KR20030055377A - The backlight unit of liquid crystal display - Google Patents

Abstract

PURPOSE: A backlight unit is provided to improve the optical efficiency and to reduce the number of optical components. CONSTITUTION: A light source(31) generates light. A prism light guide plate(35) changes the light from the light source to a backlight unit and concentrates the light. The prism light guide plate is formed by many prisms with projecting faces having mountains and valleys according to at least one concentric circle. Thereby, the number of the prism sheets are reduced. Therefore, the loosed light amount is reduced and the optical efficiency is improved.

Description

Backlight unit of liquid crystal display {TH BACKLIGHT UNIT OF LIQUID CRYSTAL DISPLAY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit of a liquid crystal display device, and more particularly to a backlight unit of a liquid crystal display device which can reduce the number of optical components and the number of processes.

Typically, a liquid crystal display (hereinafter referred to as "LCD") is a plurality of liquid crystal cells arranged in a matrix form and a plurality of control switches for switching the video signal to be supplied to each of these liquid crystal cells The amount of light transmitted from the backlight unit is adjusted by the configured liquid crystal panel to display a desired image on the screen.

Referring to FIG. 1, a conventional backlight unit includes a lamp 1 for generating light, a lamp housing 3 installed to surround the lamp 1, and light incident from the lamp 1 as a planar light source. The light guide plate 5 to be converted, the reflector 7 positioned below the light guide plate 5 to reflect the light traveling toward the lower surface and the side surface of the light guide plate 5 toward the upper surface, and light passing through the light guide plate 5 are diffused. A diffusion sheet 9 and first and second prism sheets 11 and 13 for adjusting a traveling direction of light via the diffusion sheet 9.

The liquid crystal panel is positioned on the backlight unit. The liquid crystal panel includes an upper substrate 21 having a color filter, a common electrode and an upper alignment layer, a lower substrate 17 formed of a thin film transistor array (TFT), a pixel electrode, and a lower alignment layer; It consists of a liquid crystal 19 injected into the internal space between the upper substrate 21 and the lower substrate 17.

The cold cathode fluorescent lamp is mainly used as the lamp 1 of the backlight unit, and the light generated by the lamp 1 is incident on the light guide plate 5 through an incident surface existing on the side of the light guide plate 5. The lamp housing 3 has a reflecting surface on its inner surface to reflect light from the lamp 1 toward the incident surface of the light guide plate 5. The light guide plate 5 has an inclined back surface and an exit surface that is horizontal, and is made such that the incidence surface and the exit surface of the light guide plate 5 form a right angle. The rear side of the light guide plate 5 is provided so that the reflecting plate 7 faces. The light guide plate 5 allows the light incident from the lamp 1 to reach a distance far from the lamp 1. The light guide plate 5 is generally formed of an acrylic resin (PMMA) having high strength and not easily being deformed or broken and having good transmittance. The reflector 7 serves to reduce light loss by reflecting light incident to itself through the back of the light guide plate 5 toward the light guide plate 5. When light from the lamp 1 is incident on the light guide plate 5, the light is reflected at a predetermined inclination angle from the rear surface, which is an inclined surface, and proceeds uniformly toward the exit surface. At this time, the light propagated to the lower surface and the side surface of the light guide plate 5 is reflected by the reflector 7 and proceeds toward the exit surface. Light emitted through the exit surface of the light guide plate 5 is diffused to the entire area by the diffusion sheet 9. On the other hand, when the light incident on the liquid crystal panel is vertical, the light efficiency is increased. To this end, it is preferable to stack two prism sheets so that the traveling angle of the light emitted from the light guide plate 5 is perpendicular to the liquid crystal panel.

The first and second prism sheets 11 and 13 are formed in the form of a plurality of prism bars having hills and valleys. As shown in FIG. 2, the two prism sheets 11 and 13 are arranged such that the two prism array directions are perpendicular to each other. In the first and second prism sheets 11 and 13, the x and y directions of light are directed in the z direction, that is, the direction perpendicular to the liquid crystal panel so that light incident from the light guide plate 5 is incident on the upper liquid crystal panel. It changes the path of light. That is, since each of the two prism sheets 11 and 13 has a prism rod shape, only the light component in one direction may be converted in the z direction. In other words, when the peaks and valleys of the prism are directed in the x direction, the light passing through the first prism sheet 11 enters only the y component of the light perpendicular to the z direction, that is, the liquid crystal panel. . At this time, the optical path of the x component does not change. Similarly, as shown in FIG. 3, when the prism peaks and valleys of the second prism sheet 13 face the y direction, the light passing through the second prism sheet 13 passes through the peaks and valleys of the prism. While being converted in the z direction, it is incident perpendicularly to the liquid crystal panel. At this time, the path of the y component of the incident light does not change.

The light generated from the backlight unit is incident on the liquid crystal panel.

In the liquid crystal panel, the liquid crystal 19 is driven by the voltage difference between the common electrode of the upper substrate 21 and the pixel electrode of the lower substrate 17 to selectively transmit light from the backlight unit to display an image.

Such a backlight unit should achieve lightness and high brightness according to the trend of large screen, light weight and high quality of LCD. However, in the backlight unit, two prism sheets must be used to inject light perpendicularly to the liquid crystal panel. This situation is emerging as a factor that inhibits the weight of the backlight unit.

In order to solve this problem, a light guide plate in which an exit surface is formed into a prism shape has been proposed.

As shown in FIG. 4, instead of the two prism sheets 11 and 13 used in the conventional backlight unit, one prism sheet 23 and an exit surface of the prism-shaped light guide plate 25 having a prism shape are provided.

In the prism-shaped light guide plate 25, when the peaks and valleys of the prism face the x-direction, the light passing through the prism-shaped light guide plate 25 enters only the y component of the light perpendicular to the z-direction, that is, the liquid crystal panel. At this time, the optical path of the x component does not change. That is, in order to deflect the light of the y component, in the prism of the acid and valley in the x direction, the light of the x component is not affected, and only the light of the y component is refracted by the refractive index, so that the optical path is changed in the z direction.

Similarly, when the prism peaks and valleys of the prism-shaped light guide plate 25 are directed in the y direction as shown in FIG. 5, the light passing through the prism-shaped light guide plate 25 is z as the x component of the light passes through the peaks and valleys of the prism. Is converted to the direction and is incident perpendicularly to the liquid crystal panel. At this time, the path of the y component of the incident light does not change.

However, with the trend of lighter and thinner LCDs, there is still an urgent need for optical components that can achieve lighter and thinner backlight units. In the case of using the prism sheet as described above, a lot of light is absorbed and reflected by the prism sheet, and thus the light loss is high. Accordingly, even when the prism-shaped light guide plate is used, there is still light loss.

Accordingly, an object of the present invention is to provide a backlight unit of a liquid crystal display device capable of reducing the number of optical parts and improving light efficiency.

1 is a cross-sectional view showing a backlight unit of a conventional liquid crystal display device.

FIG. 2 is a view showing a prism sheet shown in FIG. 1. FIG.

3 is a view showing an optical path via a prism sheet shown in FIG.

4 is a view showing a prism light guide plate of another conventional backlight unit;

FIG. 5 is a view showing an optical path via the prism light guide plate shown in FIG. 4. FIG.

6 is a cross-sectional view illustrating a backlight unit of a liquid crystal display according to a first exemplary embodiment of the present invention.

FIG. 7 is a view showing a concentric prism exit surface of the prism light guide plate shown in FIG. 6. FIG.

8 is a view showing the principle of the prism light guide plate shown in FIG.

FIG. 9 is a plan view of a prism having one concentric circle shown in FIG. 7; FIG.

10 illustrates a prism having a plurality of concentric circles.

11 shows a prism having concentric circles of a semicircle.

12 is a cross-sectional view illustrating a backlight unit according to a second embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

1, 31, 61: lamp 3, 33, 63: lamp housing

5, 35, 65: LGP 7, 37, 67: Reflector

9, 41, 69: diffusion sheet 11, 13, 23: prism sheet

17, 43: lower substrate 19, 45: liquid crystal

21, 47: upper substrate 25: prism light guide plate

35, 51, 53: Prismatic light guide plate having a concentric prism

71: prism sheet having a concentric prism

In order to achieve the above object, the backlight unit of the liquid crystal display according to the present invention converts the light source for generating light, the light from the light source to a surface light source, and condenses the light, the emission surface is at least one concentric circle Therefore, it characterized in that it comprises a prism light guide plate formed in the form of a plurality of prisms having mountains and valleys.

The exit surface of the prism light guide plate may be formed in a prism shape along a concentric circle of a semicircle.

The backlight unit of the liquid crystal display according to the present invention includes a light source for generating light, a light guide plate for converting light from the light source to a surface light source, and an emission surface along at least one concentric circle so as to be located on the light guide plate to focus light. It is characterized in that it comprises a prism sheet formed in the form of a plurality of prisms having a hill and valleys.

Other objects and features of the present invention other than the above object will become apparent from the description of the embodiments with reference to the accompanying drawings.

6 to 12 will be described with respect to preferred embodiments of the present invention.

Referring to FIG. 6, the backlight unit according to the first embodiment of the present invention includes a prism light guide plate 35 having an emission surface having peaks and valleys in the form of concentric circles.

The backlight unit generates a lamp 31 that generates light, a lamp housing 33 installed to surround the lamp 31, and converts light incident from the lamp 31 into a planar light source, and in the x and y directions. A prism light guide plate 35 for condensing light from the light source, a reflector plate 37 positioned below the prism light guide plate 35 to reflect light traveling toward the bottom and side surfaces of the prism light guide plate 35 toward the top surface, and the prism light guide plate 35 A diffusion sheet 41 for diffusing the light via the?).

The liquid crystal panel is positioned on the backlight unit. The liquid crystal panel includes an upper substrate 47 having a color filter, a common electrode, and an upper alignment layer, a lower substrate 43 formed of a TFT array, a pixel electrode, and a lower alignment layer, and between the upper substrate 47 and the lower substrate 43. It consists of a liquid crystal 45 injected into the inner space of the.

A cold cathode fluorescent lamp is mainly used as the lamp 31 of the backlight unit, and the light generated by the lamp 31 is incident on the prism light guide plate 35 through an incident surface existing on the side of the prism light guide plate 35. The lamp housing 33 has a reflective surface on its inner surface to reflect light from the lamp 31 toward the incident surface of the prism light guide plate 35. The prism light guide plate 35 has a prism-shaped exit surface having an inclined back and a hill and a valley formed in a concentric shape. As shown in FIG. 7, a plurality of exit surfaces of the prism light guide plate 35 are formed along a concentric circle in which a prism having a hill and a valley has one center. In general, as shown in FIG. 8, the circle is changed at the same time as the size of the x component and the y component in the xy plane. Based on this fact, the prism light guide plate 35 having a concentric prism according to the present invention deflects all incident light in any direction in the z direction. In other words, since the prism is formed in a circular shape as shown in FIG. 9, the surface of the prism light guide plate 35 is viewed in the z-direction, i.e., both of the x component and the y component of the light incident on the prism light guide plate 35. Incident in the vertical direction can be made. Accordingly, it is not necessary to use a prism sheet that had to be used conventionally, and the number of optical parts required is reduced by not using the prism sheet. In addition, it is possible to reduce the amount of light lost by using the prism sheet. The prism light guide plate 35 allows the light incident from the lamp 31 to reach a distance far from the lamp 31. The prism light guide plate 35 is generally formed of an acrylic resin (PMMA) having high strength and not easily being deformed or broken and having good transmittance.

The rear surface of the prism light guide plate 35 is provided so that the reflecting plate 37 faces. The reflector 37 serves to reduce light loss by reflecting light incident to itself through the back surface of the prism light guide plate 35 toward the prism light guide plate 35.

When the light from the lamp 31 is incident on the prism light guide plate 35, the light is reflected at a predetermined inclination angle from the rear surface, which is an inclined surface, and uniformly travels toward the exit surface. At this time, the light propagated to the lower surface and the side surface of the prism light guide plate 35 is reflected by the reflector plate 37 to travel toward the exit surface. Light emitted through the exit surface of the prism light guide plate 35 is uniformly diffused to the entire area by the diffusion sheet 41. The light generated from the backlight unit is incident on the liquid crystal panel.

In the liquid crystal panel, the liquid crystal 45 is driven by the voltage difference between the common electrode of the upper substrate 47 and the pixel electrode of the lower substrate 43 to selectively transmit light from the backlight unit to display an image.

The prism light guide plate 35 described above may have a plurality of concentric circles of the prism, as shown in FIGS. 10 and 11, and may have a semi-circular shape.

Referring to FIG. 12, the backlight unit according to the second exemplary embodiment includes a prism sheet 71 having an exit surface having peaks and valleys in the form of concentric circles.

The backlight unit includes a lamp 61 for generating light, a lamp housing 63 installed to surround the lamp 61, a light guide plate 65 for converting light incident from the lamp 61 into a planar light source, A reflection plate 67 positioned below the light guide plate 65 to reflect light traveling toward the bottom and side surfaces of the light guide plate 65 toward the top surface; a diffusion sheet 69 for diffusing light passing through the light guide plate 65; It consists of a prism sheet 71 positioned on the diffusion sheet 69.

A cold cathode fluorescent lamp is mainly used as the lamp 61 of the backlight unit, and light generated by the lamp 61 is incident on the light guide plate 65 through an incident surface existing on the side of the light guide plate 65. The lamp housing 63 has a reflecting surface on its inner surface to reflect light from the lamp 61 toward the incident surface of the light guide plate 65. The light guide plate 65 has an inclined rear surface and a plane exit surface. The light guide plate 65 allows the light incident from the lamp 61 to reach a distance far from the lamp 61. The light guide plate 65 is generally formed of an acrylic resin (PMMA) having high strength and not easily being deformed or broken and having good transmittance.

The rear surface of the prism light guide plate 65 is provided such that the reflecting plate 67 faces. The reflector 67 serves to reduce light loss by reflecting light incident to itself through the back surface of the prism LGP 65 toward the LGP 65.

When the light from the lamp 61 is incident on the light guide plate 65, the light is reflected at a predetermined inclination angle from the rear surface which is the inclined surface and proceeds uniformly toward the exit surface. At this time, the light propagated to the lower surface and the side surface of the light guide plate 65 is reflected by the reflecting plate 67 to proceed toward the exit surface. Light emitted through the exit surface of the light guide plate 65 is uniformly diffused to the entire area by the diffusion sheet 69.

The prism sheet 71 collects the light diffused from the diffusion sheet 69 and serves to vertically incident the liquid crystal panel (not shown). On the exit surface of the prism sheet 71, a plurality of prisms having peaks and valleys shown in FIG. In general, as shown in FIG. 8, the circle is changed at the same time as the size of the x component and the y component in the xy plane. Based on this fact, the prism sheet 71 having the concentric prism according to the present invention deflects all incident light in any direction in the z direction. In other words, as seen from above, the surface of the prism sheet 71 has a prism in a circular shape as shown in FIG. 9, so that both the x component and the y component of the light incident on the prism sheet 71 are z-direction, that is, the liquid crystal panel. Incident in the vertical direction can be made. Accordingly, the number of optical components required for the backlight unit can be reduced by using only one prism sheet without the need of using two prism sheets conventionally. In addition, the amount of light lost can be reduced by reducing the use of two prism sheets. The prism sheet 71 described above may have a plurality of concentric circles of the prism, as shown in FIGS. 10 and 11, and may have a semi-circular shape.

As described above, the backlight unit of the liquid crystal display according to the present invention includes a light guide plate and a prism sheet having a prism-shaped exit surface having peaks and valleys along concentric circles. Accordingly, the backlight unit of the liquid crystal display according to the present invention can reduce the number of optical components, since the number of prism sheets can be reduced as compared with the conventional case. Furthermore. By reducing the number of optical components, not only the cost of optical components can be reduced but also the moiré phenomenon can be prevented. In addition, the backlight unit of the LCD according to the present invention can reduce the amount of light absorbed or reflected by the prism sheet by reducing the number of conventional prism sheets. Accordingly, the light efficiency can be improved.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (4)

A light source for generating light, And a prism light guide plate for converting light from the light source into a surface light source and condensing the light, and having an exit surface formed into a plurality of prisms having mountains and valleys along at least one concentric circle. Backlight unit. The method of claim 1, And a light emitting surface of the prism light guide plate is formed in a prism shape along a concentric circle of a semicircle. A light source for generating light, A light guide plate for converting light from the light source into a surface light source; And a prism sheet having an exit surface in the form of a plurality of prisms having peaks and valleys along at least one concentric circle so as to focus light on the light guide plate. The method of claim 3, wherein And a light emitting surface of the prism sheet is formed in a prism shape along a concentric circle of a semicircle.