Abstract:
A liquid crystal display is provided. The liquid crystal display device comprises a light source unit, a light converting unit receiving light from the light source unit and converting a polarization property and a brightness distribution of the provided light, a screen receiving the light from the light converting unit and improving a frontal brightness of the provided light and a liquid crystal display panel disposed in front of the screen. Thus, the present invention provides a liquid crystal display having a good light efficiency without using an expensive optical film.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 2005-0101795, filed on Oct. 27, 2005, in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a liquid crystal display. More particularly, the present invention relates to a liquid crystal display having a good light efficiency without using an optical film.  
         [0004]     2. Description of the Related Art  
         [0005]     A liquid crystal display (LCD) comprises an LCD panel. The LCD panel comprises a thin film transistor (TFT) substrate on which TFTs are formed, a color filter substrate on which color filters are formed and a liquid crystal layer disposed therebetween. Since the LCD panel does not emit light by itself, the LCD may comprise a backlight unit in back of the TFT substrate. The transmittance of the light generated from the backlight unit is adjusted according to an arrangement of the liquid crystal layer.  
         [0006]      FIG. 1  is a drawing illustrating a conventional LCD.  
         [0007]     The LCD  100  comprises an LCD panel  110  and a backlight unit  120  providing light with the LCD panel  110 .  
         [0008]     The backlight unit  120  comprises lamps  121  arranged in a row, a reflecting plate  122  disposed in back of the lamps  121  and optical films  123 ,  124 ,  125  and  126  disposed in front of the lamps  121 .  
         [0009]     The lamps  121  may be provided as a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL). The light generated from each of the lamps  121  is radiated in all directions. The light radiated toward a lower direction is reflected by the reflecting plate  122  and directed toward the diffusion plate  123 .  
         [0010]     The diffusion plate  123  comprises diffusion members and diffuses the light generated from the lamps  121 . Accordingly, the LCD  100  has uniform brightness distribution. In using a line light source such as a lamp  121 , bright lines may be generated according to the arrangement of the line light source. The diffusion plate  123  may reduce the occurrence of the bright lines.  
         [0011]     The diffusion film  124  comprises fine particles having a ball shape to diffuse the incident light, and thus a uniformity of the light and the brightness in a front direction are increased.  
         [0012]     On the prism film  125 , prisms are formed to increase brightness in a front direction. Two or more prism films  125  may be used.  
         [0013]     The reflecting polarization film  126  reflects light having different polarizing directions. The polarizing direction of the reflected light is switched by the diffusion plate  123  and the reflecting plate  122 , and then the switched light re-enters the reflecting polarization film  126 . Accordingly, a polarization efficiency is increased.  
         [0014]     However, a manufacturing cost is increased due to a high cost of the prism film  125  and the reflecting polarization film  126 . The cost of the prism film  125  and the reflecting polarization film  126  is particularly high for a large-sized LCD  100 .  
         [0015]     Accordingly, there is a need for an improved liquid crystal display having high efficiency without an expensive film.  
       SUMMARY OF THE INVENTION  
       [0016]     Exemplary embodiments of the present invention address at least the above problems and/or disadvantages and provide at least the advantages described below. Accordingly, it is an object of the present invention to provide a liquid crystal display having high light efficiency without using an expensive optical film.  
         [0017]     The foregoing and/or other aspects of the present invention can be achieved by providing a liquid crystal display comprising a light source unit, a light converting unit receiving light from the light source unit and converting a polarization property and a brightness distribution of the received light, a screen receiving the light from the light converting unit and improving a frontal brightness of the provided light and a liquid crystal display panel disposed in front of the screen.  
         [0018]     According to an aspect of the present invention, a Fresnel structure is provided at an emitting surface of the screen.  
         [0019]     According to an aspect of the present invention, the light converting unit comprises a polarization converting system converting incident non-polarized light into P waves.  
         [0020]     According to an aspect of the present invention, the light converting unit further comprises a light tunnel.  
         [0021]     According to an aspect of the present invention, the light source unit comprises a lamp for generating light and a lamp reflector which surrounds the light source unit and reflects the light generated from the light source unit toward the light converting unit.  
         [0022]     According to an aspect of the present invention, the lamp reflector is of an ellipsoidal type, and the light generated from the light source unit passes through the polarization converting system and enters the light tunnel.  
         [0023]     According to an aspect of the present invention, the lamp reflector is of a parabolic type and the light generated from the light source unit passes through the light converting unit and enters the light tunnel, the liquid crystal display further comprising a condenser lens disposed between the polarization converting system and the light tunnel.  
         [0024]     According to an aspect of the present invention, the light converting unit further comprises an array of fly eye lenses provided in a pair and facing each other.  
         [0025]     According to an aspect of the present invention, the light source unit comprises a lamp for generating light, a lamp reflector of a parabolic type which surrounds the light source unit and reflects the light generated from the light source unit toward the light converting unit.  
         [0026]     According to an aspect of the present invention, the light of the light source unit passes through the array of the fly eye lenses and enters the polarization converting system.  
         [0027]     According to an aspect of the present invention, the polarization converting system comprises a sub polarization converting system corresponding to each lens of the array of the fly eye lenses.  
         [0028]     According to an aspect of the present invention, the liquid crystal display further comprises a reflecting mirror which is disposed between the light converting unit and the screen and diverts a progressive path of the light.  
         [0029]     According to an aspect of the present invention, the liquid crystal display further comprises an ultraviolet filter disposed between the light source unit and the light converting unit for blocking incident ultraviolet rays.  
         [0030]     According to an aspect of the present invention, the liquid crystal display further comprises a diffusion sheet disposed between the liquid crystal display panel and the screen. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]     The above and/or other aspects, features and advantages of the present invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompany drawings, in which:  
         [0032]      FIG. 1  is a drawing illustrating a conventional LCD;  
         [0033]      FIG. 2  is a drawing illustrating a configuration of the LCD according to a first exemplary embodiment of the present invention;  
         [0034]      FIG. 3  is a drawing illustrating a polarization converting system of the LCD according to the first exemplary embodiment of the present invention;  
         [0035]      FIG. 4  is a drawing illustrating a light tunnel of the LCD according to the first exemplary embodiment of the present invention;  
         [0036]      FIG. 5  is a drawing illustrating a screen of the LCD according to the first exemplary embodiment of the present invention;  
         [0037]      FIGS. 6 and 7  illustrate LCDs according to a second and a third exemplary embodiment of the present invention, respectively. 
     
    
       [0038]     Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures.  
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0039]     The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention and are merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. Reference will now be made in detail to exemplary embodiments of the present invention. The exemplary embodiments are described below so as to explain the present invention by referring to the drawings.  
         [0040]     An LCD according to a first exemplary embodiment of the present invention will be described referring to  FIGS. 2 through 5 .  
         [0041]     As shown in  FIGS. 2 through 5 , an exemplary LCD  1  of the present invention comprises an LCD panel  10 , a light source unit  20 , a light converting unit  40  and a screen  71 . An ultraviolet filter  31  is disposed between the light source unit  20  and the light converting unit  40 , a reflecting mirror  61  is disposed between the light converting unit  40  and the screen  71 , and a diffusion film  81  is disposed between the LCD panel  10  and the screen  71 . The LCD  1  further comprises various optical lenses  51  through  54 .  
         [0042]     The light source unit  20  comprises a lamp  21  generating light and a lamp reflector  22 . The lamp  21  generates white-colored and non-polarized light. The lamp reflector  22  reflects the light generated from the lamp  21  to guide a progressive direction of the light.  
         [0043]     The lamp reflector  22  may be of a parabolic type or an ellipsoidal type. The ellipsoidal type has a first focal point corresponding to the lamp  21  and a second focal point on which light is concentrated. The parabolic type makes parallel light from the light reflected by the lamp reflector  22 . The lamp reflector  22  is of the ellipsoidal type in the first exemplary embodiment of the present invention.  
         [0044]     The light generated from the light source unit  20  is concentrated on the second focal point by the lamp reflector  22  and passes through the ultraviolet filter  31  while the light is concentrated. An ultraviolet ray incident on the light converting unit  40  is reduced by the ultraviolet filter  31 .  
         [0045]     A polarization converting system  410  for converting a polarization state of the incident light and a light tunnel  420  are disposed in the light converting unit  40  in order.  
         [0046]     As shown in  FIG. 3 , the polarization converting system  410  comprises a polarization separation member  411 , a reflecting member  412  and a half wavelength plate  413 . The polarization separation member  411  transmits most of P-polarized light and reflects most of S-polarized light. The S-polarized light and the P-polarized light cross each other at a right angle. The reflecting member  412  reflects the S-polarized light from the polarization separation member  411  and makes the reflected light progress in parallel with the P-polarized light. The half wavelength plate  413  is disposed in a progressive path of the S-polarized light and coverts the S-polarized light into the P-polarized light. Accordingly, the light generated from the light source unit  20  is converted into the P-polarized light and then enters the light tunnel  420 .  
         [0047]     In another exemplary embodiment, the polarization separation member  411  may reflect the P-polarized light and the half wavelength plate  413  may convert the reflected P-polarized light into the S-polarized light. Then, the light generated from the light source unit  20  is converted into S-polarized light and enters the light tunnel  420 .  
         [0048]     As shown in  FIG. 4 , the light tunnel  420  has a hollow square pillar shape and the inner surface comprises light reflecting material such as a mirror. The incident light into the light tunnel  420  is repeatedly reflected by the inner surface, and thus light having uniform brightness distribution is emitted from the light tunnel  420 .  
         [0049]     The light emitted from the light tunnel  420  passes through the optical lenses  51 ,  52  and  53  and then enters the reflecting mirror  61 . The reflecting mirror  61  diverts the progressive direction of the incident light toward the screen  71 . In an exemplary embodiment, the diversion is by 90°.  
         [0050]     If the light source unit  20 , the light converting unit  40 , the screen  71  and the LCD panel  10  are disposed in a row, the thickness of the LCD  1  may be increased significantly. The increased thickness is addressed with the reflecting mirror  61 . The light source unit  20  and the light converting unit  40  may be disposed in parallel with a surface of the LCD panel  10  and may be disposed in a lower part of the LCD panel  10 . Alternatively, additional mirrors may be installed between the light converting unit  40  and the optical lens  51  as necessary.  
         [0051]     The light reflected by the reflecting mirror  61  passes through the optical lens  54  and is transferred to the screen  71 .  
         [0052]     The screen  71  has a size corresponding to the LCD panel  10 . The screen  71  improves the front brightness.  
         [0053]     As shown in  FIG. 5 , a Fresnel lens  72  is provided at a light emitting surface of the screen  71 . The Fresnel lens  72  comprises a plurality of concentric circles  72   a,    72   b,    72   c  and  72   d.  Each of the concentric circles  72   a,    72   b,    72   c  and  72   d  is protruded to have a serration shape. While a central exit surface A is relatively flat, circumferential exit surfaces B, C, D, and E are inclined toward the central exit surface A. Inclination angles of the circumferential exit surfaces B, C, D and E get smaller towards the central exit surface A. The light entering the Fresnel lens  72  is emitted vertically to the Fresnel lens  72 , and thus the frontal brightness is increased.  
         [0054]     The uniformity of the light emitted from the screen  71  increases as it passes through the diffusion film  81 , and then enters the LCD panel  10 . A viewing angle is increased by the diffusion film  81 .  
         [0055]     According to the first exemplary embodiment, the polarization converting system  410  converting a polarization state of the incident light is used in place of a conventional reflecting polarization film. The screen  71 , increasing the frontal brightness of the incident light, is used in place of a conventional prism film. Also, the light tunnel  420 , increasing the uniformity of the incident light, is used in place of a conventional diffusion plate.  
         [0056]      FIGS. 6 and 7  illustrate LCDs according to a second and a third exemplary embodiment of the present invention, respectively.  
         [0057]     The LCD  1  according to a second exemplary embodiment has a lamp reflector  22  of a parabolic type. The light emitted from a light source unit  20  progresses in parallel.  
         [0058]     The light emitted from the light source unit  20  passes through a polarization converting system  410  and is converted into P-polarized light. The polarization converting system  410  is provided having a larger size as compared with the first exemplary embodiment because the light entering the polarization converting system  410  is not concentrated on a focal point. In this configuration, the incident angle of the light entering the polarization converting system  410  is decreased, and thus a polarization efficiency of the polarization converting system  410  is increased.  
         [0059]     The light from the polarization converting system  410  passes through a condenser lens  430  and is concentrated. Then, the concentrated light enters into the light tunnel  420  located at the focal point of the condenser lens  430 .  
         [0060]     An LCD  1  according to a third exemplary embodiment has a lamp reflector  22  of a parabolic type. The light emitted from a light source unit  20  progresses in parallel.  
         [0061]     The light emitted from the light source unit  20  enters an array of fly eye lenses  440   a  and  440   b.  The array of the fly eye lenses  440   a  and  440   b  is provided in a pair and faces each other. The light from the array of the fly eye lenses  440   a  and  440   b  has uniform distribution and enters a polarization converting system  410 . The incident angle of the light entering the polarization converting system  410  is decreased as in the second exemplary embodiment, and thus the polarization efficiency of the polarization converting system  410  is increased.  
         [0062]     The polarization converting system  410  comprises a sub polarization converting system  415 . Each sub polarization converting system  415  corresponds to each lens  441  of the array of the fly eye lens  440   b  from which the light exits.  
         [0063]     In the aforementioned exemplary embodiments, the light source unit  20  and the light converting unit  40  may provide light for the large-sized LCD panel  10  without an increase in size. Accordingly, if a large-sized LCD panel  10 , for example, an LCD panel of  40  inches or more is used, a backlight unit may be provided at low cost.  
         [0064]     It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.