JP2009224030A - Led backlight unit, and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of difficulty of partial light control only for an optional area, not uniformly for all areas, of a display screen, in an LED backlight unit which is illuminated from behind of a liquid crystal display panel where light-emitting diodes are arranged on edges of a light guide plate. <P>SOLUTION: A plurality of light emitting diode (LED) elements are arranged on the edges of the light guide plate so as one pair or more of them to be set mutually orthogonal in their arrangement directions, wherein incident optical axes from the light sources on the respective edges cross mutually orthogonally within the light guide plate. The luminance control of an area where optional optical axes cross mutually orthogonally can be carried out by light control or on/off control of the LEDs as light sources whose optical axes cross mutually orthogonally. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an LED backlight unit that illuminates a liquid crystal display panel or the like from behind and a liquid crystal display device using the same, and more particularly to light control of an LED backlight unit using a light guide plate.

Since the liquid crystal display panel does not emit light by itself, in order to obtain a brighter display, the panel is illuminated from the back of the liquid crystal display panel separately from the ambient light. A backlight unit is used for this illumination. The first method includes light from, for example, an LED or a fluorescent lamp from the upper and lower or left and right edges of a light guide plate having a property of uniformly diffusing light. Is introduced into the light guide plate. A liquid crystal display panel is disposed on the front surface of the light guide plate, and a reflective plate is disposed on the back surface so that the liquid crystal display panel is uniformly illuminated.
In the second method, a direct type without using a light guide plate and arranging a large number of LEDs on the back side of the liquid crystal display panel in a matrix or a large number of fluorescent lamps so that the liquid crystal display panel is uniformly illuminated. There is.

In the second method, since there is a light source directly under the back of the liquid crystal display panel, it is possible to easily adjust light in any part of the liquid crystal display panel, so the luminance dynamic range is wide, but uneven luminance is likely to occur. If we try to suppress it, it is necessary to increase the number of light sources or increase the distance from the liquid crystal panel, and there are problems such as an increase in cost due to the increase in the number of LEDs and an increase in the thickness of the entire display device. Applications are limited to television and the like.
The LED backlight using the light guide plate of the first method has a small number of LEDs and is low in cost, but it cannot adjust light in an arbitrary part of the liquid crystal display panel.

9 and 10 are diagrams showing a schematic structure of a conventional LED backlight unit using a light guide plate used in a liquid crystal display device. In particular, FIG. 9 is a front view thereof, and FIG. 10 is a side view thereof. In these drawings, 2 is a light guide plate and 8 is an LED element. The LED element 8 is mounted on, for example, a flexible printed board 7 ′ and fixed to the upper and lower edge portions of the light guide plate 2.

In the LED backlight unit having such a structure, the respective LED elements 8 that are point light sources are arranged at equal intervals so as to face each other vertically with the light guide plate 2 interposed therebetween. A dotted arrow in FIG. 1 indicates an optical axis of light incident on the light guide plate 2 from each LED 8. The light incident on the light guide plate is uniformly diffused over the entire panel surface to constitute a planar light source. By disposing such an LED backlight unit on the back surface of the transmissive liquid crystal display panel, a backlight liquid crystal display device is configured.
JP 2004-79488 A

In the conventional LED backlight unit using the light guide plate shown in FIGS. 9 and 10 above, the entire liquid crystal display panel can be dimmed. However, for the dimming of any part of the liquid crystal display panel, the LED When part of the light is dimmed, the entire optical axis of the dimmed LED is dimmed, and a strip-shaped dimming part is formed on the liquid crystal display panel. . As a result, it is not possible to adjust the brightness in an area on an arbitrary part of the liquid crystal display panel by an external signal such as a video signal. It became a thing.

The present invention has been made for the purpose of solving the above-mentioned drawbacks of a conventional backlight unit using a light guide plate using LED elements, and the luminance of an arbitrary partial area of the LED backlight unit is reduced. The object of the present invention is to obtain an LED backlight unit that can be adjusted by an external signal such as a video signal.

In order to solve the above problems, an LED backlight unit according to the present invention includes a light guide plate that uniformly emits light incident from a light incident surface provided at an edge, and light incident on the light incident surface of the light guide plate. The first light source has a plurality of LED elements arranged along one longitudinal direction of at least one set of two orthogonal edges, and The second light source has a plurality of LEDs along the other longitudinal direction of the two orthogonal edges and so that an optical axis in the light guide plate is orthogonal to an optical axis of light incident from the first light source. The element is arranged.

The dimming of the LED is performed by adjusting the brightness of the area where the optical axes intersect by turning on / off each LED of the light source whose optical axes are orthogonal based on the video signal. The brightness of a part of the area can be adjusted.

The dimming of the LED adjusts the brightness of the area where the optical axes intersect by adjusting the luminance of the area where the optical axes intersect by increasing or decreasing the current flowing through each LED of the light source whose optical axis is orthogonal based on the video signal. The brightness of an arbitrary partial area can be adjusted.
Therefore, in a liquid crystal display device provided with such an LED backlight unit, the luminance dynamic range is widened, and display with high display quality can be performed.

In addition, in the LED backlight unit configured to turn on / off or current control a part of the LEDs arranged on the top, bottom, left, and right of the light guide plate, the luminance increases because the light source is input from the top, bottom, left, and right. In a liquid crystal display device provided with such an LED backlight unit, the brightness of the screen can be adjusted by adjusting the screen brightness in the area where the light inside the liquid crystal intersects based on the video signal. High quality display suitable for human vision can be performed. In addition, when the LED is placed at a position that is shifted by half of the mounting interval of the upper and lower LEDs or the left and right LEDs, the luminance unevenness at the time of full lighting is reduced, and the luminance of an arbitrary partial area of the LED backlight unit is further reduced. Can be adjusted.

In the LED backlight unit of the present invention, the light guide plate that uniformly emits the light incident from the light incident surface provided at the edge of the orthogonal light guide plate, and the first light that enters the light incident surface of the light guide plate. A second light source, wherein the first light source has a plurality of LED elements arranged along one longitudinal direction of at least one set of two orthogonal edges, and the second light source The light source has a plurality of LED elements arranged along the other longitudinal direction of the two orthogonal edges and so that the optical axis in the light guide plate is orthogonal to the optical axis of the light incident from the first light source. It is configured to do.
By dimming the LED elements provided at two orthogonal edges of the unit, the luminance of the area where the optical axes from the LED elements intersect in the light guide plate can be dimmed. Therefore, in a liquid crystal display device provided with such an LED backlight unit, the luminance dynamic range is widened, so that higher quality display can be performed.

Hereinafter, the present invention will be described with reference to embodiments thereof. In the following drawings, the same reference numerals as those in FIGS. 9 and 10 indicate the same or similar components, and therefore, the redundant description thereof will not be given.

FIG. 1 is a structural diagram showing the structure of a liquid crystal display device using an LED backlight unit according to the first embodiment of the present invention, and FIG. 2 is a diagram for explaining the operation of the present invention. FIG. 3 is an explanatory view showing a liquid crystal screen of a liquid crystal display device using the LED backlight unit of FIG. In the present embodiment, as shown in the figure, LED chips 8 are mounted at equal intervals on a substrate 6 composed of a printed circuit board or the like on the left edge and a lower edge of the light guide plate, and on the substrate 7. Are arranged so that their optical axes are orthogonal to each other.
Since all the LEDs emit light uniformly, there is no dimming part in any part on the liquid crystal screen.
FIG. 4 is a diagram showing a light distribution during dimming of the liquid crystal display device using the LED backlight unit according to the first embodiment of the present invention, and the optical axis of the dimming LED is indicated by a broken line. It is represented by FIG. 5 is an explanatory diagram showing a liquid crystal screen of a liquid crystal display device using the LED backlight unit of FIG.

As shown in FIG. 4 and FIG. 5, in this embodiment, the area where the left light edge of the light guide plate and the light axis where light is dimmed at the lower edge is the light control portion. On the liquid crystal screen, the portion expressed by the net is dimmed.
When one of the LEDs arranged on the left or lower edge of the light guide plate is dimmed, the brightness of the LCD screen is determined by the brightness on the bright side of the left or lower edge. For this reason, a strip-shaped dimming portion due to the dimming LED does not occur, and only the portion where the optical axes of the dimming LEDs of the left edge and the lower edge intersect is dimmed.

6, 7 and 8 are structural diagrams of an LED backlight unit according to the second embodiment of the present invention. In the second embodiment, LED chips are mounted at equal intervals on the boards 6 and 7 each composed of a printed circuit board at the four edges of the light guide plate, and the LEDs on the upper and lower edges of the light guide plate Edge LEDs are arranged so that their optical axes are orthogonal to each other.

In the second embodiment according to FIGS. 6, 7, and 8, since the first embodiment irradiates light from the left edge and the lower edge of the light guide plate, the light is irradiated from the top, bottom, left, and right. The brightness is doubled, and the shortage of brightness, which is a drawback of the light guide plate, can be significantly improved in combination with the recent increase in brightness of LEDs. In the dimming, the LEDs facing each other are dimmed simultaneously. Thereby, the brightness | luminance of the part which the optical axis of LED which light-controls the 1st and 2nd light source cross | intersects can be adjusted.

Further, the LED arrangement of the left and right light sources in the second embodiment is offset by ½ pitch of the LED interval, and similarly, the LED arrangement of the upper and lower light sources is offset by ½ pitch of the LED interval. The luminance unevenness can be reduced and the dimming area is increased, so that the luminance with the surrounding area where light is not dimmed changes smoothly.

Both the first embodiment and the second embodiment are appropriately selected according to the structure of the display panel to be configured.

The block diagram of the LED backlight unit which concerns on one Embodiment of this invention. Operation | movement explanatory drawing of the LED backlight unit which concerns on one Embodiment of this invention. The liquid crystal screen using the LED backlight unit which concerns on one Embodiment of this invention. Operation | movement explanatory drawing of the LED backlight unit which concerns on one Embodiment of this invention. (Partial dimming) The liquid crystal screen using the LED backlight unit which concerns on one Embodiment of this invention. (Partial dimming) The block diagram of the LED backlight unit which concerns on other embodiment of this invention. Operation | movement explanatory drawing of the LED backlight unit which concerns on other embodiment of this invention. (Partial dimming) The liquid crystal screen using the LED backlight unit which concerns on other embodiment of this invention. (Partial dimming) The front view which shows schematic structure of the conventional LED backlight unit. The side view of the LED backlight unit of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Housing 2 ... Light guide plate 3 ... Diffusion film 4 ... Optical film 5 ... Liquid crystal 6, 6 ', 7, 7' ... Printed circuit board 8 ... LED element 51 ... Low brightness areas

Claims (5)

In an LED backlight unit comprising a light guide plate that uniformizes and emits light incident from a light incident surface provided at an edge, and first and second light sources that make light incident on the light incident surface of the light guide plate. The first light source has a plurality of LED elements arranged along one longitudinal direction of at least one pair of two orthogonal edges, and the second light source has the two orthogonal edges. And a plurality of LED elements arranged so that the optical axis in the light guide plate is orthogonal to the optical axis of the light incident from the first light source, and orthogonal to the optical axis. An LED backlight unit characterized by dimming the luminance of an area where the optical axes intersect by dimming the LED of the light source. The dimming of the LEDs is characterized in that the brightness of an area where the optical axes intersect is adjusted by turning on / off each LED of the light source whose optical axes are orthogonal to each other based on the video signal. LED backlight unit of description. 2. The dimming of the LED adjusts the luminance of the area where the optical axes intersect by increasing or decreasing the current flowing through each LED of the light source whose optical axes are orthogonal to each other based on the video signal. LED backlight unit described in 1. Based on the video signal, adjust the screen brightness of the area where the light intersects by adjusting the brightness of each of the LEDs arranged on the top, bottom, left and right of the light guide plate installed on the back of the liquid crystal. The LED backlight unit according to claim 1. 5. A liquid crystal display device comprising the LED backlight unit according to claim 1 provided on a back surface of a transmissive liquid crystal panel.

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