 is a perspective view of an embodiment of the present invention, and FIG. 2 is a sectional view showing an example of an edge light type backlight. In the figure, reference numeral 1 denotes a light guide plate, which may be any substance that allows light to pass efficiently, and is made of quartz, glass, translucent natural or synthetic resin such as acrylic resin.

In order to form a light diffusing element (6 in the figure) on one wide surface of the light guide plate, a substance having a function of diffusing light, such as silica, barium sulfate, calcium carbonate, titanium white, glass beads, resin. A method of printing a light-diffusing substance such as beads, air bubbles, etc., a printing ink or the like in a dot shape or a stripe shape on the light guide plate surface by a screen printing method, or a dot on the surface of the light guide plate. Shape or stripe-shaped surface roughening method, small holes or small protrusions formed on the surface of the light guide plate, stepwise cutting of the light guide plate, or two types of light guide plate having different refractive indexes There is a method of making the above substances exist at minute intervals.

Reference numeral 4 denotes a linear light source (rod-shaped light source), and in a preferred embodiment, a mirror-like reflection sheet of Ag, Al or the like having a gap (slit) at the end of the light guide plate for allowing light to enter.
Or a polyethylene terephthalate (PET) or the like, which is a light reflector 5 formed of a light diffusive reflection sheet in which light is diffused by BaSO ₄ , TiO ₂ , bubbles or the like. It is covered with a gap, and is installed close to at least one end face of the light guide plate such that its central axis is substantially parallel to the end face of the light guide plate. The linear light source may be a fluorescent tube, a tungsten incandescent tube, an optical rod, an LED array, or the like. However, a fluorescent tube is preferable, and from the viewpoint of power saving, the length of the uniform light emitting portion excluding the electrode portion is close to each other. It is preferable that the length is substantially equal to the length of the end portion of the light guide plate.

[0014] Ag, specular reflection, such as Al sheet - DOO or BaSO like PET _4, TiO _{2 gas} such as a light diffuse reflection was applied a light diffusing property of foam sheet - DOO (Figure 3) is the light exit surface of the light guide plate It is placed so as to cover almost the entire surface of the side opposite to.

In the figure, 2 is a sheet made of a light-transmissive material, which is a prism having the same straight ridges or curved ridges as shown in FIG. 3, or the same plane as shown in FIG. Similarly, a convex portion is formed. The present invention is characterized in that the prism or the convex portion has a length of the apex in a certain range.

That is, the ratio of the width of the bottom of the prism or the convex portion (width in the state orthogonal to the top edge ... d of FIGS. 3 and 4) and the length of the top edge (1 of FIGS. 3 and 4). Is in the range of 1: 2 to 1: 200, and a large number of sheets on the same surface are used. This sheet is arranged on the light emitting surface side of the light guide plate so that the top edge is on the outside (the side opposite to the surface facing the light guide plate). The shape of the prism described above is not limited to the shape shown in FIG. 3, but may be a shape in which the length of the hypotenuse is different.
The width of the bottom of the prism or the convex portion is usually 1 to 150 μm.

According to the present invention, when such a sheet is arranged on the light exit surface of the light guide plate, the ratio of the width to the length of the apex is 1: 2.
The feature is that one or more sheets are arranged in the range of up to 1: 200, but by arranging the sheets in this way, the directivity of the light emitted from the light emitting surface of the backlight is changed, The directivity in the vicinity of the normal direction dropped on the light emitting surface can be made stronger, and a backlight with high power consumption-luminance conversion efficiency can be obtained, but at the same time, the concealment effect of the light diffusing element formed on the light guide plate surface (light emitting (When viewed from the surface side) is large, and a relatively thin backlight can be obtained.

If necessary, a conventional light diffusing sheet may be arranged on the light emitting surface side of the light guide plate, but the light diffusing sheet used in that case has a very large light diffusing property. Without
The effects of the present invention can be sufficiently obtained. Therefore, the light transmittance of the light diffusion sheet becomes good, and even if the light diffusion sheet is arranged between the light guide plate and the sheet, the brightness is hardly reduced.
Even if the light diffusion sheet is arranged outside the sheet, the directivity of the light obtained by the sheet does not change so much.

The sheet having a prism or a convex portion used in the present invention will be described in more detail. The material of this sheet is not particularly limited as long as it is made of a translucent material. For example, methacrylic acid ester, polycarbonate, polyvinyl chloride, polystyrene, polyamide, polyester, polyethylene, polypropylene, fibrous resin, For example, glass.

Further, as an example of the shape of the straight or curved apex formed on the light emitting surface side of the sheet, as shown in FIG. 3, a so-called prism shape (apex) having two or more optical planes is provided. And the cross-section in a state where it intersects perpendicularly forms a triangle). The apexes (8 in FIG. 3) where the two optical planes of this prism intersect are linear or curved, and the apexes are finely spaced in the same plane, and some or all of them are evenly spaced. Alternatively, a large number of curved lines are present, and preferably the bottoms are in contact with each other.

The apex angles of these apexes formed on the sheet have portions of substantially the same shape, and the apex angle (9 in the figure) is 70-.
It is preferably 150 degrees. A more preferable angle range of the apex depends on the refractive index of the sheet material used and the light distribution characteristics of the planar light emitter used. For example, when a material having a high refractive index (polycarbonate, refractive index n = 1.59) is used, when the apex angle becomes 85 degrees or less, the light emitted from the planar light-emitting body is directed in the normal direction to the light-emitting surface. If the light is emitted outside the vicinity and becomes 110 degrees or more, the directivity of the light in the vicinity of the normal direction decreases, so that it is particularly preferably 85 to 110 degrees in order to obtain a larger directivity.

As another example of the sheet used in the present invention, a convex portion in which the shape of the apex has an arc (a cross section forms a mountain shape in a state where it intersects with the apex perpendicularly ... 10 in FIG. 4). There is. The convex shape of these sheets is not particularly limited, but may be a so-called semi-cylindrical shape, a circular shape, an elliptical shape, a sine wave shape, or the like.

A large number of top ridges formed on the sheet make it difficult for human eyes to visually recognize the distance between the top ridges due to the light emitted from the surface. It is preferable that the interval is 1 to 1000 μm.
In particular, when the backlight of the present invention is used in a liquid crystal display, the distance between the top ridges formed in the sheet is narrower than the pixel pitch of the liquid crystal, and in particular, one third or less (for example, the pixel pitch of the liquid crystal is When it is 0.3 mm, the distance between the crests formed on the sheet is 0.3 mm or less, particularly preferably 0.1 mm.
The following is preferable in terms of suppressing the spatial moire phenomenon between the pixels of the liquid crystal display and the numerous apexes formed on the sheet of the backlight of the present invention.

The thickness of the apex is determined by the size of the apex or arc of the apex and the interval between the apexes and the apexes, but a large number of linear or curved apexes at fine intervals. It is necessary to have a thickness for maintaining the thickness, and it is better that the thickness is thin for light transmittance and thinning of the backlight.
For the reason of manufacturing and strength of the sheet, the total thickness of the sheet is 10 to 3000 μm, preferably 50 to 1000 μm.
m is good. Further, it is preferable that the linear or curved top ridges formed on the same surface have the same shape more effectively.

The method of molding the sheet used in the present invention is not particularly limited. For example, a die molding process by hot pressing, an embossing process, a molding process, and an ultraviolet curing resin on the base film are used. Any method can be used as long as it can be formed by a processing method, a chemical treatment method or the like so as to have a large number of substantially the same ridges at fine intervals.

In the present invention, the ratio of the length of the apex in the width direction (d in FIG. 3) to the length in the apex direction (l in FIG. 3) is in the range of 1: 2 to 1: 200. The light diffusivity of the sheet itself can be increased by setting this range, and it becomes difficult for the shape of the light diffusing element to be seen through the sheet.

Such an increase in the light diffusivity is brought about by the end portion (11 in FIGS. 3 and 4) of the apex in the apex direction. Therefore, if it is desired to further increase the light diffusivity of the sheet, the number of the end portions per unit area may be increased. In addition, the increase of the light diffusivity is shown in Fig. 3 (b).
It can also be obtained by changing from a linear shape to a curved shape as shown in FIG.

However, if the light diffusivity is extremely increased,
Since the function of imparting directivity to the light emitted from the backlight of the above-mentioned sheet and increasing the luminance in the normal direction of the light emitting surface is reduced, the width of the top ridge and the length in the top ridge direction are reduced. It is an indispensable condition that the ratio to be 1: 2 or more.
On the other hand, if the ratio of the length in the width direction of the apex to the length in the direction of the apex is made too large, the end portion (11 in FIGS. 3 and 4) per unit area of the sheet decreases, and the sheet Since the light diffusivity of the glass is extremely reduced, the above-mentioned length ratio is 1:
It is indispensable to be 200 or less. A more preferable range of the ratio of the length in the width direction of the top edge to the length in the top edge direction is 1: 5 to 1: 100.

Incidentally, the end portion of the above-mentioned ridge (see FIGS. 3 and 4).
The shape of the inside 11) is not particularly limited, but since the end portion shines with higher brightness than other apex portions,
In order to obtain a more uniform planar light emission state, it is preferable that the corner portions of the end portions (cut surfaces) are rounded. When the end portions are not rounded, for example, when two planes or two curved surfaces intersect at a corner (particularly an acute angle), that portion (corner) shines with extremely high brightness as compared with the surrounding portion. Therefore, it is not preferable to obtain a more uniform state of planar light emission.

In a liquid crystal display, the contrast becomes lower as the viewing angle from the direction of the normal to the display surface increases, so that the brightness in the vicinity of the direction of the normal is important for practical use.

The arrangement of the prisms or convex portions of the sheet (2 in the figure) made of a translucent material used in the present invention is not particularly limited, and the top ridges thereof may be in parallel with each other or may not be formed. It may be arranged in a regular state.

In the present invention, when such a sheet is arranged on the light emitting surface of the backlight, the directivity of light appears. That is,
When the brightness of the light emitted from the surface is measured substantially in the normal direction to the light emitting surface, the brightness is increased as compared with the case where no sheet is arranged, and the light is dropped onto the light emitting surface. Luminance similarly measured from a direction at an angle to the normal, for example, 40 degrees, has a larger reduction rate than luminance measured substantially in the normal direction (for example, measured in the normal direction). It is understood that the above-mentioned directivity of light appears because it decreases to about 50% of the luminance at that time).

Further, it is preferable to stack two or more sheets as described above, because the brightness is further increased as compared with the case where one sheet is used. The individual prisms or the convex portions having the straight apexes of the sheet may be arranged in an irregular state on the sheet surface, but the directivity of the light rays emitted from the light emitting surface of the sheet. When it is desired to make the vertical direction different from the horizontal direction, it is preferable that a plurality of individual prisms or the same convex portions are provided in a state in which they are substantially parallel to each other at fine intervals. With such a state, the directivity of light in the width direction of the apex can be made more remarkable than the directivity of light in the apex direction of the apex. Further, when the individual prisms or the convex portions having the straight apexes of the sheet are brought into close contact with each other in the sheet surface in a substantially parallel state, the individual prisms or the same prisms per unit area are formed. Since the area of the convex portion can be increased, the effect of the present invention can be further increased.

When the sheets in which the top edges are arranged in parallel with each other are used, the concealing power for the shape of the light diffusing element of the light guide plate is further increased, and the brightness when measured in the normal direction is also increased. In order to further improve and to prevent the moire phenomenon due to the top ridges of the sheets, it is preferable to stack at least two sheets with the top ridges of the sheets intersecting each other.

The state of intersection between the apex edges of the sheet will be described in more detail. The intersection angle at the intersection is substantially 75.
It is preferable that they intersect at an angle of 115 degrees. 75
Even if it deviates from ~ 115 degrees, the hiding power for the shape of the dot-shaped or stripe-shaped light diffusing element, which is the light diffusing element, can be secured, but a greater hiding power is obtained at 75-115 degrees, particularly preferably 90 degrees. It is in the vicinity.
Also, under this condition, the brightness is simultaneously improved.

Even when a plurality of sheets having curved apexes are used, it is preferable to stack at least two sheets in a staggered state (a state in which each side of the sheet intersects).

A material having a refractive index lower than that of the sheet is required between the light emitting surface of the light guide plate and the sheet. It is particularly preferable to dispose the air layer in terms of belonging and ease of manufacturing the backlight. As a method, the surface of the sheet facing the light guide plate may be slightly roughened or a spacer element may be provided. For the same reason, between sheets
It is particularly preferable to arrange an air layer on the light emitting surface side of the sheet. The thickness of the air layer is not particularly limited, but may be about 0.1 mm from the monomolecular layer.

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.

[0039]

【The invention's effect】

[0040]

EXAMPLES Next, the present invention will be described in more detail with reference to Comparative Examples and Examples. A rectangular light guide plate with a thickness of 4 mm as shown in FIG. 1 (Asahi Kasei Kogyo Co., Ltd., AC-999, material is PMMA, 210 mm ×
155 mm), a cold cathode fluorescent tube with a thickness of 3 mm (made by Harrison Electric Co., Ltd.) is arranged at the short end, and an Ag film having a 4 mm slit in the portion in contact with the light guide plate is used as a light source for the reflecting surface. They are arranged in an elliptical shape so as to face each other, and are arranged so that the light emitted from the slit enters the light guide plate from the end portion of the light guide plate. On the other hand, the light diffuser element formed on the surface of the light guide plate is composed of a paint containing titanium white in a circular dot pattern on the intersections (grids) of orthogonal lines with a virtual spacing of 1 mm on the light guide plate. It was printed and formed under the following conditions. Printing was carried out so that the coverage of the light diffuser element was gradually increased to 26% at the minimum point and 90% at the maximum point.

Further, the coverage of the light diffusing substance coated on the grid in a state parallel to the axis of the linear light source is such that the linear light source is located at the center on the parallel lines, that is, from the center in the longitudinal direction of the linear light source. It was printed so that it becomes 26% at the minimum point so that it becomes larger as it goes from the line on the surface of the light guide plate which is erected vertically to the both ends of the light guide plate, and gradually increases to 40% at the maximum point. .

The surface of the light guide plate on which the light diffusing element is printed has a thickness of 0.188 mm and is a light diffusing reflection sheet (manufactured by Toray Industries, Inc.).
E60L) and covered via air layer. Further, one light diffusion sheet (D-204 manufactured by Tsujimoto Electric Co., Ltd.) having a thickness of 0.1 mm was arranged on the light emitting surface side of the light guide plate through an air layer. The light emitting surface side of the light diffusion sheet (the side opposite to the light guide plate side) is in contact with air having a smaller refractive index than the light diffusion sheet.

The cold cathode tube is provided with an inverter (CDK-made by TDK).
Alternating voltage of 30KHz from 10L) and constant current (5m
A) The surface brightness when driven by a brightness meter (Topcon BM
-8), it was 1000 cd / m ² when measured in the direction normal to the light exit surface at a viewing angle of 2 degrees. At this time, the dots could not be seen through the light diffusion sheet. Further, the directivity of light was almost nonexistent as illustrated in FIG. (Comparative Example 1) Instead of the light diffusion sheet on the light emitting surface side, a polycarbonate is used instead of the light diffusing sheet, and a large number of prisms having a vertical vertex with an apex angle of 90 degrees are provided on the same surface. Direction length is 35μm
Comparative Example 1 except that a 250 μm-thick sheet processed to have a length of 210 mm in the apex direction is arranged on the light emitting surface side with an air layer so that the apex surface side is on the outside. The brightness measured by operating under the same equipment and conditions as 1500 cd / m ²
Met. At this time, the dots were visible through the sheet. In addition, the directivity of light was observed as illustrated in FIG. 6 with respect to the direction normal to the light exit surface. (Comparative Example 2) Instead of the sheet on the light emitting surface side, a convex portion having an elliptical cross section having a straight top edge parallel to the same surface made of an ultraviolet curable resin on PET having a thickness of 0.1 mm. And a sheet having a thickness of 160 μm processed so that the length in the width direction of the apex is 110 μm and the length in the direction of the apex is 210 mm. The brightness measured by operating under the same apparatus and conditions as in Comparative Example 2 was 1300 cd / m ² except that one sheet was arranged on the light emitting surface side through the. At this time, the dots were visible through the sheet. In addition, the directivity of light was observed with respect to the direction normal to the light exit surface. (Comparative Example 3) In place of the sheet on the light emitting surface side, a large number of prisms having straight vertexes with a straight vertex of 90 degrees and having vertex angles of 90 degrees are provided parallel to each other on the same surface made of polycarbonate. The width of the ridge is 50 μm and the length of the ridge is 100 μm (ratio is 1:
The thickness is 250 μm, which is irregularly arranged so that it becomes 2).
The brightness measured by operating under the same apparatus and conditions as in Comparative Example 1 was 1300 cd / m ² except that one sheet of the sheet was arranged on the light emitting surface side so that the apex surface side was on the outside. At this time, the dots could not be seen through the sheet. In addition, the directivity of light was observed with respect to the direction of the normal to the light exit surface.
(Embodiment 1) In place of the sheet on the light emitting surface side, a large number of prisms having a vertical apex of 90 degrees and having a straight apex parallel to the same surface and made of polycarbonate are provided, and the width direction of the apex is With a thickness of 50 μm and a thickness of 250 μm processed so that the length in the direction of the apex is 10 mm (ratio is 1: 200), one sheet on the light output side with the apex side facing outward. The luminance measured by operating under the same apparatus and conditions as in Comparative Example 1 except for the arrangement was 1400 cd / m ^2.
Met. At this time, the dots could not be seen through the sheet. In addition, the directivity of light was observed with respect to the direction of the normal to the light exit surface. (Example 2) The same apparatus as in Example 1 except that the linear apex of the sheet used in Example 1 was replaced with an irregularly arranged curved apex.
The brightness measured by operating under the conditions was slightly lower than that in Example 1, but the dots were not visible through the sheet as compared with Example 1. In addition, the directivity of light was observed with respect to the direction of the normal to the light exit surface. (Example 3) The same apparatus as in Example 2 except that the linear apex of the sheet used in Example 2 was replaced with a curved apex arranged irregularly,
The brightness measured by operating under the conditions was slightly lower than the brightness obtained in Example 2, but the dots were less visible through the sheet than in Example 2. In addition, the directivity of light was observed with respect to the direction of the normal to the light exit surface. (Example 4) Two sheets each having the linear apex of Example 1 were used with an air layer interposed therebetween (in a state where they were simply overlapped in air), and the sheets were arranged so that the linear apices intersect each other. The brightness measured by operating under the same apparatus and conditions as in Example 1 except for the above was improved as compared with Example 1. At this time, the dots could not be seen through the light diffusing sheet, but the hiding power was examined by rotating the two sheets and changing the intersecting angle of the linear apexes. The straight ridges of the g
The hiding power was further increased when crossing in the range of degrees. In particular, the hiding power was maximized when the intersecting angle was around 90 degrees. In addition, the brightness of the two sheet-shaped straight ridges is 7
Increased when crossing at 5 to 115 degrees, especially 90
The brightness reached the maximum (1500 cd / m ² ) in the vicinity of 100 degrees. In addition, the directivity of light was observed with respect to the direction of the normal to the light exit surface. (Example 5) Example 1 was repeated except that two sheets having the linear apex of Example 2 were used with the air layer interposed therebetween (same as above) and the linear apices were arranged so as to intersect each other. The brightness measured by operating under the same apparatus and conditions as in Example 1 was improved as compared with Example 1. At this time, the dots could not be seen through the light diffusion sheet, but the hiding power was examined in the same manner, and the linear vertexes of the two sheets were 75 to 115 with respect to each other.
The concealing power was further increased in the state of intersecting with each other. In particular, the hiding power was maximized when the intersecting angle was around 90 degrees. In addition, the brightness is such that the linear crests of the two sheets are 75 to 11 relative to each other.
It increased in the state of crossing at 5 degrees, and the luminance became maximum (1800 cd / m ² ) especially near 90 degrees. In addition, the directivity of the light was observed with respect to the normal direction dropped on the light exit surface. (Example 6) Two sheets having curved apexes used in Example 3 are used with an air layer (same as above), and the sides of those sheets are about 10
The brightness measured by operating under the same apparatus and conditions as in Example 1 except that they were arranged so as to intersect each other at a degree was improved as compared with Example 1. At this time, the dots could not be seen through the light diffusion sheet. (Example 7) Two sheets having the curved apex used in Example 4, in which the shape of the end of the prism was changed to a rounded convex shape, through an air layer (same as above) The luminance measured by operating under the same apparatus and conditions as in Example 1 except that the same was used and arranged as in Example 7 was improved as compared with Example 1. At this time, the dots could not be seen through the light diffusion sheet, but the hiding power was further increased. (Example 8)

[Brief description of drawings]

FIG. 1 is a perspective view of a backlight according to an embodiment of the present invention.

FIG. 2 is a sectional view of a backlight according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example of a structure of a surface of a translucent sheet used in the present invention.

FIG. 4 is a diagram showing another example of the structure of the surface of the translucent sheet used in the present invention.

FIG. 5 is a diagram showing an example of a state in which a light beam emitted from a light exit surface has little directivity.

FIG. 6 is a diagram showing an example of a state in which a light beam emitted from a light exit surface has directivity.

[Explanation of symbols]

 1: Light guide plate 2: Translucent sheet 3: Reflective sheet 4: Light source 5: Reflective sheet around light source 6: Light diffusing element 7: Translucent sheet exemplifying a structure 8: Top of prism 9: Apex Corner 10: Top of the convex portion 11: End of the top 12: Light emitting surface 13: Light ray

Claims (4)

[Claims] 1. A panel backlight having a light source made of a translucent material and having a light diffusing function and having a linear light source adjacent to at least one side surface end portion of the light guide plate, on the light emitting surface side of the light guide plate, It has a large number of prisms or convex portions having straight or curved apexes on the same surface, and the ratio of the bottom width in the direction orthogonal to the apex of the prisms or the aforesaid convex portions and the length of the apex is 1: 2 to
1 sheet of translucent material in the range of 1: 200
Backlight for panels with more than one panel. 2. The prism or the apex of the convex portion is fine,
2. The backlight for a panel according to claim 1, wherein a sheet made of a translucent material, which is partially or wholly provided in large numbers at equal intervals, is used. 3. The panel backlight according to claim 1, wherein at least two linear prisms or convex ridges are arranged such that the top edges thereof intersect at 75 to 115 degrees. 4. A sheet made of a translucent material and a light exit surface of the light guide plate.
The panel backlight according to any one of claims 1 to 3, wherein these are arranged with an air layer between them and / or between the sheets.