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CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Divisional of application Ser. No. 13/590,465, filed at Aug. 21 2012, the entirety of which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an electric curtain. 
         [0004]    2. Description of the Related Art 
         [0005]    The visual system in humans allows individuals to assimilate information from the environment. The act of seeing starts when the lens of the eye focuses an image of its surroundings onto a light-sensitive membrane in the back of the eye, called the retina. The retina is actually part of the brain that is isolated to serve as a transducer for the conversion of patterns of light into neuronal signals. Then, the neuronal signals are processed by the brain and humans therefore see what they are seeing. 
         [0006]    A refractive error, or refraction error, is an error in the focusing of light by the eye. The refractive error comprises different types, such as myopia, hyperopia or astigmatism. Myopia refers to a refractive defect of the optical properties of an eye that causes images to focus on a forward portion of the retina (i.e., a refractive error). Those optical defects are typically caused by, among other things, defects of the cornea, elongation of the eye structure, other conditions, or a combination of those conditions. Hyperopia, on the other hand, refers to a refractive error of the optical properties of an eye that causes images to focus on a portion behind the retina. Those optical defects are the result when the optics of the eye is not strong enough for the front to back length of the eye. Astigmatism refers to a refractive error that causes light entering the eye to focus on two points rather than one. It is caused by an uneven power of the cornea. Myopia, hyperopia, and astigmatism are the principle refractive errors that cause persons to seek treatment to correct their vision problems, but there is still no treatment that can deal with these problems at one time except for laser vision correction. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    An embodiment of the invention provides a focus adjustable apparatus adapted to be disposed on a transparent substrate to modulate a plurality of rays passing through the transparent substrate. The focus adjustable apparatus comprises a light modulation device, an eye tracking device, an eyesight status device and a controller. The light modulation device receives the rays from the transparent substrate and adjusts an emergent angle of each of the rays. The eye tracking device tracks a position of a user and estimates a distance between the user and the focus adjustable apparatus. The eyesight status device obtains an eyesight data of the user. The controller provides a control signal to drive the light modulation device by estimating the emergent angle of the each of the plurality of rays according to the distance between the user and the focus adjustable apparatus and the eyesight data of the user. 
         [0008]    Another embodiment of the invention provides a display with an adjustable focus mechanism. The display comprises a display panel, a light modulation device and a controller. The display panel emits a plurality of rays to form an image. The light modulation device receives the rays from the display panel and adjusts an emergent angle of each ray. The controller provides a control signal to drive the light modulation device by estimating the emergent angle of the each of the plurality of rays according to an eyesight data of a user and a distance between the user and the display. 
         [0009]    Another embodiment of the invention provides an electric curtain comprising sunlight detector and a light modulation device. The sunlight detector obtains a light data of sunlight. The light modulation device receives the sunlight and adjusts an emergent angle of the sunlight to refract the sunlight to a ceiling of a room. 
         [0010]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a schematic diagram of an embodiment of a focus adjustable apparatus according to the invention. 
           [0013]      FIG. 2  is a schematic diagram of an electro-wetting unit according to an embodiment of the invention. 
           [0014]      FIG. 3  is a schematic diagram of an electro-wetting unit according to another embodiment of the invention. 
           [0015]      FIG. 4  is a schematic diagram of an electro-wetting unit according to another embodiment of the invention. 
           [0016]      FIG. 5  is a cross section diagram of a light modulation device according to an embodiment of the invention. 
           [0017]      FIG. 6  is a schematic of an embodiment of a display device according to the invention. 
           [0018]      FIG. 7  is a schematic diagram of another embodiment of a focus adjustable apparatus according to the invention. 
           [0019]      FIG. 8  is a schematic diagram of an embodiment of an electric curtain according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0021]      FIG. 1  is a schematic diagram of an embodiment of a focus adjustable apparatus according to the invention. The focus adjustable apparatus is disposed on a transparent substrate  15   a  of the display  15 . The focus adjustable apparatus comprises a light modulation device  11 , an eye tracking device  13 , an eyesight status device  14  and a controller  12 . The eye tracking device  13  tracks a position of a user  16  and estimates a distance d between the user  16  and the display  15 . The eye tracking device  13  further estimates an angle θ that varies according to a relative position of the user  16  with reference to the light modulation device  11 . The eyesight status device  14  obtains an eyesight data of the user. The eyesight data comprises an astigmatism degree, a degree of myopia or a degree of hyperopia of the user  16 . The eyesight status device  14  may acquire the eyesight data of the user  16  from an electronic patient record database and the user  16  needs to provide some security authorization data to the eyesight status device  14 , and then the eyesight status device  14  acquires the eyesight data according to the security authorization data. In another embodiment, the eyesight data is directly input to the eyesight status device  14  by the user. In another embodiment, the eyesight data is determined by an eye refractometer (not shown in  FIG. 1 ). The eye refractometer is embedded in the eye tracking device. The eye refractometer projects a test pattern onto the retina of an eye to be examined, and determines the eyesight data according to the reflected test patter from the retina. Furthermore, the focus adjustable apparatus comprises a sensor for detecting an ambient light and the controller  12  controls the illumination of the rays refracted by the light modulation device  11  according to the illumination of the ambient light. 
         [0022]    The light modulation device  11  receives a plurality of rays from the transparent substrate  15   a  and adjusts an emergent angle of each of the rays. The emergent angle is determined by the controller  12 . The controller  12  estimate the emergent angle according to the eyesight data of the user  16  and the distance between the user  16  and the display  15 . In one embodiment, the focus adjustable apparatus further comprises a calculator (not shown in  FIG. 1 ) to receive the distance between the user  16  and the display  15  and the eyesight data of the user  16  to generate a control parameter, and then the controller  12  receives the control parameter and estimates the emergent angle according to the control parameter from the calculator. The rays refracted by the light modulation device  11  form an in-focus image on a retina of the user  16 . In this embodiment, the light modulation device  11  comprises a plurality of electro-wetting units arranged in a matrix form. The electro-wetting units are driven by a dielectric force and the refraction index of each electro-wetting unit can be changed according to the magnitude of the dielectric force. In another embodiment, the light modulation device  11  is implemented by a plurality of Fresnel lens or Hologram elements arranged in a matrix or array form. 
         [0023]    An electro-wetting unit is illustrated with  FIG. 2 .  FIG. 2  is a schematic diagram of an electro-wetting unit according to an embodiment of the invention. The electro-wetting unit  20  comprises a first electrode  21 , a second electrode  22 , a compartment  23 , and a first light modulating media (labeled as A) and a second light modulating media (labeled as B) filled in the compartment  23  (shown as the dotted line in  FIG. 2 ), wherein the first light modulating media and second light modulating media are substantially immiscible and are of different refractive indices. The boundary between the first light and second light modulating media is adjusted by applying voltages to the first electrode  21  and the second electrode  22  according to a control signal from the controller, such as the controller  12  in  FIG. 1 . The control signal is determined according to the emergent angle Φ by the controller. 
         [0024]      FIG. 3  is a schematic diagram of an electro-wetting unit according to another embodiment of the invention. The electro-wetting unit  30  comprises a first electrode  31 , a second electrode  32 , a compartment  33 , a third electrode  34  and a first light modulating media (labeled as A) and a second light modulating media (labeled as B) filled in the compartment  33  (shown as the dotted line in  FIG. 3 ), wherein the first light modulating media and second light modulating media are substantially immiscible and are of different refractive indices. In this embodiment, the first electrode  31 , the second electrode  32  and the third electrode  34  are optically transparent electrodes. The boundary between the first light and second light modulating media is adjusted by applying voltages to the first electrode  31 , the second electrode  32  and the third electrode  34  according to a control signal from the controller, such as the controller  12  in  FIG. 1 . The control signal is determined according to the emergent angle  0  by the controller. 
         [0025]      FIG. 4  is a schematic diagram of an electro-wetting unit according to another embodiment of the invention. The electro-wetting unit  40  comprises a first electrode  41 , a second electrode  42 , a bottom electrode  43 , a third electrode  44 , a fourth electrode  45 , a upper electrode  46 , a compartment  47 , and a first light modulating media (labeled as A), a second light modulating media (labeled as B) and a third light modulating media (labeled as C) filled in the compartment  47  (shown as the dotted line in  FIG. 4 ), wherein the first light modulating media, the second light modulating media and the third light modulating media are substantially immiscible and are of different refractive indices. In this embodiment, the first electrode  41 , the second electrode  42 , the bottom electrode  43 , the third electrode  44 , the fourth electrode  45  and the upper electrode  46  are optically transparent electrodes. The first boundary  48  and the second boundary  49  can be adjusted by applying voltages to the first electrode  41 , the second electrode  42 , the bottom electrode  43 , the third electrode  44 , the fourth electrode  45  and the upper electrode  46  according to a control signal from the controller, such as the controller  12  in  FIG. 1 . The control signal is determined according to the emergent angle Φ by the controller. In other embodiments, the electro-wetting unit is named as an electronically switchable light modulating cell which is disclosed in a pending U.S. patent application Ser. No. 13/016,384, filed Jan. 28, 2011 and entitled “LIGHT MODULATING CELL, DEVICE AND SYSTEM”, the entirety of which is incorporated by reference herein. 
         [0026]      FIG. 5  is a cross section diagram of a light modulation device according to an embodiment of the invention. The light modulation device  50  comprises a glue layer  53 , a flexible substrate  52  and an electro-wetting array  51 . The light modulation device  50  can be adhered to a display device, a plane glass, a window, a lampshade, an eyeglass or other transparent substance via the glue layer  53 . The glue layer  53  may be implemented by a pressure sensitive adhesive material or a silica gel. The flexible substrate  52  may be a PET layer, a PI layer or a roll-able glass. 
         [0027]      FIG. 6  is a schematic of an embodiment of a display device according to the invention. The display device  60  comprises a controller  61 , an eye tracking device  62 , an eyesight status device  63 , a light modulation device  64  and a panel  65 . The light modulation device  64  is adhered to the panel  65 . The eye tracking device  62  tracks a position of a user and estimates a distance d between the user and the display device  60 . The eye tracking device  62  further estimates an angle  0  that varies according to a relative position of the user with reference to the light modulation device  64 . The eyesight status device  63  obtains an eyesight data of the user. The eyesight data may comprise an astigmatism degree, a degree of myopia or a degree of hyperopia of the user. The eyesight status device  63  may acquire the eyesight data of the user from an electronic patient record database and the user needs to provide some security authorization data to the eyesight status device  63 , and then the eyesight status device  63  acquires the eyesight data according to the security authorization data. In another embodiment, the eyesight data is directly input to the eyesight status device  63  by the user. In another embodiment, the eyesight data is determined by an eye refractometer (not shown in  FIG. 6 ) that is embedded in the eye tracking device  62 . The eye refractometer projects a test pattern onto the retina of an eye to be examined, and determines the eyesight data according to the reflected test patter from the retina. The sensor  66  detects an ambient light and the controller  61  controls the illumination of the rays refracted by the light modulation device  64  according to the illumination of the ambient light. 
         [0028]    The light modulation device  64  receives a plurality of rays from the panel  65  and adjusts an emergent angle of each ray. By adjusting the emergent angle of each ray, the image therefore can be correctly focused on the retina of the eyes of the user. The emergent angle is determined by the controller  61 . The controller  61  estimates the emergent angle according to the eyesight data of the user and the distance between the user and the display  60 . In one embodiment, the controller  61  comprises a calculator (not shown in  FIG. 6 ). The calculator receives the distance between the user and the display  60  and the eyesight data of the user to generate a control parameter, and then the controller  61  receives the control parameter and estimates the emergent angle according to the control parameter from the calculator. The rays refracted by the light modulation device  64  form an in-focus image on a retina of the user. In this embodiment, the light modulation device  64  comprises a plurality of electro-wetting units arranged in a matrix form. The electro-wetting units are driven by a dielectric force and the refraction index of each electro-wetting unit can be changed according to the magnitude of the dielectric force. In another embodiment, the light modulation device  64  is implemented by a plurality of Fresnel lens or Hologram elements arranged in a matrix or array form. For examples of the electro-wetting unit, reference can be made to  FIGS. 2-4 . 
         [0029]    In another embodiment, the user can directly control the light modulation device  64  via a remote control. The user can control emergent angles of rays refracted by the light modulation device  64  via the remote control. Once the emergent angles vary, the image seen by the user may be blurred or clear, thus, the user can instinctively control the light modulation device  64  only according to the displayed image. The control of the light modulation device  64  is similar to a zoom in/zoom out control or a focus control. Simply speaking, the light modulation device  64  plays a role similar to an eyeglass to ensure that the image can be correctly formed on the retina of the eyes of the user. 
         [0030]      FIG. 7  is a schematic diagram of another embodiment of a focus adjustable apparatus according to the invention. The focus adjustable apparatus  70  comprises a light modulation device  71 , a controller  72 , an eye tracking device  73 , a motion detector  74 , a calculator  75  and an eye status device  76 . The light modulation device  71  is adhered to an inner or outer surface of a windshield of a vehicle. For the detailed structure of the light modulation device  71 , reference can be made to  FIG. 5 , and thus, is not described here for briefly. The eye tracking device  73  tracks a position of a user and estimates a first distance d 1  between the user and the light modulation device  71  (or the windshield). The eye tracking device  73  further tracks the movement of the eyeball of a user and transmits an object information to the controller  72 . The object information indicates which object, such as the object  77 , the user is looking at. The object may be an obstacle, a moving vehicle or a moving/still object. The controller  72  then transmits a control signal to control the motion detector  74  to measure a second distance d 2  between the object  77  and the light modulation device  71 . 
         [0031]    The eyesight status device  76  obtains eyesight data of the user. The eyesight data may comprise an astigmatism degree, a degree of myopia or a degree of hyperopia of the user. The eyesight status device  76  may acquire the eyesight data of the user from an electronic patient record database or a digital medical system and the user needs to provide some security authorization data to the eyesight status device  76  for acquiring the eyesight data. In another embodiment, the eyesight data is directly input to the eyesight status device  76  by the user. In another embodiment, the eyesight data is determined by an eye refractometer  77 . The eye refractometer  77  projects a test pattern onto the retina of an eye to be examined, and determines the eyesight data according to the reflected test pattern? from the retina. The sensor  78  detects an ambient light and the controller  72  controls the illumination of the rays refracted by the light modulation device  71  according to the illumination of the ambient light. In this embodiment, the eye refractometer  77  and the sensor  78  are optional for the focus adjustable apparatus  70 , but they still can be integrated into the focus adjustable apparatus  70 . 
         [0032]    The light modulation device  71  receives a plurality of rays from the object  77  and adjusts an emergent angle of each ray. By adjusting the emergent angle of each ray, the image of the object  77  therefore can be correctly focused on the retina of the eyes of the user. The emergent angle is determined by the controller  72 . The controller  72  estimates the emergent angle according to the eyesight data of the user, the first distance d 1  and the second distance d 2 . The calculator  75  receives the first distance, the second distance and the eyesight data of the user to generate a control parameter. Then, the controller  61  receives the control parameter to estimate the emergent angle accordingly. The rays refracted by the light modulation device  71  form an in-focus image on a retina of the user. In this embodiment, the light modulation device  71  comprises a plurality of electro-wetting units arranged in a matrix form. The electro-wetting units are driven by a dielectric force and the refraction index of each electro-wetting unit can be changed according to the magnitude of the dielectric force. In another embodiment, the light modulation device  71  is implemented by a plurality of Fresnel lens or Hologram elements arranged in a matrix or array form. For the examples of the electro-wetting unit, reference can be made to  FIGS. 2-4 , and thus, is not described here for briefly. 
         [0033]      FIG. 8  is a schematic diagram of an embodiment of an electric curtain according to the invention. The electric curtain comprises a light modulation device  81 , a controller  82 , sunlight detector  83  and a tracking device  84 . The tracking device  84  tracks a position of the user and measures a distance d between the user and the light modulation device  81  and a height h of the user. The height can be input by the user via a remote control. The user can also control the angle θ 2  via the remote control. The sunlight detector  83  obtains light information of sunlight, such as an incident angle θ 1  and the illumination. The controller  82  then estimates the angle θ 2  according to the incident angle θ 1 , the distance d and the height h. The light modulation device  81  receives a control signal from the controller to refract the sunlight to a ceiling of a room. In this embodiment, the controller  82  transmits a control signal to adjust the angle θ 2  and the amount of the sunlight passing through the light modulation device  81 . The light modulation device  81  is a flexible film and adheres to a window. For the detailed structure of the light modulation device  81 , reference can be made to  FIG. 5 , and thus, is not described here for briefly. 
         [0034]    Since the light modulation device  81  can refract the sunlight to the ceiling of the room, the user may not directly feel the heat from the sunlight and the temperature of the room can be regulated at a higher temperature by an air conditioner. Furthermore, the light modulation device  81  prevents the eye of a user from receiving direct sunlight. 
         [0035]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

Summary:
An aspect of the invention provides an electric curtain. The electric curtain includes a sunlight detector for obtaining light information of sunlight and a light modulation device capable of receiving the sunlight and for adjusting an emergent angle of the sunlight to refract the sunlight to a ceiling of a room.