Backlight for dual-screen liquid crystal display device, and dual-screen liquid crystal display device
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- JAPAN DISPLAY INC
- Filing Date
- 2026-01-27
- Publication Date
- 2026-07-30
Smart Images
Figure JP2026002532_30072026_PF_FP_ABST
Abstract
Description
Backlight for Dual-Screen Liquid Crystal Display Device and Dual-Screen Liquid Crystal Display Device
[0001] Embodiments of the present disclosure relate to a backlight for a dual-screen liquid crystal display device and a dual-screen liquid crystal display device.
[0002] In recent years, development of dual-screen liquid crystal display devices that simultaneously display a plurality of different images depending on the viewing direction on the same display screen has been actively carried out. Dual-screen liquid crystal display devices are useful, for example, as in-vehicle displays. An in-vehicle dual-screen liquid crystal display device can display a navigation image on the driver's seat side and an entertainment image on the passenger seat side. However, in such a dual-screen liquid crystal display device designed in this way, there is a problem that the appearance is poor because a superimposed image in which two different images overlap is observed from the center front of the display screen.
[0003] Therefore, in order to hide the superimposed image, it is known to use a two-way emission light source as the backlight of the liquid crystal display device. The two-way emission light source adjusts the luminance directivity of the light emitted from the liquid crystal display device and aligns the luminance peaks in the left and right directions. As a result, the luminance in the center front direction is suppressed, and the superimposed image can be hidden. At the same time, a clearer image is observed from the left and right directions than when using a normal backlight. However, while the two-way emission light source is beneficial when displaying two different images, it has a demerit that images are displayed only in limited directions.
[0004] When the dual-screen liquid crystal display device displays the same image in different directions, there is no difference between the image displayed in the left and right directions and the superimposed image. Therefore, there is no need to hide the superimposed image. In such a case, in a liquid crystal display device using a normal light source, an image can be observed from the center front as well. However, in a liquid crystal display device using a two-way emission light source, since the luminance with respect to the center front is suppressed, an image can be observed only from the left and right directions. Therefore, there is a problem that the position of the observer is unnecessarily restricted.
[0005] Japanese Patent Application Laid-Open No. 特開2009-86622
[0006] As mentioned above, there is room for various improvements in dual-screen liquid crystal displays. Therefore, one of the objectives of this disclosure is to improve the display quality of dual-screen liquid crystal displays.
[0007] A backlight for a dual-screen liquid crystal display according to one embodiment includes a first light guide plate, a second light guide plate facing the first light guide plate, a first light source that irradiates light onto the first light guide plate, a second light source that irradiates light onto the second light guide plate, and a first prism sheet. The first prism sheet is located between the first light guide plate and the second light guide plate. The first prism sheet also has a plurality of convex first prisms directed toward the second light guide plate.
[0008] A dual-screen liquid crystal display device according to one embodiment comprises a backlight for the dual-screen liquid crystal display device, an image display panel, and a controller for controlling the backlight for the liquid crystal display device and the image display panel. The image display panel has a plurality of pixels arranged in a matrix and a viewing barrier that overlaps the plurality of pixels. The plurality of pixels include a plurality of first pixels representing a first image and a plurality of second pixels representing a second image. The controller is configured to switch between a dual-screen display mode in which the first image and the second image are different from each other, and a single-screen display mode in which the first image and the second image are the same.
[0009] Figure 1 schematically shows a display device according to the first embodiment. Figure 2 shows an image displayed by the display device according to the first embodiment in a specific direction. Figure 3A schematically shows the configuration of the image display panel and backlight according to the first embodiment. Figure 3B schematically shows the configuration of the image display panel and backlight according to the first embodiment. Figure 4 schematically shows the configuration of the backlight according to the first embodiment. Figure 5 schematically shows the configuration of the first prism sheet and the second prism sheet of the backlight according to the first embodiment. Figure 6A schematically shows the light emitted from the second light guide plate. Figure 6B schematically shows the light emitted from the second light guide plate and after passing through the first prism sheet. Figure 7A schematically shows the light emitted from the second light guide plate. Figure 7B schematically shows the light emitted from the second light guide plate and after passing through the second prism sheet. Figure 8A schematically shows the brightness directivity of the light emitted from the first light guide plate of the backlight according to the first embodiment. Figure 8B schematically shows the luminance directivity of light emitted from the first light guide plate of the backlight according to the first embodiment. Figure 9A schematically shows the luminance directivity of light emitted from the second light guide plate of the backlight according to the first embodiment. Figure 9B schematically shows the luminance directivity of light emitted from the second light guide plate of the backlight according to the first embodiment. Figure 10 schematically shows an example of driving the image display panel and backlight according to the first embodiment in a dual-screen display mode. Figure 11 schematically shows an example of driving the image display panel and backlight according to the first embodiment in a dual-screen display mode. Figure 12 schematically shows an example of driving the image display panel and backlight according to the first embodiment in a single-screen display mode. Figure 13 schematically shows an example of driving the image display panel and backlight according to the first embodiment in a single-screen display mode. Figure 14 schematically shows another example of driving the image display panel and backlight according to the first embodiment in a single-screen display mode. Figure 15 schematically shows a display device according to Comparative Example 1. Figure 16A schematically shows a display device according to Comparative Example 2. Figure 16B schematically shows a display device according to Comparative Example 2. Figure 17 schematically shows the configuration of a display device according to the second embodiment. Figure 18 schematically shows the configuration of a display device according to the third embodiment.
[0010] Several embodiments will be described with reference to the drawings. The disclosure is merely an example, and any modifications that a person skilled in the art could easily conceive of while maintaining the spirit of the disclosure are naturally included within the scope of this disclosure.
[0011] Furthermore, in order to clarify the explanation, the drawings may schematically represent the width, thickness, shape, etc., of each part compared to the actual embodiment, but these are merely examples and do not limit the interpretation of this disclosure. In addition, in this specification and each drawing, the same reference numerals are used for components that perform the same or similar functions as those described above with respect to previously shown drawings, and redundant detailed explanations may be omitted as appropriate.
[0012] Furthermore, the X, Y, and Z axes are indicated in the drawings as needed to facilitate understanding. The direction along the X axis is referred to as the X direction, the direction along the Y axis is referred to as the Y direction, and the direction along the Z axis is referred to as the Z direction. Viewing various elements parallel to the Z direction is called a plan view. In one example, the X, Y, and Z directions are orthogonal to each other, but they may intersect at angles other than 90 degrees.
[0013] In the following explanation, "overlapping" includes not only cases where another element overlaps the target element from the Z direction, but also cases where it overlaps from the opposite direction. Furthermore, "overlapping" includes not only cases where the target elements are directly touching each other, but also cases where there is a gap between the target elements, or where another element is located between the target elements.
[0014] One embodiment of the display device is a dual-screen liquid crystal display device equipped with a backlight for a dual-screen liquid crystal display device. The display device according to this embodiment can be mounted on an automobile or the like, but its use is not limited thereto. The dual-screen liquid crystal display device can display two different images simultaneously.
[0015] In one embodiment, a dual-screen liquid crystal display device hides overlapping images observed from the center front in dual-screen display mode, and displays a clear image in all directions in single-screen display mode. Single-screen display mode refers to a mode in which the dual-screen liquid crystal display device displays the same image in all directions. Dual-screen display mode refers to a mode in which the dual-screen liquid crystal display device displays two different images in two directions.
[0016] [First Embodiment] Figure 1 shows an example configuration of a display device DSP (dual-screen liquid crystal display device) according to the first embodiment. The display device DSP comprises a backlight BL (backlight for dual-screen liquid crystal display device), an image display panel PA, and a controller CNTL that controls the backlight BL and the image display panel PA. The image display panel PA is superimposed on the backlight BL. The controller CNTL includes, for example, ICs that drive the image display panel PA and the backlight BL, respectively.
[0017] In the example shown in Figure 1, the image display panel PA has a rectangular shape that is elongated in the X direction (first direction). However, the shape of the image display panel PA is not limited to this example; for example, it may be a rectangular or square shape that is elongated in the Y direction (second direction).
[0018] The image display panel PA includes a first polarizing plate PL1, a second polarizing plate PL2, an array substrate AR, a liquid crystal layer LC, a counter substrate CT, a color filter CF, a field of view barrier BA, and a plurality of pixels Pix.
[0019] The array substrate AR and the opposing substrate CT are facing each other in the Z direction. The liquid crystal layer LC is sealed between the array substrate AR and the opposing substrate CT. The color filter CF is provided, for example, on the opposing substrate CT. However, the color filter CF may also be provided on the array substrate AR. The first polarizer PL1 is attached to the outer surface of the array substrate AR. The second polarizer PL2 is attached to the outer surface of the opposing substrate CT. These first polarizer PL1 and second polarizer PL2 have mutually orthogonal absorption axes, for example. Note that the arrangement of each element is not limited to that shown in Figure 1 and can be changed as appropriate. For example, the field of view barrier BA may be located between the opposing substrate CT and the second polarizer PL2.
[0020] Multiple pixels Pix are arranged in a matrix in the X and Y directions within the display area where the image display panel PA displays an image. For example, each pixel Pix includes sub-pixels for red, green, and blue to achieve color display. A pair of electrodes is positioned on these sub-pixels to form an electric field that acts on the liquid crystal layer LC.
[0021] Figure 2 shows an example of an image that a display device (DSP) displays in a specific direction.
[0022] The display device DSP is capable of simultaneously displaying a first image V1, which is observed when the display area is viewed from a first position P1, and a second image V2, which is observed when the display area is viewed from a second position P2. The first image V1 and the second image V2 may be the same image, or they may be different images.
[0023] Here, the first position P1 is the position shifted to the left from the front (normal direction) of the display area when the display device DSP is positioned so that the X direction is the left-right direction. The second position P2 is the position shifted to the right from the front of the display area when the display device DSP is positioned so that the X direction is the left-right direction.
[0024] Figures 3A and 3B schematically show the configuration of the image display panel PA and the backlight BL.
[0025] The aforementioned multiple pixels Pix include multiple first pixels Pix1 and multiple second pixels Pix2. In Figures 3A and 3B, the first pixels Pix1 are denoted with the code L, and the second pixels Pix2 are denoted with the code R.
[0026] In the examples shown in Figures 3A and 3B, the first pixel Pix1 and the second pixel Pix2 are arranged alternately in the X direction. Multiple first pixels Pix1 display the first image V1 shown in Figure 2. Multiple second pixels Pix2 display the second image V2 shown in Figure 2.
[0027] The field of view barrier BA is made of a light-shielding material. The field of view barrier BA is provided with a plurality of gaps G arranged at regular intervals in the X direction. The gaps G may be holes or slits made in the field of view barrier BA.
[0028] When the display device DSP is observed from the first position P1, the observer can see the first pixel Pix1 through the gap G provided in the field of view barrier BA (Figure 3A). On the other hand, the second pixel Pix2 is blocked by the field of view barrier BA, so the observer cannot see the second pixel Pix2 from the first position P1 (Figure 3B). In other words, the field of view barrier BA is formed to block the light from the second pixel Pix2 when the display device DSP is viewed from the first position P1.
[0029] When the display device is observed from the second position P2, the observer can see the second pixel Pix2 through the gap G provided in the field of view barrier BA (Figure 3A). On the other hand, the first pixel Pix1 is blocked by the field of view barrier BA, so the observer cannot see the first pixel Pix1 from the second position P2 (Figure 3B). In other words, the field of view barrier BA is formed to block the light from the first pixel Pix1 when the display device DSP is viewed from the second position P2.
[0030] Thus, the display device DSP is configured to display the first image V1 to an observer at the first position P1, while simultaneously hiding the second image V2. The display device DSP is also configured to display the second image V2 to an observer at the second position P2, while simultaneously hiding the first pixel.
[0031] Figure 4 shows a schematic configuration of the backlight BL.
[0032] The backlight BL has a structure in which a reflective sheet REF, a second light guide plate LGP2, a first diffusion layer EXS1 (first diffusion sheet), a first prism sheet PS1, a second prism sheet PS2, a second diffusion layer EXS2 (second diffusion sheet), and the first light guide plate LGP1 are stacked in the Z direction.
[0033] The first light guide plate LGP1 has a first emission surface EM1, a first back surface BS1 opposite to the first emission surface EM1, and a first side surface SS1 connecting the first emission surface EM1 and the first back surface BS1. The second light guide plate LGP2 has a second emission surface EM2 facing the first back surface BS1, a second back surface BS2 opposite to the second emission surface EM2, and a second side surface SS2 connecting the second emission surface EM2 and the second back surface BS2.
[0034] The backlight BL further comprises a first light source LS1 and a second light source LS2. The first light source LS1 irradiates light onto the first side surface SS1 of the first light guide plate LGP1. The light irradiated onto the first side surface SS1 is emitted from the first emission surface EM1 of the first light guide plate LGP1. The second light source LS2 irradiates light onto the second side surface SS2 of the second light guide plate LGP2. The light irradiated onto the second side surface SS2 is emitted from the second emission surface EM2 of the second light guide plate LGP2.
[0035] The reflective sheet REF reflects the light emitted from the second back surface BS2. After being reflected, the light emitted from the second back surface BS2 enters the second light guide plate LGP2 and is emitted from the second emission surface EM2. Therefore, the reflective sheet REF allows for efficient use of light.
[0036] The first diffusion layer EXS1 and the second diffusion layer EXS2 improve the uniformity of image brightness across the entire display area by diffusing the incident light. Light emitted from the second emission surface EM2 of the second light guide plate LGP2 travels in a specific direction, but this directional bias causes unevenness in the brightness of the display area. Light that has passed through the first diffusion layer EXS1 and the second diffusion layer EXS2 is diffused evenly in various directions by refraction and scattering. In this way, the first diffusion layer EXS1 and the second diffusion layer EXS2 diffuse the light, improving the uniformity of brightness and, consequently, the quality of the image.
[0037] Brightness-enhancing films may be used as the first diffusion layer EXS1 and the second diffusion layer EXS2. Brightness-enhancing films convert passing light into polarization in a specific direction. The first polarizer PL1 of the image display panel PA allows only light with polarization in a specific direction to pass through. That is, of the light incident from the backlight BL to the image display panel PA, only that which can pass through the first polarizer PL1 reaches the liquid crystal layer LC and is used to display the image. Therefore, brightness is improved by increasing the polarization in a specific direction using a brightness-enhancing film. For example, 3M Company's DBEF (registered trademark) can be used as a brightness-enhancing film.
[0038] Referring to Figure 5, the configurations of the first prism sheet PS1 and the second prism sheet PS2 will be explained in more detail. In Figure 5, some of the configurations of the backlight BL are omitted.
[0039] The first prism sheet PS1 has a plurality of convex first prisms Pri1 directed toward the second emission surface EM2. The plurality of first prisms Pri1 are arranged along the X direction. The plurality of first prisms Pri1 also extend along the Y direction.
[0040] The second prism sheet PS2 has a plurality of convex second prisms Pri2 that are directed opposite the first prism sheet PS1. The plurality of second prisms Pri2 are arranged along the Y direction. The plurality of second prisms Pri2 also extend along the X direction.
[0041] Light emitted from the second light source LS2 onto the second side surface SS2 of the second light guide plate LGP2 is emitted from the second emission surface EM2. The light emitted from the second emission surface EM2 then passes through the first prism sheet PS1. The light that has passed through the first prism sheet PS1 then passes through the second prism sheet PS2 and illuminates the image display panel PA.
[0042] The function of the first prism sheet PS1 will be explained with reference to Figures 6A and 6B. These figures show the spread of light emitted from the second light guide plate LGP2 (white arrows in the figures) in the X-Z plane parallel to the X and Z directions.
[0043] In the X-Z plane, the light emitted from the second emission surface EM2 is directed in various directions (Figure 6A). When the first prism sheet PS1 is superimposed on the second light guide plate LGP2, brightness directivity is generated in the light incident on the image display panel PA (Figure 6B). That is, the brightness distribution of the light has peaks in the tilt direction Da (third direction) and tilt direction Db (fourth direction) that are deviated from the normal N of the second emission surface EM2. In addition, the brightness of the light irradiated in the direction parallel to the normal N (Z direction) is lower due to the first prism sheet PS1 compared to when the first prism sheet PS1 is not present.
[0044] The tilt direction Da is a direction that forms an angle θ1 with respect to the normal line N in the X-Z plane. The tilt direction Db is a direction that forms an angle θ2 in the opposite rotation direction to the angle θ1 with respect to the normal line N in the X-Z plane. The angles θ1 and θ2 are both 0° or more and less than 90°. In one example, the angles θ1 and θ2 are equal.
[0045] In the present embodiment, the direction from the display device DSP toward the first position P1 is the tilt direction Da. Also, the direction from the display device DSP toward the second position P2 is the tilt direction Db. That is, the image display panel PA displays the first image V1 in the tilt direction Da. Also, the image display panel PA displays the second image V2 in the tilt direction Db. By increasing the luminance of the light emitted in the tilt direction Da and the tilt direction Db, a clearer image is observed from the first position P1 and the second position P_{2}.
[0046] The apex angle of the first prism Pri1 included in the first prism sheet PS1 can be appropriately changed according to the direction in which the image display panel PA displays an image. For example, in-vehicle display devices are designed such that the first position P1 and the second position P2 are the positions of the passenger seat and the driver's seat, respectively. In one example, the apex angle of the first prism Pri1 is 90 degrees.
[0047] Referring to FIGS. 7A and FIG. 7B, the function of the second prism sheet PS2 will be described. These figures show the spread of the light (white arrows in the figure) emitted from the second light guide plate LGP2 in the Y-Z plane parallel to the Y direction and the Z direction. In FIGS. 7A and FIG. 7B, the figure of the second light source LS2 is omitted. [[ID=ll]]
[0048] As described above, the light emitted from the second emission surface EM2 is directed in various directions. Therefore, even in the Y-Z plane, the light has a spread (FIG. 7A).
[0049] When the second prism sheet PS2 is placed on the second light guide plate LGP2, the viewing angle in the Y-Z plane of the light emitted to the image display panel PA becomes narrower, and the brightness of the light within that viewing angle increases (Figure 7B). In this specification, the viewing angle is the angle expressed by the inclination from the normal to the image display panel PA, and refers to the range in which light with sufficient brightness is emitted. In this specification, "sufficient brightness" means that the light emitted from the image display panel PA in a certain direction is bright enough to display a clear image in that direction. In this specification, "narrow viewing angle in a certain direction" means that the spread of the viewing angle in that direction is small.
[0050] In other words, the second prism sheet PS2 narrows the viewing angle, thereby suppressing light irradiation in a specific direction. For example, if the display device DSP according to this embodiment is used as an in-vehicle display device with the Y direction coinciding with the vertical direction, the second prism sheet PS2 narrows the viewing angle, suppressing light irradiation in the vertical direction of the display device. This prevents light reflection from the car's windshield.
[0051] Furthermore, a narrower field of view increases the brightness of light emitted in directions within that field of view, resulting in a clearer image.
[0052] The apex angle of the second prism Pr2 in the second prism sheet PS2 can be appropriately changed according to the application of the display device DSP. In one example, the apex angle of the second prism Pr2 is 90 degrees.
[0053] Referring to Figures 8A and 8B, the luminance directivity of the light irradiated from the backlight BL to the image display panel PA according to this embodiment when the first light source LS1 is lit will be explained. Figure 8A shows the spread of light emitted from the first light guide plate LGP1 in the X-Z plane. Figure 8B shows the spread of light emitted from the first light guide plate LGP1 in the Y-Z plane. In Figure 8B, the diagram of the first light source LS1 is omitted.
[0054] When the first light source LS1 is lit, light incident from the first side surface SS1 and emitted from the first output surface EM1 irradiates the image display panel PA. That is, light without brightness directionality in the X direction irradiates the image display panel PA (Figure 8A). Also, light without narrowed viewing angle in the Y direction irradiates the image display panel PA (Figure 8B).
[0055] Referring to Figures 9A and 9B, the luminance directivity of the light irradiated from the backlight BL to the image display panel PA according to this embodiment when the second light source LS2 is lit will be explained. In Figure 9B, the diagram of the second light source LS2 is omitted.
[0056] When the second light source LS2 is lit, light incident from the second side surface SS2 and emitted from the second exit surface EM2 passes through the first prism sheet PS1 and the second prism sheet PS2 before illuminating the image display panel PA. That is, light with luminance directionality in the X direction is illuminated onto the image display panel PA (Figure 9A). In the Y direction, light with a narrowed viewing angle is illuminated onto the image display panel PA (Figure 9B).
[0057] The operation of the controller CNTL will be described below, using the case where the display device DSP according to this embodiment is used as an in-vehicle display device as an example.
[0058] <Dual-Screen Display Mode> An example of driving the image display panel PA and backlight BL will be explained with reference to Figures 10 and 11. In Figures 10 and 11, the controller CNTL is omitted. Figures 10 and 11 show an example of a dual-screen display mode in which the first image V1 and the second image V2 are different from each other. For example, when the shift lever is in drive, i.e., while the car is in motion, the controller CNTL drives the backlight BL and image display panel PA in dual-screen display mode. At this time, for example, a navigation image may be displayed on the driver's side, and an entertainment image such as a television may be displayed on the passenger side.
[0059] In dual-screen display mode, the controller CNTL turns off the first light source LS1 and turns on the second light source LS2 (Figure 10). At this time, the light emitted from the display device DSP has brightness directionality in the X direction (Figure 11).
[0060] Because the light emitted in the tilt directions Da and Db has high brightness, the first image V1 is clearly visible to the observer at the first position P1. Similarly, the second image V2 is clearly visible to the observer at the second position P2.
[0061] Light directed in the Z direction has lower brightness than light emitted in the inclined directions Da and Db. In other words, light with sufficient brightness to display an image is not emitted to the third position P3, which is the central front of the display device DSP. As a result, the overlapping image V3, which is an image in which the first image V1 and the second image V2 overlap, can be hidden.
[0062] Furthermore, the light emitted from the DSP display device has a narrow viewing angle in the Y direction. This prevents the light from reflecting off the windshield and obstructing the driver's view.
[0063] <First Single-Screen Display Mode> Referring to Figures 12 and 13, another example of driving the image display panel PA and backlight BL will be described. In Figures 12 and 13, the controller CNTL is omitted. Figures 12 and 13 show an example of the first single-screen display mode in which the first image V1 and the second image V2 are identical. For example, when the shift lever is in the parking position, i.e., when the car is stopped, the controller CNTL is driven in the first single-screen display mode. At this time, the same image is displayed on the driver's side and the passenger's side.
[0064] In the first single-screen display mode, the controller CNTL turns on the first light source LS1 and turns off the second light source LS2 (Figure 12). At this time, the light emitted from the display device DSP does not have brightness directionality in the X direction (Figure 13).
[0065] In other words, in the first single-screen display mode, light with sufficient brightness to display the image is emitted in the Z direction, tilt direction Da, and tilt direction Db. Therefore, a clear image is displayed even at the third position P3, which is the central front of the display device DSP. For example, in the first single-screen display mode, passengers in the rear seats can also see the image from the third position P3.
[0066] <Second Single-Screen Display Mode> Referring to Figure 14, another example of driving the image display panel PA and backlight BL will be described. In Figure 14, the controller CNTL is omitted. Figure 14 shows an example of the second single-screen display mode in which the first image V1 and the second image V2 are identical. The second single-screen display mode can be used as an alternative to the first single-screen display mode.
[0067] In the second single-screen display mode, the controller CNTL lights up the first light source LS1 and simultaneously lights up the second light source LS2. At this time, the light emitted from the first light guide plate LGP1 and the light emitted from the second light guide plate LGP2 simultaneously illuminate the image display panel PA. Looking at the light emitted from the display device DSP as a whole, the brightness in the tilt direction Da and tilt direction Db is higher than the brightness in other directions. In addition to the light in the tilt direction Da and tilt direction Db, light with sufficient brightness to display a clear image is emitted towards the center front of the display device.
[0068] The second single-screen display mode has the advantage of higher brightness of light emitted from the DSP display device compared to the first single-screen display mode. However, it has inferior brightness uniformity compared to the first single-screen display mode. That is, the brightness of the image may differ depending on the viewing position of the DSP display device, potentially resulting in uneven clarity. The first and second single-screen display modes can be appropriately selected depending on the purpose of the DSP display device.
[0069] For example, the controller CNTL may drive the backlight BL and the image display panel PA in a second single-screen display mode when the interior of the vehicle is bright, such as during the day, and drive the backlight BL and the image display panel PA in a first single-screen display mode when the interior of the vehicle is dark, such as at night.
[0070] [Comparative Example] Figure 15 shows Comparative Example 1 of this embodiment.
[0071] The display device DSP1 according to Comparative Example 1 comprises a backlight consisting of a first light guide plate LGP1 and a first light source LS1, and an image display panel PA with the same configuration as in this embodiment. In Comparative Example 1, even in dual-screen display mode, relatively strong light is emitted towards the center front of the display device DSP1. As a result, from the third position P3, an overlapping image V3 in which the first image V1 and the second image V2 are superimposed is observed, which is visually unappealing.
[0072] Figures 16A and 16B show Comparative Example 2 of this embodiment.
[0073] The display device DSP2 according to Comparative Example 2 comprises a backlight consisting of a second light guide plate LGP2, a second light source LS2, a first prism sheet PS1 and a second prism sheet PS2, and an image display panel PA with the same configuration as in this embodiment. In Comparative Example 2, the light emitted from the display device DSP2 has brightness directionality, and the light in the direction of the center front is weak. Therefore, the problem of overlapping images V3 being observed in the dual-screen display mode can be avoided. However, in the display device DSP2 according to Comparative Example 2, in the single-screen display mode, an observer from the third position P3 cannot see a clear image.
[0074] On the other hand, the display device DSP according to this embodiment includes a backlight BL having a first light guide plate LGP1, a first light source LS1, a second light guide plate LGP2, a second light source LS2, a first prism sheet PS1, and a second prism sheet PS2 (see Figure 4). Furthermore, the display device DSP is configured to allow switching of the light source of the backlight BL depending on whether it is a dual-screen display mode or a single-screen display mode (see Figures 10, 11, 12, 13, and 14).
[0075] In other words, in dual-screen display mode, the first light source LS1 is turned off and the second light source LS2 is turned on. At this time, the light emitted from the display device DSP has brightness directionality, so a clear image cannot be observed from the third position P3. Also, in single-screen display mode, the first light source LS1 is turned on and the second light source LS2 is turned off. At this time, the display device DSP emits light with sufficient brightness in the Z direction, tilt direction Da, and tilt direction Db. Therefore, the display device DSP according to this embodiment hides the overlapping image V3 in dual-screen display mode and clearly displays the overlapping image V3 in single-screen display mode. Furthermore, in dual-screen display mode, a clearer image can be displayed at a specific position compared to when a backlight without brightness directionality is used.
[0076] [Second Embodiment] Figure 17 schematically shows the configuration of a display device DSP according to the second embodiment. The display device DSP according to the second embodiment includes a backlight BL, an image display panel PA, and a controller CNTL that controls the backlight BL and the image display panel PA. In Figure 17, the controller CNTL is omitted. The second embodiment differs from the first embodiment in that the backlight BL has a third diffusion layer EXS3 (third diffusion sheet) and does not include the second diffusion layer EXS2. The third diffusion layer EXS3 is arranged between the first light guide plate LGP1 and the image display panel PA and faces the first emission surface EM1 of the first light guide plate LGP1. A brightness-enhancing film may be used as the third diffusion layer EXS3.
[0077] In this embodiment, the same effects as in the first embodiment can be obtained. The display device DSP according to this embodiment has a third diffusion layer EXS3 located between the first light guide plate LGP1 and the image display panel PA. As a result, in single-screen display mode, the light emitted from the first emission surface EM1 is diffused in various directions, improving the brightness uniformity of the display area and, consequently, the image quality.
[0078] [Third Embodiment] Figure 18 schematically shows the configuration of a display device DSP according to the third embodiment. The display device DSP according to the third embodiment comprises a backlight BL, an image display panel PA, and a controller CNTL that controls the backlight BL and the image display panel PA. In Figure 18, the controller CNTL is omitted. The third embodiment differs from the first embodiment in that the backlight BL has a third diffusion layer EXS3.
[0079] The display device DSP according to this embodiment, like the first embodiment, has a second diffusion layer EXS2 located between the second prism sheet PS2 and the first light guide plate LGP1. As a result, in dual-screen display mode, the light emitted from the second emission surface EM2 is diffused in various directions, improving the uniformity of the displayed image. Furthermore, the display device DSP according to this embodiment has a third diffusion layer EXS3 located between the first light guide plate LGP1 and the image display panel PA. As a result, like the third embodiment, in single-screen display mode, the light emitted from the first emission surface EM1 is diffused in various directions, improving the brightness uniformity of the display area and, consequently, the image quality.
[0080] All backlights and display devices that a person skilled in the art can design and implement based on the backlights and display devices described above as embodiments of this disclosure also fall within the scope of this disclosure insofar as they encompass the gist of this disclosure.
[0081] Within the scope of the ideas presented hereto, a person skilled in the art could conceive of various modifications, and such modifications are understood to fall within the scope of this disclosure. For example, any modifications made by a person skilled in the art to each of the above embodiments, such as adding, deleting, or changing components, or adding, omitting, or changing processes, are also included within the scope of this disclosure, as long as they retain the essence of this disclosure.
[0082] Furthermore, any other effects and advantages brought about by the embodiments described above that are obvious from the description herein or that can be appropriately conceived by a person skilled in the art are naturally provided by this disclosure.
[0083] DSP...Display device, BL...Backlight, PA...Image display panel, CNTL...Controller, PL1...First polarizer, PL2...Second polarizer, AR...Array substrate, CT...Opposite substrate, BA...Viewing barrier, G...Gap, Pix...Pixel, Pix1...First pixel, Pix2...Second pixel, LC...Liquid crystal layer, CF...Color filter, V1...First image, V2...Second image, V3...Overlap image, REF...Reflective sheet, LGP1...First light guide plate, LGP2...Second light guide plate, EXS1...First diffuser layer EXS2...Second diffusion layer, EXS3...Third diffusion layer, PS1...First prism sheet, PS2...Second prism sheet, Pri1...First prism, Pri2...Second prism, LS1...First light source, LS2...Second light source, SS1...First side, SS2...Second side, EM1...First emission surface, EM2...Second emission surface, BS1...First back surface, BS2...Second back surface, X...X direction, Y...Y direction, Z...Z direction, Da...Inclination direction, Db...Inclination direction, P1...First position, P2...Second position, P3...Third position
Claims
1. A backlight for a dual-screen liquid crystal display device, comprising: a first light guide plate having a first emission surface, a first back surface opposite to the first emission surface, and a first side surface connecting the first emission surface and the first back surface, and emitting light irradiated onto the first side surface from the first emission surface; a second light guide plate having a second emission surface facing the first back surface, a second back surface opposite to the second emission surface, and a second side surface connecting the second emission surface and the second back surface, and emitting light irradiated onto the second side surface from the second emission surface; a first light source that irradiates light onto the first side surface; a second light source that irradiates light onto the second side surface; and a first prism sheet located between the first light guide plate and the second light guide plate, wherein the first prism sheet has a plurality of convex first prisms directed toward the second emission surface, and the plurality of first prisms are arranged along a first direction and extend along a second direction perpendicular to the first direction.
2. The backlight for a dual-screen liquid crystal display device according to claim 1, further comprising a first diffusion sheet located between the first prism sheet and the second light guide plate.
3. The backlight for a dual-screen liquid crystal display device according to claim 1, further comprising a second prism sheet located between the first light guide plate and the first prism sheet, wherein the second prism sheet has a plurality of convex second prisms toward the first back surface, and the plurality of second prisms are arranged along the second direction and extend along the first direction.
4. The backlight for a dual-screen liquid crystal display device according to claim 3, further comprising a second diffusion sheet located between the first light guide plate and the second prism sheet.
5. The backlight for a dual-screen liquid crystal display device according to claim 4, wherein the second diffusion sheet is a brightness-enhancing film.
6. The backlight for a dual-screen liquid crystal display device according to claim 1, further comprising a third diffusion sheet facing the first emission surface.
7. The backlight for a dual-screen liquid crystal display device according to claim 6, wherein the third diffusion sheet is a brightness-enhancing film.
8. The backlight for a dual-screen liquid crystal display device according to claim 1, further comprising a reflective sheet facing the second back surface.
9. The light from the second light source that is emitted from the second emission surface and passes through the first prism sheet and the first light guide plate has a luminance distribution that includes two peaks that are offset from the normal to the first emission surface, as described in claim 1, for a dual-screen liquid crystal display device.
10. A dual-screen liquid crystal display device comprising: a backlight for a dual-screen liquid crystal display device according to any one of claims 1 to 9; an image display panel facing the first emission surface; and a controller for controlling the backlight for the dual-screen liquid crystal display device and the image display panel.
11. The dual-screen liquid crystal display device according to claim 10, wherein the image display panel has a plurality of pixels arranged in a display area and a viewing barrier that overlaps the plurality of pixels, the plurality of pixels include a plurality of first pixels representing a first image and a plurality of second pixels representing a second image, the viewing barrier is formed to block light from the second pixels when the image display panel is viewed from a third direction inclined with respect to the normal of the image display panel, and is formed to block light from the first pixels when the image display panel is viewed from a fourth direction inclined with respect to the normal of the image display panel and different from the third direction, and the controller is configured to switch between a dual-screen display mode in which the first image and the second image are different from each other and a single-screen display mode in which the first image and the second image are the same.
12. The dual-screen liquid crystal display device according to claim 11, wherein the controller lights up the second light source and simultaneously turns off the first light source when in the dual-screen display mode, and lights up the first light source and simultaneously turns off the second light source when in the single-screen display mode.
13. The dual-screen liquid crystal display device according to claim 11, wherein the controller lights up the second light source and simultaneously turns off the first light source when in the dual-screen display mode, and lights up the first light source and the second light source when in the single-screen display mode.
14. The dual-screen liquid crystal display device according to claim 11, wherein the viewing barrier is provided with a plurality of gaps arranged at regular intervals in the first direction, and the gaps are holes or slits made in the viewing barrier.