Patent Publication Number: US-2011051029-A1

Title: Display device, electronic apparatus, and projection imaging apparatus

Description:
The entire disclosure of Japanese Patent Application No. 2009-201336, filed Sep. 1, 2009 is expressly incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a display device, an electronic apparatus provided with display device, and a projection imaging apparatus. 
     2. Related Art 
     As the display device, a head-up display (HUD) has been developed which is installed in a vehicle to project an image displayed on a display unit to a windshield of the vehicle. 
     In such a head-up display, it has been known that sunlight entering the display unit through the windshield of the vehicle has various influences. 
     For example, in JP-A-2007-65011, it is described that when a liquid crystal display is used as the display unit, a polarization member is damaged by the sunlight, and at worst, an image cannot be displayed. 
     In consideration of the problem, in JP-A-2007-65011, a transreflective member, which transmits display light and reflects infrared light, and a polarization member are provided on the front side of a liquid crystal cell, and they are not parallel to the liquid crystal cell. 
     Accordingly, the sunlight entering the liquid crystal cell is reflected from the transreflective member, thereby preventing the damage of the polarization member and the liquid crystal cell caused by the heat of the sunlight. In addition, the display light output from the liquid crystal cell is reflected from the transreflective member provided on the front side, and enters the liquid crystal cell again, which is stray light. The stray light can be also prevented. 
     For example, in JP-A-2007-148092, it is disclosed that sunlight enters a display unit at various angles, the sunlight reflected from the display unit overlaps with the display light according to an incident angle, and thus the image may not be recognized. 
     In consideration of the problem, in JP-A-2007-148092, an optical member which is provided on the front side of the display unit and enlarges and transmits the image output from the display unit is pivotably configured to vary an angle formed between a projection plane on which the enlarged image is projected and a transmission plane opposed to the projection plane of the optical member. The display unit is provided at an angle such that the sunlight transmitted through the optical member does not perpendicularly enter the display unit. 
     Accordingly, the optical member is pivoted such that the sunlight and the projection light (display light) do not overlap with each other, and thus it is possible to show a stable image. 
     In JP-A-2007-65011, a part of the sunlight is reflected and removed by the transreflective member, but there is a problem in that most of the light is transmitted through the transreflective member, is reflected from the surface of the liquid crystal cell, and overlaps with the display light, thereby decreasing contrast. 
     In JP-A-2007-148092, a mechanism to pivot the optical member is necessary, and a structure thereof is complicated. 
     For example, when a liquid crystal display device is used as the display unit and the display unit is provided at an angle from the sunlight which is transmitted through the optical member, there is a problem that a real visual angle range of the liquid crystal display device may deviate from a range in which the optimal contrast can be obtained. 
     SUMMARY 
     An advantage of some aspects of the invention is that it provides a display device, an electronic apparatus, and a projection imaging apparatus which are capable of solving at least a part of the above-mentioned problems. The invention can be realized by the following configuration or applications. 
     Application 1 
     According to an aspect of the application, there is provided a display device including a display panel, and a prism that is installed on a display face of the display panel and has an inclination face inclined from the display face, wherein an inclination angle of the inclination face of the prism with respect to the display face is set such that an output angle of display light output from the display face and transmitted through the prism is equal to or more than a small angle of an incident angle and a reflection angle of sunlight with respect to the inclination face based on a normal line of the display face. 
     With such a configuration, it is hard for the sunlight reflected from the inclination face of the prism or the sunlight transmitted through the prism and reflected from the display face of the display panel to overlap with the output direction of the display light. That is, the display on the display panel is prevented from being hardly seen by the influence of the sunlight reflection. The prism is provided on the display face, and thus it is possible to view an image in a state where optical characteristics such as contrast are optimal when viewing the display panel from the output direction of the display light, even when the output direction of the display light deviates from the normal line direction of the display face. In other words, it is possible to view the image with stable optical characteristics, as compared with the case of viewing the display panel in a state where there is no prism in a direction deviating from the normal line direction. 
     Application 2 
     In the display device of the application, it is preferable that the inclination angle of the inclination face is equal to or less than 30°. 
     With such a configuration, the color of the display light input from the display face to the prism is prevented from being significantly dispersed by the wavelength dispersion characteristics of the prism. That is, it is possible to obtain stable optical characteristics. 
     Application 3 
     In the display device of the application, when a sum of the incident angle and the reflection angle of the sunlight with respect to the inclination face based on the normal line of the display face is equal to or more than 20° and equal to or less than 50°, the inclination angle of the inclination face with respect to the display face is equal to or more than 6° and equal to or less than 18.5°. 
     With such a configuration, when the visual angle range based on the normal line of the display face is equal to or more than 20° and equal to or less than 50°, the influence of the sunlight reflection is suppressed and it is possible to obtain a display with high visual angle quality. 
     Application 4 
     In the display device of the application, it is preferable that the prism is provided in close contact with the display face of the display panel. 
     With such a configuration, it is hard for the sunlight input to the prism to be reflected on the display face, and it is possible to further suppress the influence of the sunlight reflection in the display on the display panel. 
     Application 5 
     In the display device of the application, wherein the prism may be a prism sheet having a plurality of inclination faces inclined and arranged in the same direction. 
     With such a configuration, it is possible to reduce the thickness of the display device including the prism, as compared with the case of providing the prism having a single inclination face on the display face. Therefore, it is possible to provide a smaller display device. 
     Application 6 
     In the display device of the application, it is preferable that the display panel has a plurality of pixels arranged in a first direction and a second direction intersecting the first direction, and the prism is provided on the display panel such that an extending direction of the plurality of inclination faces intersects the first direction and the second direction. 
     With such a configuration, it is possible to avoid interference of light between the plurality of inclination faces and the plurality of pixels, and it is possible to obtain a display with high visual angle quality. 
     Application 7 
     In the display device of the application, it is preferable that the display panel has at least a polarization element on the incident side of the sunlight, and the polarization element is provided on the inclination face of the prism. 
     With such a configuration, the polarization element which is easily heated by absorbing the sunlight is disposed at a position separated from the display face. Accordingly, it is hard for the display panel to be affected by the heat of the sunlight, as compared with the case of disposing the prism on the display face with the polarization element interposed therebetween. 
     Application 8 
     In the display device of the application, it is preferable that the display panel is a liquid crystal panel, initial alignment of liquid crystal molecules in the liquid crystal panel is substantially parallel to the display face, the prism is provided on the display face such that the inclination direction of the inclination face and the initial alignment direction of the liquid crystal molecules intersect with each other based on the normal line of the display face, and the polarization element is provided on the inclination face such that an absorption axis is substantially the same as the initial alignment direction. 
     With such a configuration, even when the polarization element is disposed on the inclination face of the prism, it is possible to obtain stable optical characteristics for the display on the display panel since the absorption axis and the initial alignment direction of the liquid crystal molecules are substantially the same, regardless of the inclination direction of the inclination face. 
     Application 9 
     According to another aspect of the application, there is provided an electronic apparatus provided with the display device of the applications. 
     With such a configuration, it is hard to be affected by the sunlight reflection in a predetermined visual angle range, and it is possible to provide the electronic apparatus by which a display state with high visual angle quality can be obtained. 
     Application 10 
     According to a still another aspect of the application, there is provided a projection imaging apparatus provided with the display device of the applications. 
     With such a configuration, it is hard to be affected by the sunlight reflection in a predetermined visual angle range, and it is possible to provide the projection imaging apparatus by which a projection image with high visual angle quality can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1A  is a schematic perspective view illustrating a configuration of a display device according to a first embodiment. 
         FIG. 1B  is a schematic cross-sectional view illustrating the display device according to the first embodiment. 
         FIG. 2A  is a schematic plan view illustrating a configuration of a display panel. 
         FIG. 2B  is a schematic cross-sectional view illustrating the display panel. 
         FIG. 3  is a schematic plan view illustrating a configuration of pixels. 
         FIG. 4  is a schematic cross-sectional view of main parts illustrating a structure of pixels. 
         FIG. 5A  is a schematic view illustrating an optical design condition in the display panel. 
         FIG. 5B  is a schematic view illustrating an optical design condition in the display panel. 
         FIG. 5C  is a schematic view illustrating an optical design condition in the display panel. 
         FIG. 6  is a schematic cross-sectional view illustrating an influence of sunlight in the display device according to the first embodiment. 
         FIG. 7  is a schematic cross-sectional view illustrating optical disposition of a lighting device and a display panel of a comparative example. 
         FIG. 8  is a graph illustrating contrast characteristics in the display panel. 
         FIG. 9  is a graph illustrating contrast characteristics in the display device according to the first embodiment. 
         FIG. 10  is a schematic cross-sectional view illustrating a configuration of a display device according to a second embodiment. 
         FIG. 11A  is a schematic perspective view illustrating a configuration of a display device according to a third embodiment. 
         FIG. 11B  is a front view illustrating the display device according to the third embodiment. 
         FIG. 12  is a schematic cross-sectional view illustrating a configuration of the display device according to the third embodiment. 
         FIG. 13  is a schematic view illustrating the configuration of a head-up display as a projection imaging apparatus. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, embodiments of the invention will be described with reference to the drawings. The drawings are appropriately enlarged and reduced such that described parts can be recognized. 
     First Embodiment 
     A display device according to the embodiment will be described with reference to  FIG. 1A  to  FIG. 6 .  FIG. 1A  is a schematic perspective view illustrating a configuration of the display device,  FIG. 1B  is a schematic cross-sectional view illustrating the display device,  FIG. 2A  is a schematic plan view illustrating a configuration of a display panel,  FIG. 2B  is a schematic cross-sectional view illustrating the display panel,  FIG. 3  is a schematic plan view illustrating a configuration of pixels,  FIG. 4  is a schematic cross-sectional view of main parts illustrating a structure of pixels,  FIG. 5A  is a schematic view illustrating an optical design condition in the display panel,  FIG. 5B  is a schematic view illustrating an optical design condition in the display panel,  FIG. 5C  is a schematic view illustrating an optical design condition in the display panel, and  FIG. 6  is a schematic cross-sectional view illustrating an influence of sunlight in the display device. 
     As shown in  FIG. 1A , a display device  100  of the embodiment includes a display panel  120 , and a prism  110  provided on a display face  120   a  of the display panel  120 . In this case, the display panel  120  is a light receiving type and performs displaying by illumination of a lighting device  150  provided on the opposite side (rear side) to the display face  120   a . Accordingly, the display device  100  may have a configuration including the lighting device  150 . 
     The lighting device  150  is a light source provided to obtain uniform brightness from a light emitting face  150   a , for example, includes a cold cathode fluorescent lamp (CCFL) and a light emitting diode (LED), and a light guide plate, a reflection plate and a diffusion plate which leads light from the light source to the light emitting face  150   a . As a lighting type, an underlying type in which the light source is provided right under the light emitting face  150   a  or a side type in which the light source is provided at the end portion of the light guide plate is conceivable. 
     The prism  110  provided on the front side of the display panel  120  has a single inclination face  110   b  inclined from the display face  120   a  at a predetermined angle. Such a prism  110  is generally called a wedge prism. 
     As shown in  FIG. 1B , the prism  110  is provided on the display panel  120  such that a first face  110   a  opposed to the inclination face  110   b  comes into close contact with the display face  120   a.    
     As a method of bringing the first face  110   a  into close contact with the display face  120   a  without a gap, there is a method in which they are pressed together with an intermediate material such as a transparent adhesive or cohesive agent or a gel type member. For example, a method uniformly interposing an adhesive agent therebetween is disclosed in JP-A-2009-3067. 
     Illumination light emitted from the lighting device  150  and perpendicularly input to the display face  120   a  is transmitted through the display panel  120  to be display light L based on display information, and the display light L is input to the prism  110 . The prism  110  has a declination angle θd regulated by an inclination angle (or wedge angle) θw of the inclination face  110   b  and a refractive index n. The display light L transmitted through the prism  110  is output from the inclination face  110   b  in a direction inclined by the declination angle θd with respect to a normal line  120   v  of the display face  120   a . That is, the inclination angle θd may be called an output angle θd of the display light L on the inclination face  110   b.    
     Such a display device  100  is appropriately used for a head-up display (HUD) as an electronic device to be described later. 
     In this case, the following description is made by considering that the display panel  120  is rectangular, a long-side direction of the display face  120   a  is an X direction, a short-side direction is a Y direction, and a normal line direction of the display face  120   a  is a Z direction. 
     The prism  110  is provided on the display panel  120  such that the inclination face  110   b  of the prism  110  is inclined in the short-side direction (Y direction) of the display panel  120 , but is not limited thereto. A method of optically disposing the prism  110  will be described later. 
     Next, the display panel  120  will be described. As shown in  FIG. 2A  and  FIG. 2B , the display panel  120  is provided with an element substrate  10 , and an opposite substrate  20  smaller in size than the element substrate  10  in the plan view, which are opposed to each other. 
     A gap between the element substrate  10  and the opposite substrate  20  bonded by a seal member  40  is filled with liquid crystal having positive dielectric anisotropy, to form a liquid crystal layer  50 . That is, the liquid crystal layer  50  is sandwiched between the element substrate  10  and the opposite substrate  20 . 
     The outside of the seal member  40  is a peripheral circuit area, where a data line driving circuit  70  and a plurality of terminals  80  for connection to external circuits are provided along one side of the element substrate  10  in the long-side direction (X direction). In addition, scanning line driving circuits  90  are provided along the two other sides in the short-side direction (Y direction) of the element substrate  10 . A plurality of wires  13  connecting the two scanning line driving circuits  90  to each other are provided along the one other side of the element substrate  10 . 
     A plurality of pixels arranged in a matrix shape are provided inside the seal member  40  in the X direction as a first direction and the Y direction as a second direction perpendicular to the X direction. One pixel is formed of three sub-pixels corresponding to 3-color filters  22 R (red),  22 G (green), and  22 B (blue). The 3-color filters  22 R,  22 G, and  22 B are formed on the opposite substrate  20  such that the color filters  22  of the same color are continuous in the Y direction. A plurality of TFTs (Thin Film Transistor)  30  are provided as switching elements for sub-pixels on the element substrate  10  to control the sub-pixels. That is, the display panel  120  is an active liquid crystal panel capable of color display with stripe-type color filters  22 . 
     In the embodiment, an area of a plurality of pixels contributing to real display is a display area AR, and a light shield film  61  partitioning the sub-pixels and shielding light of the display area AR in a frame shape is provided. A light shield area  60  where the light shield film  61  is provided is a reference regulating a position of the display area AR when the display panel  120  and the prism  110  are attached to each other. 
     Polarization plates  14  and  24  as polarization elements are attached to the outward surfaces (surfaces opposite to the liquid crystal layer  50 ) of the element substrate  10  and the opposite substrate  20 . The display panel  120  excluding the polarization plates  14  and  24  may be called a liquid crystal cell  101  for descriptive purposes. 
     As shown in  FIG. 3 , one pixel of the display panel  120  is formed of three sub-pixels SG corresponding to the 3-color (R, G, and B) filters  22 R,  22 G, and  22 B. Each sub-pixel SG is provided with a rectangular pixel electrode  9  in which a plurality of slits (gap)  29  are formed in a substantially ladder shape. That is, the sub-pixel SG is rectangular. 
     The plurality of pixels are provided in a matrix shape such that the long-side direction of the sub-pixels SG is a column direction of the pixels. 
     A scanning line  3   a , a common line  3   b , and a plurality of data lines  6   a  are provided to surround the outer periphery of the pixel electrodes  9 . 
     The TFTs  30  are formed in the vicinity of the cross portion of the scanning line  3   a  and the data lines  6   a , and the TFTs  30  are electrically connected to the data lines  6   a  and the pixel electrodes  9 . 
     Rectangular common electrodes  19  are formed at positions overlapping with the pixel electrodes  9  in the plan view. The common electrodes  19  may be provided in a solid shape throughout the sub-pixels adjacent SG connected along the common line  3   b.    
     The pixel electrode  9  is a transparent conductive film formed of a conductive material such as ITO (Indium Tin Oxide). The pixel electrode  9  of one sub-pixel SG is provided with a plurality ( 24  in  FIG. 3 ) of slits  29 . The slits  29  extend in a cross direction (inclination direction in  FIG. 3 ) of the scanning line  3   a  and both of the data lines  6   a , and are formed to be arranged at the same interval in the Y direction along the data lines  6   a . The slits  29  are formed with substantially the same width and are parallel to each other. Accordingly, the pixel electrode  9  has stripe-shaped electrode portions  9   a  with a plurality of lines ( 23  in  FIG. 3 ). Since the slits  29  are arranged at a regular width at the same interval, the stripe-shaped electrodes portions  9   a  are arranged at a regular width at the same interval. All of the width of the slits  29  and the width of the stripe-shaped electrode portions  9   a  are about 4 μm. It is preferable that the pixel electrode  9  coming into contact with the liquid crystal layer  50  has the stripe-shaped electrode portion  9   a , and the portion between the stripe-shaped electrode portions  9   a  is not limited to the slit  29 , both ends of which are closed, and may be a slit, one end of which is opened. 
     In this case, an inclination angle of the slit  29  in the X direction along the scanning line  3   a  is 5°. Hereinafter, such a slit  29  is called a right-rising (5°) slit  29 . 
     The common electrode  19  is a transparent conductive film formed of a conductive material such as ITO, and is formed integrally with the common line  3   b  extending parallel to the scanning line  3   a . Accordingly, the common electrode  19  is electrically connected to the common line  3   b.    
     From the viewpoint of transmitting electrical signals, it is preferable that the scanning line  3   a , the data line  6   a , and the common line  3   b  are formed of conductive materials with low resistance, for example, aluminum, aluminum alloy, or the like. 
     The TFT  30  is provided with a semiconductor layer  35  formed of an island-shaped amorphous silicon film partially formed on the scanning line  3   a , a source electrode  31  branched from the data line  6   a  and extending on the semiconductor layer  35 , and a rectangular drain electrode  32  extending from the upside of the semiconductor layer  35  to the forming area of the pixel electrode  9 . 
     The scanning line  3   a  functions as a gate electrode of the TFT  30  at a position opposed to the semiconductor layer  35 . The drain electrode  32  and the pixel electrode  9  are electrically connected to each other through a contact hole  47  formed at an overlapping position of both in the plan view. 
     In the sub-pixel SG, since an area where the pixel electrode  9  overlaps with the common electrode  19  in the plan view functions as a capacitor of the sub-pixel SG, it is not necessary to provide a special capacitor for keeping image signals in the forming area of the sub-pixel SG, and thus it is possible to obtain a high aperture ratio. 
     In this case, the area where the pixel electrode  9  overlaps with the common electrode  19  in the plan view is a transmission display area T. 
     As shown in  FIG. 4 , in the display panel  120 , the liquid crystal layer  50  is sandwiched between the element substrate  10  having the pixel electrode  9  and the common electrode  19 , and the opposite substrate  20 . 
     The light shield film  61 , the color filters  22  ( 22 R,  22 G, and  22 B), and an alignment layer  23  covering the color filters  22  are formed toward the liquid crystal layer  50  on the opposite substrate  20  formed of transparent glass or the like. 
     The light shield film  61  is called a black matrix (BM) provided to substantially divide the color filters  22  for each sub-pixel SG (for each color) as viewed from the opposite substrate  20  side. As method of forming the same, for example, there is a method in which a thin film of metal or metal compound as a lightproof material is formed on the surface (liquid crystal layer  50  side) of the opposite substrate  20 , and patterning is performed to have an opening portion corresponding to the sub-pixel SG by photolithography. As a general metal or metal compound, there is chrome (Cr) or chrome oxide. In addition, there is a method of patterning resin including a black pigment as the lightproof material by a printing method such as offsetting. 
     The color filters  22  may be formed, for example, in a manner that a photosensitive resin material including a coloring material of each color is applied to the opposite substrate  20  on which the light shield film  61  is formed, and it is exposed and developed by photolithography to fill the opening portion of the light shield film  61 . Methods such as spin coat and slit coat may be used as the applying method. The color filters  22  may be formed by providing a partition wall portion on the light shield film  61  and using a method of applying liquid including the coloring material of each color as liquid droplets to an area partitioned by the partition wall portion. A thickness of the color filter  22  is about 1 μm to 2 μm. 
     Similarly, the scanning line  3   a , the common electrode  19 , and the common line  3   b  are formed on the element substrate  10  formed of transparent glass or the like. A gate insulating film  11  formed of a silicon oxide film or the like is formed to cover the scanning line  3   a , the common electrode  19 , and the common line  3   b.    
     The island-shaped semiconductor layer  35 , a source electrode  31 , and a drain electrode  32  are formed on the gate insulating film  11  such that the source electrode  31  and the drain electrode  32  partially overlap with the semiconductor layer  35 . 
     An interlayer insulating film  12  formed of a silicon oxide film or a resin film is formed to cover the semiconductor layer  35 , the source electrode  31 , and the drain electrode  32 . 
     The pixel electrode  9  is formed on the interlayer insulating film  12 , and the pixel electrode  9  is electrically connected to the drain electrode  32  through a contact hole  47  penetrating the interlayer insulating film  12  and reaching the drain electrode  32 . 
     That is, the gate insulating film  11  and the interlayer insulating film  12  as insulating films are interposed between the common electrode  19  and the pixel electrode  9 . 
     An alignment layer  18  formed of polyimide or the like is formed to cover the pixel electrode  9  of the element substrate  10 . The alignment layer  18  on the element substrate  10  side and the alignment layer  23  on the opposite substrate  20  side coming into contact with the liquid crystal layer  50  are subjected to an alignment process such as a rubbing process, to align liquid crystal molecules in a predetermined direction. Details of the alignment process will be described in optical design conditions to be described later. 
     A polarization plate  24  is attached to the surface (surface opposite to the liquid crystal layer  50  side) of the opposite substrate  20 , and a polarization plate  14  is attached to the surface (surface opposite to the liquid crystal layer  50  side) of the element substrate  10 . 
     The display panel  120  with such a structure controls the alignment direction of the liquid crystal molecules of the liquid crystal layer  50  by an electric field generated between the pixel electrode  9  having the stripe-shaped electrode portion  9   a  and the common electrode  19  to perform displaying, and is called an FFS (Fringe Field Switching) method. 
     Next, the optical design conditions of the display panel  120  will be described with reference to  FIG. 5A  to  FIG. 5C . 
     As shown in  FIG. 5A , the initial alignment of the liquid crystal cell  101  in the display panel  120  is homogeneous alignment taken along a line direction of pixels, that is, the X direction. More specifically, the rubbing direction in the alignment layer  18  of the element substrate  10  and the rubbing direction in the alignment layer  23  of the opposite substrate  20  are taken along the X direction, but are reversed by 180°. 
     Optical disposition of the pair of polarization plates  14  and  24  is in a cross-Nicol state (transmission axes or absorption axes are perpendicular to each other) with the liquid crystal cell  101  interposed therebetween. Specifically, an absorption axis  14   a  of the polarization plate  14  provided on the side to which light is input from the lighting device  150  is perpendicular to the initial alignment direction of the liquid crystal cell  101 . That is, a transmission axis  14   t  is the same direction as the initial alignment direction. On the contrary, an absorption axis  24   a  of the polarization plate  24  provided on the side from which light is output is the same direction as the initial alignment direction of the liquid crystal cell  101 . The transmission axis  24   t  is perpendicular to the initial alignment direction. 
     That is, the illumination light is transmitted through the polarization plate  14  and converted into straight polarized light, and the straight polarized light is transmitted through the liquid crystal cell  101 . However, the light is absorbed by the polarization plate  24 . Accordingly, the non-driving state, that is, the initial alignment state is black display. 
     As shown in  FIG. 5B , the slit  29  of the pixel electrode  9  is inclined at a right-rising from the alignment process direction by 5°. Accordingly, as shown in  FIG. 5C , when driving voltage is applied between the pixel electrode  9  having the stripe-shaped electrode portion  9   a  and the common electrode  19  opposed thereto, electric field is generated in a direction perpendicular to the extending direction of the stripe-shaped electrode portion  9   a  (or slit  29 ) in the plan view. 
     The liquid crystal molecules LC having positive dielectric anisotropy is aligned such that long axes thereof are in the electric field direction, and thus the liquid crystal molecules LC are twisted clockwise in the vicinity of the stripe-shaped electrode portion  9   a . Accordingly, optical activation is generated in the liquid crystal layer  50 . The illumination light converted into the straight polarized light by the polarization plate  14  is rotated and transmitted through the polarization plate  24  while it is transmitted through the liquid crystal cell  101 . That is, at the driving time, colors colored by the color filters  22  are observed, a white color is displayed when all the sub-pixels SG constituting one pixel are in the driving state. Such a display mode is called a normally black mode. 
     The angle formed between the alignment process direction and the stripe-shaped electrode portion  9   a  (or slit  29 ) is not limited to 5°. When the electric field is generated, the liquid crystal molecules LC stabilized in a regular direction are set to a twisted angle. 
     Next, optical disposition of the prism  110  in the display device  100  will be described with reference to  FIG. 6 . 
     As shown in  FIG. 6 , when the display panel  120  is driven, the illumination light output from the light emitting face  150   a  of the lighting device  150  is transmitted through the display panel  120  as described above and input to the prism  110 . The prism  110  has a polarization angle θd regulated by an inclination angle θw of the inclination face  110   b  and an refractive index n, and the display light L input to the prism  110  is output in a direction inclined from the normal line  120   v  of the display face  120   a  by an output angle θd. 
     When such a display device  100  is used for the head-up display or the like to be described later, the display device  100  is set such that sunlight SL is input in a direction opposite to the output direction of the display light L. A part of the sunlight SL input to the prism  110  is reflected from the inclination face  110   b  in a direction symmetrical about the normal line  110   v  as an axis. 
     The sunlight SL transmitted through the prism  110  may be reflected on several interfaces of the display panel  120 , such as an interface between the polarization plate  24  and the opposite substrate  20 . However, a refractive index difference in the interface is small, the sunlight SL is absorbed by the polarization plate  24  or the color filters  22 , and thus intensity of the reflection light of the sunlight SL gets lower. The sunlight SL transmitted through the polarization plate  14  and reaching the lighting device  150  is dispersed and mixed with the illumination light again since a gap is formed between the polarization plate  14  and the light emitting face  150   a . Accordingly, it has no influence on displaying. 
     An incident angle θ 1  of the sunlight SL input to the inclination face  110   b  of the prism  110  is not necessarily regular. From such a viewpoint, it is necessary to miss the sunlight SL such that the sunlight SL reflected from the inclination face  110   b  does not come into contact with a viewer&#39;s eyes. In other words, the inclination angle θw of the inclination face  110   b  of the prism  110  is set such that the display light L reaches a range other than a range which the reflection light of the sunlight SL reaches. 
     An angle formed between the normal line  110   v  of the inclination face  110   b  and the normal line  120   v  of the display face  120   a  is the same as the inclination angle θw of the inclination face  110   b . For example, when the incident angle θ 1  of the sunlight SL to the normal line  120   v  is the same the output angle θd of the display light L, the reflection angle θ 2  of the sunlight SL is a value obtained by subtracting the output angle θd from double of sum of the inclination angle θw and the output angle θd. 
     The relation of the incident angle θ 1  and the reflection angle θ 2  of the sunlight SL, the inclination angle θw of the prism  110 , and the output angle (polarization angle) θd can be calculated by Formula (1) and Formula (2) based on Snell&#39;s law. 
         n ×sin θ w =sin(θ w+θd )  (1)
 
       θ1+θ2 =θt= arcsin( n ×sin θ w )×2  (2)
 
     where n is a refractive index of the prism  110 . 
     The sum θt of the incident angle θ 1  and the reflection angle θ 2  of the sunlight SL is not necessarily regular, but is set in the range of 20° to 50° when the display device  100  is used for the head-up display or the like to be described later. 
     For example, the prism  110  is formed of glass or the like mainly including SiO 2 , and a refractive index n thereof is 1.45. When the sum θt of the incident angle θ 1  and the reflection angle θ 2  of the sunlight SL is 20°, the inclination angle θw is about 7°. In addition, the output angle θd is about 3°. Accordingly, in a visual angle range of ±10° (the sum of the inclination angle θw and the output angle θd) to the normal line  110   v  of the inclination face  110   b , the image displayed on the display panel  120  is not affected by the sunlight SL. In other words, when the output angle θd of the display light L is equal to or larger than a small angle of the incident angle θ 1  and the reflection angle θ 2  of the sunlight SL input to the inclination face  110   b , the reflection light of the sunlight SL does not reach the viewer&#39;s eyes. That is, when the sum θt is 20°, the inclination angle θw is made into 7° or more. 
     Similarly, when the sum θt is 50°, the inclination angle θw is about 17°. In this case, the output angle θd is about 8°. In other words, in a visual angle range of ±25° (the sum of the inclination angle θw and the output angle θd) to the normal line  110   v  of the inclination face  110   b , the image displayed on the display panel  120  is not affected by the sunlight SL. 
     When the inclination angle θw of the inclination face  110   b  in the prism  110  gets larger, color separation of the display light L transmitted through the prism  110  occurs by the influence of wavelength dispersion. Accordingly, it is preferable that the inclination angle θw is equal to or less than 30° at which it is hard to be affected by the wavelength dispersion. 
     It is obvious that the prism  110  is preferably formed of a transparent material through which a visible layer passes. 
     For example, the prism  110  is formed of a resin material such as polycarbonate, and a refractive index n thereof is 1.59. When the sum θt is 20°, the inclination angle θw is about 6.5°. In addition, the output angle θd is about 3.5°. 
     Similarly, when the sum θt is 50°, the inclination angle θw is about 15.5°. In this case, the output angle θd is about 9.5°. 
     The resin material may be episulfide-based resin in addition to the polycarbonate, a refractive index n thereof is about 1.70. When the sum θt is 20°, the inclination angle θw is about 6°. In addition, the output angle θd is about 4°. 
     Similarly, when the sum θt is 50°, the inclination angle θw is about 14.5°. In this case, the output angle θd is about 10°. 
     The prism  110  may have a configuration in which it is filled with liquid such as water, and a refractive index n thereof is 1.33. When the sum θt is 20°, the inclination angle θw is about 7.5°. In addition, the output angle θd is about 2.5°. 
     Similarly, when the sum θt is 50°, the inclination angle θw is about 18.5°. In this case, the output angle θd is about 6.5°. 
     When the refractive n index of a proper material of the prism  110  is assumed as described above, the inclination angle θw of the inclination face  110   b  to the display face  120   a  is equal to or more than about 6° and equal to or less than 18.5°. 
     When the sum θt of the incident angle θ 1  and the reflection angle θ 2  of the sunlight SL is 30° that is an intermediate value of 20° to 50° and when the influence of the wavelength dispersion of the prism  110  and the refractive index n (about 1.5) of an easily available prism material (e.g., BK7) are considered, it is preferable that the inclination angle (wedge angle) θw of the prism  110  is about 10°. 
     Since the sunlight SL may be input to the inclination face  110   b  at various angles, as shown in  FIG. 6 , the incident direction of the real sunlight SL is projected to a cross section taken by cutting the prism  110  in the Y direction and the incident angle θ 1  is prescribed. 
     Comparative Example 
     Next, Comparative Example will be described with reference to  FIG. 7 .  FIG. 7  is a schematic cross-sectional view illustrating optical disposition of a display panel and a lighting device according to Comparative Example. 
     As shown in  FIG. 7 , in the display panel  120  and the lighting device  150  according to Comparative Example, the light emitting face  150   a  is inclined and the lighting device  150  is disposed with respect to the display panel  120  such that the illumination light is input to the surface  120   b  opposite to the display face  120   a  in the inclination direction. 
     When an inclination angle of the light emitting face  150   a  to the surface  120   b  is θ 3 , an output angle θ 4  of the display light L to the normal line  120   v  of the display face  120   a  is substantially the same as the inclination angle θ 3 . 
     The sunlight SL input to the display face  120   a  at the incident angle θ 1  from the output direction of the display light L to the normal line  120   v  of the display face  120   a  is reflected at the reflection angle θ 2 . In this case, the incident angle θ 1  is equivalent to the reflection angle θ 2 . 
     For example, when the inclination angle θ 3  of the lighting device  150  is 15°, all of the output angle θ 4  of the display light L and the incident angle θ 1  of the sunlight SL are 15°. Accordingly, in a visual angle range of ±15° to the normal line  120   v , it is hard to be affected by the reflection of the sunlight SL. That is, the same operation and effect as the display device  100  provided with the prism  110  are obtained. 
     However, when the lighting device  150  is disposed to be inclined from the display panel  120  as described in Comparative Example, there is a problem that the desired optical characteristics cannot obtained in a predetermined visual angle range. 
       FIG. 8  is a graph illustrating contrast characteristics in the display panel. Specifically, diffused light is input to the surface  120   b  of the display panel  120 , an angle to the normal line  120   v  is changed, and brightness of the display light L is measured, thereby obtaining a contour contrast curve. The center of  FIG. 8  denotes the normal line direction, axes passing through the center denote orientation angles, and concentric circles denote polar angles from the normal line  120   v , which represent 20°, 40°, 60°, and 80° in order from the inside. 
     As shown in  FIG. 8 , in the display panel  120 , the highest contrast (CR) is obtained as viewed in the normal line direction. It is a good balanced state capable of high contrast in the left-right direction (X direction) and the up-down direction (Y direction). However, when the lighting device  150  is disposed to be inclined from the display panel  120  at about 15° as described in Comparative Example, the output direction of the display light L is inclined at 15° in the Y direction. Accordingly, contrast distribution in real displaying deviates to be a rectangular range surrounded by the broken line. That is, the contrast decreases in the upside corner of an image. 
       FIG. 9  is a graph illustrating contrast characteristics in the display device according to the embodiment. Specifically, it is a contour contrast curve when the inclination angle θw of the inclination face  110   b  of the prism  110  is 10°. As shown in  FIG. 9 , in the case of the display device  100  of the embodiment, the illumination light output from the lighting device  150  is input in the direction perpendicular to the display face  120   a  of the display panel  120 . The display light L output from the display face  120   a  is input to the prism  110 , and then is output from the inclination face  110   b  in the direction inclined at the output angle θd from the normal line  120   v.    
     In this case, when the refractive index n of the prism  110  is 1.5, the output angle θd is about 5°. That is, the contour contrast curve deviates in the up-down direction (Y direction) by 5°, and thus the optimal visual angle range also deviates in the up-down direction (Y direction) by 5°. Accordingly, contrast distribution in real displaying is a rectangular range surrounded by the broken line, the contrast in the corner portion of an image does not decrease as compared with Comparative Example shown in  FIG. 8 , and it is possible to obtain overall high contrast. 
     In Comparative Example, the illumination light is transmitted obliquely to the thickness direction (Z direction) through the display panel  120 , color shift occurs on an image face. However, in the display device  100 , it is possible to obtain the effect of reducing such color shift. 
     According to the first embodiment described above, it is possible to obtain the following advantages. 
     (1) The display device  100  has the prism  110  disposed on the display face  120   a  of the display panel  120 , the inclination angle θw of the inclination face  110   b  of the prism  110  to the display face  120   a  is equal to or more than 6° and equal to or less than 18.5°. Accordingly, when the sum θt of the incident angle θ 1  and the reflection angle θ 2  of the sunlight SL to the inclination face  110   b  is set in the range of 20° to 50°, the reflection light of the sunlight SL can be missed in a direction in which the display light L reaches the viewer. Therefore, it is possible to suppress the influence which the sunlight SL has on displaying. 
     (2) Since the prism  110  is disposed in close contact with the display face  120   a  of the display panel  120 , it is suppressed that the sunlight SL is transmitted through the prism  110  and is reflected from the surface of the polarization plate  24  of the display panel  120 . 
     (3) Since the display device  100  is provided with the prism  110  having the inclination face  110   b  inclined at a predetermined angle on the display face  120   a  of the display panel  120 , it is possible to avoid that the visual angle direction in which the optimal contrast of the display panel  120  can be obtained deviates from the output direction of the display light L as compared with Comparative Example. 
     (4) In JP-A-2007-65011, when the sunlight SL input to the display face of the liquid crystal cell, for example, at the incident angle θ 1  is missed at an angle corresponding to the sum θt of the incident angle θ 1  and the reflection angle θ 2  from the output direction of the display light L, it is necessary to incline the transreflective member from the display face at an angle of a half of the sum θt. On the contrary, in the display device  100 , since the prism  110  having the inclination face  110   b  with the inclination angle θw smaller than the half of the sum θt is disposed on the display face  120   a , it is possible to provide the smaller display device  100 . 
     Second Embodiment 
     Next, a display device according to a second embodiment will be described with reference to  FIG. 10 .  FIG. 10  is a schematic cross-sectional view illustrating a configuration of the display device according to the second embodiment. The same reference numeral and sign are given to the same configuration as the display device  100  of the first embodiment, and detailed description thereof is not repeated. 
     As shown in  FIG. 10 , basically, the display device  200  of the second embodiment has the same configuration as the display device  100  of the first embodiment, but there are differences in the following points. 
     The surface of the opposite substrate  20  opposed to the liquid crystal layer  50  is the display face  120   a , and the prism  110  is disposed to come into close contact with the display face  120   a . The polarization plate  24  as a polarization element on the side to which the sunlight SL is input is attached to the inclination face  110   b  of the prism  110 . 
     The polarization plate  24  is attached to the inclination face  110   b  such that the direction of the absorption axis  24   a  is the same as the initial alignment direction of the liquid crystal molecules in the liquid crystal layer  50 . In other words, the inclination direction (Y direction) of the inclination face  110   b  of the prism  110  crosses (perpendicularly) to the direction of the absorption axis  24   a  of the polarization plate  24 . 
     According to the display device  200  of the embodiment, the relation of the sum θt of the incident angle θ 1  and the reflection angle θ 2  of the sunlight SL to the inclination face  110   b  based on Snell&#39;s law, the inclination angle θw of the prism  110 , and the polarization angle θd is kept similarly to the display device  100  of the first embodiment, and the same operation and effect as the first embodiment is obtained. 
     In addition, since the polarization plate  24  easily heated by the sunlight SL is attached to the inclination face  110   b  of the prism  110  separated from the liquid crystal cell  101 , it is possible to prevent the optical characteristics of the display panel  120  from being changed by the influence of the heat of the sunlight SL. 
     Since the absorption axis  24   a  of the polarization plate  24  is the same direction of the initial alignment direction of the liquid crystal molecules, it is possible to prevent the visual angle characteristics from being changed even when the polarization plate  24  is attached to the inclination face  110   b.    
     Third Embodiment 
     Next, a display device according to a third embodiment will be described with reference to  FIG. 11A , FIG.  11 B, and  FIG. 12 .  FIG. 11A  is a schematic perspective view illustrating a configuration of the display device of the third embodiment,  FIG. 11B  is a front view illustrating the display device of the third embodiment, and  FIG. 12  is a schematic cross-sectional view illustrating a configuration of the display device of the third embodiment. The same reference numeral and sign are given to the same configuration as the display device  100  of the first embodiment, and detailed description thereof is not repeated. 
     As shown in  FIG. 11A , the display device  300  has a display panel  120  and a prism  115  provided on the display face  120   a  of the display panel  120 . The display panel  120  is a light receiving type, and is illuminated by the lighting device  150  provided on the side (rear side) opposite to the display face  120   a  and performs displaying. Accordingly, the display device  300  may include the lighting device  150 . 
     The prism  115  provided in front of the display panel  120  has a plurality of inclination faces  115   b  inclined in the Y direction (direction crossing to the initial alignment direction of the liquid crystal molecules) at a predetermined angle from the display face  120   a . Such a prism  115  is processed in a sheet shape, and is generally called a prism sheet. Hereinafter, the prism  115  is referred to as a prism sheet  115 . 
     As shown in  FIG. 11B , when viewing the display device  300  from the side on which the display light L is output, a long side crosses to a corner  115   c  of the inclination face  115   b  at a predetermined angle θ 5 . In other words, the prism sheet  115  is disposed on the display panel  120  such that the corner  115   c  representing the extending direction of the inclination face  115   b  is inclined to the X direction, that is, the line direction of pixels. 
     The method of inclining the corner  115   c  is not limited thereto, and may cross the corner  115   c  to the line direction (X direction) or the column direction (Y direction) of the pixels. Accordingly, it is possible to prevent an interference pattern from occurring, by avoiding optical interference with the pixels arranged in the X direction and Y direction. 
     As shown in  FIG. 12 , the prism sheet  115  is provided such that a first face  115   a  opposed to the inclination face  115   b  comes into close contact with the display face  120   a  of the display panel  120  that is an FFS transmission liquid crystal panel. 
     An inclination angle θw formed between the inclination face  115   b  inclined from the Y direction and the display face  120   a  is set equal to or more than 6° and equal to or less than 18.5° in the same manner as the prism  110  in the display device  100  of the first embodiment, when the sum θt of the incident angle θ 1  and the reflection angle θ 2  of the sunlight SL on the inclination face  115   b  is equal to or more than 20° and equal to or less than 50°. 
     As a material of the prism sheet  115 , a resin material such as polycarbonate is appropriately used from the viewpoint of workability, and a refractive index n thereof is about 1.59. In  FIG. 12 , the sum θt of the incident angle θ 1  and the reflection angle θ 2  of the sunlight SL is about 32°, the inclination angle θw is about 10°, and the output angle θd is about 6°. 
     That is, the illumination light substantially perpendicularly input from the light emitting face  150   a  of the lighting device  150  to the surface  120   b  of the display panel  120  is transmitted through the display panel  120  to be converted into the display light L representing display information, and is output from the inclination face  115   b  in a direction inclined at about 6° from the normal line  120   v  of the display face  120   a.    
     For example, a part of the sunlight SL input from the output direction of the display light L is reflected from the inclination face  115   b  in a direction symmetrical to the normal line  115   v , and is missed from a viewer&#39;s visible direction. The sunlight SL transmitted through the prism sheet  115  may be reflected on several interfaces of the display panel  120 , such as an interface between the polarization plate  24  and the opposite substrate  20 . However, a refractive index difference is small, the sunlight SL is absorbed by the polarization plate  24  or the color filters  22 , and thus intensity of the reflection light of the sunlight SL gets lower. Since the sunlight SL transmitted through the polarization plate  14  and reaching the lighting device  150  is dispersed and mixed with the illumination light again, it has no influence on displaying. 
     According to display device  300  of the third embodiment, the relation of the sum θt of the incident angle θ 1  and the reflection angle θ 2  of the sunlight SL to the inclination face  115   b  based on Snell&#39;s law, the inclination angle θw of the prism sheet  115 , and the polarization angle θd is kept similarly to the display device  100  of the first embodiment, and the same operation and effect as the first embodiment is obtained. 
     In addition, since the prism sheet  115  having the plurality of fine inclination faces  115   b  is attached to the display face  120   a  of the display panel  120 , the thickness thereof can be made smaller to reduce the size as compared with the display device  100  provided with the prism  110  having the single inclination face  110   b.    
     Fourth Embodiment 
     Next, a projection imaging apparatus as the electronic apparatus of the embodiment will be described by way of example.  FIG. 13  is a schematic view illustrating a configuration of a head-up display as the projection imaging apparatus. 
     As shown in  FIG. 13 , the head-up display  500  as the projection imaging apparatus of the invention is provided, for example, in a vehicle  600  that is a car, and is provided with the display device  100  of the first embodiment, the lighting device  150 , a concave mirror  501  as a reflection optical system which projects the display light L (image light) output from the display device  100  onto a front window  603 , and a front window shield  502  which reflects the display light L projected onto the front window  603  to a rider  605 . 
     The concave mirror  501 , the display device  100 , and the lighting device  150  are accommodated in a dashboard  601  such that the inclination face  110   b  of the prism  110  is opposed to a mirror surface of the concave mirror  501 . The display device  100  and the lighting device  150  are inclined at an angle corresponding to the polarization angle θd of the prism  110  such that the display light L output from the inclination face  110   b  is input to the concave mirror  501  in a substantially horizontal direction in  FIG. 13 . 
     The dashboard  601  is provided with an opening portion  602  for transmitting the display light L to the downside of the front window  603 . 
     The display light L output from the display device  100  is reflected by the concave mirror  501 , is transmitted through the opening portion  602 , and is projected onto the front window shield  502 . The projected display light L, that is, an image is visible as a virtual image by the rider  605  in the vehicle  600 . The projected image may be information such as velocity meter, the amount of remaining fuel, and various warnings, and the rider  605  can confirm such information without greatly turning away the driver&#39;s eyes during the driving. 
     The front window shield  502  is formed of, for example, a sheet-shaped film such as a semitransparent mirror, but the inner face of the front window  603  may be subjected to a surface treatment to reflect a part of the display light L. 
     According to the head-up display  500 , the display device  100  is provided with the prism  110  having the inclination face  110   b  on the incident side of the sunlight SL. Accordingly, the sunlight SL input over the front window  603 , is transmitted through the opening portion  602 , is reflected by the concave mirror  501 , and is input to the display device  100 , and a part of the sunlight SL is reflected in a direction different from the incident direction to the inclination face  110   b  of the prism  110 . That is, the reflection light of the sunlight SL on the inclination face  110   b  is missed in a direction different from the output direction of the display light L. The sunlight SL transmitted through the prism  110  is absorbed in the display panel  120 , or the sunlight SL is transmitted through the display panel  120 , is diffused, and is mixed with the illumination light output from the lighting device  150 . That is, it is hard for the projected image to be affected by the reflection of the sunlight SL, the head-up display  500  is realized, by which the optimal contrast characteristics can be obtained in a predetermined visual angle range. 
     Of course, the display device  200  of the second embodiment or the display device  300  of the third embodiment may be employed instead of the display device  100 . 
     In the embodiment, the display device  100  is disposed with respect to the concave mirror  501  such that the sunlight SL reflected by the inclination face  110   b  of the prism  110  is missed downward in  FIG. 13 , but is not limited thereto. Since the reflection light of the sunlight SL on the inclination face  110   b  can be missed from the output direction of the display light L, the display device  100  and the lighting device  150  may be turned by 90° about the output direction of the display light L in  FIG. 13 . Of course, the display direction of the image on the display panel  120  is also turned according to the turning. 
     In addition to the embodiments, various modified examples are conceivable. Hereinafter, modified examples will be described. 
     Modified Example 1 
     The configuration of pixels of the display panel  120  and the optical design are not limited thereto. For example, the inclination angle of the stripe-shaped electrode portion  9   a  (or slit  29 ) of the pixel electrode  9  in  FIG. 3  may be right-rising 0°, that is, horizontal. In that case, the alignment process direction is made into right-falling 5°. Even in such a configuration, the liquid crystal molecules LC are aligned in the electric field direction and are twisted clockwise. The direction of the absorption axis  24   a  of the polarization plate  24  is similarly made into right-falling 5°. 
     Accordingly, in the second embodiment, in case of attaching the polarization plate  24  to the inclination face  110   b  of the prism  110 , when the polarization plate  24  is disposed such that the absorption axis  24   a  is the same as the alignment process direction, the absorption axis  24   a  is not perpendicular to the inclination direction (Y direction) of the inclination face  110   b . However, according to an optical simulation result, in fluctuation of the angle of attaching the polarization plate  24  of about ±10° about the inclination direction, there is no influence on the visual angle characteristics of the display panel  120 . 
     Modified Example 2 
     The disposition of the prism  110  or the prism sheet  115  with respect to the display panel  120  is not limited to the direct contact to the display face  120   a . For example, the display panel  120  and the prism  110  or the prism sheet  115  may be optically attached to each other through a transparent material having an intermediate refractive index between the refractive index of the material (polarization element or opposite substrate  20 ) constituting the display face  120   a  and the refractive index n of the prism  110  or the prism sheet  115 . 
     With such a configuration, even when there is a difference between the refractive index of the material and the refractive index n of the prism  110  or the prism sheet  115 , it is possible to suppress interface reflection by reducing the difference in refractive index on the interface therebetween. 
     Modified Example 3 
     The display panel  120  is not limited to the FFS transmission liquid crystal panel. For example, even when an IPS (In Plane Switching) transmission liquid crystal panel or a VA (Vertical Alignment) transmission liquid crystal panel is used, the same operation and effect can be obtained. 
     In case of the VA type, the direction of the absorption axis  24   a  of the polarization plate  24  with respect to the inclination face  110   b  of the prism  110  is the same as the second embodiment. For example, an alignment control portion such as a slit or a protrusion is provided on at least one side of a pair of electrodes opposed to each other with the liquid crystal layer interposed therebetween such that the liquid crystal molecules LC are inclined in a direction forming 45° about the absorption axis  24   a  of the polarization plate  24  at the driving time. 
     Modified Example 4 
     The display panel  120  is not limited to the light receiving type liquid crystal panel. For example, in an organic electro luminescent panel, a plasma panel, an FED (Field Emission Display), an SED (Surface conduction Electron emitter Display), which have a light emitting element and is a self light emitting type, the same operation and effect can be obtained. Accordingly, when the display panel  120  is the self light emitting type, the lighting device  150  is unnecessary. 
     Since the self light emitting organic electro luminescent panel has so-called visual angle characteristics that the light emitting characteristics are changed according to a viewing direction, it is effective to dispose the prism  110  in close contact with the display face  120   a , to obtain the optimal brightness and emission colors. 
     Also in the self light emitting display panel, there is a case where the polarization element is disposed on the incident side of the sunlight SL, the sunlight SL is absorbed, or the reflection of the sunlight SL is made to be weakened. Accordingly, it is effective to dispose the polarization element on the inclination face  110   b  of the prism  110  as described in the second embodiment. 
     Modified Example 5 
     The electronic apparatus to which the display devices  100 ,  200 , and  300  are applied is not limited to the head-up display  500  that is the projection imaging device. For example, it can be appropriately used for a teleprompter allowing a lecturer to read a document without turning away the lecturer&#39;s eyes in a television studio, a lecture meeting, or the like under strong lighting, and a projector projecting advertisement onto a show window or the like, which may be exposed to strong light.