Backlight and display device using the same

Abstract

To provide a back light that can achieve cost reduction while improving discontinuity of luminance.SOLUTION: A back light of the present invention includes a first light guide plate 130, a first LED light source 132 that emits light from an end surface of the first light guide plate 130, a second light guide plate 140 in a laminated relationship with the first light guide plate 130, and a second LED light source 142 that emits light from an end surface of the second light guide plate 140. A light-emitting region 134 for emitting light toward a main surface is formed in the center of the first light guide plate 130, and a light-emitting region 144 for emitting light toward the main surface is formed around the second light guide plate 140. A gradation in which the brightness changes is formed in the boundary area between the light-emitting region 134 and the light-emitting region 144.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a backlight, and particularly to a structure of a backlight used for a liquid crystal panel or the like.

Background Art

[0002] Liquid crystal display units for digitally displaying the instrument panel in front of the driver's seat are becoming popular. For example, as shown in FIG. 1(A), a liquid crystal display unit 1 is arranged in front of the driver's seat, and as shown in FIG. 1(B), meters such as speed, distance, and fuel, and warnings 2 such as seat belt wearing, remaining gasoline amount, and half door are displayed (for example, Patent Document 1).

[0003] In a liquid crystal display unit, in order to reduce costs and thickness, a side edge type backlight that irradiates LED light from the end face of a light guide plate is adopted (for example, Patent Document 1). On the other hand, the practical application of a local dimming type backlight in which a plurality of LEDs are two-dimensionally arranged and the LED light is directly irradiated onto the back surface of the liquid crystal panel is also in progress (for example, Patent Documents 2 and 3). The local dimming method has the advantage of improving the visual contrast ratio by irradiating the area where an image is displayed or by extinguishing or reducing the irradiation of the black area.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] As in-car LCD display units become larger, problems arise such as noticeable black level issues at night or worsening of black level uniformity due to the larger screen size. These problems are difficult to solve with side-edge backlighting, and require solutions using local dimming backlighting.

[0006] Figure 2 is a schematic diagram showing the general configuration of a conventional local dimming type backlight. The backlight 10 includes a plurality of LEDs 20 arranged in two dimensions, a local dimming controller 30, and an LED driver 40 for driving each LED 20. The local dimming controller 30 controls the illumination of each LED 20 to enable partial brightness adjustment, for example, by illuminating the LEDs 20 according to the area to be displayed on the liquid crystal panel, thereby improving the contrast ratio.

[0007] However, the local dimming method has the drawback that as the number of LEDs 20 increases, the number of LED drivers 40 needed to drive them also increases, leading to higher costs. To avoid this drawback, a hybrid method is being considered in which only the peripheral parts of the LCD panel are illuminated using the local dimming method, while the central part is illuminated collectively with a side-edge backlight.

[0008] Figure 3 is a schematic diagram showing the configuration of a hybrid backlight. As shown in the figure, the backlight 12 has multiple LEDs 20 arranged in the area corresponding to the peripheral part of the liquid crystal panel, and a surface light source 22 using a side edge type light guide plate in the central part. Since the central part of the liquid crystal panel is the area where the image is normally displayed, the local dimming controller 32 illuminates the surface light source 22 all at once via the surface light source LED driver 42. On the other hand, to suppress black level distortion in the peripheral part at night and to make the boundary with the black print area outside the liquid crystal panel less noticeable, the LEDs 20 are individually controlled via the LED driver 40.

[0009] The hybrid method allows for a significant reduction in costs by reducing the number of LEDs and LED drivers compared to the local dimming method, which places LEDs across the entire surface of the LCD panel. However, further cost reductions are still required.

[0010] Furthermore, optical problems with the hybrid backlight system were also revealed. As shown in Figure 4(A), when a black screen is displayed on the liquid crystal display 50, the continuity of the brightness gradient becomes insufficient at the boundary B between the display area 52 using the side-edge method in the center of the screen and the display area 54 using the local dimming method around the screen, making the boundary easily visible.

[0011] Figure 4(B) shows the change in brightness of the A-A' line that crosses the boundary B between display area 52 and display area 54. While it is possible to create a gradient in the brightness change as shown by the solid line Q using the local dimming method, the continuity of brightness becomes insufficient where a constant brightness intersects with the solid line Q in the circular area D, making the discontinuity in that area easily visible. This problem can be solved by increasing the width of the display area 54 using the local dimming method and increasing the number of LEDs in that area to further smooth the change in brightness. However, this would increase the number of LEDs and LED drivers, undermining the cost-saving advantage of the hybrid method.

[0012] The present invention aims to solve these conventional problems and provide a backlight and a display device using the same that can reduce costs while improving brightness discontinuity. [Means for solving the problem]

[0013] The backlight device according to the present invention includes a first light guide plate, a second light guide plate stacked with the first light guide plate, a first light source that irradiates light onto the end face of the first light guide plate, and a second light source that irradiates light onto the end face of the second light guide plate, wherein the first light guide plate includes a first light-emitting region in the center that reflects incident light toward the main surface, and the second light guide plate includes a second light-emitting region around the periphery that reflects incident light toward the main surface.

[0014] In one embodiment, when light is irradiated onto the first light guide plate and the second light guide plate by the first light source and the second light source, the first light-emitting region and the second light-emitting region form a light-emitting region covering the entire main surface. In one embodiment, the first light-emitting region includes a first gradient portion where the brightness decreases from a region where the brightness is constant, and the second light-emitting region includes a second gradient portion where the brightness decreases from a region where the brightness is constant. In one embodiment, the first gradient portion and the second gradient portion are in an overlapping positional relationship when viewed in plan. In one embodiment, the brightness of the first and second gradient portions changes linearly. In one embodiment, the brightness of the first and second gradient portions changes curvilinearly. In one embodiment, the first light-emitting region includes a first dot pattern with irregularities that reflects light incident on the bottom or bottom surface of the first light guide plate, and the second light-emitting region includes a second dot pattern with irregularities that reflects light incident on the bottom or bottom surface of the second light guide plate, and the change in brightness is adjusted by the density or size of the first and second dot patterns.

[0015] The display device according to the present invention comprises a backlight device described above, a display means for displaying an image using light from the backlight device, and a first driving means for driving the first light source. The system includes a second driving means for driving the second light source and a control means for controlling the first and second driving means.

[0016] In one aspect, when it is daytime or a bright environment, the control means lights the first and second light sources via the first and second driving means. In one aspect, when it is nighttime or a dark environment, the control means lights the first light source via the first driving means. In one aspect, the control means controls the lighting of the first and second light sources via the first and second driving means based on display content displayed on the display means.

Advantages of the Invention

[0017] According to the present invention, by laminating a first light guide plate having a first light emitting region in the center and a second light guide plate having a second light emitting region in the periphery, it is possible to provide a backlight that improves luminance discontinuity while being low-cost.

Brief Description of the Drawings

[0018] [Figure 1] It is a diagram showing an example of a liquid crystal display unit for digitally displaying meters. [[ID=十六]]<0> [[ID=十七]]<0> [Figure 2] It is a diagram showing the configuration of a conventional backlight of a local dimming method. [Figure 3] It is a diagram showing the configuration of a conventional hybrid method backlight. [Figure 4] It is a diagram for explaining the problems of a liquid crystal display device using a conventional hybrid method backlight. [Figure 5] It is an exploded perspective view showing the configuration of a display device according to an embodiment of the present invention. [Figure 6] It is a block diagram showing the electrical configuration of a display device according to an embodiment of the present invention. [Figure 7] FIG. 7(A) is a diagram showing the emission luminance by the first and second light guide plates, FIG. 7(B) is a diagram showing the cross-sectional structure of the display device, and FIGS. 7(C) and (D) are diagrams showing the lighting patterns of the first and second light guide plates. [Figure 8]FIG. 8(A) is a schematic cross-sectional view of a light guide plate for explaining luminance gradation, and FIGS. 8(B), (C), and (D) are diagrams for explaining the relationship between the density of a dot pattern and the light emission amount. [Figure 9] It is a table showing an example of switching of the lighting pattern of the light guide plate of the display device according to an embodiment of the present invention. [Figure 10] It is a diagram for explaining a method of verifying the luminance gradation of a backlight according to an embodiment of the present invention. [Figure 11] It is a diagram for explaining another verification example of the luminance gradation of a backlight according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] The backlight device according to the present invention is not particularly limited, but for example, it has a function of irradiating a display medium such as a liquid crystal panel from the back. Further, the display device according to the present invention is not particularly limited, but for example, it constitutes a liquid crystal display unit that displays meters such as speed, distance, and fuel on an instrument panel of a vehicle.

EXAMPLE

[0020] Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 5 is an exploded perspective view of a display device according to an embodiment of the present invention. The display device 100 of the present embodiment includes a liquid crystal panel 110 for image display, a plurality of optical sheets 120 disposed below the liquid crystal panel 110, a first light guide plate (LGP1) 130 disposed below the optical sheets 120, a second light guide plate (LGP2) 140 disposed below the first light guide plate 13, a first LED light source 132 disposed at an end of the first light guide plate 130, and a second LED light source 142 disposed at an end of the second light guide plate 140, which are stacked and configured.

[0021] The liquid crystal panel 110 is composed of, for example, a TFT (Thin Film Transistor) liquid crystal structure. In the TFT liquid crystal structure, liquid crystal cells, RGB color filters, etc. are provided on a TFT array substrate on which multiple thin film transistors are formed in a matrix, and a polarizing plate is provided below the TFT array substrate. One pixel consists of three RGB subpixels, and one subpixel corresponds to one thin film transistor.

[0022] The optical film 120 may include an anti-reflective film to prevent reflection of light irradiated from the first and second light guide plates 130 and 140, and a diffusion film to diffuse light.

[0023] The backlight of this embodiment has a two-layer backlight system including a first light guide plate 130 for illuminating the central part of the liquid crystal panel 110 and a second light guide plate 140 for illuminating the peripheral part. The first and second light guide plates 130 and 140 are generally the same rectangular shape, but are characterized by having different light-emitting areas due to differences in the dot patterns that reflect or scatter light.

[0024] In the example shown in Figure 5, the first light guide plate 130 includes the central rectangular area indicated by hatching as the light-emitting area 134, and the rest of the plate does not function as a light-emitting area. On the other hand, the second light guide plate 140 includes the frame-shaped outer peripheral area indicated by hatching as the light-emitting area 144, and the rest of the plate does not function as a light-emitting area. The light-emitting areas 134 and 144 function as if they were surface light sources.

[0025] The shape and size of the light-emitting region 134 of the first light guide plate 130 are approximately the same as the shape and size of the non-light-emitting region of the second light guide plate 140, and the shape and size of the light-emitting region 144 of the second light guide plate 140 are approximately the same as the shape and size of the non-light-emitting region of the first light guide plate 130. When the liquid crystal panel 110 is illuminated by the first and second light guide plates 130 and 140, the light emitted in the light-emitting region 134 illuminates the central region of the liquid crystal panel 110, and the light emitted in the light-emitting region 144 illuminates the peripheral region of the liquid crystal panel 110 through the non-light-emitting region of the first light guide plate 130.

[0026] The first light guide plate 130 and the second light guide plate 140 are made of a light-transmitting material such as acrylic. A plurality of dot patterns for forming a light-emitting region 134 are formed on the bottom or bottom surface of the center of the first light guide plate 130, and a plurality of dot patterns for forming a light-emitting region 144 are formed on the bottom or bottom surface of the outer periphery of the second light guide plate 140. The dot patterns are minute reflective parts such as convex parts, concave parts, steps, and protrusions, and the dot patterns can be formed by laser processing, printing, molding, etc. Light incident from the end face of the light guide plate is scattered or reflected by the dot patterns, and the scattered or reflected light is extracted from the top surface, which is the main surface of the light guide plate.

[0027] The method of stacking the first light guide plate 130 and the second light guide plate 140 is not particularly limited. For example, the bottom surface of the first light guide plate 130 and the top surface of the second light guide plate 140 may be in direct contact, or an anti-reflective sheet or a transparent adhesive may be interposed between them. In the example shown in Figure 5, the second light guide plate 140 is placed below the first light guide plate 130, but the stacking order may be reversed.

[0028] The first LED light source 132 is positioned on the shorter side of the first light guide plate 130. The first LED light source 132 includes a plurality of LEDs arranged in a line, and the light emitted from each LED is incident on the first light guide plate 130 from the end face toward the interior. The second LED light source 142 is positioned on the shorter side of the second light guide plate 140. The second LED light source 142 includes a plurality of LEDs arranged in a line, and the light emitted from each LED is incident on the second light guide plate 140 from the end face toward the interior.

[0029] In the example shown in Figure 5, the first LED light source 132 is located on the side opposite to the second LED light source 142, but the first LED light source 132 and the second LED light source 142 may be located on the same side. If the effective thickness of the first and second LED light sources 132 and 142 is greater than the thickness of the first and second light guide plates 130 and 140, the thickness of the backlight can be reduced by arranging the first LED light source 132 and the second LED light source 142 on opposite sides. On the other hand, if there is no limit to the thickness of the backlight, the bezel (outer edge of the liquid crystal panel) of the display device on the side without LED light sources can be reduced by arranging the first LED light source 132 and the second LED light source 142 on the same side.

[0030] Figure 6 is a block diagram showing the electrical configuration of the display device of this embodiment. The display device 100 of this embodiment includes a liquid crystal driver 210 for driving a liquid crystal panel 110, a first LED driver 220 for driving a first LED light source 132, a second LED driver 230 for driving a second LED light source 142, and a controller 240 for controlling these drivers. The display device 100 is mounted, for example, on the instrument panel of a vehicle, and the liquid crystal panel 110 displays meters, navigation screens, and the like.

[0031] Figure 7(A) shows the luminescence of the first and second light guide plates, Figure 7(B) shows the cross-sectional structure of the display device, and Figures 7(C) and (D) schematically show the lighting patterns. LGP1 and LGP2 refer to the first light guide plate 130 and the second light guide plate 140, respectively.

[0032] As shown in Figure 7(B), the display device 100 includes a black housing 150 that holds the ends of a stacked structure of an optical sheet 120, a first light guide plate 130, and a second light guide plate 140, on which a liquid crystal panel 110 is placed.

[0033] When the controller 240 lights up the first LED light source 132 via the first LED driver 220, the central light-emitting region 134 of the first light guide plate 130 emits light like a surface light source, and when the second LED light source 142 is lit via the second LED driver 230, the outer light-emitting region 144 of the second light guide plate 140 emits light like a surface light source. The solid line in Figure 7(A) shows the horizontal luminance of the first light guide plate 130. The luminance in the center is generally constant, and a gradient is formed in which the luminance gradually decreases in the region P from the center toward the edges. The dashed line shows the horizontal luminance of the second light guide plate 140. The luminance at the periphery is generally constant, and a gradient is formed in which the luminance gradually decreases in the region P from the periphery toward the center.

[0034] When both the first light guide plate 130 and the second light guide plate 140 emit light, their respective emissions are combined, and the entire surface of the liquid crystal panel 110 is illuminated with approximately the same brightness, which is equivalent to a normal side-edge backlight. At this time, it is desirable that the boundary between the light-emitting area 134 and the light-emitting area 144 overlaps with the gradient area P. In the example in Figure 7(A), the brightness changes with a fairly steep slope, but the change in brightness of area P can be made smoother by adjusting the density or size of the dot pattern (details of this will be described later).

[0035] Figure 7(C) shows the lighting pattern when the first LED light source 132 and the second LED light source 142 are lit simultaneously, in which case the entire backlight emits light at approximately the same brightness. Figure 7(D) shows the lighting pattern when only the first LED light source 132 is lit, in which case only the central part of the backlight emits light, and the outer edge becomes dark.

[0036] Next, we will explain how to form a gradient (luminance gradient) using a light guide plate. Figure 8(A) shows a schematic cross-sectional structure of the light guide plate. LEDs 310 are arranged on the side of the light guide plate 300, a media sheet 330 and a diffuser plate 340 are arranged on the top side of the light guide plate 300, and a reflective sheet 350 is arranged on the bottom side, with the ends of these layers supported by a black housing 360.

[0037] First, the principle of the light guide plate will be explained with reference to the diagram. The light guide plate 300 is generally formed by processing a transparent plate such as acrylic. When light L1 with a constant directional angle is incident on the acrylic plate from the LED 310 from the edge, most of the incident light L1 is reflected at the interface with the air and emitted to the outside from the opposite end. However, if a minute uneven dot pattern 320 is formed on the bottom surface of the acrylic plate (laser processing marks in the example shown in the diagram), the incident light L1 is reflected by the dot pattern 320, its angle changes, and it becomes possible to extract it as light L2 to the outside from the top surface of the light guide plate 300.

[0038] For example, as shown in Figure 8(B), increasing the size and density (generally density) of the dot pattern 320 formed on the bottom surface of the light guide plate 300 increases the amount of light that can be extracted from the top surface of the light guide plate 300. Conversely, as shown in Figure 8(C), decreasing the density of the dot pattern 320 reduces the amount of light emitted. Therefore, as shown in Figure 8(D), by continuously changing the density of the dot pattern for light extraction within a single light guide plate, it is possible to create a gradient of light emission. In this case, the amount of light decreases in the direction of propagation of the LED light L1 by the amount of light extracted to the outside, so in practice, it is necessary to design the dot pattern taking this into account.

[0039] As shown in Figure 7(C), by simultaneously lighting the first light guide plate 130 and the second light guide plate 140, it becomes possible to uniformly illuminate the entire screen of the liquid crystal panel 110 with light of the same brightness. By lighting only the first light guide plate 130, the brightness around the liquid crystal panel 110 is reduced, enabling a display that reduces the appearance of black levels being washed out at night or in dark places.

[0040] Figure 9 is a table illustrating the lighting patterns of the first and second light guide plates. It has been found that the effect of local dimming is not realized during the daytime or in bright environments. This is because the leakage light luminance during black display < the reflected luminance of the liquid crystal panel, and even if the backlight is partially reduced, the difference is almost imperceptible. In this situation, display luminance is also important, so the lighting pattern "LGP1 + LGP2" is used.

[0041] At night or in dark environments, ambient light decreases, causing the "reflective brightness of the LCD panel" to asymptotically approach zero. This makes light leakage from black displays more noticeable and is perceived as "black level distortion." Therefore, by using the "LGP1 only" illumination pattern, this black level distortion is reduced. However, if the display covers the entire LCD panel and it is not desirable to darken the surroundings (such as navigation images or television footage), the "LGP1 + LGP2" illumination pattern should be selected.

[0042] Switching between "LGP1+LGP2" and "LGP1" is performed by the controller 240. The controller 240 determines whether it is daytime or nighttime based on lighting signals indicating the on / off status of vehicle dimmer lights, etc., acquired, for example, via an in-vehicle bus (not shown), and controls the lighting of the first and second light guide plates 130 and 140 via the first and second LED drivers 220 and 230 based on the determination result. The controller 240 also identifies display content from image resources (e.g., navigation devices, audio / video devices, TV devices, etc.) that provide image data to the display device 100, and controls the lighting of the first and second light guide plates 130 and 140 via the first and second LED drivers 220 and 230 based on the identification result.

[0043] A key feature of the two-layer backlight system according to this embodiment is that the gradation of the amount of light emitted from the light guide plate can be easily changed by adjusting the density or size of the dot pattern formed on the light guide plate.

[0044] Next, we will explain the results of our verification of the relationship between the light guide plate's gradient (luminance slope) and the actual appearance. Figure 10 shows the lighting pattern of the light guide plate during the verification. Specifically, we verified the case where there was no luminance slope up to x%, and the luminance changed linearly from x% onward, with the distance from the center to the edge of the screen being 100%. The gradient direction is only vertical and horizontal. As a result of the verification, when x% was around 80% to 70%, the boundary between the area with constant luminance in the center and the area with a luminance slope around the periphery was still clearly recognizable. However, when x% reached around 60%, the boundary became almost indistinguishable, and when it reached around 40%, the existence of the boundary became almost impossible to discern.

[0045] Figure 11 shows an example of what happens when the lighting pattern is changed. Specifically, the brightness was linearly reduced by 20% up to x%, with the distance from the center to the edge of the screen being 100%, and then the brightness change was further increased linearly beyond x%. In this case as well, the gradient direction was limited to vertical and horizontal. The results of the verification showed that the boundary was even less noticeable than with the lighting pattern shown in Figure 10, and a reduction in black level distortion could be expected even at around 60% to 70%.

[0046] In the above embodiment, an example of linearly reducing brightness was shown, but it is more desirable to change the brightness in a curve, as this would eliminate the boundary region where the brightness change is even more abrupt. In other words, the brightness should change as smoothly as possible at the boundary between the region where the brightness is constant and the region where the brightness decreases. Also, the degree to which a gradient is allowed depends on the image being displayed, so the brightness of the LED light source may be adjusted according to the image. Furthermore, when displaying a navigation image or other image in full screen even at night (i.e., when local dimming is not very effective), it is desirable to light up the LGP2.

[0047] In the above embodiment, the gradient is configured only in two directions: up and down and left and right of the light guide plate. However, the gradient is not limited to this configuration, and may change linearly in a concentric circle. In this case, the light-emitting area 134 of the first light guide plate 130 may be circular instead of rectangular. Furthermore, the gradient may be in the vertical direction only, the horizontal direction only, or in a specific direction only.

[0048] In the above embodiment, the light-emitting area 134 of the first light guide plate 130 is rectangular, but it is not limited to this and can be any other shape. For example, the shape of the light-emitting area may be made to match the shape of the light guide plate. In any case, by appropriately selecting the shape and size of the dot pattern formed on the bottom surface or bottom of the light guide plate, a light-emitting area of ​​any shape and size can be formed.

[0049] In this embodiment, the backlight is configured using a two-layer backlight system in which LED light is incident from the edge, which further reduces costs compared to the conventional hybrid system. Furthermore, by controlling the brightness gradient, the discontinuity of brightness is improved, and the boundary between the two layers becomes less noticeable. In addition, by blacking out the area around the liquid crystal panel, black level distortion at night is made less noticeable, and the brightness difference with the black printed area is also reduced, making the overall appearance of black level distortion less noticeable.

[0050] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims. [Explanation of Symbols]

[0051] 100: Display device 110: Liquid crystal panel 120: Optical sheet 130: First light guide plate 132: First LED light source 134: Light-emitting area 140: Second light guide plate 142: Second LED light source 144: Illumination area 150: Housing

Claims

1. The first light guide plate, A second light guide plate is stacked with the first light guide plate, A first light source that irradiates light onto the end face of the first light guide plate, A second light source that irradiates light onto the end face of the second light guide plate, Includes control means for controlling the switching of lighting patterns, The first light guide plate includes a first light-emitting region in the center that reflects incident light toward the main surface, and the second light guide plate includes a second light-emitting region around the periphery that reflects incident light toward the main surface. The first light-emitting region includes a first gradient region in which the brightness decreases horizontally and vertically from a region with relatively high brightness, and the second light-emitting region includes a second gradient region in which the brightness decreases horizontally and vertically from a region with relatively high brightness. The first gradient region and the second gradient region are in an overlapping positional relationship when viewed in a planar manner. The control means controls the switching of a lighting pattern between a first lighting pattern that drives the first light source and the second light source, and a second lighting pattern that drives only the first light source.

2. The backlight device according to claim 1, wherein when light is irradiated onto the first light guide plate and the second light guide plate by the first light source and the second light source, the first light-emitting region and the second light-emitting region form a light-emitting region over the entire main surface.

3. The backlight device according to claim 1, wherein the brightness of the first and second gradient regions changes linearly.

4. The backlight device according to claim 1, wherein the brightness of the first and second gradient regions changes in a curved manner.

5. The backlight device according to claim 1, wherein the first light-emitting region includes a first dot pattern with uneven surfaces that reflects light incident on the bottom or bottom surface of the first light guide plate, and the second light-emitting region includes a second dot pattern with uneven surfaces that reflects light incident on the bottom or bottom surface of the second light guide plate, and the change in brightness is adjusted by the density or size of the first and second dot patterns.

6. The backlight device according to claim 1, A display means that displays an image using light from the backlight device, A first driving means for driving the first light source, A second driving means for driving the second light source, A display device that includes a display device.

7. The display device according to claim 6, wherein the control means illuminates the first and second light sources via the first and second driving means when it is daytime or in a bright environment.

8. The display device according to claim 6, wherein the control means illuminates the first light source via the first driving means when it is nighttime or in a dark environment.

9. The display device according to claim 6, wherein the control means controls the illumination of the first and second light sources via the first and second driving means based on the display content displayed on the display means.

10. The display device according to claim 6, wherein the display means is a liquid crystal panel.

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