Patent Publication Number: US-2009225244-A1

Title: Image display device and light source control device therefor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims benefit of U.S. provisional application No. 61/034,729 filed on Mar. 7, 2008 under 35 U.S.C. §119(e); the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image display device, and more particularly, to an image display device having the function of switching among various display modes. 
     2. Description of the Related Art 
       FIG. 1  shows a schematic diagram illustrating an image display device  100  in the prior art that utilizes the parallax optical component to generate three dimensional image automatically. The image display device  100  as shown in  FIG. 1  comprises a liquid crystal panel  102 , a parallax barrier plate  104 , and a backlight module  116 . The parallax barrier plate  104  includes a glass substrate  118  and a plurality of stripe-type light shading portions  120  formed on the glass substrate  118  and is in contact with the surface of the liquid crystal panel  102  to work as the light separating device for separating the images for the left eye and the right eye. A liquid crystal layer  110  is sandwiched between the glass substrates  106  and  108  of the liquid crystal panel  102 . A polarizer  112  is disposed on the glass substrate  106  of the observer  122 &#39;s side (the light exit side) while a polarizer  114  is disposed on the side of the backlight module  116  (the light incident side). According to the method in the prior art as shown in  FIG. 1 , the three-dimensional image is generated by displaying the image for the left eye and the image for the right eye alternately disposed in the liquid crystal layer. The light emitted from the backlight module  116  passes through the image for the left eye and the image for the right eye and is mutually separated by the parallax barrier plate  104 . Parallax effect is generated when the left eye of the observer  122  only observes the image for the left eye while the right eye only observes the image for the right eye and, thereby, the observer  122  automatically senses a three-dimensional image. Such a design can only allow the display device  100  to display a three-dimensional (3D) image but cannot switch between a two-dimensional (2D) display mode and a three-dimensional (3D) display mode. 
     On the other hand, although a light collimating device disposed between the backlight module  116  and the liquid crystal panel  102  prohibits the light at a large viewing angle from passing through to show the narrow viewing angle effect, it cannot make the image display device  100  switch between the narrow viewing angle mode and the wide viewing angle mode. A structure that controls turning the liquid crystal molecule must be provided in the liquid crystal layer of the liquid crystal panel  102  to control the viewing angle and the manufacturing process for such a structure is very complicated. 
     BRIEF SUMMARY OF THE INVENTION 
     One embodiment of the invention provides an image display device having the function of switching among various display modes and the light source control device thereof. The display brightness variation between two display modes is smaller when the image display device switches from a first display mode to a second display mode. One embodiment of the invention provides an image display device having the function of switching between the two-dimensional (2D) and three-dimensional (3D) display modes or between the narrow viewing angle and wide viewing angle display modes and the light source control device thereof. 
     One embodiment of the invention provides an image display device, suitable for showing a first display mode and a second display mode that is different from the first display mode. The image display device comprises a display panel, a backlight module, a light path modifying device, and a switchable diffuser. The backlight module is disposed facing the display panel for emitting light as the display light source of the display panel. The light path modifying device is disposed between the display panel and the backlight module for changing the light path of the light to generate the first display mode in coordination with the display panel. The switchable diffuser is disposed between the light path modifying device and the display panel, and is capable of switching between a transparent mode and a scattering mode. The switchable diffuser receiving a first voltage does not scatter the light in the transparent mode, and the switchable diffuser receiving a second voltage scatters the light in the scattering mode. The display device displays the first display mode in the transparent mode and displays the second display mode in the scattering mode. 
     One embodiment of the invention provides a backlight module for optionally showing a first brightness mode or a second brightness mode on the basis of whether the switchable diffuser shows the transparent mode or the scattering mode. More specifically, the switchable diffuser shows the transparent mode when receiving a first voltage and shows the scattering mode when receiving the second voltage. Preferably, the backlight module receives a third voltage when the switchable diffuser receives the first voltage and the backlight module receives a fourth voltage when the switchable diffuser receives the second voltage. In one embodiment, the image display device further comprises a first power controller and a second power controller. The first power controller optionally provides the first voltage or the second voltage and the second power controller optionally provides the third voltage or the fourth voltage. 
     The image display device according to one embodiment of the invention further comprises a light sensor. The light sensor is to sense the light passing through the switchable diffuser and performs a brightness measurement. The backlight module shows different brightness modes according to the brightness measurement. Preferably, the image display device further comprises a power controller. The power controller provides different voltages to the backlight module according to the brightness measurement. 
     The light path modifying device according to one embodiment of the invention is a parallax optical component. The parallax optical component shows the visual separating effect and the first display mode is the three-dimensional (3D) display mode while the second display mode is the two-dimensional (2D) display mode. 
     The light path modifying device according to one embodiment of the invention is a light collimating device. The light collimating device collimates the light emitted from the backlight module and the first display mode shows the narrow viewing angle mode while the second display mode shows the wide viewing angle mode. 
     According to the design of the above-mentioned various embodiments, one embodiment of the invention can provide an image display device having the function of switching among various display modes. 
     Another embodiment of the invention provides a light source control device disposed between a display panel and a light source provided for the display panel. The light source control device is turned on to be in a first mode and is turned off to be in a second mode. In the first mode, the light being already collimated or separated passes through without changing the original propagation route. In the second mode, the light being already collimated or separated is scattered and changes the original propagation route. The first mode corresponds to a three-dimensional (3D) display mode or a narrow viewing angle display mode while the second mode corresponds to a two-dimensional (2D) display mode or a wide viewing angle mode. According to the design of the above-mentioned embodiments, a switchable diffuser, disposed between the display panel and the light source provided for the display panel, functions as the light source control device which is turned on to be in a first mode and is turned off to be in a second mode. In the first mode, the light being already collimated or separated passes through without changing the original propagation route, while, in the second mode, the light being already collimated or separated is scattered and changes the original propagation route. The light source control device can enable an image display device to switch between the two-dimensional (2D) display mode and the three-dimensional (3D) display mode for providing different visual effect. In addition, the light source control device may enable an image display device to switch between the narrow viewing angle display mode and the wide viewing angle display mode for displaying the information publicly or privately. 
     Other purposes and benefits of the invention can be further understood by the technical features disclosed in the above-mentioned embodiments. In order to provide better and more obvious understanding of the purposes, features, and benefits of the invention, the detailed descriptions of the embodiments according to the invention will be given in the following together with figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram illustrating a traditional image display device that utilizing a parallax optical component to generate three dimensional image automatically; 
         FIGS. 2A and 2B  show schematic diagrams illustrating the image display device according to one embodiment of the invention where  FIG. 2A  shows a two-dimensional (2D) display mode and  FIG. 2B  shows a three-dimensional (3D) display mode; 
         FIGS. 3A and 3B  show schematic diagrams illustrating another embodiment of the invention to describe the effect of the parallax barrier plate having opaque blocks that are made of reflective material; 
         FIGS. 4 and 5  show schematic diagrams illustrating different parallax optical components according to other embodiments of the invention; 
         FIGS. 6A and 6B  show schematic diagrams illustrating the image display device according to another embodiment of the invention where  FIG. 6A  shows a wide viewing angle display mode and  FIG. 6B  shows a narrow viewing angle display mode; 
         FIGS. 7-11  show schematic diagrams illustrating different light collimating devices according to other embodiments of the invention; 
         FIGS. 12A and 12B  show schematic diagrams illustrating another embodiment of the invention to describe the effect of the light collimating device having opaque blocks that are made of reflective material; and 
         FIG. 13  shows a schematic diagram illustrating the image display device according to another embodiment of the invention. 
         FIGS. 14A and 14B  respectively show a schematic diagram illustrating the image display device according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The above mentioned and other technical contents, uniqueness, and effects of the invention can be illustrated more clearly by the following detailed descriptions together with the corresponding figures. The wording describing directions used in the following descriptions, such as: up, down, left, right, front, back or the like, indicates the directions with respect to the figure only. Therefore, the wording used to describe directions is for illustration but not to limit the scope of the invention. 
       FIGS. 2A and 2B  show schematic diagrams illustrating the image display device  10  according to one embodiment of the invention where  FIG. 2A  shows a two-dimensional (2D) display mode and  FIG. 2B  shows a three-dimensional (3D) display mode. As shown in  FIGS. 2A and 2B , the image display device  10  can switch between 2D and 3D display modes. The image display device  10  comprises a display panel  12 , a backlight module  14 , a parallax optical component  16 , and a switchable diffuser  18 . The backlight module  14  is disposed facing the display panel  12  for emitting light I as the display light source of the display panel. The parallax optical component  16  is disposed between the display panel  12  and the backlight module  14  for generating the visual separating effect. In this embodiment, the parallax optical component  16  is a parallax barrier plate  22 . The parallax barrier plate  22  comprises a plurality of alternately disposed transparent blocks  22   a  and opaque blocks  22   b.  The light I emitted from the backlight module  14  is mutually separated into two portions respectively passing through the image for the left eye and the image for the right eye by the parallax barrier plate  22 . As a result, the parallax effect is generated such that the left eye of the observer  20  only observes the image for the left eye and the right eye of the observer  20  only observes the image for the right eye. Thus, the observer  20  automatically senses a 3D image. The switchable diffuser  18  is disposed between the parallax barrier plate  22  and the display panel  12 . In this embodiment, the switchable diffuser  18  being turned on (ON) shows transparent when a voltage is applied thereto; the switchable diffuser  18  being turned off (OFF) shows haze when no voltage is applied thereto. In another embodiment, the switchable diffuser  18  being turned off (OFF) may show transparent when no voltage is applied thereto; the switchable diffuser  18  being turned on (ON) may show haze when a voltage is applied to thereto. Therefore, when the switchable diffuser  18  is turned off as shown in  FIG. 2A , the light mutually separated by the parallax barrier plate  22  is scattered by the hazed switchable diffuser  18  and, thereby, the light entering the observer  20  does not shows the visual separating effect so that the image display device  10  displays two-dimensional (2D) images. On the other hand, when the switchable diffuser  18  is turned on as shown in  FIG. 2B , the light mutually separated by the parallax barrier plate  22  can pass through the transparent switchable diffuser  18  along the original light path without any influence and, thereby, the light entering the observer  20  shows the visual separating effect so that the image display device  10  displays three-dimensional (3D) images. 
     In one embodiment, the image display device  10  further comprises a first voltage controller  24 . The first voltage controller  24  is coupled to the switchable diffuser  18  for optionally providing a first voltage or a second voltage to the switchable diffuser  18 . The switchable diffuser  18  shows the transparent mode when receiving the first voltage and shows the haze mode when receiving the second voltage. Preferably, the second voltage is zero so that the switchable diffuser  18  is turned on when receiving the first voltage and is turned off when receiving the second voltage at zero, that is, turned off when not receiving any voltage. 
     The display brightness of the normal direction of the image display device  10  reduces when the switchable diffuser  18  switches from the transparent mode to the haze mode. The human eyes detect the brightness change instantly, and the display quality is affected due to decrease in the display brightness after switching. In one embodiment, the backlight module  14  optionally shows a first brightness mode or a second brightness mode according to whether the switchable diffuser  18  shows the transparent mode or the haze mode. Preferably, the brightness of the second brightness mode is higher than that of the first brightness mode. Therefore, when the switchable diffuser  18  switches to the haze mode from the transparent mode, the backlight module  14  also switches from the first brightness mode to the second brightness mode. Not only the display brightness variation of the image display device  10  sensed by the human eyes is reduced, but the light intensity loss induced by the haze mode of the switchable diffuser  18  is also compensated. As a result, the display brightness of the normal direction is compensated and the display quality is improved. On the other hand, the backlight module  14  also switches to the first brightness mode from the second brightness mode when the switchable diffuser  18  switches from the haze mode to the transparent mode. The display brightness variation of the image display device  10  sensed by the human eyes can also be reduced and the display quality is improved. 
     In one embodiment, the image display device  10  can further comprise a second voltage controller  24   a  being coupled to the backlight module  14 . When the switchable diffuser  18  receives the first voltage, the second voltage controller  24   a  provides a third voltage to the backlight module  14  for showing the first brightness mode. When the switchable diffuser  18  receives the second voltage, the second voltage controller  24   a  provides a fourth voltage to the backlight module  14  for showing the second brightness mode. Preferably, the fourth voltage is higher than the third voltage. 
     In one embodiment, the switchable diffuser  18  can be a polymer dispersed liquid crystal (PDLC) panel or a bi-stable cholesteric liquid crystal panel. 
       FIGS. 3A and 3B  show schematic diagrams illustrating another embodiment of the invention. Referring to  FIGS. 3A and 3B , the effect provided by the parallax barrier plate having opaque blocks that are made of reflective material will be described. The material for the opaque block  22   b  of the parallax barrier plate  22  is not limited and can be made by, for example, metallic material, plastic material, or ink material. Please refer to the  FIGS. 3A and 3B . When the opaque block  22   b  of the parallax barrier plate  22  is formed by utilizing the reflective material such as metallic material, the light IR shaded by the opaque block  22   b  can be reflected back into the backlight module  14  and, then, reflected by the backlight module  14  again towards the direction of the parallax barrier plate  22  for emitting. The light that may be absorbed originally can be recycled and utilized to increase the light emitting efficiency. 
     Furthermore, the parallax optical component according to the invention providing parallax effect is not limited to the parallax barrier plate  22 . A single focusing lens set  26  ( FIG. 4 ) or a single cylindrical lens set  28  ( FIG. 5 ) can also be used. The single focusing lens set  26  comprises a plurality of focusing lens structures  26   a  and the single cylindrical lens set  28  comprises a plurality of cylindrical lens structures  28   a.  Obviously, the focusing lens structure  26   a  and the cylindrical lens structure  28   a  can also be mixed to form one single parallax optical component  16 . The focusing lens structure  26   a  or the cylindrical lens structure  28   a  can be arranged on the top surface or the bottom surface of the same parallax optical component  16 , or they may be formed on the top surface and the bottom surface of the same parallax optical component  16  together. 
       FIGS. 6A and 6B  show schematic diagrams illustrating the image display device  30  according to another embodiment of the invention where  FIG. 6A  shows a wide viewing angle display mode and  FIG. 6B  shows a narrow viewing angle display mode. The image display device  30  can be switched between the wide viewing angle and the narrow viewing angle display modes. Please refer to  FIG. 6A  and  FIG. 6B . The image display device  30  comprises a display panel  32 , a backlight module  34 , a light collimating device  36 , and a switchable diffuser  38 . The backlight module  34  is disposed facing the display panel  32  for emitting light I as the display light source of the display panel  32 . The light collimating device  36 , disposed between the display panel  32  and the backlight module  34 , collimates the light I. The light collimating device  36  can be, for example, a single cylindrical lens set  52  ( FIG. 7 ), a single cylindrical prism set  54  ( FIG. 8 ), a parallax barrier plate  56  ( FIG. 9 ) or the like. Or, the cylindrical lens structure  52   a  and the cylindrical prism structure  54   a  can be mixed to form one single light collimating device  36  ( FIG. 10 ,  FIG. 11 ). The cylindrical lens structure  52   a  and the cylindrical prism structure  54   a  may be arranged on the top surface or the bottom surface of the same light collimating device  36 , or they may be formed on the top surface and the bottom surface of the same light collimating device  36  together ( FIG. 10 ). The switchable diffuser  38  is disposed between the light collimating device  36  and the display panel  32 . In this embodiment, the switchable diffuser  38  being turned on shows transparent when a voltage is applied thereto; the switchable diffuser  38  being turned off shows haze when no voltage is applied thereto. In another embodiment, the switchable diffuser  38  being turned off may show transparent when no voltage is applied thereto; the switchable diffuser being turned on  38  may show haze when a voltage is applied thereto. Therefore, after the light emitted by the backlight module  34  is collimated by the light collimating device  36  as shown in  FIG. 6A , the light at a large viewing angle cannot pass through the light collimating device  36  and thus the image display device  30  shows the narrow viewing angle effect. However, when the switchable diffuser  38  is turned off, the light is scattered by the hazed switchable diffuser  38  to increase the viewing angle and thereby the image display device  30  shows the wide viewing angle display mode. On the other hand, after the light emitted by the backlight module  34  is collimated by the light collimating device  36  as shown in  FIG. 6B , the light at a large viewing angle cannot pass through the light collimating device  36  and thus the image display device  30  shows the narrow viewing angle effect. But, when the switchable diffuser  38  is turned on, the light at a narrow viewing angle can pass through the transparent switchable diffuser  38  along the original light path without any influence and thereby the image display device  30  shows the narrow viewing angle display mode. 
     In one embodiment, the image display device  30  further comprises a first voltage controller  44 . The first voltage controller  44  is coupled to the switchable diffuser  38  for optionally providing a first voltage or a second voltage to the switchable diffuser  38 . The switchable diffuser  38  shows the transparent mode when receiving the first voltage and shows the haze mode when receiving the second voltage. Preferably, the second voltage is zero so that the switchable diffuser  38  is turned on when receiving the first voltage and turned off when receiving the second voltage at zero, that is, turned off when not receiving any voltage. 
     The display brightness of the normal direction of the image display device  30  reduces when the switchable diffuser  38  switches from the transparent mode to the haze mode. The human eyes detect the brightness change instantly and the display quality is affected due to decrease of the display brightness after switching. In one embodiment, the backlight module  34  optionally shows a first brightness mode or a second brightness mode on the basis of whether the switchable diffuser  38  shows the transparent mode or the haze mode. Preferably, the brightness of the second brightness mode is higher than that of the first brightness mode. Therefore, when the switchable diffuser  38  switches to the haze mode from the transparent mode, the backlight module  34  also switches from the first brightness mode to the second brightness mode. Not only the display brightness variation of the image display device  30  sensed by the human eyes is reduced, but the light intensity loss induced by the haze mode of the switchable diffuser  38  is also compensated. As a result, the display brightness of the normal direction is compensated and the display quality is improved. On the other hand, the backlight module  34  also switches to the first brightness mode from the second brightness mode when the switchable diffuser  38  switches from the haze mode to the transparent mode. The display brightness variation of the image display device  30  sensed by the human eyes can also be reduced and the display quality is improved. 
     In one embodiment, the image display device  30  further comprises a second voltage controller  44   a  that couples to the backlight module  34 . When the switchable diffuser  38  receives the first voltage, the second voltage controller  44   a  provides a third voltage to the backlight module  34  for showing the first brightness mode. When the switchable diffuser  38  receives the second voltage, the second voltage controller  44   a  provides a fourth voltage to the backlight module  34  for showing the second brightness mode. Preferably, the fourth voltage is higher than the third voltage. 
       FIGS. 12A and 12B  show schematic diagrams illustrating another embodiment of the invention. Referring to  FIGS. 12A and 12B , the effect provided by the light collimating device having opaque blocks that are made of reflective material will be described. When the light collimating device is a parallax barrier plate  56 , the material for the opaque block  22   b  of the parallax barrier plate  56  is not limited and can be made by, for example, metallic material, plastic material, or ink material. Please refer to the  FIGS. 12A and 12B . When the opaque block  22   b  of the parallax barrier plate  56  is formed by the reflective material such as metallic material, the light IR at a large viewing angle shaded by the opaque block  56   b  can be reflected back into the backlight module  34  and then reflected by the backlight module  34  again towards the direction of the parallax barrier plate for emitting. The light can be recycled and utilized to increase the light emitting efficiency. 
     According to the design of the above-mentioned various embodiments of the invention, a switchable diffuser can be utilized as the light source control device and disposed between a display panel and the light source provided for the display panel. The light source control device is turned on to be in a first mode and is turned off to be in a second mode. In the first mode, the light being already collimated or separated may pass through the light source control device without changing the original propagation route. In the second mode, the light being already collimated or separated is scattered and changes the original propagation route after passing through the light source control device. Thus, the light source control device can enable an image display device to switch between the two-dimensional (2D) display mode and the three-dimensional (3D) display mode for providing different visual effect. In addition, it may enable an image display device to switch between the narrow viewing angle display mode and the wide viewing angle display mode for displaying the information publicly or privately. 
     According to the design of the above-mentioned various embodiments of the invention, the image display device is not limited to comprise a parallax optical component or a light collimating device. The image display device can comprise a light path modifying device for changing the light path of the light emitted from the backlight module to generate the first display mode in coordination with the display panel. The parallax optical component or the light collimating device according to the above-mentioned various embodiments of the invention is just one example for the light path modifying device. The light path modifying device, which is used for changing the light path of the light emitted from the backlight module to show a display mode in coordination with the display panel, can be implemented by the existing devices or devises to be developed in the future. 
       FIG. 13  shows a schematic diagram illustrating the image display device  30   a  according to another embodiment of the invention. Since the embodiment shown in  FIG. 13  is similar to that in  FIG. 6 , the same symbols are applied to the same devices and the descriptions of the same portion will be omitted so that only the portion that is different between the two embodiments will be described in the followings. 
     Please refer to  FIG. 13 . The image display device  30   a  comprises a display panel  32 , a backlight module  34 , a light path modifying device  35 , a light sensor  45   a,  and a switchable diffuser  38 . In this embodiment, the light path modifying device  35  is a light collimating device  36 . Therefore, the image display device  30   a  can be switched between the wide viewing angle and the narrow viewing angle display modes. In one embodiment, the light path modifying device  35  can also be a parallax optical component. The light sensor  45   a  is disposed on the light exiting side of the switchable diffuser  38  for performing a brightness measurement of the light passing through the switchable diffuser  38 . In this embodiment, the light sensor  45   a  is disposed on one side of the switchable diffuser  38  facing the display panel  32  and between the display panel  32  and the switchable diffuser  38 . In another embodiment, the light sensor  45   a  can be disposed on the light exiting side of the display panel  32  (not shown in the figure). 
     Besides, the backlight module  34  shows different brightness modes according to the brightness measurement measured by the light sensor  45   a.  More specifically, the display brightness of the image display device  30  is reduced when the switchable diffuser  38  switches from the transparent mode to the haze mode and thus the brightness measurement measured by the light sensor  45   a  also changes from a first level to a second level that is lower than the first level. After receiving the brightness measurement, the backlight module  34  also changes from a first brightness mode to a second brightness mode by sensing the change in the brightness measurement where the brightness of the second brightness mode is higher then the brightness of the first brightness mode. In one embodiment, the image display device  30   a  can further comprise a second voltage controller  44   a  coupled to the backlight module  34  and the light sensor  45   a.  The second voltage controller  44   a  is for receiving the result of the brightness measurement and providing different voltages to the backlight module  34  according to the brightness measurement. More specifically, the second voltage controller  44   a  provides a third voltage when the brightness measurement measured by the light sensor  45   a  is at the first level so that the backlight module  34  shows a first brightness mode after receiving the third voltage. When the brightness measurement measured by the light sensor  45   a  is at the second level, the second voltage controller  44   a  provides a fourth voltage so that the backlight module  34  shows a second brightness mode after receiving the fourth voltage. Since the second level is lower than the first level, preferably the fourth voltage is set to be higher than the third voltage. 
     There are a number of reasons that cause the reduction of the display brightness of the normal direction of the image display device  30 . For example, the aging of the backlight module  34  is one of the reasons. Comparing to the embodiment shown in  FIG. 6B , the light sensor  45   a  utilized in this embodiment can sense the display brightness reduction caused by the aging of the backlight module  34  and the voltage provided to the backlight module  34  correspondingly can be increased so that the backlight module  34  can have higher brightness. Therefore, the display brightness shown by the image display device  30   a  can be more stable and the display quality can be increased. 
     In addition, according to an embodiment of the present invention, the switchable diffuser may not be disposed between the light path modifying device and the display panel for having the function of switching among various display modes.  FIGS. 14A and 14B  respectively show a schematic diagram illustrating the image display device according to another embodiment of the invention. For convenience in explanation, the components of the embodiment of  FIGS. 14A and 14B  that are the same as the components of the embodiment of  FIG. 13  will be assigned the same component symbols, and the detailed description thereof will not be repeated hereinafter and the difference therebetween is described as follows. As shown in  FIG. 14A  and  FIG. 14B , the display panel  32  and the light path modifying device  35  are disposed between the backlight module  34  and the switchable diffuser  38  in the image display device  30   b  and  30   c.  Specifically, the light path modifying device  35  is further disposed between the backlight module  34  and the display panel  32  in the image display device  30   b,  while the display panel  32  is further disposed between the backlight module  34  and the light path modifying device  35  in the image display device  30   c.    
     On the basis of the design of the image display device  30   a,  the light passing through the display panel  32  is observed by an observer without passing through the switchable diffuser  38  as the image display device  30   b  and  30   c  do not. Accordingly, the image display device  30   a,  comparing to the image display device  30   b  and  30   c,  may display a clearer image and has a better display quality. 
     Although the preferred embodiments of the present invention has been fully described by way of examples with reference to the accompanying drawings, it should not be construed as any limitation on the implementation range of the invention. Various equivalent changes and modifications can be performed by those who are skilled in the art without deviating from the scope of the invention. The scope of the present invention is to be encompassed by the claims of the present invention. Any embodiment or claim of the present invention does not need to reach all the disclosed objects, advantages, and uniqueness of the invention. Besides, the abstract and the title are only used for assisting the search of the patent documentation and should not be construed as any limitation on the implementation range of the invention.