Abstract:
A display device including a display panel, a first polarizer, a second polarizer, a first phase compensation film, and a second phase compensation film is provided. The first polarizer and the second polarizer are disposed on two sides of the display panel. The first polarizer has a first light-absorption axis, and the second polarizer has a second light-absorption axis. The first phase compensation film and the second phase compensation film are disposed between the first polarizer and the second polarizer. The second phase compensation film obeys a first formula: 
                   R   ⁢           ⁢   λ1     λ1     &gt;       R   ⁢           ⁢   λ2     λ2     &gt;       R   ⁢           ⁢   λ3     λ3       ,         
wherein Rλ 1 , Rλ 2  and Rλ 3  are horizontal phase retardation values of the second phase compensation film when wavelengths of lights passing through the second phase compensation film are respectively λ 1, λ2  and λ 3 , and λ 1&lt;λ2&lt;λ3.

Description:
BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The document relates to a display device, and more particularly, to a display device including a phase compensation film with positive wavelength dispersion. 
     2. Description of the Prior Art 
     Liquid crystal displays have advantages of light weight, thin thickness, low power consumption, and low radiation; therefore, the liquid crystal displays have replaced traditional cathode ray tube (CRT) displays of laptop computers to be widely applied to many kinds of portable electronic products in the market, such as notebooks and personal digital assistants (PDA). 
     A traditional vertical alignment liquid crystal display typically includes a top polarizer, a bottom polarizer, a top substrate, a bottom substrate, and a liquid crystal layer disposed between the top substrate and the bottom substrate. The top polarizer and the bottom polarizer are disposed at the outside of the top substrate and the outside of the bottom substrate respectively, and an absorption axis of the top polarizer and an absorption axis of the bottom polarizer are perpendicular to each other. When the vertical alignment liquid crystal display is a normally black mode liquid crystal display, and there is no voltage difference provided between the top substrate and the bottom substrate, the liquid crystal molecules of the liquid crystal layer do not provide different phase retardation values. Accordingly, light passing through the bottom polarizer have the same polarizing direction as the light passing through the liquid crystal layer, and the display is in a dark state. When a voltage difference is applied between the top substrate and the top substrate, the liquid crystal layer produces a half wave phase retardation, so that the polarizing direction of the light passing through the bottom polarizer is perpendicular to the absorption axis of the top polarizer because of the half wave phase retardation, and the display is in a bright state. 
     However, the liquid crystal molecules closer to the top substrate and the bottom substrate have larger anchoring force on the top substrate and the bottom substrate because of the rubbings of the surfaces of the top substrate and the bottom substrate. That is the top substrate and the bottom substrate may include alignment films having rubbing directions on the inner surfaces thereof. Accordingly, even in a condition of applying no voltage difference, the liquid crystal molecules closer to the surfaces of the top substrate and the bottom substrate still lie down and do not stand up. For this reason, the liquid crystal molecules lying down closer to the top substrate and the bottom substrate will affect the phase retardation value of the polarized light passing therethrough, and an observer seeing the display in a direction of a large viewing angle will see light leakage when the display is in the dark state. Also, the absorption axis of the top polarizer and the absorption axis of the bottom polarizer are not perpendicular to each other in the direction of the large viewing angle, so that the observer easily sees the light leakage, and the contrast ratio of the liquid crystal display is also affected. Furthermore, when the liquid crystal molecules are perpendicular to the top substrate or the bottom substrate, the liquid crystal molecules do not provide only one refractive index, and provides uneven refractive indexes. Since that, the light passing through the liquid crystal molecules along the direction of the large viewing angle have different phase retardation values, and the light leakage is easily generated. 
     Although the contrast ratio of the liquid crystal display has been improved by the phase compensation film disposed at the outside of the top substrate or the bottom substrate, the phase compensation film composed of single one material only can compensate the phase difference of the light with one wavelength. For example, when a short wavelength is 450 nm, and a long wavelength is 730 nm, the light leakage is still generated. 
     Besides, since the light with a shorter wavelength has larger phase retardation values while passing through the liquid crystal molecules, the material of the phase compensation film adapted to compensate the liquid crystal display generally is designed to have negative wavelength dispersion. That is to say that the light with the shorter wavelength has a smaller phase retardation values while passing through the phase compensation film with negative wavelength dispersion, so that the phase retardation values generated from the liquid crystal molecules can be compensated. However, the material with negative wavelength dispersion is not easy to be designed, and it is quite complex to manufacture this kind of material. Thus, it is not easy to use the present phase compensation film with negative wavelength dispersion to compensate the phase retardation values in all visible wavelengths, and the cost for manufacturing the liquid crystal display is easily increased largely. 
     Therefore, to provide a new liquid crystal display to reduce the light leakage in the direction of the large viewing angle is an objective in this field. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect, a display is provided to reduce the light leakage in the direction of the large viewing angle. 
     A display device is provided according to an exemplary embodiment. The display device comprises a display panel, a first polarizer, a second polarizer, a first phase compensation film, and a second phase compensation film. The display panel comprises a light-incident surface and a light-emitting surface. The first polarizer is disposed on the light-incident surface of the display panel, and the first polarizer comprises a first light-absorption axis. The second polarizer is disposed on the light-emitting surface of the display panel, and the second polarizer comprises a second light-absorption axis. The first phase compensation film is disposed between the first polarizer and the second polarizer. The second phase compensation film is disposed between the first polarizer and the second polarizer, and the second phase compensation film obeys a first formula: 
                   R   ⁢           ⁢   λ1     λ1     &gt;       R   ⁢           ⁢   λ2     λ2     &gt;       R   ⁢           ⁢   λ3     λ3       ,         
wherein Rλ 1 , Rλ 2  and Rλ 3  respectively are horizontal phase retardation values of the second phase compensation film when wavelengths of lights passing through the second phase compensation film are respectively λ 1 , λ 2  and λ 3 , and λ 1 &lt;λ 2 &lt;λ 3 .
 
     The display of the invention combines the second phase compensation film that obeys the first formula: 
                 R   ⁢           ⁢   λ1     λ1     &gt;       R   ⁢           ⁢   λ2     λ2     &gt;       R   ⁢           ⁢   λ3     λ3           
with the first phase compensation film to effectively compensate the phase retardation values of the lights with different wavelengths in the direction of the large viewing angle, so that the light leakage of the display in the direction of the large viewing angle can be effectively solved.
 
     These and other aspects of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  and  FIG. 2  are schematic diagrams illustrating a display according to a first exemplary embodiment. 
         FIG. 3  is a schematic diagram illustrating the relationship between normalized horizontal phase retardation values of the first phase compensation film and the second phase compensation film and the wavelength. 
         FIG. 4  is a schematic diagram illustrating a relationship between the horizontal phase retardation value of the second phase compensation film and the wavelength according to the first exemplary embodiment. 
         FIG. 5  is a schematic diagram illustrating a relationship between the transmittance of the display corresponding to different relationship lines in  FIG. 4  and the wavelength. 
         FIG. 6  is a schematic diagram illustrating the relationship between the transmittance and the azimuth angle of the display when the viewing angle is 70 degrees according to the first exemplary embodiment. 
         FIG. 7  is a schematic diagram illustrating the change paths of the polarizing directions of the lights with different wavelengths on the Poincare sphere when the display is in the dark state according to the first exemplary embodiment. 
         FIG. 8  is a schematic diagram illustrating a display according to a second exemplary embodiment. 
         FIG. 9  is a schematic diagram illustrating the change paths of the polarizing directions of the lights with different wavelengths on the Poincare sphere when the display is in the dark state according to the second exemplary embodiment. 
         FIG. 10  is a schematic diagram illustrating a display according to a third exemplary embodiment. 
         FIG. 11  is a schematic diagram illustrating a display according to a fourth exemplary embodiment. 
         FIG. 12  is a schematic diagram illustrating the change paths of the polarizing directions of the lights with different wavelengths on the Poincare sphere when the display is in the dark state according to the fourth exemplary embodiment. 
         FIG. 13  is a schematic diagram illustrating a display according to a fifth exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     To provide a better understanding of the invention, exemplary embodiments will be detailed as follows. The exemplary embodiments of the invention are illustrated in the accompanying drawings with numbered elements to elaborate the contents and effects to be achieved. 
     Please refer to  FIG. 1  and  FIG. 2 , which are schematic diagrams illustrating a display according to a first exemplary embodiment, wherein  FIG. 2  is a schematic diagram illustrating a relationship between slow axes and absorption axes of films according to the first exemplary embodiment. As shown in  FIG. 1 , the display  100  of this embodiment includes a display panel  102 , a first polarizer  104 , a second polarizer  106 , a first phase compensation film  108 , and a second phase compensation film  110 . In this embodiment, the display panel  102  may be, for example, a liquid crystal display panel, but the invention is not limited herein. When the display panel  102  is the liquid crystal display panel, the display  100  is a liquid crystal display, and further includes a backlight module  112 . The invention is not limited to this. The following description takes the display panel  102  to be the liquid crystal display panel as an example, but the invention is not limited herein. The display panel  102  may include a thin-film transistor substrate  114 , a color filter substrate  116 , and a liquid crystal layer  118 . The liquid crystal layer  118  is disposed between the thin film transistor substrate  114  and the color filter substrate  116 , and includes a plurality of liquid crystal molecules  118   a  disposed between the thin film transistor substrate  114  and the color filter substrate  116 . Preferably, the liquid crystal layer  118  may be a vertically aligned liquid crystal layer, and the liquid crystal molecules  118   a  may be a uniaxial crystal material. For example, when no voltage difference is applied between the thin-film transistor substrate  114  and the color filter substrate  116 , the liquid crystal molecules  118   a  of the vertical aligned liquid crystal layer  118  are affected by bumps, protrusions or alignment films of the color filter substrate  116  and the thin-film transistor film  114  to have a pre-tilt angle close to 90 degrees, so that the vertical aligned liquid crystal layer  118  doesn&#39;t have phase retardation in a vertical direction, but the invention is not limited to this. The liquid crystal molecules  118   a  also can use other methods to have vertical alignment. A side of the thin-film transistor substrate  114  facing the backlight module  116 , which is an outer surface of the thin-film transistor substrate  114 , is a light-incident surface  102   a , and a side of the color filter substrate  116  opposite to the thin-film transistor substrate  114 , which is an outer surface of the color filter substrate  116 , is a light-emitting surface. The first polarizer  104  is disposed on the light-incident surface  102   a  of the display panel  102 , and the second polarizer  106  is disposed on the light-emitting surface  102   b . The first phase compensation film  108  and the second phase compensation film  110  are disposed between the first polarizer  104  and the second polarizer  106 . In this embodiment, the first phase compensation film  108  and the second phase compensation film  110  are disposed between the first polarizer  104  and the display panel  102 , and the second phase compensation film  110  is disposed between the first phase compensation film  108  and the display panel  102 , but the invention is not limited to this. 
     In this embodiment, the first polarizer  104  may include a first polarizing layer  120  and a protection film  122 , and the first polarizing layer  120  is disposed between the first protection film  122  and the light-incident surface  102   a  of the display panel  10 . The first polarizing layer  120  is adapted to polarize light passing through the first polarizing layer  120 , and a material of the first polarizing layer  120  may include, for example, polyvinyl alcohol (PVA), but the invention is not limited herein. The first protection film  122  is used to protect the first polarizing layer  120 , and a material of the first protection film  122  include, for example, triacetyl cellulose (TAC), but the invention is not limited herein. The second polarizer  106  may include a second polarizing layer  124  and a second protection film  126 , and the second polarizing layer  124  is disposed between the second protection film  126  and the light-emitting surface  102   b  of the display panel  102 . The second polarizing layer  124  is adapted to polarize light passing through the second polarizing layer  124 , and a material of the second polarizing layer  124  may include, for example, PVA, but the invention is not limited herein. The second protection film  126  is used to protect the second polarizing layer  124 , and a material of the second protection film  126  include, for example, triacetyl cellulose (TAC), but the invention is not limited herein. 
     As shown in  FIG. 2 , the first polarizer  104  has a first light-absorption axis  104   a  disposed along a first direction  128 . Light with a polarizing direction substantially parallel to the first light-absorption axis  104   a  cannot pass through the first polarizer  104 , and the first polarizer  104  allows light with a first linear polarizing direction  104   b  substantially perpendicular to the first light-absorption axis  104   a  to pass through itself. The second polarizer  106  has a second light-absorption axis  106   a  disposed along a second direction  130 . The second polarizer  106  allows light with a second linear polarizing direction  106   b  substantially perpendicular to the second light-absorption axis  106   a  to pass through itself. In this embodiment, the first direction  128  is substantially perpendicular to the second direction  130 , and the first direction  128  and the second direction  130  are substantially parallel to the light-incident surface  102   a  or the light-emitting surface  102   b , so that the first light-absorption axis  104   a  is substantially perpendicular to the second light-absorption axis  106   a , and the display  100  is a normally black mode liquid crystal display. The invention is not limited to this, and the first light-absorption axis and the second light-absorption axis of the invention also can be substantially parallel to each other, so that the display can be a normally white mode liquid crystal display. Furthermore, in the invention, the viewing angle θ, which is a tilt angle, is defined as an included angle formed between a viewing direction and a normal direction of the display  100 , and the azimuth angle ψ is defined as an included angle formed between a direction of the viewing direction projected onto the surface of the display  100  and a side of the display  100 . 
     Besides, the first phase compensation film  108  is a biaxial film. Accordingly, the refractive index of the first phase compensation film  108  in the first direction  128 , the refractive index of the first phase compensation film  108  in the second direction  130  and the refractive index of the first phase compensation film  108  in a third direction  132  substantially perpendicular to the first direction  128  and the second direction  130  are different, and the first phase compensation film  108  has a first slow axis  108   a  and a first fast axis  108   b . The first slow axis  108   a  and the first fast axis  108   b  are substantially perpendicular to each other, and are substantially parallel to a plane of the light-incident surface  102   a.  The slow axis is defined as a pre-determined axis of the phase compensation film with a largest refractive index, and the fast axis is defined as another pre-determined axis of the phase compensation film with a smallest refractive index. The second phase compensation film  110  is also a biaxial film. Accordingly, the refractive index of the second phase compensation film  110  in the first direction  128 , the refractive index of the second phase compensation film  110  in the second direction  130  and the refractive index of the second phase compensation film  110  in the third direction  132  substantially perpendicular to the first direction  128  and the second direction  130  are different, and the second phase compensation film  110  has a second slow axis  110   a  and a second fast axis  110   b . The second slow axis  110   a  and the second fast axis  110   b  are substantially perpendicular to each other, and are substantially parallel to the plane of the light-incident surface  102   a . In this embodiment, the first slow axis  108   a  is disposed along the second direction  130 , and is substantially perpendicular to the first light-absorption axis  104   a . The second slow axis  110   b  is disposed along the first direction  128 , and is substantially parallel to the first light-absorption axis  104   a.    
     In this embodiment, the display  100  may further include a third phase compensation film  134  and the fourth phase compensation film  136  disposed between the second polarizer  106  and the display panel  102 , and the fourth phase compensation film  136  is disposed between the third phase compensation film  134  and the display panel  102 . The third phase compensation film  134  may be constituted by a material substantially the same as the first phase compensation film  108  so as to have substantially the same relationship between the horizontal phase retardation value and the wavelength. The fourth phase compensation film  136  may be constituted by a material substantially the same as the second phase compensation film  110  so as to have substantially the same relationship between the horizontal phase retardation value and the wavelength. For example, the third phase compensation film  134  and the fourth phase compensation film  136  are also biaxial films. Accordingly, the refractive index of the third phase compensation film  134  in the first direction  128 , the refractive index of the third phase compensation film  134  in the second direction  130  and the refractive index of the third phase compensation film  134  in the third direction  132  are different, and the refractive index of the fourth phase compensation film  136  in the first direction  128 , the refractive index of the fourth phase compensation film  136  in the second direction  130  and the refractive index of the fourth phase compensation film  136  in the third direction  132  are different. The third phase compensation film  134  has a third slow axis  134   a  and a third fast axis  134   b . The third slow axis  134   a  and the third fast axis  134   b  are substantially perpendicular to each other, and are substantially parallel to the plane of the light-incident surface  102   a . The fourth phase compensation film  136  has a fourth slow axis  136   a  and a fourth fast axis  136   b . The fourth slow axis  136   a  and the fourth fast axis  136   b  are substantially perpendicular to each other, and are substantially parallel to the plane of the light-incident surface  102   a . In this embodiment, the third slow axis  134   a  is disposed along the first direction  128 , and is substantially perpendicular to the second light-absorption axis  106   b . The fourth slow axis  136   a  is disposed along the second direction  130 , and is substantially parallel to the second light-absorption axis  106   b.    
     The second phase compensation film  110  obeys a first formula: 
                   R   ⁢           ⁢   λ1     λ1     &gt;       R   ⁢           ⁢   λ2     λ2     &gt;       R   ⁢           ⁢   λ3     λ3       ,         
so that the first phase compensation film  108  combined with the second phase compensation film  110  can compensate the phase retardation values generated from the liquid crystal layer  118 , the first polarizer  104  and the second polarizer  106  in the direction of the large viewing angle θ, wherein Rλ 1 , Rλ 2  and Rλ 3  are respectively horizontal phase retardation values of the second phase compensation film  110  when the wavelengths of the lights passing through the second phase compensation film  110  are respectively λ 1 , λ 2  and λ 3 , and λ 1 &lt;λ 2 &lt;λ 3 . For example, the large viewing angle θ may be substantially 60 degrees or 70 degrees. The horizontal phase retardation value is defined as a product of a difference between the refractive index n x  and the refractive index n y  of each phase compensation film respectively in the slow axis and in the fast axis and a thickness d of each phase compensation film in the third direction  132 , and can be represented as (n x −n y )×d. Furthermore, the first phase compensation film  108  may obey a second formula:
 
                   R   ⁢           ⁢     λ1   ′         R   ⁢           ⁢     λ2   ′         ≅   1   ≅       R   ⁢           ⁢     λ3   ′         R   ⁢           ⁢     λ2   ′           ,         
where Rλ 1 ′, Rλ 2 ′ and Rλ 3 ′ are respectively horizontal phase retardation values of the first phase compensation film  108  when the wavelengths of the lights passing through the first phase compensation film  108  are respectively λ 1 , λ 2   and λ 3   and λ 1 &lt;λ 2 &lt;λ 3 . In this embodiment, the wavelengths λ 1 , λ 2  and λ 3  are 440 nm, 550 nm and 650 nm, respectively, but the invention is not limited to this. The first phase compensation film  108  may include a polymer material, such as cyclo olefin polymer (COP), but is not limited herein. Also, the fourth phase compensation film  136  may obey a third formula:
 
                   R   ⁢           ⁢   λ4     λ4     &gt;       R   ⁢           ⁢   λ5     λ5     &gt;       R   ⁢           ⁢   λ6     λ6       ,         
wherein Rλ 4 , Rλ 5  and Rλ 5  are respectively horizontal phase retardation values of the second phase compensation film  136  when the wavelengths of the lights passing through the second phase compensation film  136  are respectively λ 4 , λ 5  and λ 6 , and λ 1 &lt;λ 2 &lt;λ 3 . The third phase compensation film  134  may obey a fourth formula:
 
                   R   ⁢           ⁢     λ4   ′         R   ⁢           ⁢     λ5   ′         ≅   1   ≅       R   ⁢           ⁢     λ6   ′         R   ⁢           ⁢     λ5   ′           ,         
where Rλ 4 ′, Rλ,  5 ′ and Rλ,  6 ′ are respectively horizontal phase retardation values of the third phase compensation film  134  when the wavelengths of the lights passing through the third phase compensation film  134  are respectively λ 4 , λ 5  and λ 6 . In this embodiment, the third phase compensation film  134  may include a polymer material, such as cyclo olefin polymer (COP), but is not limited herein. The wavelengths λ 4 , λ 5  and λ 6  also may be 440 nm, 550 nm and 650 nm, respectively in this embodiment, but the invention is not limited to this. For example, when the wavelength of the light is 440 nm, the horizontal phase retardation values and the vertical phase retardation values of the second phase compensation film  110  and the fourth phase compensation film  136  may be 19.5 nm and 33.15 nm respectively. When the wavelength of the light is 550 nm, the horizontal phase retardation values and the vertical phase retardation values of the second phase compensation film  110  and the fourth phase compensation film  136  may be 10.6 nm and 18.2 nm respectively, and the horizontal phase retardation values and the vertical phase retardation values of the first phase compensation film  108  and the third phase compensation film  134  may be 73.3 nm and 124.61 nm respectively. When the wavelength of the light is 650 nm, the horizontal phase retardation values and the vertical phase retardation values of the second phase compensation film  110  and the fourth phase compensation film  136  may be 3.3 nm and 5.69 nm respectively. The vertical phase retardation value may be represented as
 
                 [         (       n   x     +     n   y       )     2     -     n   Z       ]     ×   d     ,         
wherein n z  is a refractive index of the phase compensation film in the third direction  132 , which is the refractive index in a direction of thickness, but the invention is not limited to this.
 
     In this embodiment, the first phase compensation film  108  and the third phase compensation film  134  are substantially composed of the same material, and the second phase compensation film  110  and the fourth phase compensation film  136  are substantially composed of the same material, so the following description take the first phase compensation film  108  and the second phase compensation film  110  as an example to describe their characteristics. In other embodiments, the first phase compensation film and the third phase compensation film may be composed of different materials, and the second phase compensation film and the fourth phase compensation film may be composed of different materials. Please refer to  FIG. 3 , which is a schematic diagram illustrating the relationship between normalized horizontal phase retardation values of the first phase compensation film  108  and the second phase compensation film  110  and the wavelength, wherein the normalized horizontal phase retardation value is produced by the horizontal phase retardation value in any wavelength divided by the horizontal phase retardation value in the wavelength of 550 nm. Accordingly, the normalized horizontal phase retardation values shown in this diagram and in the following diagrams have no unit. As shown in  FIG. 3 , a relationship line L 1  represents the relationship between the normalized horizontal phase retardation value of the first phase compensation film  108  and the wavelength of the light, which is the second formula: 
                 R   ⁢           ⁢     λ1   ′         R   ⁢           ⁢     λ2   ′         ≅   1   ≅         R   ⁢           ⁢     λ3   ′         R   ⁢           ⁢     λ2   ′         .           
The relationship line L 2  represents the relationship between the normalized horizontal phase retardation value of the second phase compensation film  110  and the wavelength of the light, which is the first formula:
 
                 R   ⁢           ⁢   λ1     λ1     &gt;       R   ⁢           ⁢   λ2     λ2     &gt;         R   ⁢           ⁢   λ3     λ3     .           
As we can see from the above-mentioned description, for the light with the wavelength smaller than 550 nm, the second phase compensation film  110  has larger horizontal phase retardation value than the first phase compensation film  108 , and for the light with the wavelength larger than 550 nm, the second phase compensation film  110  has smaller horizontal phase retardation value than the first phase compensation film  108 . That is to say that the decrease of the horizontal phase retardation value of the second phase compensation film  110  is larger than the decrease of the horizontal phase retardation value of the first phase compensation film  108  with the increase of the wavelength of the light, so that the slope of the relationship line L 2  is negative. Preferably, the second phase compensation film  110  has positive wavelength dispersion. Also, the first phase compensation film  108  and the second phase compensation film  110  may be used to compensate the phase difference between the lights with different wavelength passing through the liquid crystal layer  118  through disposing the first slow axis  108   a  and the second slow axis  110   a  to be perpendicular to each other, so that the light leakage in the direction of the large viewing angle can be reduced.
 
     In addition, the slope of the relationship line of the second phase compensation film is preferably larger in the invention. Please refer to  FIG. 4  and  FIG. 5 .  FIG. 4  is a schematic diagram illustrating a relationship between the horizontal phase retardation value of the second phase compensation film and the wavelength according to the first exemplary embodiment, and  FIG. 5  is a schematic diagram illustrating a relationship between the transmittance of the display corresponding to different relationship lines in  FIG. 4  and the wavelength. As shown in  FIG. 4  and  FIG. 5 , the relationship lines L 3 , L 4 , L 5 , L 6 , and L 7  represent the relationships between horizontal phase retardation values of the second phase compensation films  110  according to different examples and the wavelength. The curved lines C 1 , C 2 , C 3 , C 4 , C 5  represent the relationships between the transmittances of the displays according to different examples viewed in the direction of the viewing angle θ being 60 degrees and the azimuth angle φ being 45 degrees when the displays in the dark state and the wavelength. The curved line C 6  represent the relationship between the transmittance of the display without the second phase compensation film and the fourth phase compensation film and the wavelength of the light passing therethrough. The relationship line L 3  corresponds to the curved line C 1 . The relationship line L 4  corresponds to the curved line C 2 . The relationship line L 5  corresponds to the curved line C 3 . The relationship line L 6  corresponds to the curved line C 4 . The relationship line L 7  corresponds to curved line C 5 . As we can see from these relationships, when the slopes of the relationship lines are larger, the transmittances of the display with respect to the light with short wavelength and the light with long wavelength are smaller. That is to say that when the horizontal phase retardation value of the second phase compensation film  110  is larger in shorter wavelength, the light leakage of the display  100  is lower. When the display  100  includes the second phase compensation film  110  and the fourth phase compensation film  136 , the light leakage of the display  100  is less than the light leakage of the display without the second phase compensation film  110  and the fourth phase compensation film  136 . In the display  100  of this embodiment, the second phase compensation film  110  and the fourth phase compensation film  136  with positive wavelength dispersion are disposed with the first phase compensation film  108  and the third phase compensation film  134 , so that the phase retardation values of the lights with different wavelengths passing through the first phase compensation film  108  and the third phase compensation film  134  can be effectively compensated, and the light leakage can be reduced. 
     Please refer to  FIG. 6 , which is a schematic diagram illustrating the relationship between the transmittance and the azimuth angle of the display at the viewing angle of 70 degrees according to the first exemplary embodiment. As shown in  FIG. 6 , the curved line C 7  represent the relationship between the transmittance and the azimuth angle when the wavelength of the light passing through the display is 440 nm. The curved line C 8  represent the relationship between the transmittance and the azimuth angle when the wavelength of the light passing through the display is 550 nm. The curved line C 9  represent the relationship between the transmittance and the azimuth angle when the wavelength of the light passing through the display is 650 nm. The unit of the azimuth angle is degree, and the transmittance has no unit. No matter how long the wavelength of the light is, the transmittance of the display  100  in this embodiment can be effectively reduced at the direction of the azimuth angles of 45 degrees, 135 degrees and 315 degrees, so that the light leakage of the display in the direction of different viewing angles can be reduced when the display is in dark state. 
     The method of the first phase compensation film  108 , the second phase compensation film  110 , the third phase compensation film  134  and the fourth phase compensation film  136  compensating the phase retardation values of the light with different wavelengths in the display  100  of this embodiment will be further mentioned in the following description. Please refer to  FIG. 7  together with  FIG. 1  and  FIG. 2 .  FIG. 7  is a schematic diagram illustrating the change paths of the polarizing directions of the lights with different wavelengths on the Poincare sphere when the display is in the dark state according to the first exemplary embodiment. As shown in  FIG. 1 ,  FIG. 2  and  FIG. 7 , when the observer sees the display  100  in the direction of the viewing angle of 0 degree, the normal lights generated from the backlight module  112  will be transformed to be the lights having the first polarizing direction  104   b  that is substantially perpendicular to the second polarizing direction  106   b  of the second polarizer  106 . When the display  100  is observed in the direction of the large viewing angle θ, such as θ&gt;60, the first polarizing direction  104   b  tilts and is changed to be the polarizing direction of point P 1 , and the second polarizing direction  106   b  also tilts and is changed to be the polarizing direction of point P 2 . Also, an acute included angle between the polarizing direction of point P 1  and the polarizing direction of point P 2  is substantially smaller than 90 degrees. Then, when the light passes through the first phase compensation film  108 , the polarizing directions of the lights move on the Poincare sphere and rotate with respect to the first slow axis  108   a , and the moving distances are determined by the phase retardation values of the first phase compensation film  108  with respective to the wavelengths of the lights. The lights may include the lights with wavelengths λ 1 , λ 2  and λ 3 , such as blue light, green light and red light, and λ 1 &lt;λ 2 &lt;λ 3 . The lights with different wavelengths take the blue light, the green light and the red light as an example in the following description, but the invention is not limited herein. When the lights with the polarizing direction of point P 1  pass through the first phase compensation film  108 , the polarizing direction of the blue light will move from the point P 1  to the point P 3 ; the polarizing direction of the green light will move from the point P 1  to the point P 4 ; and the polarizing direction of the red light will move from the point P 1  to the point P 5 . Next, when the lights pass through the second phase compensation film  110 , the polarizing directions of the lights move on the Poincare sphere and rotate with respect to the second slow axis  110   a , and the moving distances are determined by the phase retardation values of the second phase compensation film  110  with respective to the wavelengths of the lights. Since the first slow axis  108   a  and the second slow axis  110   a  are substantially perpendicular to each other, the moving directions of the polarizing directions of the lights on the Poincare sphere are different. When the lights pass through the second phase compensation film  110 , the polarizing direction of the blue light moves from the point P 3  to the point P 6 ; the polarizing direction of the green light moves from the point P 4  to the point P 7 ; and the polarizing direction of the red light moves from the point P 5  to the point P 8 . Moreover, the liquid crystal molecules  118   a  also retard the phases of the lights in the direction of the large viewing angle θ, such as θ&gt;60, so when the lights pass through the liquid crystal layer  118 , the polarizing direction of the blue light will move from the point P 6  to the point P 9 ; the polarizing direction of the green light will move from the point P 7  to the point P 10 ; and the polarizing direction of the red light will move from the point P 8  to the point P 11 . After the lights passing through the liquid crystal layer  118 , the lights pass through the fourth compensation film  136 , and the polarizing directions of the lights move on the Poincare sphere with respect to the fourth slow axis  136   a . In this time, the polarizing direction of the blue light moves from the point P 9  to the point P 12 ; the polarizing direction of the green light moves from the point P 10  to the point P 13 ; and the polarizing direction of the red light moves from the point P 11  to the point P 14 . Next, when the lights pass through the third phase compensation film  136 , the polarizing directions of the lights move on the Poincare sphere with respect to the third slow axis  136   a . Accordingly, the polarizing direction of the blue light moves from the point P 12  to the point P 15  or close to the point  15 ; the polarizing direction of the green light moves from the point P 13  to the point P 15 . Since the point  15  and the point P 2  together with the center point of the Poincare sphere are disposed in a straight line, the polarizing direction of the point P 15  is perpendicular to the polarizing direction of point P 2 , and the lights with the polarizing direction of the point P 15  does not pass through the second polarizer  106  with the polarizing direction of point P 2 . Accordingly, the lights in the direction of the large viewing angle θ, such as θ&gt;60, does not pass through the display  100 . Or, most of the lights in the direction of the large viewing angle θ can be absorbed by the second polarizer  106 , so that the light leakage of the display  100  can be reduced or solved. Furthermore, since the distances of the lights moving on the Poincare sphere corresponds to the phase retardation values of the first phase compensation film  108 , the second phase compensation film  110 , the third phase compensation film  134  and the fourth phase compensation film  136 , the method of compensating the phase retardation values in the direction of the large viewing angle is not limited to the above-mentioned method of the invention, and the phase retardation values of the first phase compensation film, the second phase compensation film, the third phase compensation film and the fourth phase compensation film may be adjusted to compensate the phase retardation values in the direction of the large viewing angle and to avoid light leakage accord to the actual requirements. 
     According to the above-mentioned description, the second phase compensation film  110  and the fourth phase compensation film  136  with positive wavelength dispersion are disposed with the first phase compensation film  108  and the third phase compensation film  134  in the display  100  of this embodiment, so that the phase retardation values of the lights with different wavelengths in the direction of the large viewing angle θ, such as θ&gt;60, can have the same polarizing direction as the lights passing through the first phase compensation film  108 , the second phase compensation film  110 , the liquid crystal layer  118 , the fourth phase compensation film  136  and the third phase compensation film  134 , and this polarizing direction is substantially perpendicular to the linear polarizing direction of the second polarizing direction  106  viewed in the direction of the large viewing angle θ. Therefore, the light leakage of the display  100  in the direction of the large viewing angle θ can be effectively solved. 
     The display is not limited by the above-mentioned embodiment. The following description continues to detail the other embodiments or modifications, and in order to simplify and show the difference between the other embodiments or modifications and the above-mentioned embodiment, the same numerals denote the same components in the following description, and the same parts are not detailed redundantly. 
     Please refer  FIG. 8 , which is a schematic diagram illustrating a display according to a second exemplary embodiment. As shown in  FIG. 8 , as compared with the first embodiment, the display  200  of this embodiment doesn&#39;t include the third phase compensation film and the fourth compensation film. In other words, the display  200  of this embodiment only uses the first phase compensation film  108  and the second phase compensation film  110  to compensate the phase retardation values of the lights passing the first polarizer  104 , the display panel  104  and the second polarizer  106  in the direction of the large viewing angle. In this embodiment, only the second polarizer  106  is disposed on the outer surface of the substrate  116  that is the light-emitting surface  102   b  in the display  200 . 
     The method of the display  200  in this embodiment using the first phase compensation film and the second phase compensation film to compensate the phase retardation values of the lights with different wavelengths will be further mentioned in the following description. Please refer to  FIG. 9  together with  FIG. 8 .  FIG. 9  is a schematic diagram illustrating the change paths of the polarizing directions of the lights with different wavelengths on the Poincare sphere when the display is in the dark state according to the second exemplary embodiment. As shown in  FIG. 8  and  FIG. 9 , when the lights with the polarizing direction of point P 1  pass through the first phase compensation film  108 , the polarizing direction of the blue light moves from the point P 1  to the point P 16 ; the polarizing direction of the green light moves from the point P 1  to the point P 17 ; and the polarizing direction of the red light moves from the point P 1  to the point P 18 . Next, when the lights pass through the second phase compensation film  110 , the polarizing direction of the blue light moves from the point P 16  to the point P 19 ; the polarizing direction of the green light moves from the point P 17  to the point P 20 ; and the polarizing direction of the red light moves from the point P 18  to the point P 21 . Moreover, the liquid crystal molecules  118   a  also retard the phases of the lights in the direction of the large viewing angle θ, so when the lights pass through the liquid crystal layer  118 , the polarizing direction of the blue light moves from the point P 19  to the point P 22 ; the polarizing direction of the green light moves from the point P 20  to the point P 22 ; and the polarizing direction of the red light moves from the point P 21  to the point P 22 . Thus, the display  200  in this embodiment also can compensate the phase retardation values of the lights in the direction of the large viewing angle θ, such as θ&gt;60, through adjusting the phase retardations of the first phase compensation film  108  and the second phase compensation film  110 . Also, the third phase compensation film and the fourth phase compensation film can be omitted in the display  200  of this embodiment. 
     Please refer  FIG. 10 , which is a schematic diagram illustrating a display according to a third exemplary embodiment. As shown in  FIG. 10 , as compared with the first embodiment, the display  300  of this embodiment doesn&#39;t include the first phase compensation film and the second compensation film in the first embodiment. In other words, the first phase compensation film  302  and the second compensation film  304  in the display  300  of this embodiment are respectively the third phase compensation film  134  and the fourth phase compensation film  136  in the first embodiment. The first phase compensation film  302  and the second compensation film  304  are disposed between the second polarizer  106  and the display panel  102 . In this embodiment, only the first polarizer  104  is disposed on the outer surface of the substrate  114  that is the light-incident surface  1022  in the display  300 . The first slow axis  302   a  of the first phase compensation film  302  is disposed along the first direction  128 , and is substantially perpendicular to the second light-absorption axis  106   a . The second slow axis  304   a  of the second phase compensation film  304  is disposed along the second direction  130 , and is substantially parallel to the second light-absorption axis  106   a . The method of compensating the phase retardation values of the lights in the direction of the large viewing angle θ, such as θ&gt;60, in this embodiment is similar to the compensating method of the third phase compensation film and the fourth phase compensation film in the first embodiment, and the difference between this embodiment and the first embodiment is that the phase retardation values of the first phase compensation film  302  and the second phase compensation film  304  in this embodiment are different from the phase retardation values of the third phase compensation film and the fourth phase compensation film in the first embodiment, so that the method of compensating the phase retardation values of the lights in this embodiment are not detailed redundantly. 
     Please refer to  FIG. 11 , which is a schematic diagram illustrating a display according to a fourth exemplary embodiment. As shown in  FIG. 11 , as compared with the first embodiment, the display  400  of this embodiment doesn&#39;t include the second phase compensation film and the third compensation film in the first embodiment. In other words, the first phase compensation film  402  and the second compensation film  404  in the display  400  of this embodiment are respectively the first phase compensation film  108  and the fourth phase compensation film  136  in the first embodiment. There is only the first phase compensation film  402  disposed between the first polarizer  104  and the display panel  102 , and no other phase compensation film is disposed between the first polarizer  104  and the display panel  102 . Also, there is only the second phase compensation film  404  disposed between the second polarizer  106  and the display panel  102 , and no other phase compensation film is disposed between the second polarizer  106  and the display panel  102 . The first slow axis  402   a  of the first phase compensation film  402  is disposed along the second direction  130 , and is substantially perpendicular to the first light-absorption axis  104   a . The second slow axis  404   a  of the second phase compensation film  404  is disposed along the second direction  130 , and is substantially parallel to the second light-absorption axis  106   a.    
     The method of the display  400  in this embodiment using the first phase compensation film  402  and the second phase compensation film  404  to compensate the phase retardation values of the lights with different wavelengths will be further mentioned in the following description. Please refer to  FIG. 12  together with  FIG. 11 .  FIG. 12  is a schematic diagram illustrating the change paths of the polarizing directions of the lights with different wavelengths on the Poincare sphere when the display  400  is in the dark state according to the fourth exemplary embodiment. As shown in  FIG. 11  and  FIG. 12 , when the lights with the polarizing direction of point P 1  pass through the first phase compensation film  402 , the polarizing direction of the blue light moves from the point P 1  to the point P 23 ; the polarizing direction of the green light moves from the point P 1  to the point P 24 ; and the polarizing direction of the red light moves from the point P 1  to the point P 25 . Next, when the lights pass through the display panel  102 , the polarizing direction of the blue light moves from the point P 23  to the point P 26 ; the polarizing direction of the green light moves from the point P 24  to the point P 27 ; and the polarizing direction of the red light moves from the point P 25  to the point P 28 . Then, when the lights pass through the second phase compensation film  404 , the polarizing direction of the blue light moves from the point P 26  to the point P 29 ; the polarizing direction of the green light moves from the point P 27  to the point P 29 ; and the polarizing direction of the red light moves from the point P 28  to the point P 29 . Thus, the display  400  in this embodiment also can compensate the phase retardation values of the lights in the direction of the large viewing angle to reduce the light leakage. 
     Please refer to  FIG. 13 , which is a schematic diagram illustrating a display according to a fifth exemplary embodiment. As shown in  FIG. 13 , as compared with the first embodiment, the display  500  of this embodiment doesn&#39;t include the first phase compensation film and the fourth compensation film in the first embodiment. In other words, the first phase compensation film  502  and the second compensation film  504  in the display  500  of this embodiment are respectively the third phase compensation film  134  and the second phase compensation film  110  in the first embodiment. There is only the first phase compensation film  502  disposed between the second polarizer  106  and the display panel  102 , and no other phase compensation film is disposed between the second polarizer  106  and the display panel  102 . Also, there is only the second phase compensation film  504  disposed between the first polarizer  104  and the display panel  102 , and no other phase compensation film is disposed between the first polarizer  104  and the display panel  102 . The first slow axis  502   a  of the first phase compensation film  502  is disposed along the first direction  128 , and is substantially perpendicular to the second light-absorption axis  106   a . The second slow axis  504   a  of the second phase compensation film  504  is disposed along the first direction  128 , and is substantially parallel to the first light-absorption axis  104   a.    
     In summary, the display of the invention combines the second phase compensation film that obeys the first formula: 
                 R   ⁢           ⁢   λ1     λ1     &gt;       R   ⁢           ⁢   λ2     λ2     &gt;       R   ⁢           ⁢   λ3     λ3           
with the first phase compensation film to effectively compensate the phase retardation values of the lights with different wavelengths in the direction of the large viewing angle, so that the light leakage of the display in the direction of the large viewing angle can be effectively solved.
 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.