Abstract:
Disclosed are a backlight unit capable of guiding light generated by LEDs to a light guide panel in order to eliminate brightness fault, as well as a light crystal display including the same. The backlight unit includes a light guide panel, an LED arranged at a lateral side of the light guide panel, and a light guide bar with at least one light diffusion pattern to scatter light generated by the LED and admit the scattered light into the light guide panel, thereby uniformly guiding the light generated by the LED to the light guide panel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority benefit of Korean Patent Application No. 2009-14815, filed on Feb. 23, 2009 with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Embodiments relate to a back light unit capable of uniformly guiding light generated by an LED to a light guide panel region in order to eliminate brightness fault and a liquid crystal display including the same. 
     2. Description of the Related Art 
     A liquid crystal display (LCD) displays an image by electrical or optical properties of liquid crystals. As compared to other display devices, an LCD has reduced thickness and light weight and may be operated at a low operating voltage with reduced power consumption. Therefore, LCDs are widely used for various purposes in industrial applications. 
     An LCD may have a liquid crystal display panel fabricated by sealing liquid crystal between two transparent sheets and applying a desired voltage thereto in order to alter directions of liquid crystal molecules which in turn varies light transmission efficiency so as to optically display an image, as well as a backlight assembly to provide light to the liquid crystal display panel. 
     The backlight assembly may have a light source such as a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), a flat fluorescent lamp (FFL), and the like. Since such CCFLs have limitations in terms of film thickness reduction and simplification of an apparatus, improved quality of the apparatus, etc., there is a trend towards use of a light emitting diode (LED) with improved performance such as high brightness, extended lifespan and/or high color purity, as a light source. Moreover, since environmentally harmful substances such as mercury are subject to increasingly stringent regulations, use of CCFLs tends to decrease and CCFLs are gradually being replaced by LEDs, which are more environmentally friendly. 
     A backlight assembly using such LEDs as a light source may be classified into a direct type and a side-emitting type assembly in view of constructional features such as arrangement of the LED and shape of a light guide panel. Such direct type backlight assembly has a construction of LEDs aligned at a front side of the assembly, which makes a slim structure difficult to achieve and requires too many LEDs, causing increased production costs. 
     On the other hand, a side-emitting type LED backlight assembly has LEDs at both sides and leads light to a front side of the assembly via a light guide panel, so that an entire thickness of the backlight assembly is relatively decreased to attain a slim structure, as compared to the direct type assembly. 
     Since the side-emitting LED backlight assembly includes an LED which is a point light source to emit light at a certain radiation angle, if plural LEDs are aligned in a row, a dark spot at which emission of light is faint may exist between LEDs. 
     Briefly, the side-emitting type LED backlight assembly having LEDs directly aligned at lateral sides of a light guide panel as the point light source entails a hot spot problem in that light radiation angle regions and dark spot regions are repeated, causing non-uniform brightness. 
     SUMMARY 
     Therefore, it is an aspect of exemplary embodiments to provide a backlight unit capable of uniformly guiding light generated by an LED to a light guide panel in order to reduce non uniformity of brightness and to enhance light efficiency, as well as a liquid crystal display (LCD) including the backlight unit described above. 
     According to an exemplary embodiment, there is provided a backlight unit including: a light guide panel; at least one LED arranged at a lateral side of the light guide panel; and a light guide bar with a desired light diffusion pattern to scatter the light generated by the LED and admit the scattered light into the light guide panel. 
     The LED may be aligned to emit light in a direction far away from the light guide panel. 
     The light diffusion pattern may have a protrusion part extending in a length direction of the light guide bar. 
     The light diffusion pattern may include a first diffusion pattern positioned opposite the light guide panel. 
     The light diffusion pattern may include a second diffusion pattern positioned opposite the light guide panel, in order to scatter light admitted into the light guide panel. 
     The light guide bar may include: a light incident part having the first diffusion pattern to scatter light generated by the LED; a light exit part having the second diffusion pattern to scatter light admitted into the light guide panel; a light reflection part arranged between the light incident part and the light exit part, wherein the light incident part and the light exit part are positioned stepwise to each other. 
     The light reflection part may include a first reflecting part for total reflection of the light scattered by the first diffusion pattern, and a second reflecting part for total reflection of the light reflected by the first reflecting part toward the second diffusion pattern. 
     The LED emits light in a thickness direction of the light guide bar and the emitted light may be admitted into the light guide panel after being scattered by the light guide bar. 
     The light guide bar may include a base part in a plate form and a threshold part formed in a stepwise position at one end of the base part. The light incident part may be formed on a front side of the threshold part opposite to the LED and the light exit part may be formed on a front side of the base part opposite to the light guide panel. 
     Alternatively, the light guide bar may include a base part in a plate form and a depression part formed in a portion of the base part. The light incident part may be formed on a top side of the depression part opposite to the LED and the light exit part may be formed on a front side of the base part opposite to the light guide panel. 
     In another aspect of exemplary embodiments, a backlight unit according to an exemplary embodiment may include: a plurality of LEDs spaced at a certain interval; a light guide bar with a light diffusion pattern to convert light generated by the LEDs into a linear light source; and a light guide panel to receive the converted light from one side of the light guide bar. 
     The light guide bar may have a light incident part and a light exit part positioned opposite the light guide panel, wherein the light incident part and the light exit part are positioned stepwise to each other. 
     Alternatively, the light guide bar may be arranged to scatter light emitted from the LEDs in a thickness direction, followed by admitting the scattered light into the light guide panel. 
     The light diffusion pattern described above may include a first diffusion pattern positioned opposite the LEDs and a second diffusion pattern positioned opposite the light guide panel in order to scatter light admitted into the light guide panel. 
     The liquid crystal display according to an exemplary embodiment may include a liquid crystal panel to display an image and a backlight unit to provide light to the liquid crystal panel, wherein the backlight unit includes: a light guide panel; a plurality of point light sources arranged at a lateral side of the light guide panel; a light guide bar having at least one light diffusion pattern to scatter light generated by the point light sources so as to uniformly admit the light into the light guide panel. 
     The point light source generates light in an opposite direction or a thickness direction of the light guide panel, in order to extend a path of the light. 
     The light guide bar having the light diffusion pattern may include: a light incident part with a first diffusion pattern to scatter light generated by the point light sources; a light exit part with a second diffusion pattern to scatter the light admitted into the light guide panel; and a light reflection part arranged between the light incident part and the light exit part. 
     The point light source may include an LED. 
     Accordingly, the backlight unit and the liquid crystal display including the same according to an exemplary embodiment adopt a light guide bar to uniformly provide light generated by an LED to a light guide panel, thereby reducing non-uniformity of brightness and enhancing light efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of exemplary embodiments will become apparent and more readily appreciated from the following detailed description, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a perspective view illustrating a liquid crystal display according to an exemplary embodiment; 
         FIG. 2  is a perspective view illustrating a part of the liquid crystal display shown in  FIG. 1  according to an exemplary embodiment, as observed from its bottom side; 
         FIG. 3  is a perspective view illustrating a light guide bar shown in  FIG. 2 ; 
         FIG. 4  is a schematic cross-sectional view illustrating a path of the light passing through the light guide bar shown in  FIG. 3 ; 
         FIGS. 5A and 5B  are enlarged views illustrating a part shown in  FIG. 3 , respectively; 
         FIG. 6  is a perspective view illustrating a light guide bar according to another exemplary embodiment; and 
         FIG. 7  is a schematic plan view illustrating a path of the light passing through the light guide bar shown in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
       FIG. 1  is a perspective view illustrating a liquid crystal display according to an exemplary embodiment and  FIG. 2  is a perspective view illustrating a part of the liquid crystal display shown in  FIG. 1  according to an exemplary embodiment, as observed from the bottom side. 
     As shown in  FIGS. 1 and 2 , the liquid crystal display  10  includes a liquid crystal panel  100 , a driving element  200  connected at one side of the liquid crystal panel  100  to drive the liquid crystal panel  100 , and a backlight unit  300  placed at a rear side of the liquid crystal panel  100  to provide light to the liquid crystal panel  100 . 
     A periphery of the liquid crystal panel  100  is supported by a mold frame  140 . The mold frame  140  and the backlight unit  300  are combined with a top cover  150  and a bottom cover  160 , which enclose a front side and a rear side of the liquid crystal panel  100 , respectively. 
     The liquid crystal panel  100  includes a thin film transistor substrate  110 , a color filter substrate  120  attached opposite the thin film transistor substrate  110 , and liquid crystal (not shown) introduced between the thin film transistor substrate  110  and the color filter substrate  120 . Such liquid crystal panel  100  controls light transmittance of liquid crystal cells depending on image signal information received from the driving element  200 , thus forming an image. 
     The driving element  200  is located at one side of the thin film transistor substrate  110  in order to apply driving signals to the liquid crystal panel  100 . The driving element  200  may include a flexible printed circuit board  210 , a driving chip  220  fixed to the flexible printed circuit board  210 , and a circuit board  230  connected at the other side of the flexible printed circuit board  210 . 
     The backlight unit  300  is positioned at a rear side of the liquid crystal panel  100 . The backlight unit  300  includes an optical sheet  310  laminated on the rear side of the liquid crystal panel  100  to diffuse and collect light; a light guide panel  400  positioned at a rear side of the optical sheet  310 ; a light source  500  placed on at least one side of the light guide panel  400  to provide light to the liquid crystal panel  100 ; and a light reflection sheet  320  placed on a rear side of the light guide panel  400 . 
     The optical sheet  310  formed in parallel to the rear side of the liquid crystal panel  100  may be fabricated by laminating a diffusion sheet  311 , a prism sheet  312  and a protective sheet  313  in ascending order. The diffusion sheet  311  includes a base film (not shown) and a diffusion coating layer (not shown) formed on a front side of the base film, which serves to diffuse the light generated by the light source  500  and provide the diffused light to the liquid crystal panel  100 . 
     The prism sheet  312  and the protective sheet  313  are placed on a top of the diffusion sheet  311 . The prism sheet  312  has triangular prisms formed in a certain arrangement on a top thereof and vertically orients light passing through the diffusion sheet  311 , thus improving brightness. The protective sheet  313  is formed on the prism sheet  312  in order to protect the diffusion sheet  311  and the prism sheet  312  which are susceptible to dust and/or scratches. 
     The light guide panel  400  may have a rectangular shape with a desired thickness. The light guide panel  400  is positioned opposite the light source  500  and includes a light incident side  400   a  to receive light emitted from the light source  500  and a light exit side  400   b  through which the light admitted through the light incident side  400   a  exits. The light guide panel  400  may be fabricated using polymethylmethacrylate (PMMA) which has high strength sufficient to prevent deformation or breakage thereof and excellent light transmission. 
     The light source  500  is placed along the light incident side  400   a  at one side of the light guide panel  400 . The light source  500  may be arranged to face at least one side of the light guide panel  400 . 
     The light source  500  may include an LED  510 , a circuit board  520  to apply electric signals to the LED  510 , and a light guide bar  600  to broaden a radiation angle of the light generated by the LED  510  which in turn uniformly guides the light to the light guide panel  400 . 
     The LED  510  may have a rectangular shape. Since the LED  510  generates a large amount of heat, the circuit board  520  may be fabricated using aluminum with excellent heat transfer properties as a main material. A plurality of LEDs  510  is used and aligned on the circuit board  520  at equal intervals. Each of the LEDs  510  may include a white light emitting unit including blue, red and green LEDs  510 . 
     The light guide bar  600  includes a first diffusion pattern  611  and a second diffusion pattern  631  in order to scatter light generated by the LED  510  and to guide the scattered light to a certain region. The light guide bar  600  may be fabricated using a material with excellent light reflection properties, which functions to convert LEDs  510  aligned in a row as a point light source into a linear light source form. 
     The light reflection sheet  320  reflects light leaked in an opposite direction of the liquid crystal panel  100 , among the light emitted from the light source  500 , to the light guide panel  400  so as to reduce loss of the light. The light reflection sheet  320  may be fabricated using polyethylene terephthalate (PET), polycarbonate (PC), etc. 
     The above described light guide panel  400 , the light source  500  and the light reflection sheet  320  are enclosed in the bottom cover  160 . As described above, the bottom cover  160  is combined with the mold frame  140  made of insulative synthetic resin. 
       FIG. 3  is a perspective view illustrating a light guide bar shown in  FIG. 2 ,  FIG. 4  is a schematic cross-sectional view illustrating a path of the light passing through the light guide bar shown in  FIG. 3 , and  FIGS. 5A and 5B  are enlarged views illustrating a part shown in  FIG. 3 , respectively. 
     As shown in  FIGS. 2 ,  3 ,  4 ,  5 A and  5 B, the backlight unit  300  includes a light guide bar  600  to uniformly guide light generated by an LED  510  to the light guide panel  400 . 
     The light guide bar  600  includes the light incident part  610  with the first diffusion pattern  611  to receive light generated by the LED  510 , a light reflection part  620  to reflect the light admitted through the light incident part  610 , and the light exit part  630  with the second diffusion pattern  631  through which the light reflected through the light reflection part  620  to the light guide panel  400  exits. 
     The light guide bar  600  may include a base part  600   a  in a plate form and a threshold part  600   b  formed stepwise with a certain thickness at one end of the base part  600   a . The light incident part  610  may be formed at a front side of the threshold part  600   b  opposite to the LED  510  while the light exit part  630  is formed at a front side of the base part  600   a  opposite to the light guide panel  400 . 
     The light incident part  610  of the light guide bar  600  is placed facing the light guide panel  400  in order to extend a light path of the LED  510  and cause the light to overlap in a wide area between LEDs  510 . That is, the plural LEDs  510  are aligned to generate light in a direction distant from the light guide panel  400 . The light guide bar  600  uniformly admits the light into the light guide panel  400  by scattering and reflection. 
     The first diffusion pattern  611  extends in a length direction of the light guide bar  600 . The first diffusion pattern  611  includes a plurality of first protrusions  611   a  and first depressions  611   b  repeatedly arranged at desired intervals in the length direction of the light guide bar  600 . Each of the first protrusions  611   a  may have a triangular shape. However, a cross-sectional shape of the first protrusion  611   a  is not particularly restricted and may include an arc shape. 
     The light incident part  610  with the first diffusion pattern  611  may be formed with a certain height difference relative to the light exit part  630  with the second diffusion pattern  631 . That is, the LED  510  is arranged between the base part  600   a  and the threshold part  600   b , which are positioned stepwise to each other with a certain height difference. The LED  510  emits light in a direction distant from the light guide panel  400 , and the light passes through the light incident part  610 , the light reflection part  620  and the light exit part  630  of the light guide bar  600  in sequential order and is admitted into the light guide panel  400  so as to extend a path of the light, thus uniformly mixing light generated by the LED  510 . 
     The first diffusion pattern  611  enlarges a radiation angle θ 2  of the light passing through the first protrusion  611   a , as compared to a radiation angle θ 1  of the light admitted into the light guide bar  600  without the first protrusion  611   a , thus distributing the light over a wider area. Therefore, the light generated by the LED  510  is first scattered in the first diffusion pattern  611  to provide uniform light power over the entire region of the light guide bar  600 . 
     The light reflection part  620  includes a first reflecting part  621  for total reflection of the light with a wider radiation angle θ 2  scattered by the first diffusion pattern  611  and a second reflecting part  622  for total reflection of the light reflected by the first reflecting part  621  to the second diffusion pattern side  631 . The first reflecting part  621  performs total reflection of the light to the second reflecting part  622  and the second reflecting part  622  performs total reflection of the light to admit the light into the light guide panel  400 . Here, the first reflecting part  621  may be placed at an edge of the threshold part  600   b , while the second reflecting part  622  may be placed at an edge of the base part  600   a.    
     Like the first diffusion pattern  611 , the second diffusion pattern  631  extends in a length direction of the light guide bar  600 . The second diffusion pattern  631  includes a plurality of second protrusions  631   a  and second depressions  631   b  repeatedly arranged at desired intervals. Each of the first protrusions  631   a  may also have a triangular or an arc shape. 
     The second diffusion pattern  631  enlarges a radiation angle θ 2  of the light passing through the second protrusion  631   a , as compared to a radiation angle θ 1  of the light admitted into the light guide bar  600  without the second protrusion  631   a , thus distributing the light over a wider area. Therefore, the light reflected from the second reflecting part  622  is finally scattered in the second diffusion pattern  631  to emit the light with uniform light power which in turn admits the light into the light guide panel  400 . 
     Accordingly, light emitted from the LED  510  in an opposite direction of the light guide panel  400  follows a wider light path, thus being uniformly mixed. Moreover, scattering and reflection of the light in the light guide bar  600  may emit light with uniform light power and admit the light into the light guide panel  400 , thereby solving a non-uniform brightness problem caused using the LED  510 . 
     Another exemplary embodiment will be described in greater detail with reference to  FIGS. 6 and 7 . In these drawings, like reference numerals refer to like elements according to the previous exemplary embodiment and further detailed description of these elements will be omitted.  FIG. 6  is a perspective view illustrating a light guide bar according to another exemplary embodiment, and  FIG. 7  is a schematic plan view illustrating a path of the light passing through the light guide bar shown in  FIG. 6 . 
     As shown in  FIGS. 6 and 7 , a light guide bar  600 ′ includes a light incident part  610 ′ with a first diffusion pattern  611 ′ to receive light generated by an LED  510 ′; a light reflection part  620 ′ to reflect the light admitted into the light incident part  610 ′; and a light exit part  630 ′ with a second diffusion pattern  631 ′ through which the light reflected through the light incident part  610 ′ to the light guide panel  400  exits. 
     The light guide bar  600 ′ may have a base part  600   a ′ in a plate form and a depression part  600   b ′ formed at a part of the base part  600   a ′ to have a certain depth. The light incident part  610 ′ may be formed at a top side of the depression part  600   b ′ opposite to the LED  510  while the light exit part  630 ′ is formed at a front side of the base part  600   a ′ opposite to the light guide panel  400 . 
     The LED  510 ′ generates light downward, that is, in a thickness direction of the light guide bar  600 ′ or the light guide panel (not shown), so as to extend a light path and uniformly mix the light generated by the LED  510 ′. 
     The light is first scattered by the light incident part  610 ′ with the first diffusion pattern  611 ′ in the light guide bar  600 ′ and the scattered light is entirely reflected through the light reflection part  620 ′ to the light exit part  630 ′. The light is finally scattered by the light exit part  630 ′ with the second diffusion pattern  631 ′ and admitted into the light guide panel (not shown). 
     Accordingly, the light emitted from the LED  510 ′ in a thickness direction of the light guide panel (not shown) is scattered and reflected in the light guide bar  600 ′, and then, is emitted with uniform light power and admitted into the light guide panel (not shown), thereby solving a non-uniform brightness problem caused using the LED  510 ′. 
     As is apparent from the above description, it may be understood that the backlight unit and the liquid crystal display according to exemplary embodiments adopt a light guide bar as a technical concept so as to uniformly provide light generated by LEDs to a light guide panel, thereby reducing non-uniformity of brightness and enhancing light efficiency. 
     Although a few exemplary embodiments have been shown and described, it would be appreciated by those skilled in the art that changes or modifications may be made in these exemplary embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.