KR20100078687A - Optical sheet for control of side lobe and viewing angle in back light unit - Google Patents

Abstract

PURPOSE: An optical sheet for controlling a side lobe is provided to improve brightness by recycling light irradiated at a low angle to a reflective plate and to eliminate a side lobe. CONSTITUTION: An optical sheet for controlling a side lobe comprises a flat plate-shaped substrate(2), lens groups(12), and second optical members(20). The back surface of the substrate receives light, and the front surface of the substrate irradiates the light. The lens groups continuously arrange multiple first optical members(10) on the front surface of the substrate. The second optical members are arranged in both sides of the lens groups.

Description

Side lobe adjustment optical sheet {OPTICAL SHEET FOR Control of Side lobe and Viewing angle in BACK LIGHT UNIT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit used in a liquid crystal display, and more particularly, to provide high brightness by condensing light emitted from a lower light source to a center and to emit light at a low angle. It relates to an optical sheet of the backlight unit for recycling the.

LCDs have the advantages of light weight, low power consumption, and thin product. Due to these features, the application range of thin-screen TVs, monitors, portable displays, etc. is gradually increasing. In particular, in the TV market, which has become larger, achieving low power consumption and high brightness becomes an important problem.

The part which is closely related to such power consumption and high brightness is especially a backlight unit. The backlight unit includes a direct type method of irradiating light by arranging lamps on a lower surface of the liquid crystal panel, and an edge type method of installing a light guide plate under the liquid crystal panel and irradiating light from a lamp at one end of the light guide plate. Direct-type backlights are commonly used in large liquid crystal displays because they have high light utilization efficiency, simple configuration, and no limitation on the size of the display surface.

1 is an exploded perspective view illustrating a structure of a liquid crystal display device.

As shown, the liquid crystal display device is largely composed of a liquid crystal panel 10 and a backlight unit 20. In the liquid crystal panel 10, liquid crystal cells are arranged in a matrix to adjust the transmittance of light by application of an electric field, and a polarizing plate 11 is attached to change light emitted from the backlight unit 20 into polarized light. have.

The backlight unit 20 is composed of a lamp 21 serving as a light source, a reflecting plate 22, a diffusion plate 23, an optical sheet 24, and the like.

A plurality of lamps 21 are provided to emit light, and a specific configuration thereof uses a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED).

The reflector 22 is disposed on the lower surface of the lamp 21 to reflect the light emitted from the lamp 21, and reflects the light reflected from the optical sheet 24 or the polarizing plate 11 to improve light efficiency. Play a role of

The diffusion plate 23 is disposed on the upper surface of the lamp 21 to diffuse the light emitted from the lamp 21 so that the bright line of the lamp 21 is not visible. In order to diffuse the light, beads having a size of several micrometers are used in the diffusion plate 23.

The light passing through the diffuser plate 23 becomes a Lambertian shape having almost uniform luminance in all directions, and an optical sheet 24 is provided to condense such wide spread light in a desired direction.

As the optical sheet 24, a sheet in the form of a prism sheet, a lenticular lens, or a micro lens array is used. The prism sheet has a shape in which a prism of a triangular shape is regularly arranged on a surface thereof, and serves to improve the central luminance by changing a path of light emitted at a low angle at a high angle. However, due to the characteristics of the prism shape, light emitted from the low angle is strongly emitted, which causes the viewing angle characteristic of the display device to be reduced and causes the central luminance to decrease. In addition, the vertical viewing angle is very small, there is a problem that does not satisfy the viewing angle criteria required by the backlight unit.

2 is a cross-sectional view showing an optical sheet in the form of a conventional lenticular lens.

In general, an optical sheet in the form of a lenticular lens is used to increase luminance. However, as shown, the light (Ray 2) emitted at a low angle of the light passing through the lenticular lens is a component that does not help to improve the brightness. More specifically, as shown in Ray 1 of FIG. 2, when the light traveling to the right passes through the right side of the lens, the light is concentrated to increase the central luminance. However, when the light traveling in the right direction such as Ray 2 passes through the left side from the center of the lens, the light is emitted lower than the incident angle to decrease the luminance.

Accordingly, the optical sheet in the form of a lenticular lens also has light emitted at a low angle, similar to the optical sheet in the form of a prism sheet, which causes the viewing angle characteristic of the display device to be reduced and causes a decrease in the central luminance.

An object of the present invention is to arrange the optical member (prism or lenticular lens) having two or more height to recycle the light emitted from the optical member at low angle to the reflector to remove the side lobe and improve the central luminance have.

The present invention is a plate-like substrate that the light is incident on the back and exited to the front; A lens group in which a plurality of first optical members are continuously arranged on a front surface of the substrate; And a second optical member disposed on both sides of the lens group and having a height in a range of 17 to 57% of the width of the lens group.

The optical sheet of the backlight unit according to the present invention removes side lobes emitted at low angles by a lenticular lens having two or more heights formed on the front surface, and recycles light emitted at low angles to improve luminance. Can be improved.

In addition, the center luminance can be improved while satisfying a predetermined viewing angle standard through optimization of the cross-sectional shape of the lens, the distance between the lenses, and the height difference of the lens.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of an optical sheet according to the present invention.

In this process, the thickness of the lines or the size of the components shown in the drawings may be exaggerated for clarity and convenience of description.

In addition, terms to be described later are terms defined in consideration of functions in the present invention, which may vary according to a user's or operator's intention or custom.

Therefore, definitions of these terms should be made based on the contents throughout the specification.

3 is a graph showing luminance distribution for each angle of an optical sheet having a prism as an optical member on a surface thereof.

In the graph, the horizontal axis represents the angle with the surface of the optical sheet, and the vertical axis represents the measured luminance at that angle.

As shown, the prism improves the luminance in the range of 30 ° (60 ° to 120 °) relative to the vertical plane, which is the central luminance, but ranges from 70 ° to 90 ° (0 ° to 20 ° from the front direction). Range and 160 ° ~ 180 °) strong light is emitted.

The light emitted from the low angle is called a side lobe, and it is preferable that there is no light leaking sideways in the display device, and the side lobe causes a decrease in the central luminance.

4 is a cross-sectional view showing the structure of an optical sheet according to a first embodiment of the present invention.

As shown, the optical sheet 1 according to the first embodiment of the present invention is a substrate (2) in which light is incident on the rear surface 3 and exits to the front surface (4), and the front surface of the substrate ( And a first optical member 10 and a second optical member 20 formed at 4).

In the case of the first embodiment, the first optical member 10 and the second optical member 20 are formed of a prism lens, but there are sufficient optical members capable of collecting light such as a lenticular lens and an aspherical lens.

The plurality of first optical members 10 are continuously arranged to form the lens group 12.

The second optical member 20 is arranged at both sides of the lens group 12 composed of the first optical member 10.

The second optical member 20 is for refracting and recycling light emitted from the first optical member 10 at a low angle.

As shown by the arrows in the drawing, the light incident on the first optical member 10 having a relatively low height among the light incident on the rear surface 3 of the substrate 2 is totally reflected on one surface and then emitted at a low angle. .

However, since the second optical member 20 having a height higher than that of the first optical member is arranged at both sides of the lens group 12 formed of the first optical member 10, the light emitted at a low angle is second to the second optical member 20. It is incident on the optical member 20 and returned to the back surface 3 side.

Without the second optical member 20 having a relatively high height, it would have been a light emitted at a low angle and discarded for no use.

The direction of the light emitted at a low angle by the second optical member 20 is changed and recycled toward the rear surface 3 of the optical sheet, and the recycled light is reflected by the diffuser plate or the reflecting plate and recycled to the luminance. To improve.

Although the first optical member 10 and the second optical member 20 are both shown to have the same height in the drawing, the height of each optical member may be two or more types, and the pitch may be different. have.

The cross-sectional shape of each optical member may have an ellipse, a circle or any shape, as well as a prism.

The first optical member 10 and the second optical member 20 may have the same type of cross-sectional shape or may have different types of cross-sectional shapes.

5 is a view showing a relationship between the width of the lens group and the height of the second optical member.

The first optical member 10 is continuously arranged to form the lens group 12, and the height of the second optical member 20 is determined according to the width A of the lens group 12.

When the light emitted from the lens group 12 to the side lobe is incident on the side surface of the second optical member 20, the recycling effect of the light may be obtained.

Referring to FIG. 5, when the width of the lens group is A and the height of the second optical member 20 is B, tan θ = A / B.

Therefore, in order for the angle of the emitted light to be incident on the second optical member by 10 °,

Since tan 10 degrees ≒ 0.17, the height B of the second optical member may be 17% of the width A of the lens group.

Since tan 20 ° ≒ 0.36, tan 30 ° ≒ 0.57,

When the second optical member is configured to recycle up to 30 ° of light, the height B of the second optical member should be 57% of the width A of the lens group.

The angle emitted to the side lobe will vary depending on the characteristics of the first optical member, but since it is in the range of 10 ° to 30 °, the height of the second optical member is preferably in the range of 17% to 57% of the width of the lens group.

As described above, the ratio of the side lobe removal may be adjusted by the ratio of the width A of the lens group to the height B of the second optical member, and the viewing angle may be adjusted.

6 is a cross-sectional view showing the structure of an optical sheet according to a second embodiment of the present invention.

As shown, the optical sheet 1 according to the second embodiment of the present invention is characterized in that the lens group is formed to have different widths.

The regularity in the optical sheet 1 may cause a problem in that the moiré phenomenon and the pattern are visually recognized by the interference, so that the lens group is composed of different numbers of the first optical members 30, thereby preventing the problem of regularity. Can be removed

In the illustrated embodiment, the first lens group 32 includes four first optical members 10, and the second lens group 34 includes six first optical members 10.

The height of the second optical member is determined according to the width of the lens group. When the widths of the lens groups on both sides are different, the second optical member is determined by the lens group having a wider width.

The second optical member 40 on the left side of the drawing has a height according to the width of the first lens group 32, and the second optical member 40 in the center is formed by a wider second lens group 34. The height is determined.

7 is a cross-sectional view showing the structure of an optical sheet according to a third embodiment of the present invention.

The third embodiment has the same arrangement as the second embodiment, except that the first optical member 50 and the second optical member 60 are formed of a lenticular lens.

As described above, the first optical member and the second optical member are sufficient as long as they have a cross-sectional shape for collecting light, and a prism, a lenticular lens, an aspherical lens, or the like may be used.

<Examples>

The first optical member is composed of a prism having a pitch of 100 μm and a height of 50 μm,

The width (A) of the lens group is 7.5mm

The second optical member was composed of a prism having a pitch of 0.5 mm and a height H of 1.4 mm (a level of 18% of the width A of the lens group).

Comparative Example

Optical sheet with a prism with a pitch of 50 μm, a height of 50 μm, and a vertex angle of 90 °

The comparative example has a principle that the prism having a triangular cross section in the optical sheet is periodically arranged to change the path of the light emitted at a low angle to a high angle to improve the front brightness.

However, in the comparative example, due to the characteristics of the prism shape, the light emitted at a low angle is not condensed with all the light emitted at a low angle, and this reduces the efficiency of the light.

FIG. 8 is a result chart of simulating the optical characteristics of the comparative example, and FIG. 9 is a result chart of simulating the optical characteristics of the example.

Referring to FIG. 8, it can be seen that the optical sheet using the prism having a uniform height in the comparative example has a very small vertical viewing angle and a large side lobe emitted at a low angle.

Referring to FIG. 9, it can be seen that in the embodiment, by recycling the light emitted from the second lobe to the side lobe, the light emitted to the side lobe is reduced to half compared to FIG. 8 and the central luminance is improved.

FIG. 10 is a result diagram of a simulation of optical characteristics according to the area ratio of the second optical member.

As shown, it can be seen that the side lobe decreases when the ratio of the second optical member to the total area is within 10%. However, when the ratio of the second optical member exceeds 10%, it can be seen that the central luminance decreases, and the side lobe also increases.

The second optical member is for recycling side lobes generated by the first optical member, but the second optical member also generates side lobes. When the ratio of the second optical member is increased to 10% or more, there is more sidelobe increase occurring in the second optical member than reducing the sidelobe of the first optical member, resulting in an increase in the sidelobe as a whole.

Therefore, the area ratio of the second optical member in the total area is preferably in the range of 5 to 10%.

Although the present invention has been described with reference to the illustrated embodiments, it is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible.

Therefore, the true technical protection scope of the present invention will be defined by the claims below.

1 is an exploded perspective view showing the structure of a liquid crystal display device;

2 is a cross-sectional view showing an optical sheet in the form of a conventional lenticular lens,

3 is a graph showing a luminance distribution for each angle of an optical sheet having a prism as an optical member on a surface thereof;

4 is a cross-sectional view showing the structure of an optical sheet according to a first embodiment of the present invention;

5 is a view showing a relationship between a width of a lens group and a height of a second optical member;

6 is a cross-sectional view showing the structure of an optical sheet according to a second embodiment of the present invention;

7 is a cross-sectional view showing the structure of an optical sheet according to a third embodiment of the present invention;

8 is a result of simulating the optical characteristics of the comparative example,

9 is a result chart simulating the optical characteristics of the embodiment;

FIG. 10 is a graph showing simulation results of optical characteristics according to the area ratio of the second optical member. FIG.

Claims (8)

A plate-shaped substrate on which light is incident on the rear surface and exits to the front surface; A lens group in which a plurality of first optical members are continuously arranged on a front surface of the substrate; And An optical sheet including a second optical member disposed on both sides of the lens group, the second optical member having a height in the range of 17 to 57% of the width of the lens group. The method of claim 1, The first optical member is any one of a prism, a lenticular lens, an aspherical lens. The method of claim 1, The second optical member is any one of a prism, a lenticular lens, an aspherical lens. The method of claim 1, The second optical member is an optical sheet, characterized in that formed in an area of 5 to 10% of the total area of the front surface. The method of claim 1, A plurality of lens groups are formed on the front surface, and each lens group has a different width. The method of claim 5, The optical sheet, characterized in that the second optical member disposed between the lens group having a different width has a height in the range of 17 to 57% of the width of the lens group having a wider width. A backlight unit comprising the optical member of claim 1. A liquid crystal display device comprising the backlight unit of claim 7.

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