Patent Publication Number: US-2010128464-A1

Title: Light diffusion plate, method for manufacturing the same and backlight assembly having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 2008-116273, filed on Nov. 21, 2008 in the Korean Intellectual Property Office (KIPO), the contents of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light diffusion plate, a method for manufacturing the light diffusion plate, and a backlight assembly having the light diffusion plate. More particularly, the present invention relates to a light diffusion plate disposed under a display panel to control light provided to the display panel, a method for manufacturing the light diffusion plate, and a backlight assembly having the light diffusion plate. 
     2. Description of the Related Art 
     Generally, a liquid crystal display (LCD) apparatus widely used as a flat panel display apparatus is a passive illumination type apparatus. Thus, the LCD apparatus includes a backlight assembly disposed on a rear surface of the display panel to provide light to the display panel. 
     The backlight assembly is classified as either an edge illumination type backlight assembly or a direct illumination type backlight assembly. In the edge illumination type backlight assembly, a lamp is disposed at a side of a light guide plate. In the direct illumination type backlight assembly, a plurality of lamps is disposed under the display panel. The direct illumination type backlight assembly is widely used for large display apparatuses due to high light efficiency, simple structure and suitability for wide display panels. 
     The direct illumination type backlight assembly includes a plurality of lamps disposed under the display panel, a reflective sheet disposed under the lamps, a diffusion plate and a diffusion sheet disposed between the lamps and the display panel to diffuse the light and to improve luminance uniformity, and a prism sheet concentrating the light to improve front luminance. 
     In the direct illumination type backlight assembly, bright lines occur on the display panel so that display quality may be decreased. In this case, a predetermined distance between the lamp and the display panel should be maintained to prevent the bright lines. However, the predetermined distance may increase the thickness of the LCD apparatus, and the luminance uniformity of the display panel may be decreased. 
     SUMMARY OF THE INVENTION 
     The present invention provides a light diffusion plate preventing a profile of a light source from being visible. 
     The present invention also provides a method for manufacturing the light diffusion plate. 
     The present invention also provides a backlight assembly having the light diffusion plate so that the thickness of the backlight assembly may be decreased and the luminance uniformity of the backlight assembly may be increased. 
     According to one aspect of the present invention, a light diffusion plate includes a base layer and a plurality of light diffusion dots. The base layer includes a first surface where a plurality of unit areas is defined and a second surface facing the first surface. A plurality of light diffusion dots is respectively formed in each unit area. The light diffusion dots are formed having a random pattern so that the area of each of the light diffusion dots irregularly varies along arbitrary directions on the first surface. 
     According to another aspect of the present invention, a backlight assembly includes a light source, an optical sheet disposed over the light source and a light diffusion plate disposed between the light source and the optical sheet. The light diffusion plate includes a base layer and a plurality of light diffusion dots. The base layer includes a first surface where a plurality of unit areas is defined. A plurality of light diffusion dots is respectively formed in the unit areas. The light diffusion dots are formed having a random pattern so that the area of each of the light diffusion dots irregularly varies along arbitrary directions on the first surface. 
     According to still another aspect of the present invention, in a method of manufacturing a light diffusion plate, a plurality of the unit areas is defined on a first surface of a base layer. A plurality of light diffusion dots is respectively formed in the unit areas so that the area of each of the light diffusion dots irregularly varies along arbitrary directions on the first surface. 
     According to the present invention, the area of a light diffusion dot irregularly varies so that the profile of a light source on a front surface of an optical sheet may be prevented from being visible. Thus, a distance between the light source and a light diffusion plate may be decreased so that the thickness of a backlight assembly may be decreased. In addition, costs for manufacturing the light diffusion plate having the light diffusion dot may be decreased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present disclosure will become more apparent by describing embodiments thereof with reference to the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view illustrating a backlight assembly according to an example embodiment of the present invention; 
         FIG. 2  is a plan view illustrating a rear surface of a light diffusion plate; 
         FIG. 3  is a flowchart illustrating a method for manufacturing the light diffusion plate according to the example embodiment of the present invention; 
         FIG. 4  is a block diagram illustrating a random pattern generating algorithm used for the method for manufacturing the light diffusion plate in  FIG. 3 ; 
         FIG. 5  is a plan view illustrating a unit area display based on unit area information outputted from a unit area generating part in  FIG. 4 ; 
         FIG. 6  is a noise image display based on noise image information outputted from a noise image generating part; 
         FIG. 7  is a plan view illustrating a light diffusion dot formed in the unit area in  FIG. 5 ; 
         FIG. 8  is a plan view illustrating the light diffusion dot printed in the unit area in  FIG. 5 ; 
         FIG. 9  is a plan view illustrating the rear surface of the light diffusion plate on which the light diffusion dots are regularly distributed; 
         FIG. 10  is a graph showing the luminance of the light diffusion plate in  FIGS. 1 to 8 ; 
         FIG. 11  is a graph showing the luminance of the light diffusion plate in  FIG. 9 ; and 
         FIG. 12  is a plan view illustrating a rear surface of a light diffusion plate according to another example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the present disclosure is described more fully hereinafter with reference to the accompanying drawings, the underlying concepts may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its teachings to those skilled in the pertinent art. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for sake of clarity. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numerals refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the apparatus in use or operation in addition to the orientation depicted in the figures. For example, if the apparatus in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” can encompass both an orientation of above and below. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized example embodiments (and intermediate structures) of the present invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments herein should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of an apparatus and are not intended to limit the scope of the present invention. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the pertinent art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Hereinafter, the present disclosure of invention will be explained in detail with reference to the accompanying drawings. 
       FIG. 1  is a cross-sectional view illustrating a backlight assembly according to an example embodiment of the present invention. 
     Referring to  FIG. 1 , the backlight assembly  100  according to the present example embodiment includes a light source  5 , a reflective sheet  40 , an optical sheet  7 , and a light diffusion plate  101 . 
     The light source  5  may include a cold cathode fluorescent lamp (CCFL) in one example. The CCFL (hereinafter referred to as a lamp) may include a straight-type lamp tube and discharging gas injected into the lamp tube. A plurality of the light sources  5  is arranged parallel with each other and are spaced apart from each other by a uniform distance. 
     The reflective sheet  40  is disposed under the light sources  5  and reflects light emitted from the light sources  5  back toward the light sources  5 . 
     The optical sheet  7  is disposed over the light sources  5  and improves the luminance uniformity of the light emitted from the light sources  5 . In the present example embodiment, the optical sheet  7  may include three diffusion-condensing sheets  10 ,  20  and  30 . The diffusion-condensing sheets  10 ,  20  and  30  may include a base film diffusing the light and condensing lens having a lenticular shape formed on the base film. Alternatively, the optical sheet  7  may include a single diffusion sheet and two prism sheets disposed on the diffusion sheet. 
       FIG. 2  is a plan view illustrating a rear surface of the light diffusion plate  101 . 
     Referring to  FIGS. 1 and 2 , the light diffusion plate  101  according to the present example embodiment is disposed between the optical sheet  7  and the light sources  5 . The light diffusion plate  101  is disposed close to the light sources  5 . For example, when a distance between central portions of adjacent light sources  5  is defined as a lamp distance D 01  and a distance between the light diffusion plate  101  and a central portion of the light sources  5  is defined as an optical distance H 01 , the lamp distance D 01  may be three or four times larger than the optical distance H 01  so that the thickness of the backlight assembly  100  may be decreased. Alternatively, the lamp distance D 01  of a conventional backlight assembly may be about 1.7 times larger than the optical distance H 01 . Thus, the backlight assembly  100  according to the present example embodiment may provide the backlight assembly  100  having a very small thickness. 
     As mentioned above, although the optical distance H 01  is very small, the light diffusion plate  101  effectively diffuses the light from the light sources  5  so that shapes of the light sources  5  may be prevented from being visible from a front-viewing angle. The light diffusion plate  101  includes a base layer  110  and a plurality of light diffusion dots  130 . 
     The base layer  110  includes a first surface  111  facing the light sources  5  and a second surface  113  facing the first surface  111 . A plurality of unit areas DA 01  is defined on the first surface  111  as illustrated in  FIG. 2 . Each of the unit areas may be formed on the first surface  111  with various types, to control a dot density of the light diffusion dot  130  more easily. 
     The area of the light diffusion dot  130  is smaller than that of the unit area DA 01 . The light diffusion dots  130  partially reflect the light incident to the first surface  111 , and partially transmit the incident light to the first surface  111 , so that the light diffusion dots  130  diffuse the light. In the present example embodiment, the light diffusion dot  130  has a random pattern so that the area of the light diffusion dot irregularly varies along arbitrary directions on the first surface. 
       FIG. 3  is a flowchart illustrating a method for manufacturing the light diffusion plate according to the example embodiment of the present invention. 
     Referring to  FIG. 3 , the plurality of the unit areas DA 01  is defined on the first surface  111  of the base layer  110  to manufacture the light diffusion plate  101  (step S 10 ). The unit area DA 01  may equally divide an area in which the light diffusion dot  130  is formed. 
       FIG. 4  is a block diagram illustrating a random pattern generating algorithm used for the method for manufacturing the light diffusion plate in  FIG. 3 . 
     Referring to  FIG. 4 , for example, a pattern generator  201  may be used to perform the random pattern generating algorithm. The pattern generator  201  may include a unit area generating part  210 , a noise image generating part  230  and a random pattern generating part  250 . 
       FIG. 5  is a plan view illustrating a unit area display based on unit area information outputted from a unit area generating part in  FIG. 4 . 
     Referring to  FIGS. 4 and 5 , the unit area generating part  210  outputs the unit area information  213  based on area division information  211  inputted from the exterior. The area division information  211  may include information on the unit area DA 01  such as a shape, arrangement form, a side size along a first direction Y 01  and a side size along a second direction X 01 / 2 . In this case, the first and second directions may be perpendicular to each other. The shape, the arrangement form and the side sizes are not limited to the present example embodiment in  FIG. 5 . The unit area information  213  may be displayed as an image illustrated in  FIG. 5 . 
     In the present example embodiment, each of the unit areas DA 01  has a uniform size and is formed to make contact with each other. The unit area DA 01  has a rectangular shape. The unit areas DA 01  are arranged in a line along a first direction, so that the entire side of the unit area DA 01  along the second direction may make contact with the entire side of an adjacent unit area DA 01  along the second direction. The unit areas DA 01  disposed adjacent to each other along the first direction are shifted along the first direction with respect to each other. Thus, the unit areas DA 01  disposed adjacent to each other may make partial contact with each other along the first direction. For example, the side of the unit area DA 01  may make half contact with the side of an adjacent unit area DA 01 . 
     Then, the light diffusion dots  130  are respectively formed in the unit areas DA 01 , so that the area of each of the light diffusion dots  130  irregularly varies along arbitrary directions on the first surface  111  (step S 20 ). 
     To form the light diffusion dot  130 , the area of the light diffusion dot  130  is firstly determined using the random pattern generating algorithm so that the area of the light diffusion dot follows luminance distribution of a noise image (step S 21 ). 
       FIG. 6  is a noise image display based on noise image information outputted from a noise image generating part. 
     Referring to  FIGS. 4 and 6 , the noise image generating part  230  outputs the noise image information  233  based on noise signals  231 . The noise image generating part  230  may include a noise filter such as a paint shop. The noise signals  231  applied to the noise filter may include various types. For example, the noise signals  231  may include noise patterns selected among various types of noise patterns and processing information. The processing information may include data processing parameters compensating the noise patterns. For example, the processing information may include information on upper and lower limits related to luminance differences between adjacent pixels in the image having the selected noise patterns, and on increases and decreases in size of each pixel, etc. 
     The noise image generating part  230  generates the noise image information  233  through compensating the noise patterns based on the processing information. The noise image information  233  may include the compensated luminance of the pixels of the noise patterns. The noise image display based on the noise image information  233  may be a bitmap image as illustrated in  FIG. 6 . 
     The random pattern generating part  250  may determine the area of the light diffusion dot  130  formed in the unit areas DA 01 , based on the unit area information  213 , the noise image information  233  and the transmittance of the light diffusion dot  130 . For example, the random pattern generating part  250  may determine the average luminance of the unit areas DA 01  based on the luminance of the pixels included in the unit area DA 01  of the noise information. In this case, the luminance of pixels may be provided from the information on the luminance information of the pixels included in the noise image information  233 . Thus, the random pattern generating part  250  may determine the area of the light diffusion dot  130  based on the average luminance of the unit area DA 01 , the transmittance of the light diffusion dot  130  and the average luminance of the light from the light sources  5 . The area of the light diffusion dot  130  may be calculated by the random pattern generating part as follows. 
       FIG. 7  is a plan view illustrating a light diffusion dot formed in the unit area in  FIG. 5 . 
     Referring to  FIG. 7 , the area of the light diffusion dot  130  is smaller than that of the unit area DA 01 , and the light diffusion dot  130  is spaced apart from the sides of the unit area along the first and second directions. 
     An equilibrium {total amount of light emitted from the unit area DA 01 =amount of light from the area having no light diffusion dots  130 +amount of light from the light diffusion dot  130 } may be satisfied based on geometrical shapes of the unit area DA 01  and the light diffusion dot  130 . 
     The total amount of light from the unit area DA 01 , I avg (lumen; lm), may be expressed as Equation 1. 
         I   avg   =∫i   avg   dA=i   avg   ∫dA=i   avg   A   [Equation 1] 
     I avg : average quantity of light per unit area (lm/m 2 ) 
     A=(Y 01 )(X 01 / 2 ): area of unit area DA 01   
     The amount of light from the area having no light diffusion dot  130  of the unit area DA 01 , (1−ρ) I lamp , may be expressed as Equation 2. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
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     ρ=A d /A: dot density defined as ratio of area of light diffusion dot  130  with respect to unit area DA 01   
     I lamp : average luminance of light source  5   
     A d : area of light diffusion dot  130   
     i(X): quantity of light per unit area (lm/m 2 ) from differential area dA, wherein i(X) is a function only related to X. 
     The amount of light from the light diffusion dot  130  of the unit area DA 01 , ρTI lamp , may be expressed as Equation 3. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     T: transmittance of light diffusion dot  130 , T&lt;1.0 
     Equation 1 may be simply expressed as Equation 4 from Equation 2 and Equation 3. 
         I   avg =(1−ρ) I   lamp   +ρTI   lamp   [Equation 4] 
     As mentioned above, the random pattern generating part  250  may determine the average luminance of the unit area DA 01 , I avg , based on the luminance of the pixels included in the unit area DA 01 . In this case, the noise image information  233  may include the information on the luminance of the pixels. The average luminance of the light source  5 , I lamp , may be easily measured using a luminance measurement apparatus. When the average luminance of the unit area DA 01  calculated by the random pattern generating part  250  is equal to the average luminance of the light source  5 , I lamp , the dot density of the light diffusion dot  130  may be calculated. Thus, the area of the light diffusion dot  130 , A d , may be calculated using the equation ρ=A d /A. 
       FIG. 8  is a plan view illustrating the light diffusion dot printed in the unit area in  FIG. 5 . 
     Then, the light diffusion dots  130  are printed in the unit areas DA 01  so that each of the light diffusion dots  130  has the above-mentioned predetermined area (step S 25 ). 
     For example, the light diffusion dots  130  may be formed using a silkscreen printing process. In the silkscreen printing process, a silkscreen printing apparatus  270  may print the light diffusion dots  130  on the first surface  111  of the base layer  110  based on printing information  253  provided from the pattern generator  201  in  FIG. 4 , so that the light diffusion plate  101  may be manufactured. The printing information  253  may include information on the area of the light diffusion dot  130  and randomized patterns. 
     For example, the light diffusion dots  130  may be formed using an ink including a filler having the light transmittance in a range between about 40% to about 80%. The ink may be formed using a white ink and a transparent ink. For example, the filler may include titanium dioxide (TiO 2 ). For example, considering dispersibility of the ink, TiO 2  may be in the range between about 13 wt % and about 17 wt %, and more specifically TiO 2  may be about 13 wt % in the blend of the ink and the filler. 
     When the amount of TiO 2  in the ink is increased, the blocking function and reflectivity of the light diffusion plate  101  may be increased. However, when the ink includes too much filler, a chromaticity diagram of the light passing through the light diffusion plate  101  in the area where the dot density of the light diffusion dot  130  is higher than that in other areas may become yellowish. In this case, a blue colorant may be included in the blend in the range between about 0.2 wt % to about 0.4 wt % for preventing the yellowing, and more specifically the blue colorant may be included in the blend at about 0.3 wt %. 
     A protective layer may be further formed on the first surface  111  to cover and protect the light diffusion dots  130 . In addition, a condensing lens may be further formed on the second surface  113  of the base layer  110 . For example, the condensing lens may be a lenticular-type lens. A light diffuser which may have a particle shape may be distributed in the base layer  110 , and scatters incident light, so that the light diffusion plate  101  may diffuse light more effectively. 
     In  FIG. 8 , the dot density is determined according to the noise image. Thus, the area of the light diffusion dot  130  irregularly varies along arbitrary directions. Thus, the shape of the lamps may be hardly visible through the optical sheet  7  due to the random pattern of the light diffusion dots  130 . For example, irregular and aperiodic patterns of the light diffusion dots  130  may have profiles of the light sources  5  that are dispersed, so that the profiles of the light sources  5  may be hardly visible. 
       FIG. 9  is a plan view illustrating the rear surface of the light diffusion plate on which the light diffusion dots are regularly distributed. 
     Referring to  FIG. 9 , the regular light diffusion plate  301  is formed to compare the regular light diffusion plate  301  to the light diffusion plate  101  according to the present example embodiment. For example, the regular light diffusion plate  301  may have a periodic pattern. The areas of the light diffusion dots  330  of the regular diffusion plate  301  are uniform along the first direction, and periodically vary along the second direction. For example, the areas of the light diffusion dots  330  of the regular diffusion plate  301  increases when a dot position is close to a position corresponding to the light sources  5 , and decreases when the dot position is close to a middle point between the light sources  5 . 
       FIG. 10  is a graph showing the luminance of the light diffusion plate in  FIGS. 1 to 8 .  FIG. 11  is a graph showing the luminance of the light diffusion plate in  FIG. 9 . 
     Referring to  FIGS. 10 and 11 , a horizontal axis indicates positions where the light sources  5  are disposed. The light sources  5  are arranged parallel with each other, and spaced apart from each other by a uniform distance. The light sources  5  are disposed on L 1 , L 2 , L 3 , L 4  and L 5  in  FIGS. 11 and 12 . A vertical axis in  FIG. 10  indicates the luminance observed in front of the optical sheet  7  of the backlight assembly  100 . The vertical axis in  FIG. 11  indicates the luminance observed in front of the optical sheet  7  of the backlight assembly  100  having the regular light diffusion plate  301  in  FIG. 9 . 
     In  FIGS. 10 and 11 , when the average luminance in front of the optical sheet is indicated as 1.00, the luminance observed in front of the optical sheet  7  varies according to the position related to the light sources  5 . 
     In  FIGS. 10 and 11 , a first luminance curve LC 1  shows luminance distribution when the light sources  5  is directly observed without the light diffusion plate  101 , the regular light diffusion plate  301  and the optical sheet  7 . Referring to the first luminance curve LC 1 , luminance differences between points directly above the light sources  5  and middle points between the light sources  5  are very large, and the first luminance curve LC 1  follows a sine shape or a cosine shape. 
     In  FIGS. 10 and 11 , a second luminance curve LC 2  and a third luminance curve LC 3  show the luminance distribution in front of the optical sheet  7  when the backlight assembly  100  is under ideal conditions without external disturbances. The external disturbances may include distortion of the light diffusion plate  101  and the regular light diffusion plate  301 , deviation in the reflection and transmittance of the light diffusion dots  130  and  330  due to excess ink, deformation of the reflective sheet  40  and high-sensitive eyes of user for periodic light and shade. 
     Referring to the second luminance curve LC 2  in  FIG. 11 , under ideal conditions, the luminance distribution of the regular light diffusion plate  301  may be uniform due to the periodic dot pattern. However, referring to the third luminance curve LC 3  in  FIG. 10 , under ideal conditions, the luminance distribution of the light diffusion plate  101  according to the present example embodiment is very irregular due to the random pattern of the light diffusion dots  130 , but the range of fluctuation of the third luminance curve LC 3  is small and wave patterns are very minute. Thus, the profiles of the light sources  5  may be dispersed, so that the profiles of the light sources  5  may be hardly visible. 
     However, to remove or prevent the external disturbances is nearly impossible. Thus, the luminance distribution with the external disturbances may be probable. In  FIGS. 10 and 11 , a fourth luminance curve LC 4  and a fifth luminance curve LC 5  show the luminance distribution in the front of the optical sheet  7  when the backlight assembly  100  is under actual conditions with the external disturbances. 
     Referring to the fourth luminance curve LC 4  in  FIG. 11 , under actual conditions, the luminance distribution of the regular light diffusion plate  301  may be irregular but fluctuate according to the periodic pattern related to the light sources  5  positions. Thus, the profiles of the light sources  5  in front of the optical sheet  7  may be easily visible due to the periodic luminance distribution. Thus, in a liquid crystal display (LCD) apparatus including the regular light diffusion plate  301 , bright lines on a liquid crystal display panel may be visible, so that display quality of the LCD apparatus may be decreased. 
     However, referring to the third luminance curve LC 5  in  FIG. 10 , under actual conditions, the luminance distribution of the light diffusion plate  101  according to the present example embodiment is very irregular due to the random pattern of the light diffusion dots  130 , but the range of fluctuation of the third luminance curve LC 3  is small and wave patterns are very minute. Thus, the profiles of the light sources  5  may be dispersed, so that the profiles of the light sources  5  may be hardly visible. 
     Thus, in accordance with this embodiment, the luminance uniformity of the backlight assembly  100  may be increased. Also, the light diffusion plate  101  may be manufactured by using conventional silk printing methods excluding the random pattern of the light diffusion dots  130 . Thus, additional costs may not be required for the light diffusion plate  101  in this embodiment. 
       FIG. 12  is a plan view illustrating a rear surface of a light diffusion plate according to another example embodiment of the present invention. 
     Referring to  FIG. 12 , the light diffusion plate  501  may be applied to a backlight assembly including a point light source such as a light-emitting diode (LED). Light diffusion dots  530  having a random pattern are formed on a first surface of a base layer  510  of the light diffusion plate  501  as illustrated in  FIG. 12 , so that the areas of the light diffusion dots  530  may irregularly vary along arbitrary directions on the first surface. An algorithm such as the pattern generator may be used to form the random pattern. Noise pattern information used in the present example embodiment may be different from the noise pattern information used in the previous example embodiment in  FIGS. 1 to 8 . For example, a noise pattern may be selected by trial and error, considering a light source type and a light source arrangement. 
     A method for manufacturing the light diffusion plate according to the present example embodiment is substantially the same as the method for manufacturing the light diffusion plate according to the previous example embodiment described above with reference to  FIGS. 3 to 8 , except for changing the noise pattern. Thus, further descriptions of the method for manufacturing the light diffusion plate according to the present example embodiment will be omitted. 
     A backlight assembly according to the present example embodiment is substantially the same as the backlight assembly according to the previous example embodiment described with reference to  FIGS. 1 to 8 , except for including the light diffusion plate  501  illustrated in  FIG. 12 . Thus, further descriptions of the backlight assembly according to the present example embodiment will be omitted. 
     According to example embodiments of the present invention, the profiles of a light source such as a lamp may be hardly visible in front of a sheet disposed on a light diffusion plate, so that the distance between the light source and the light diffusion plate may be decreased. Thus, the thickness of a backlight assembly may be decreased, and costs for manufacturing the light diffusion plate may be decreased. Thus, the example embodiments of the present invention may be used in improving luminance uniformity and decreasing the thickness of the backlight assembly. 
     The foregoing is illustrative and is not to be construed as limiting of the teachings provided herein. Although a few example embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of the present teachings. In the below claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also functionally equivalent structures. Therefore, it is to be understood that the foregoing is illustrative and is not to be construed as limited to the specific example embodiments disclosed, and that modifications to the disclosed example embodiments, as well as other example embodiments, are intended to be included within the scope of the teachings.