Abstract:
A backlight assembly includes a first light guide having a first light incident face, a first light reflective face connected to the first light incident face and having a stepped portion, and a first light exiting face facing the first light reflective face. The backlight assembly further includes a second light guide having a second light incident face corresponding to the first light incident face, a second light reflective face connected to the second light incident face and facing the first light reflective face, and second light exiting face facing the second light reflective face. A light reflective plate is inserted into a gap between the first and second light guides. The first and second display panels, respectively, are installed on the first light guide and the second light guide. The generated light is used more efficiently and the overall thickness of an LCD device is decreased.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The disclosure relates to a backlight assembly and a liquid crystal display device using the same. More particularly, the disclosure relates to a backlight assembly and liquid crystal display device using the same in which light generated from a single light source is respectively supplied to two light guiding plates to display two different images, to minimize light loss and to decrease the thickness of elements of the backlight assembly while minimizing the light loss.  
           [0003]    2. Description of the Related Art  
           [0004]    Generally, liquid crystal is a material in an intermediate state between solid and liquid. As for its electrical property, liquid crystal may change its aligned angle according to an applied electric field. As for its optical property, liquid crystal may change transmissivity thereof according to its aligned angle. The liquid crystal display (LCD) device displays images using these properties of liquid crystal.  
           [0005]    A generalized liquid crystal display device has an LCD panel assembly for controlling the liquid crystal and a backlight assembly for supplying light to the LCD panel assembly.  
           [0006]    The LCD panel assembly includes an LCD panel and a driving module. The LCD panel precisely controls the aligned angle of the liquid crystal in an area ranging from a few μm 2  to a few hundred μm 2 , and the driving module generates driving signals for driving the LCD panel.  
           [0007]    The backlight assembly includes a light source, a light guiding plate, and optical sheets.  
           [0008]    As the light source, either cold cathode fluorescent lamp (CCFL) or light emitting diode (LED) is frequently used because of its long life span, easy manufacturability, and low heat generation. The CCFL is mainly used in large-screen LCD devices, whereas LED is mainly used in small-screen LCD devices.  
           [0009]    The light guiding plate changes the optical distribution of the light generated from the light source and supplies the redistributed light to the LCD panel. Specifically, the light guiding plate changes a line source of light or a point source of light into a surface source of light.  
           [0010]    The optical sheets are installed between the LCD panel assembly and the light guiding plate. The optical sheets make uniform the brightness of the light emitted from the light guiding plate and also control the viewing angle.  
           [0011]    In the conventional LCD device having the above construction, images are displayed while light passes through the light guiding plate, optical sheets and the LCD panel assembly sequentially. As a consequence, image can be displayed only in one direction.  
           [0012]    Recently, an improved LCD device called “dual liquid crystal display device” is disclosed, and the dual liquid crystal display device can overcome the one directional displaying limitation of the conventional LCD device and can display information in two different directions.  
           [0013]    In a conventional dual LCD device, two LCD panels, each performing image display independently, are arranged in an overlapping configuration to display images in two different directions. Specifically, the conventional dual LCD device includes a first LCD device and a second LCD device. The first LCD device includes a first LCD panel, a first light source, a first light guiding plate, first optical sheets, a first light reflective plate and a first receiving container. The second LCD device includes a second LCD panel, a second light source, a second light guiding plate, second optical sheets, a second light reflective plate and a second receiving container.  
           [0014]    The first LCD device displays images in a first direction, and the second LCD device display images in a second direction.  
           [0015]    The conventional dual LCD device enables displaying images in two different directions, but does so at the expense of other desirable qualities. For example, the extra parts necessary to achieve this dual-display quality increase volume and thickness of the LCD device, making the LCD device bulkier and less desirable.  
         SUMMARY OF THE INVENTION  
         [0016]    Accordingly, the present invention is provided to substantially obviate one or more problems due to limitations and disadvantages of the related art.  
           [0017]    It is a first feature of the present invention to provide a backlight assembly in which images are displayed in two different directions by using a single light source to decrease the number of elements, volume and weight of the backlight assembly.  
           [0018]    It is a second feature of the invention to provide an LCD device in which images are displayed in two different directions by using a single light source to decrease the number of elements, volume and weight of the LCD device.  
           [0019]    To accomplish the first feature of the invention, the present invention includes a backlight assembly.  
           [0020]    In one aspect of the present invention, the backlight assembly comprises: a first light guiding member including i) a first light incident face onto which a light is incident, ii) a first light exiting face connected to the first light incident face, iii) a first light reflective face portion connected to the first light incident face, a first portion between the first light exiting face and the first light reflective face portion having a first thickness and iv) a second light reflective face portion connected to the first light reflective face portion, a second portion between the first light exiting face and the second light reflective face portion having a second thickness thinner than the first thickness; a second light guiding member being overlapped with the first light guiding member and including i) a second light incident face corresponding to the first light incident face, and onto the second light incident face the light being incident, ii) a second light reflective face, a portion of the second light reflective face being closely in contact with the first light reflective face portion, and a remaining portion of the second light reflective face being spaced apart from the second light reflective face portion by a gap corresponding to a difference between the first thickness and the second thickness to face the second light reflective face portion, and iii) a second light exiting face connected to the second light incident face and facing the second light reflective face, and a third portion between the second light exiting face and the second light reflective face having a third thickness; a light reflective member interposed between the second light reflective face and the second light reflective face portion to cover the second light reflective face; and a light source for supplying the light to the first and second light incident faces. In another aspect of the present invention, the backlight assembly comprises: a first light guiding member comprising i) a first light incident face, ii) a first light exiting face, and iii) a first light reflective face including a first light reflective face portion and a second light reflective face portion connected to the first light reflective face portion, a first portion between the first light exiting face and the first light reflective face portion having a first thickness, and a second portion between the first light exiting face and the second light reflective face portion having a second thickness thinner than the first thickness; a second light guiding member overlapped with the first light guiding member and comprising i) a second light incident face, ii) a second light exiting face, and iii) a second light reflective face including a third light reflective face portion and a fourth light reflective face portion connected with the third light reflective face portion, a third portion between the second light exiting face and the third light reflective face portion having a third thickness, and a fourth portion between the second light exiting face and the fourth light reflective face portion having a fourth thickness thinner than the third thickness; a light reflective member having a first reflection face arranged at the second light reflective face portion and a second reflection face arranged at the fourth light reflective face portion; and a light source for supplying a light to the first and second light incident faces.  
           [0021]    To accomplish the second feature of the present invention, there is provided a liquid crystal display device comprising: a first light guiding member including i) a first light incident face onto which a light is supplied, ii) a first light exiting face connected to the first light incident face, iii) a first light reflective face portion connected to the first light incident face, a first portion between the first light exiting face and the first light reflective face portion having a first thickness and iv) a second light reflective face portion connected to the first light reflective face portion, a second portion between the first light exiting face and the second light reflective face portion having a second thickness thinner than the first thickness; a second light guiding member being overlapped with the first light guiding member and including i) a second light incident face corresponding to the first light incident face, and onto the second light incident face the light being supplied, ii) a second light reflective face, a portion of the second light reflective face being closely in contact with the first light reflective face portion, and a remaining portion of the second light reflective face being spaced apart from the second light reflective face portion by a gap corresponding to a difference between the first thickness and the second thickness, and iii) a second light exiting face connected to the second light incident face and facing the second light reflective face, and a third portion between the second light exiting face and the second light reflective face having a third thickness; a light reflective member interposed between the second light reflective face and the second light reflective face portion; a light source for supplying the light to the first and second light incident faces; a first display panel facing the first light exiting face; a second display panel facing the second light exiting face; and a receiving container for fixing the first display panel and the second display panel.  
           [0022]    According to the present invention, two different images can be displayed in two different directions by splitting a light generated from a single light source into two different directions using two light guiding plates. The different images may be displayed simultaneously.  
           [0023]    In addition, light loss due to the reflection plate arranged between two light guiding plates can be minimized to enhance light efficiency and perform a high quality display.  
           [0024]    In addition, the invention provides various effects such as decrease in an overall thickness of the two light guiding plates. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    The above features and other advantages of the present invention will become more apparent by describing in detail the preferred embodiments thereof with reference to the accompanying drawings, in which:  
         [0026]    [0026]FIG. 1 is a perspective view of a backlight assembly according to a first exemplary embodiment of the present invention;  
         [0027]    [0027]FIG. 2 is a sectional view taken along the line II-II of FIG. 1;  
         [0028]    [0028]FIG. 3 is a sectional view taken along the line III-III of FIG. 1;  
         [0029]    [0029]FIG. 4 is a sectional view showing a coupling structure of a first light guiding plate and a second light guiding plate according to a first exemplary embodiment of the present invention;  
         [0030]    [0030]FIG. 5 is a sectional view showing a first light guiding plate, a second light guiding plate and a light reflective plate according to a first exemplary embodiment of the present invention;  
         [0031]    [0031]FIG. 6 is an enlarged view of the portion “A” in FIG. 5 according to a first exemplary embodiment of the present invention;  
         [0032]    [0032]FIG. 7 is an enlarged view of the portion “A” in FIG. 5 and shows a modification in the attachment of the first light guiding plate and the second light guiding plate according to a first exemplary embodiment of the present invention;  
         [0033]    [0033]FIG. 8 is an enlarged view of the portion “A” in FIG. 5 and shows another modification in the attachment of the first light guiding plate and the second light guiding plate according to a first exemplary embodiment of the present invention;  
         [0034]    [0034]FIG. 9 is a sectional view showing yet another modification in the attachment of the first light guiding plate and the second light guiding plate according to a first exemplary embodiment of the present invention;  
         [0035]    [0035]FIG. 10 is a sectional view showing a backlight assembly according to a second exemplary embodiment of the present invention;  
         [0036]    [0036]FIG. 11 is an exploded perspective view of a liquid crystal display device according to an exemplary embodiment of the present invention; and  
         [0037]    [0037]FIG. 12 is a sectional view taken along the line B-B of FIG. 11 after the liquid crystal display device is assembled.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    Hereinafter, reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0039]    Embodiment 1  
         [0040]    [0040]FIG. 1 is a perspective view of a backlight assembly according to a first exemplary embodiment of the present invention.  
         [0041]    Referring to FIG. 1, a backlight assembly  100  includes a light source  110 , a first light guiding plate  120 , a second light guiding plate  130  and a light reflective plate  140 .  
         [0042]    Alternatively, the backlight assembly  100  can further include a receiving container  150  in which the first light guiding plate  120 , the second light guiding plate  130 , the light reflective plate  140  and the light source are received.  
         [0043]    The light source  110  generates a first light radially. In FIG. 1, the light source  110  may be a point light source such as a light emitting diode. Alternatively, the light source  110  may be a line light source such as a cold cathode fluorescent lamp (CCFL).  
         [0044]    [0044]FIG. 2 is a sectional view taken along the line II-II of FIG. 1.  
         [0045]    Referring to FIG. 2, the first light guiding plate  120  has a three-dimensional shape such as a rectangular parallelepiped plate. Specifically, the first light guiding plate  120  has at least three side faces, a top face and a bottom face, wherein the top and the bottom faces are connected with the side faces. For example, the first light guiding plate  120  has four side faces.  
         [0046]    Here, the light source  110  supplies a first light  160  into at least one of the four side faces. Hereinafter, the side face onto which the first light  160  from the light source  110  is supplied is referred to as a first light incident face  121 .  
         [0047]    The first light  160  generated from the light source  110  is refracted to change the advancing direction thereof while the first light  160  passes through the first light incident face  121 . This is because the first light guiding plate  120  has a different refractive index than air. Hereinafter, the light that has passed through the first light incident face  121  is referred to as a second light  162 .  
         [0048]    A first light reflective face  123  reflects the second light  162  toward a first light exiting face to be described later.  
         [0049]    The first light reflective face  123  is comprised of a first light reflective face portion  123   a  and a second light reflective face portion  123   b . The first light reflective face  123  has a first width (W1) and a first length (L1).  
         [0050]    The first light reflective face portion  123   a  has the first width (W1) and a second length (L2) that is less than the first length (L1) when measured from the first light incident face  121  toward an opposite direction of the first light incident face  121 .  
         [0051]    The second light reflective face portion  123   b  is connected with the first light reflective face portion  123   a , and has a third length (L3) that is somewhat shorter than a length remaining after the second length (L2) is subtracted from the first length (L1). The second light reflective face portion  123   b  lies in a plane that is different from and substantially parallel to the plane of the first light reflective face portion  123   a.    
         [0052]    The first light reflective face portion  123   a  is connected with the second light reflective face portion  123   b  by an inclined face  123   c . The inclined face  123   c , i.e., the connecting portion (or stepped portion) has a length that corresponds to a value remaining after the second length (L2) and the third length (L3) are subtracted from the first length (L1).  
         [0053]    The portion of the inclined face  123   c  that meets the first light reflective face portion  123   a  and the portion of the inclined face  123   c  that meets the second light reflective face portion  123   b  may have smooth curve shapes. This is because the inclined face  123   c  causes occurrence of discontinuous bright line in the first light guiding plate  120 .  
         [0054]    The first light exiting face  125  allows the second light  162  reflected by the first light reflective face portion  123   a  and the second light reflective face portion  123   b  of the first light reflective face  123  to be output therethrough. The light output from the first light exiting face  125  proceeds with a different angle from the proceeding direction of the second light  162 , and accordingly it is referred to as a third light  164 .  
         [0055]    The first light exiting face  125  is in parallel with the first light reflective face portion  123   a  and the second light reflective face portion  123   b . The portion between the first light exiting face  125  and the first light reflective face portion  123   a  has a first thickness (T1), and the portion between the first light exiting face  125  and the second light reflective face portion  123   b  has a second thickness (T2) that is thinner than the first thickness (T1).  
         [0056]    [0056]FIG. 3 is a sectional view taken along the line III-III of FIG. 1.  
         [0057]    Referring to FIG. 3 and FIG. 1, the second light guiding plate  130  overlies the first light guiding plate  120 . The second light guiding plate  130  is similar in shape to the first light guiding plate  120 , and has a second width (W2) and a fourth length (L4). The second width (W2) is wider than the first width (W1), and the fourth length (L4) is longer than the first length (L1).  
         [0058]    The second light guiding plate  130  is comprised of a second light incident face  131 , a second light reflective face  135  and a second light exiting face  133 .  
         [0059]    The second light incident face  131  is arranged such that it does not disaccord with the first light incident face  121  of the first light guiding plate  120 . In other words, the second light incident face  131  is aligned with the first light incident face  121  of the first light guiding plate  120  to receive the first light  160 . The first light  160  generated from the light source  110  is partially incident onto the second light incident face  131 . Hereinafter, the first light  160  that is incident onto the second light incident face  131  is referred to as a fourth light  166 .  
         [0060]    The second light reflective face  135  connected to the second light incident face  131  faces the first light reflective face portion  123   a  and the second light reflective face portion  123   b  of the first light guiding plate  120 . The second light reflective face  135  reflects the fourth light  166  to direct the reflected fourth light  166  toward the second light exiting face  133 .  
         [0061]    [0061]FIG. 4 is a sectional view showing a coupling structure of a first light guiding plate and a second light guiding plate according to a first exemplary embodiment of the present invention.  
         [0062]    Referring to FIG. 4, the second light reflective face  135  is directly in contact with the first light reflective face portion  123   a . Between the second light reflective face  135  and the second light reflective face portion  123   b , there is a gap (G). In other words, a part of the second light reflective face  135  is spaced apart from the second light reflective face portion  123   b  by the gap (G).  
         [0063]    Referring again to FIG. 3, the fourth light  166  reflected by the second light reflective face  135  is directed toward the second light exiting face  133 . Hereinafter, the light output from the second light exiting face  133  is referred to as a fifth light  168 . The second light exiting face  133  faces the second light reflective face  135 . The second light exiting face  133  and the second light reflective face  135  have a uniform third thickness of T3 throughout an entire area of the second light guiding plate  130 . The third thickness (T3) of the second light guiding plate  130  is thinner than the first thickness (T1) of the first light guiding plate  120 .  
         [0064]    [0064]FIG. 5 is a sectional view showing a first light guiding plate, a second light guiding plate and a light reflective plate according to a first exemplary embodiment of the present invention.  
         [0065]    Referring to FIG. 1 and FIG. 5, the light reflective plate  140  is interposed between the first light guiding plate  120  and the second light guiding plate  130 . The light reflective plate  140  has a thickness that is equal to the gap between the second light reflective face portion  123   b  and the second light reflective face  135 .  
         [0066]    Also, among the edges of the light reflective plate  140 , the edge facing the inclined face  123   c  of the first light guiding plate  120  has an inclined face  141  that is designed to fit with the inclined face  123   c  so as to be closely in contact with the inclined face  123   c.    
         [0067]    The first light guiding plate  120  and the second light guiding plate  130  are attached to each other by means of an attaching member, which is to prevent the first light guiding plate  120  from getting displaced with respect to the second light guiding plate  130 .  
         [0068]    [0068]FIG. 6 is an enlarged view of the portion “A” in FIG. 5 according to a first exemplary embodiment of the present invention.  
         [0069]    Referring to FIG. 6, a double-layered adhesive tape  160  is interposed between the first light reflective face portion  123   a  of the first light guiding plate  120  and the second light reflective face  135  of the second light guiding plate  130  facing the first light reflective face portion  123   a . The double-layered adhesive tape  160  includes a transparent base film  161 , and adhesive layers  162  and  163  coated on both surfaces of the base film  161 .  
         [0070]    [0070]FIG. 7 is an enlarged view of the portion “A” in FIG. 5 and shows a modification in the attachment of the first light guiding plate and the second light guiding plate according to a first exemplary embodiment of the present invention.  
         [0071]    Referring to FIG. 7, a thin adhesive layer  170  is interposed between the first light reflective face portion  123   a  of the first light guiding plate  120  and the second light reflective face  135  of the second light guiding plate  130  facing the first light reflective face portion  123   a . The thin adhesive layer  170  allows the first light guiding plate  120  and the second light guiding plate  130  to adhere to each other.  
         [0072]    [0072]FIG. 8 is an enlarged view of the portion “A” in FIG. 5 and shows another modification in the attachment of the first light guiding plate and the second light guiding plate according to a first exemplary embodiment of the present invention.  
         [0073]    Referring to FIG. 8, at least one adhering protrusion  135   a  is formed on the second light reflective face portion  135  of the second light guiding plate  120 . In a state that the first light reflective face portion  123   a  of the first light guiding plate  120  is in contact with the adhering protrusion  135   a  formed on the second light reflective face  135  of the second light guiding plate  130 , ultrasonic waves or heat is applied to the adhering protrusion  135   a . As a result, the adhering protrusion  135   a  is melted and the melted adhering protrusion  135   a  allows the first light reflective face portion  123   a  and the second light reflective face portion  135  to adhere to each other. The adhering protrusion  135   a  is preferably processed to form a minimum gap between the first light reflective face portion  123   a  and the second light reflective face  135 .  
         [0074]    [0074]FIG. 9 is a sectional view showing yet another modification in the attachment of the first light guiding plate and the second light guiding plate according to a first exemplary embodiment of the present invention.  
         [0075]    Referring to FIG. 9, in a state that the first light guiding plate  120  and the second light guiding plate  130  overlap with each other, some portions of the first light guiding plate  120  may be fixed to the second light guiding plate  130  by means of a transparent clip  180  or the like. Specifically, a portion of the clip  180  presses the first light exiting face  125  of the first light guiding plate  120  against the second light guiding plate  130  and the remainder of the clip  180  presses the second light exiting face  133  of the second light guiding plate  130  against the first light guiding plate  120 .  
         [0076]    The first light guiding plate  120 , the light reflective plate  140 , the second light guiding plate  130  and the light source  110  having the aforementioned coupling structure are received in the receiving container  150  shown in FIG. 1 during the assemblage of the backlight assembly  100 .  
         [0077]    The receiving container  150  encloses the sidewalls of the first light guiding plate  120  and the sidewalls of the second light guiding plate  130 , and has an opening or an opened bottom face such that the first light exiting face  125  of the first light guiding plate  120  and the second light exiting face  133  of the second light guiding plate  130  are exposed.  
         [0078]    Also, the light source  110  is installed within the receiving container  150  such that the light source  110  faces the first light incident face  121  and the second light incident face  131 .  
         [0079]    Embodiment 2  
         [0080]    [0080]FIG. 10 is a sectional view showing a backlight assembly according to a second exemplary embodiment of the present invention.  
         [0081]    Referring to FIG. 10, a backlight assembly  100  includes a light reflective plate  140 , a first light guiding plate  120 , a second light guiding plate  130 , a light source  110  and a receiving container  150 .  
         [0082]    The light reflective plate  140  may be a plate having a predetermined thickness. Also, the light reflective plate  140  is manufactured by coating a material having a high reflectivity on both surfaces of the light reflective plate  140 .  
         [0083]    The light reflective plate  140  has two light reflective faces  143  and  144 . One of the two light reflective faces is the first light reflective face  143  and the other is the second light reflective face  144 .  
         [0084]    The first light guiding plate  120  is arranged to face the first light reflective face  143 , and the second light guiding plate  130  is arranged to face the second light reflective face  144 .  
         [0085]    The first light guiding plate  120  is comprised of a first light incident face  121 , a first light reflective face  123  having a first light reflective face portion  123   a  and a second light reflective face portion  123   b , and a first light exiting face  125  facing the first light reflective face  123 . Reference numeral  123   c  represents a transitional region between the first light reflective face portion  123   a  and the second light reflective face portion  123   b . The transitional region  123   c  may have a smooth curve structure or an inclined surface structure.  
         [0086]    A first thickness of T1 between the first light reflective face portion  123   a  and the first light exiting face  125  is different from a second thickness of T2 between the second light reflective face portion  123   b  and the first light exiting face  125 . Preferably, the first thickness of T1 is greater than the second thickness of T2.  
         [0087]    The first light reflective face  143  of the light reflective plate  140  is laid over the first light guiding plate  120  and aligned with the second light reflective face portion  123   b  of the first light guiding plate  120 , so that the overall thickness of the backlight assembly can be decreased.  
         [0088]    The second light guiding plate  130  is comprised of a second light incident face  131 , a second light reflective face  135  having a third light reflective face portion  135   a  and a fourth light reflective face portion  135   b , and a second light exiting face  133  facing the second light reflective face  135 . Reference numeral  135   c  represents a transitional region between the third light reflective face portion  135   a  and the fourth light reflective face portion  135   b . The transitional region boundary  135   c  may have a smooth curve structure or an inclined surface structure.  
         [0089]    A third thickness of T3 between the third light reflective face portion  135   a  and the second light exiting face  133  is different from a fourth thickness of T4 between the fourth light reflective face portion  135   b  and the second light exiting face  133 . Preferably, the third thickness of T3 is thicker than the fourth thickness of T4.  
         [0090]    The second light reflective face  144  of the light reflective plate  140  is positioned to lie over the second light guiding plate  130  and align with the fourth light reflective face portion  135   b , so that an overall thickness of the backlight assembly can be decreased.  
         [0091]    By the above arrangement, the light reflective plate  130  is interposed between the first light guiding plate  120  and the second light guiding plate  130 .  
         [0092]    The first light guiding plate  120 , the light reflective plate  140 , the second light guiding plate  130  and the light source  110  having the aforementioned coupling structure are installed in the receiving container  150  shown in FIG. 10 during the assemblage of the backlight assembly  100 .  
         [0093]    The receiving container  150  encloses the sidewalls of the first light guiding plate  120  and the sidewalls of the second light guiding plate  130 , and has an opening or an opened bottom face such that the first light exiting face  125  of the first light guiding plate  120  and the second light exiting face  133  of the second light guiding plate  130  are exposed.  
         [0094]    Also, the light source  110  is installed within the receiving container  150  such that the light source  110  faces the first light incident face  121  and the second light incident face  131 .  
         [0095]    Embodiment 3  
         [0096]    [0096]FIG. 11 is an exploded perspective view of a liquid crystal display device according to an exemplary embodiment of the present invention; and FIG. 12 is a sectional view taken along the line B-B of FIG. 11 after the liquid crystal display device is assembled.  
         [0097]    Referring to FIG. 11 or FIG. 12, a liquid crystal display device  900  includes a light source  800 , a backlight assembly  100 , optical sheets ( 200 ,  300 ), a first display panel  400 , a second display panel  500  and receiving containers ( 600 ,  700 ).  
         [0098]    The light source  800  generates light radially. The light source  800  may be a line light source such as a cold cathode fluorescent lamp (CCFL) or a point light source such as a light emitting diode.  
         [0099]    The backlight assembly  100  includes a first light guiding plate  120 , a second light guiding plate  130 , and a light reflective plate  140 .  
         [0100]    Since the backlight assembly  100  has the same construction as those of the first and second exemplary embodiment, repeated description thereof will be omitted. Hereinafter, like reference numerals identify identical elements of the backlight assembly  100  throughout the drawings.  
         [0101]    The first display module  400  is installed to face a first light exiting face  125  of the first light guiding plate  120 . The first display module  400  has a plain surface area that is substantially equal to the surface area of the first light exiting face  125 .  
         [0102]    Any construction for the first display module  400  may be allowed as long as the first display module  400  can display images by using the liquid crystal and the light passing through liquid crystal molecules.  
         [0103]    Preferably, the first display module  400  includes a first color filter substrate  410 , a first TFT substrate  430 , and a first liquid crystal  420  interposed between the first color filter substrate  410  and the first TFT substrate  430 .  
         [0104]    The second display module  500  includes a second color filter substrate  520 , a second TFT substrate  510 , and a second liquid crystal  530  interposed between the second color filter substrate  520  and the second TFT substrate  510 . The second display module  500  is installed to face a second light exiting face  133  of the second light guiding plate  130 . The second display module  500  has a surface area that is substantially equal to the area of the second light exiting face  133 . Since the area of the second light exiting face  133  is larger than that of the first light exiting face  125 , the area of the second display module  500  is larger than that of the first display module  400 .  
         [0105]    The optical sheets are comprised of the first optical sheets  200  and the second optical sheets  300 .  
         [0106]    The first optical sheets  200  are installed between the first display module  400  and the first light guiding plate  120 , and the second optical sheets  300  are installed between the second display module  500  and the second light guiding plate  130 .  
         [0107]    In order to enhance light efficiency in the LCD device, each of the first and second optical sheets ( 200 ,  300 ) includes at least one sheet. Preferably, each of the first and second optical sheets ( 200 ,  300 ) includes a diffusion sheet and a prism sheet. A brightness enhanced film may be further added to the diffusion sheet and the prism sheet.  
         [0108]    The first display module  400 , the optical sheets ( 200 ,  300 ), the backlight assembly  100 , and the second display module  500  are received in the receiving containers ( 600 ,  700 ).  
         [0109]    The receiving containers ( 600 ,  700 ) are comprised of a top chassis  600  and a bottom mold frame  700 . “Top” and “bottom,” as used herein, refers to the top and the bottom in reference to the orientation of the figure in FIG. 11.  
         [0110]    The bottom mold frame  700  has a square frame structure that is sized to receive four sidewalls of the second light guiding plate  130 .  
         [0111]    The bottom mold frame  700  is comprised of sidewalls only, and allows the second display module  500 , the optical sheets ( 200 ,  300 ), the backlight assembly  100  and the first display module  400  to be received therein. The bottom mold frame  700  has a fixing rib  710  which the second display module  500  is hung on and fixed to. Also, in the bottom mold frame  700 , the sidewall adjacent to the first light incident face  121  of the first light guiding plate  120  and the second light incident face  131  of the second light guiding plate  130  has a light source receiving groove  720  into which the light source  800  is placed.  
         [0112]    The top chassis  600  is coupled with the bottom mold frame  700  to keep the first display module  400  inside the bottom mold frame  700 .  
         [0113]    The top chassis  600  has an opening  610  such that users can view images displayed through the first display module  400 .  
         [0114]    Hereinafter, an assembling method of the LCD device is described.  
         [0115]    First, the first display module  500  for displaying images is placed in the bottom mold frame  700  such that a first face of the first display module  500  faces the inner bottom face of the bottom mold frame  700 , and the first face of the first display module  500  is fixed to the bottom mold frame  700  by using the fixing rib  710 . Then, the second optical sheets  300  are mounted on a second face of the first display module which is the face opposite the first face.  
         [0116]    After the second optical sheets  300  are placed in the bottom mold frame  700 , an assembly including the first light guiding plate  120 , the light reflective plate  140  and the second light guiding plate  130  coupled with each other is mounted on the upper face of the second optical sheets  300 . The second light exiting face  133  of the second light guiding plate  130  is coupled to the bottom mold frame  700  such that the second light exiting face  133  faces the second optical sheets  300 .  
         [0117]    The first optical sheets  200  are closely mounted on the first light guiding plate  120 , and then the first display module  400  is mounted on the first optical sheets  200 .  
         [0118]    After the second display module  500  and the first display module  400  are sequentially placed in the bottom mold frame  700 , the top chassis  600  is coupled with the first display module  400 . The top chassis  600  is coupled with the bottom mold frame  700  while the top chassis  600  presses edges of the first display module  400 .  
         [0119]    While the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by appended claims.