Patent Application
20120075326
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-215008, filed on Sep. 27, 2010; the entire contents of which are incorporated herein by reference.
The present invention is related to a backlight device and a liquid crystal display device.
Recently, local dimming (area control) has been employed in liquid crystal display devices, in which brightness of a display screen is locally dimmed in accordance with brightness information of an image. For example, suppressing brightness of a portion, where a dark image is displayed, may improve contrast in the display screen and reduce power consumption.
Local dimming is effectively realized by using a direct type backlight, in which a plurality of light emitting diodes (LED) are arranged in a two-dimensional manner corresponding to the display screen and the LED is easily controlled to be locally turned on. On the other hand, a sidelight type backlight is considered not to be suitable for the local dimming, where thinner device and uniform light emission are required. In the sidelight type backlight, light sources are arranged on the side face of a light guide plate and the light incident into the light guide plate propagates not only in the optical axis direction but also in an angular direction. Therefore, it is difficult for the sidelight type backlight to control brightness of a desired light emission region.
Japanese Unexamined Patent Application Publication No. 2008-117730 describes a sidelight type planar light-source device in which two guide light plates having different light emission regions are combined in order to suppress color unevenness on the display screen. However, this device does not have a configuration intended for local dimming in the display screen.
In the liquid crystal display device provided with a sidelight type back light, if a bright image is to be displayed at the center of the screen and a dark image is displayed in the periphery, for example, a dark image in the periphery may be displayed by throttling the aperture ratio of the liquid crystal. However, contrast cannot be improved better than the limit of the throttle value of the liquid crystal, and power consumption cannot be also reduced in this method. Thus, it is demanded for a sidelight type backlight device with thinner thickness to effectively execute the local dimming.
According to an embodiment, a backlight device includes a plurality of light guide plates, a plurality of light sources and a light-source substrate. The light guide plates overlap each other with a same light output direction, each of the light guide plates includes a plurality of stripe-shaped projections aligned on a light output face and a light output pattern making a part of the light output face emit light at relatively high brightness. Each of the light sources emits light incident into any one of the light guide plates and propagating in an extending direction of the stripe-shaped projections. The light-source substrate includes a plurality of interconnections, a turning-on signal is selectively supplied via the interconnections to at least one of light source groups, and each of the light source groups includes at least one of the light sources. At least one part of a light emission face, including the light output faces overlapped on plan view from the light output direction, emits light output from the light source group receiving the turning-on signal.
Embodiments of the present invention will be described below by referring to the attached drawings. The same portions in the drawings are given the same reference numerals, for which detailed description will be omitted as appropriate, and different portions will be described.
The liquid crystal display device 100 is provided with a liquid crystal panel 110 and a sidelight type backlight 120. In
The liquid crystal display device 100 is provided, for example, with a signal conversion portion 50 that converts an image signal, input from the outside, into a control signal of the liquid crystal panel 110 and a dimming control portion 70 that extracts brightness information from the image signal. The liquid crystal panel 110 is driven by the control signal output from the signal conversion portion 50 and displays an image on a display screen 10 thereof. The dimming control portion 70 outputs a brightness signal that drives the backlight 120.
As illustrated in
In the backlight 120 according to the embodiment, the light sources 3 are grouped into a plurality of light-source groups. Each of the light-source group corresponds to any one of a plurality of light emission regions 20a in the light emission face 20. The light sources 3 may be individually turned on or turned on by each light-source group that includes at least one or more light sources 3. As a result, turning-off and turning-on can be controlled in each of the light emission regions 20a. Moreover, it is possible to control the brightness in each of the light emission region 20a by controlling light emission intensity of the light source 3.
On the other hand, the display screen 10 of the liquid crystal panel 110 arranged overlapping the backlight 120 includes a plurality of dimming regions 10a corresponding to each of the light emission regions 20a of the backlight 120. The dimming region 10a is capable of individual dimming by changing the brightness of the light emission region 20a. As a result, the contrast of the image in the display screen 10 can be improved beyond the limit of throttle of the liquid crystal panel. Also, in the light emission face 20 of the backlight 120, power consumption can be reduced, for example, by turning off the light emission region 20a corresponding to a dark part of the image or by controlling it to low brightness.
The dimming region 10a in the display screen 10 of the liquid crystal panel 110 is not a region obtained by physically dividing the display screen 10 but is defined as a region illuminated by each light emission region 20a of the backlight 120.
The backlight 120 is, as will be described later, provided with two light guide plates 12 and 13, which constitute a rectangular light emission face 20. The light guide plates 12 and 13 are arranged overlapping each other with the light radiation directions (Z directions) matched with each other. The light emission face 20 illustrated in
The backlight 120 is provided with the light-source substrates 2 arranged along two sides in the Y direction of the light emission face 20. A plurality of the light sources 3 are mounted and arranged on the light-source substrates 2. Moreover, the backlight 120 includes a turning-on circuit 4 that turns on the light sources 3 through interconnections included in the light-source substrate 2. A driving circuit 90 may also be included, which supplies a turning-on signal to the turning-on circuit 4. The turning-on circuit 4 selectively supplies a turning-on signal via the interconnections to at least one of light source groups, which include at least one of the light sources 3. Then, the light emission regions 20a emit light from the light sources 3 including in the light source group which receive the turning-on signal. Thereby, the turning-on/off control is performed in each of the light emission regions 20a.
The light source 3 is an LED, for example, and is controllably turned on by the turning-on signal sent to the turning-on circuit 4 from the driving circuit 90. The turning-on circuit 4 may supply power to the individual light sources 3 through a interconnection provided on the light-source substrate 2, for example, so as to turn them on. Then, the turning-on circuit 4 selects the light source 3 to be turned on in accordance with the turning-on signal of the driving circuit 90 and controls turning-on/turning-off through ON/OFF signal control. Moreover, it may be so configured that an electric current flowing through the LED is changed so as to change light emission intensity.
Subsequently, by referring to
The light guide plates 12 and 13 may be made from transparent resins such as polymethylmethacrylate resin (PMMA) and cycloolefinpolymer resin (COP), polycarbonate resin (PC) and the like or glass, for example.
Moreover, light output patterns 15 are provided on a back face 12b of the light guide plate 12 and a back face 13b of the light guide plate 13. The light output pattern 15 changes the light propagation direction along the light output faces 12a and 13a to the direction of the display screen 10 (Z direction). The light output pattern 15 is provided on a part of the back faces of the light guide plates 12 and 13, which becomes a high brightness region where light is emitted with relatively high brightness.
The light output patterns 15 can be formed by using printing method, laser processing and the like, for example. The pattern can be provided in the shape of dots, grained pattern, full-reflection/refraction pattern and the like.
The light output patterns 15 are not limited to form on the back-face sides of the light guide plates 12 and 13. It may be possible to form on the light emission face sides.
The light guide plates 12 and 13 are contained in a tray-shaped back frame 21 having an opening 23 on the upper face in the Z direction. The light output face 12a of the light guide plate 12 and the light output face 13a of the light guide plate 13 are arranged in the direction of the opening 23 (Z direction) with the back-face sides thereof directed to a bottom face 21a of the back frame 21. The light-source substrate 2 provided with the light sources 3 is attached on a side face 21b of the back frame 21.
As indicated by arrows in
The light sources 3a and 3b can be arranged such that when the light emitted from the light sources 3a and 3b are made to enter the respective side faces of the light guide plates 12 and 13, for example, the emitted light enters the center of the width in the thickness direction (Z direction) of the light guide plates.
As illustrated in
In the staggered arrangement illustrated in
In the backlight 120 according to the embodiment, as illustrated in
As illustrated in
Then, as illustrated in
The light-source substrate 2 may include a plurality of the interconnections, for example. The turning-on circuit 4 may also be provided on the light-source substrate 2 in addition to the light sources 3a and 3b.
The opening side of the back frame 21 is covered by a front frame 22, and the light guide plates 12 and 13 are fixed to the inside of the back frame 21.
A reflection sheet 16 is arranged between the back face 13b of the light guide plate 13 and the bottom face 21a of the back frame 21. Moreover, a reflection sheet 17 is arranged also between the light guide plate 12 and a frame 22a on the side of an opening 23 of the front frame 22.
By means of the reflection sheet 16, the light leaking to the back face side of the light guide plate 13 is reflected to the direction of the opening 23, while by means of the reflection sheet 17, the light not entering the light guide plates 12 and 13 but leaking upward is returned to the light guide plates 12 and 13 so that brightness in the light output faces 12a and 13a and flatness in brightness distribution are improved.
Ann optical sheet 19 is arranged on the light output face 12a of the light guide plate 12. With regard to the optical sheet 19, a plurality of the optical sheets such as a diffusion sheet, a polarization plate and the like may be provided in combination in order to adjust brightness, a view angle, and polarization to a desired state in the display screen 10 of the liquid crystal panel 110.
The backlight 130 has a point in common with the backlight 120 illustrated in
On the other hand, the backlight 130 according to the variation is different from the backlight 120 in a point that a reflection sheet 18, which is a reflection member that works as a shield, is further provided between the light source 3a arranged on the light guide plate 12 and the light source 3b arranged on the light guide plate 13.
As illustrated in
Subsequently, by referring to
As illustrated in
The light emitted from the light sources 3a (See
On the other hand, as illustrated in
As illustrated in
Moreover, on the boundary between the high brightness region 12c and the high brightness region 13c, an overlapping region W is formed where the periphery portion of the high brightness region 12c and the periphery portion of the high brightness region 13c overlap each other. As a result, a dark line or a bright line in the boundary portion is suppressed, which might occur if the overlapping region W is not provided, and an image quality displayed on the boundary portion can be improved.
The image quality can be also improved by gradually changing the pattern depth, density or the like of the light output pattern 15 from the center part side toward the ends in the periphery of the respective high brightness regions.
In the backlights 120 and 130 according to the embodiment, a plurality of stripe-shaped projections 25 can be provided on the light emission faces of the light guide pates 12 and 13. The projections 25 are formed so as to extend along the propagation direction of the light emitted from the light sources 3.
For example, as illustrated in
As illustrated in
In the light emission pattern illustrated in
On the other hand, in the example illustrated in
In an example illustrated in
On the other hand, if the apex angle θ is made smaller than 90°, a pattern can be realized that the width in the Y direction is smaller than that in the light emission pattern illustrated in
By providing the stripe-shaped projections on the light output face of the light guide plate as above, the light emission pattern of the light emitted from the light sources 3 can be changed. That is, the light emission pattern can be adjusted in accordance with the position and size of the light emission region in the light emission face. By combining the incident position of the light which can be changed by selection of the light sources 3 and the light output pattern provided selectively on the light guide plate, for example, light emission of an arbitrary region in the light emission face becomes possible. As a result, local dimming can be realized using the sidelight type backlight.
Subsequently, by referring to
As illustrated in
As illustrated in
Light sources 31a to 38a on the left side face of the light emission face 20 are arranged on the upper side of a light-source substrate 2L and light sources 31b to 38b are arranged on the lower side, respectively, and emit light toward the light guide plates 12 and 13. The light output pattern 15 corresponding to the light emission regions L1 to L4 are provided on the back face 13b of the light guide plate 13, while the light output pattern 15 corresponding to the light emission regions L5 to L8 are provided on the back face 12b of the light guide plate 12.
On the other hand, the light sources 41a to 48a on the right side face of the light emission face are arranged on the upper side of a light-source substrate 2R and the light sources 41b to 48b are arranged on the lower side, respectively, and emit light toward the light guide plates 12 and 13. The light output pattern 15 corresponding to the light emission regions R1 to R4 is provided on the back face 13b of the light guide plate 13, while the light output pattern 15 corresponding to the light emission regions R5 to R8 is provided on the back face 12b of the light guide plate 12.
For example, as illustrated in
Also, in order to selectively control light emission in the light emission region L6, as illustrated in
As described above, in the backlight 120, by individually turning on the light source groups arranged on the both sides of the light emission face 20, a desired region can be made to emit light.
At this time, the stripe-shaped projections 25a are adjusted on the surface of the light guide plate 12, in order to suppress the light emitted from the light sources 33a and 34a in the light emission region R6. That is, the projections 25a provided on the surface of the light guide plate 12 are provided so that the emitted light from one light source group of the light sources 33a and 34a propagates beyond the light emission region L2 and sufficient brightness can be obtained in the light emission region L6. Furthermore, the values of the apex angle θ and d/h are adjusted, for example, so that the bright region does not extend to the light emission region R6.
As described above, in the backlight 120 according to the embodiment, the 16 light emission regions (L1 to L8 and R1 to R8) can be individually made to emit light by turning on the corresponding light sources in the 16 light sources (31 to 38 and 41 to 48).
When the light emission region L1 emits light as illustrated in
As illustrated in
When the light emission region L5 emits light as illustrated in
As illustrated in
In the example illustrated in
In an example illustrated in
The band-shaped light mission illustrated in
When the liquid crystal display device 100 is to be used as a monitor for a TV or a computer, a uniformity ratio is required to be 0.5 or more. For example, the uniformity ratio of brightness in the display screen can be expressed as follows:
Uniformity ratio=1−(maximum brightness−minimum brightness)/maximum brightness
The uniformity ratio is 0.5 or more in the brightness distribution of the light emission face 20 illustrated in
As described above, in the backlight 120 according to the embodiment, the 16 light emission regions included in the light emission face 20 can be individually made to emit light by individually turning on the light sources arranged on the two sides of the light emission face 20. Therefore, the local dimming can be performed in the liquid crystal display device 100 using the backlight 120, and may realizes reduction of power consumption and improvement of light contrast.
In the example in
As illustrated in
In the embodiment, the light output pattern 15 is provided at the center of the back face 12b of the light guide plate 12 arranged on the uppermost stage, and the light output pattern 15 is provided on the both ends of the back face 14b of the light guide plate 14 arranged on the lowermost stage. On the back face of the light guide plate 13 arranged between the light guide plate 12 and the light guide plate 14, the light output pattern 15 is provided between the center and the ends. As a result, they can correspond to the six light emission regions divided in the X direction.
On the other hand, the light sources 3 are provided in alignment of three stages in the Z direction in order to make the emitted light incident to each of the light guide plates 12, 13, and 14. For example, assuming that two light sources are arranged in one light emission region, 24 light sources 3a, 3b, and 3c are arranged on one side in the Y direction divided into four parts.
By means of the above configuration, it is possible to configure the backlight 140 including 24 light emission regions. In order to increase the number of light emission regions included in the light emission face, it is only necessary to increase the number of light guide plates and the number of light sources arranged on the side face of the light guide plate and to segmentalize the light emission face.
Moreover, fine dimming of each light emission region can be performed by changing the brightness of the light sources 3, in addition to the pattern of turning-on and non-turning-on. For example, if the light sources 3 are LED, by changing a current flowing through the LED, the brightness can be continuously changed. As a result, local dimming can be performed, which loyally reflects brightness information of the input image signal.
The light sources 51 to 66 are arranged in vertical two stages attached with suffixes a and b in a light-source substrate 2U arranged on the upper side and emit light incident to the light guide plates 12 and 13, respectively. The light sources 71 to 86 are arranged in vertical two stages attached with suffixes a and b in a light-source substrate 2L arranged on the lower side.
As illustrated in
For example, the light output pattern 15 is provided on the back face 13b of the light guide plate 13 corresponding to the light emission regions U1 to U4 and L1 to L4. On the other hand, the light output pattern 15 is also provided on the back face 12b of the light guide plate 12 corresponding to the light emission regions U5 to U8 and L5 to L8 (See
As illustrated in
As described above, the light sources 3 can be arranged along the long sides of the rectangular light guide plates 12 and 13.
In the liquid crystal display device and the backlight thereof described in the first to third embodiments above, the plurality of dimming regions are included in the display screen of the liquid crystal display device, and the respective light output faces of the plurality of light guide plates provided in the backlight have a light emission region corresponding to at least any one of the dimming regions of the display screen. Each of the dimming regions corresponds to at least any one of the light emission regions included in the light guide plates.
By providing the light emission regions, which divide the whole light emission face of the backlight into plural parts, the whole face of the display screen can be covered by the plurality of corresponding dimming regions.
Each of the light emission regions corresponds to any of the plurality of light sources arranged on the side face of the light guide plate and emits light by turning on the light source. As a result, turning-on of the individual light sources can be controlled and local dimming which locally dims the display screen can be performed in the sidelight type backlight. Then, a liquid crystal display device can be realized with low power consumption and improved contrast.
The present invention has been described above by referring to the first to third embodiments according to the present invention, but the present invention is not limited by these embodiments. For example, embodiments having the same technical idea as the present invention such as design changes that can be made by those skilled in the art on the basis of the technical standards at the time of filing, change of the material and the like are also included in the technical scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-215008 | Sep 2010 | JP | national |
