Patent Publication Number: US-8976316-B2

Title: Lighting device, display device and television receiver

Description:
TECHNICAL FIELD 
     The present invention relates to a lighting device, a display device and a television receiver. 
     BACKGROUND ART 
     A liquid crystal panel included in a liquid crystal display device such as a liquid crystal television does not emit light, and thus a backlight device is required as a separate lighting device. A backlight device arranged behind the liquid crystal panel (i.e., on a side opposite from a display surface side) is known. It includes a plurality of light sources (e.g., LEDs). 
     Such a backlight device has a configuration in which white LEDs are installed. The white LEDs tend to produce color variances in white color. A device disclosed in Patent Document 1 is know as a device that can produce white light with a target color using white LEDs that tend to produce color variations. In this lighting device, an arrangement of the white LEDs is adjusted to obtain white light with a target color. 
     Patent Document 1: Japanese Unexamined Patent Publication No. 2009-54563 
     PROBLEM TO BE SOLVED BY THE INVENTION 
     In the device disclosed in Patent Document 1, white LEDs need to be arranged such that an amount of light emitted from the center of each of the adjacent LEDs apart from each other at a minimum distance is in a range between 80% and 120% of an average of a total amount of light emitted from the white LEDs. Therefore, the arrangement of the white LEDs is difficult to design and thus a large amount of time is required for arranging the white LEDs. 
     DISCLOSURE OF THE PRESENT INVENTION 
     The present invention was made in view of the foregoing circumstances. An object of the present invention is to provide a lighting device that can produce light with substantially uniform overall color. Other objects of the present invention are to provide a display device including such a lighting device, and a television receiver including such a display device. 
     MEANS FOR SOLVING THE PROBLEM 
     To solve the above problem, a lighting device of the present invention includes a plurality of light source boards and a plurality of point light sources mounted on the light source boards. The point light sources mounted on each light source board have colors, an average of which is in an equivalent color range. The color range is defined by a square with two sides that are opposed sides each having an X-axis coordinate length of 0.015 and two sides that are opposed side each having a Y-axis coordinate length of 0.015 in a CIE 1931 color space chromaticity diagram. 
     In general, the point light sources tend to produce color variations. The color variations may cause color variations in the lighting device. According to the present invention, an average color range is defined for each light source board on which the point light sources are mounted. Therefore, the color variations are less likely to occur in the lighting device. Specifically, the average color is set in the equivalent color range. The equivalent color range is defined by the square with two sides that are opposed sides each having the X-axis coordinate length of 0.015 and two sides that are opposed sides each having the Y-axis coordinate length of 0.015 in the CIE 1931 color space chromaticity diagram. The equivalent color range, which is defined by the square with two sides that are opposed sides each having the X-axis coordinate length of 0.015 and two sides that are opposed sides each having the Y-axis coordinate length of 0.015 in the CIE 1931 color space chromaticity diagram, is a range in which the colors are equivalent and color variations are less likely to be recognized. With this configuration, the color variations among the light source boards are less likely to occur. Therefore, the colors in an entire area are evened. Especially during movie display, illumination with a substantially uniform color can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view illustrating a general construction of a television receiver according to a first embodiment of the present invention; 
         FIG. 2  is an exploded perspective view illustrating a general construction of a liquid crystal display device included in the television receiver; 
         FIG. 3  is a cross-sectional view illustrating a cross-sectional configuration of the liquid crystal display device along the long-side direction; 
         FIG. 4  is a cross-sectional view illustrating a cross-sectional configuration of the liquid crystal display device along the short-side direction; 
         FIG. 5  is a plan view illustrating an arrangement of LED boards inside the chassis; 
         FIG. 6  is a partial magnified cross-sectional view illustrating a part mounted on the LED board; 
         FIG. 7  is a partial magnified plan view illustrating the part mounted on the LED board; 
         FIG. 8  is a schematic view for explaining an average color of LEDs on each LED board; 
         FIG. 9  is a color space chromaticity diagram created by the International Commission on Illustration (CIE) in 1931; 
         FIG. 10  is a partial magnified view of an equivalent color range in  FIG. 9 ; 
         FIG. 11  is a partial magnified view illustrating color ranges of LEDs in a backlight unit of a second embodiment of the present invention, the colors being defined in the color space chromaticity diagram created by the International Commission on Illustration (CIE) in 1931; 
         FIG. 12  is a schematic view illustrating arrangements of the LEDs in different color ranges on LED boards; 
         FIG. 13  is a schematic view illustrating other arrangements of the LEDs in different color ranges on LED boards; 
         FIG. 14  is a schematic view illustrating other arrangements of the LEDs in different color ranges on LED boards; 
         FIG. 15  is a schematic view illustrating other arrangements of the LEDs in different color ranges on LED boards; 
         FIG. 16  is a partial magnified view illustrating color ranges of LEDs in a backlight unit of a third embodiment of the present invention, the color ranges being defined in the color space chromaticity diagram created by the International Commission on Illustration (CIE) in 1931; and 
         FIG. 17  is a schematic view illustrating arrangements of the LEDs in different color ranges on the LED boards. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     A first embodiment of the present invention will be explained with reference to  FIGS. 1 to 10 . 
     First, a television receiver TV including a liquid crystal display device  10  will be explained. 
     As illustrated in  FIG. 1 , the television receiver TV of this embodiment includes the liquid crystal display device  10 , front and rear cabinets Ca, Cb that house the liquid crystal display device  10  therebetween, a power source P, a tuner T and a stand S. An overall shape of the liquid crystal display device (a display device)  10  is a landscape rectangular. The liquid crystal display device  10  is held in a vertical position. As illustrated in  FIG. 2 , it includes a liquid crystal panel  11  as a display panel, and a backlight unit (a lighting device)  12 , which is an external light source. They are integrally held by a bezel  13  having a frame-like shape. 
     Next, the liquid crystal panel  11  and the backlight unit  12  included in the liquid crystal display device  10  will be explained (see  FIGS. 2 to 4 ). 
     The liquid crystal panel (display panel)  11  is constructed such that a pair of glass substrates is bonded together with a predetermined gap therebetween and liquid crystal is sealed between the glass substrates. On one of the glass substrates, switching components (e.g., TFTs) connected to source lines and gate lines that are perpendicular to each other, pixel electrodes connected to the switching components, and an alignment film are provided. On the other substrate, a color filter having color sections such as R (red), G (green) and B (blue) color sections arranged in a predetermined pattern, counter electrodes, and an alignment film are provided. Polarizing plates are attached to outer surfaces of the substrates. 
     As illustrated in  FIG. 2 , the backlight unit  12  includes a chassis  14 , an optical sheet set  15  (a diffuser plate  15   a  and a plurality of optical sheets  15   b  arranged between the diffuser plate  15   a  and the liquid crystal panel  11 ), and frames  16 . The chassis  14  has a box-like shape and an opening on the light emitting side (on the liquid crystal panel  11  side). The optical sheet set  15  is arranged so as to cover the opening of the chassis  14 . The frames  16  are arranged along the long sides of the chassis  14 . The frames  16  hold the long-side edges of the diffuser plate  15   a  to the chassis  14 . The outer edges of the diffuser plate  15   a  are sandwiched between the chassis  14  and the frames  16 . Light emitting diodes (point light sources, hereinafter referred to as LEDs)  17  are arranged in the chassis  14 . A light emitting side of the backlight unit  12  is a side closer to the diffuser plate  15   a  than the cold cathode tubes  17 . 
     The chassis  14  is made of metal. It includes a bottom plate  14   a , side plates  14   b , and receiving plates  14   c . The bottom plate  14   a  has a rectangular shape similar to the liquid crystal panel  11 . Each side plate  14   b  rises from an outer edge of the corresponding side of the bottom plate  14   a . Each receiving plate  14   c  projects from the top edge of the corresponding side plate  14   b . The chassis  14  has a shallow-box-like overall shape with an opening on the front side. As illustrated in  FIGS. 3 and 4 , the frames  16  are placed on the respective receiving plates  14   c  of the chassis  14 . Outer edges of a reflection sheet  18  and optical sheet set  15  are sandwiched between the receiving plates  14   c  and the frames  16 . The reflection sheet  18  will be explained later. Furthermore, mounting holes  16   a  are provided in the top surfaces of the frames  16 . The bezel  13 , the frames  16  and the chassis  14  are bound together with screws  19 . 
     The optical sheet set  15  including the diffuser plate  15   a  and the optical sheets  15   b  is arranged on the opening side of the chassis  14 . The diffuser plate  15   a  is constructed of a plate-like member made of synthetic resin with light-scattering particles dispersed therein. The diffuser plate  15   a  diffuses point light emitted from the LEDs  17  that are the point light sources. The outer edges of the diffuser plate  15   a  are placed on the receiving plates  14   c  of the chassis  14 , as explained earlier. The outer edges of the diffuser plate  15   a  do not receive strong vertical forces that restrain the outer edges in the vertical direction. 
     Two optical sheets  15   b  layered and arranged on the diffuser plate  15   a . Each optical sheet  15   b  has a sheet-like shape with a thickness larger than that of the diffuser plate  15   a . Examples of the optical sheets  15   b  are a diffuser sheet, a lens sheet and a reflection-type polarizing sheet. Each optical sheet  15   b  can be selected from those sheets accordingly. The optical sheet  15   b  converts light emitted from the LEDs  17  and passed through the diffuser plate  15   a  into a planar light. The liquid crystal display panel  11  is arranged on the top surface of the optical sheet  15   b.    
     A light reflection sheet  18  is arranged on inner surfaces of the bottom plate  14   a  and the side plates  14   b  of the chassis  14  so as to cover the substantially entire surfaces. The light reflection sheet  18  is a synthetic resin sheet having a surface in white color that provides high light reflectivity. The reflection sheet  18  has holes  18   a  at locations corresponding to the diffuser lenses  21 , which will be explained later. An entire area of the bottom plate  14   a  of the chassis  14  is covered by the reflection sheet  18  except for areas in which the diffuser lenses  21  are arranged. The diffuser lenses  21  appear on the optical sheet set  15  side through the holes  18   a . The edge portions of the light reflection sheet  18  are lifted at angles so as to cover the inner surfaces of the side plates  14   b . The outer edges of the reflection sheet  18  are placed on the respective receiving plate  14   c  of the chassis  14 . With this light reflection sheet  18 , light emitted from the LEDs  17  is reflected toward the diffuser plate  15   a.    
     The LED boards (a light-source board)  20  on which the LEDs  17  and the diffuser lenses  21  are mounted are arranged on the inner surface of the bottom plate  14   a  of the chassis  14 . Each LED board  20  is a synthetic resin board with a surface on which wiring patterns (not illustrated) are provided. The wiring patterns are metal films such as copper foils formed on the surface of the LED board  20 . As illustrated in  FIG. 5 , each LED board  20  is an elongated plate-like member. The LED boards  20  are arranged with the longitudinal direction thereof aligned with the long-side direction (the X-axis direction) of the chassis  14 . More specifically, three LED boards  20 ,  20 ,  20  are arranged with their longitudinal direction aligned with the long-side direction of the chassis  14 . The LED boards  20 ,  20 ,  20  are electrically and physically connected by connectors  22 . Nine lines, each of which includes three LED boards  20 ,  20 ,  20  connected in series in the short-side direction (the Y-axis direction) of the chassis  14 . A control unit, which is not illustrated, is connected to the LED boards  20 . The control unit is configured to supply power required for turning on the LEDs  17  and control driving of the LEDs  17 . 
     Each connector  22  that connects the adjacent LED boards  20 ,  20  is in white color that provides high light reflectivity. In  FIG. 5 , each connector  22  includes a first connector  22   a  and a second connector  22   b . The first connector  22   a  is attached to the left LED board  20  of the adjacent LED boards  20 . The second connector  22   b  is attached to the right LED board  20  of the adjacent LED boards  20 . The first connector  22   a  projects outward from the edge of the LED board  20  in the longitudinal direction. A connection between the adjacent LED boards  20 ,  20  is completed when the first connector  22   a  and the second connector  22   b  are engaged. 
     Six LEDs  17  are arranged in line on each LED board  20  along the longitudinal direction of the LED board  20 . More specifically, six LEDs  17  are arranged at equal intervals and surface mounted on the LED board  20 . Each LED  17  is prepared by applying a phosphor that has a light-emitting peak in a yellow range to a mono-color light emitting chip that emits blue light so that the LED  17  emits white light. The LEDs  17  are electrically connected in series via the wiring pattern on the LED board  20 . The LED  17  may be prepared by applying a phosphor that has a light emitting peak in a green range and a phosphor that has a light emitting peak in a red range to a blue light emitting chip so that the LED  17  emits white light. The LED  17  may be prepared by a phosphor that has a light-emitting peak in a green range to a blue light emitting chip and combing it with a red light emitting chip so that the LED  17  emits white light. The LED  17  may be prepared by combining a blue light emitting chip, a green light emitting chip, and a red light emitting chip so that the LED  17  emits white light. 
     As illustrated in  FIG. 6 , the diffuser lenses  21  are mounted on each LED board  20 . Each diffuser lens  21  has a dome-like shape and covers the corresponding LED  17 . Each diffuser lens  21  is a light diffusing member having high light diffuseness. The diffuser lens  21  is made of synthetic resin such as acrylic resin. Three legs  23  project from edge areas of the bottom surface of each diffuser lens  21 . As illustrated in  FIG. 7 , the legs  23  are arranged at about equal intervals (about 120-degree intervals) along the edge of the diffuser lens  21 , and fixed to the surface of the LED board  20  with adhesive or thermoset resin. An incident recess  21   a  is provided in an area of the bottom surface of the diffuser lens  21  (facing the LED  17  and the LED board  20 ) overlapping the LED  17  in plan view. The incident recess  21  is a cone-like hole that extends toward the top. The light from the LED  17  enters the incident recess  21   a . The bottom surface of the diffuser lens  21  is treated by surface roughing such as texturing. A recess  21   b  is provided in a central area (overlapping the LED  17  in plan view) of the top surface of the diffuser lens  21  (facing the diffuser plate  15   a ). The recess  21   b  extends toward the bottom. The top surface includes two gently curved continuous light exit surfaces  21   c . Light emitted from the LED  17  is refracted as it travels through an air layer, the incident recess  21   a , and the light exit surface  21   c . As a result, the light is diffused and emitted as planar light that travels in a wide-angle area from the recess  21   b  and the light exit surface  21   c  toward the diffuser plate  15   a.    
     Each LED board  20  is fixed to the bottom plate  14   a  of the chassis  14  by rivets  24 . Each rivet  24  includes a holddown portion  24   a  and a lock portion  24   b . The holddown portion  24   a  has a disk-like shape. The lock portion  24   b  projects downward from the holddown portion  24   a . The LED board  20  has insertion holes  20   c  through which the lock portion  24   b  are passed. The bottom plate  14   a  of the chassis  14  has mounting holes  14   d  that communicate with the respective insertion holes  20   c . An end of the lock portion  24   b  of each rivet  24  is a wide portion that is elastically deformable. When the end of the lock portion  24   b  is passed through the insertion hole  20   c  and the mounting hole  14   d , it is held against the rear surface of the bottom plate  14   a  of the chassis  14 . With this configuration, each rivet  24  fixes the LED board  20  to the bottom plate  14   a  while pressing the LED board  20  with the holddown portion  24   a.    
     As illustrated in  FIG. 2 , support pins  25  are arranged on the top surfaces of the rivets  24  located near the central part of the bottom plate  14   a  of the chassis  14 . Each support pin  25  has a cone-like shape that narrows toward the tip. If the diffuser plate  15   a  bends downward, the tips of the support pins  25  are in point contact with the diffuser plate  15   a . Namely, the support pins  25  support the diffuser plate  15   a  from below. Furthermore, the rivets  24  can be easily handled by holding the support pins  25 . 
     Colors of white light emitted by the white LEDs  17  are not uniform. Some variations in color of white light may be present. In this embodiment, color variations of the LEDs  17  on each LED board  20  are allowed but color variations of the LEDs  17  on different LED boards  20  are controlled to be within a range. The range will be discussed below with reference to  FIGS. 8 to 10 .  FIG. 8  is a schematic view for explaining an average color of LEDs on each LED board.  FIG. 9  is a color space chromaticity diagram created by the International Commission on Illustration (CIE) in 1931.  FIG. 10  is a partial magnified view illustrating a partial magnified view of an equivalent color range in  FIG. 9 . 
     As illustrated in  FIG. 8 , six LEDs  17  are mounted on each LED board  20  in this embodiment. The colors of the LEDs  17  may be the same or may be different. When the colors of the LEDs  17  on each LED board  20  are averaged, an average color of the LEDs  17  on the LED board  20  is within an equivalent color range H illustrated in  FIGS. 9 and 10 . The equivalent color range H is defined by two opposed lines each having a length of 0.015 x-coordinate distance and two opposed lines each having a length of 0.015 y-coordinate distance in the CIE 1931 color space chromaticity diagram in  FIGS. 9 and 10 . In the equivalent color range H corresponds to a target color or a range including the target color. 
     As describe above, the average color of the LEDs  17  on each LED board  20  is within the equivalent color range H. The equivalent color range H is defined by two opposed lines each having a length of 0.015 x-coordinate distance and two opposed lines each having a length of 0.015 y-coordinate distance in the CIE 1931 color space chromaticity diagram. The equivalent color range H defined by two opposed lines each having a length of 0.015 x-coordinate distance and two opposed lines each having a length of 0.015 y-coordinate distance in the CIE 1931 color space chromaticity diagram is a range in which the colors are equivalent and thus color variations are less likely to be recognized. Therefore, the color variations are less likely to be recognized between the LED boards  20 . As a result, a uniform overall color can be achieved and thus light with a substantially uniform color can be achieved. 
     The LEDs  17  are arranged in line along the longitudinal direction of the LED boards  20  in this embodiment. The arrangement of the LEDs  17  is defined according to the arrangement of the LED boards  20 . Therefore, the arrangement of the LEDs  17  can be easily designed. 
     The LEDs  17  are arranged at equal intervals on each LED board  20  in this embodiment. The arrangement of the LEDs  17  is not altered according to the LED boards  20 . Therefore, even when the size of the backlight unit  12  is altered, the LED boards  20  can be still used. 
     The LED boards  20  are arranged along the longitudinal direction thereof and the adjacent LED boards  20  are connected by the connectors  22 . 
     By preparing the LED boards  20  having different lengths, that is, on which different numbers of LEDs  17  are arranged, and connecting them by the connectors  22 , the LED boards  20  can be used for different sizes (or lengths) of the backlight units  12 . Namely, the LED boards  20  exclusively for a specific size of the backlight unit  12  are not required. This contributes to a cost reduction. 
     In this embodiment, each connector  22  includes the first connector  22   a  and the second connector  22   b . The first connector  22   a  projects from the end of the long side of the LED board  20 . 
     Because at least one of the first connector  22   a  and the second connector  22   b  project outward from the LED board  20 , the first connector  22   a  and the second connector  22   b  can be smoothly engaged when the adjacent LED boards  20 ,  20  are connected by the first connector  22   a  and the second connector  22   b.    
     The connectors  22  are in white color. The connectors  22  have relatively high light reflectivity. Therefore, the connectors  22  are less likely to absorb light and thus uneven brightness is less likely to occur. 
     The chassis  14  has a rectangular plan-view shape. Each LED board  20  is arranged with the long-side direction thereof aligned with the longitudinal direction of the chassis  14 . 
     In comparison to the configuration in which each LED board  20  is arranged with the longitudinal direction thereof aligned with the short-side direction of the chassis  14 , the number of the LED boards  20  can be reduced. Therefore, the number of control units for turning on and off the LEDs  17  can be reduced. As a result, the cost can be reduced. 
     The LEDs  17  are used as light sources. Therefore, the light sources with long lives and low power consumptions can be provided. 
     In this embodiment, each LED  17  is prepared by applying the phosphor having the light emitting peak in the yellow range to the blue light emitting chip and used as a light source. 
     When the white LEDs  17  are used, the colors tend to vary. The light may be bluish white depending on conditions of the phosphors (e.g., concentrations, film thicknesses). With the configuration of this embodiment, the colors in the entire area are evened, and light with a substantially uniform overall color can be achieved. 
     The LEDs  17  are electrically connected in series. 
     Because an equal amount of current is supplied to each LED  17 , the amounts of light emitted from the LEDs  17  can be equalized. Therefore, evenness in brightness on the illuminated surface of the backlight unit  12  improves. 
     The diffuser lenses  21  configured to diffuse the light from the respective LEDs  17  are mounted so as to cover the respective LEDs  17 . The light is diffused by the diffuser lenses  21 . Therefore, even when a distance between the adjacent LEDs  17 ,  17  is increased, dot-like lamp images are less likely to appear. By reducing the number of the LEDs  17 , the cost can be reduced. Furthermore, a substantially uniform brightness distribution can be achieved. With the diffuser lenses  21 , colors of light from the LEDs  17  are mixed and thus color variations can be reduced. Therefore, the colors are further evened. 
     The diffuser lenses  21  are light diffusing members configured to diffuse light. Therefore, the light can be properly diffused. 
     Because the surfaces of the diffuser lenses  21  on the LED board  20  side are treated by surface roughing. Therefore, the light is further properly diffused. 
     &lt;Second Embodiment&gt; 
     Next, a second embodiment of the present invention will be explained with reference to  FIGS. 11 and 12 . In this embodiment, a color of LEDs on each LED board will be explained. Other configurations are the same as the first embodiment. The same parts as those in the first embodiment will be indicated by the same symbols and will not be explained. 
       FIG. 11  is a partial magnified view illustrating colors of LEDs in a backlight unit of a second embodiment of the present invention, the colors being defined in the color space chromaticity diagram created by the International Commission on Illustration (CIE) in 1931.  FIG. 12  is a schematic view illustrating arrangements of the LEDs with different colors on LED boards. 
     The colors of the LEDs  17  in this embodiment vary within a use rage R defined by solid lines in the CIE 1931 diagram in  FIG. 11 . The use range R is divided into three color ranges A, B, and C, each of which is defined by a square. Each side of the square has a length of 0.015 coordinate distance, which means an actual distance between points of two adjacent corners of the square, that is, the actual distance between ends of one side is 0.015. More specifically, the center area of the use range R is the color range A (a first color range). The color range A corresponds to a target color and a large number of the LEDs is within this range. The range below the color range A is the color range B (a third color range). The range above the color range A is the color range C. The LEDs  17  having the colors off the target color are in the color ranges B and C. The color ranges A and B are the adjacent color ranges. The color ranges A and C are the adjacent color ranges. Namely, the color ranges B and C are not the adjacent color ranges. Each color range A, B, or C, which is a square having 0.015-long sides, is a color range of the LEDs  17  in which colors are not recognized as different colors. The color range A includes the equivalent color range H. A border between the color range A and the color range C is one of the sides of the equivalent color range H. A boarder between the color range A and the color range B is one of the sides of the equivalent color range H. 
     Next, the arrangements of the LEDs  17  on the LED boards  20  will be explained with reference to  FIG. 12 . 
     As illustrated in  FIG. 12 , on each LED board  20  ( 20   a ,  20   b ), the LEDs  17  with different colors A, B, and C are mounted. When the LED boards  20  are viewed with respect to the row direction (the X-axis direction, the longitudinal direction of the chassis  14 , the longitudinal direction of the LED boards  20   a ,  20   b ), three first LED boards (a first light source board)  20   a ,  20   a ,  20   a  are connected in series by the connectors  22  in the first row at the uppermost of the arrangement of the LED boards  20 . Each first LED board  20   a  includes the LEDs  17  in the color ranges A, C, A, C, A, C arranged in this sequence from the left in  FIG. 12 . The LEDs  17  in the color range A and the LEDs  17  in the color range C are alternately arranged. The adjacent LEDs  17 ,  17  on the first LED board  20   a  are in the adjacent color ranges (A and C). 
     In the second row below the first row, three second LED boards (a second light source board)  20   b ,  20   b ,  20   b  are connected in series by the connectors  22 . Each second LED board  20   b  includes the LEDs  17  in the color ranges B, A, B, A, B, A in this sequence from the left in  FIG. 12 . The LEDs  17  in the color range A and the LEDs  17  in the color range B are alternately arranged. The adjacent LEDs  17 ,  17  on the second LED board  20   b  are in the adjacent color ranges (A and B). In the third row, the first LED boards  20   a  are arranged. In the fourth row, the second LED boards  20   b  are arranged. In rows under the fourth row, the first LED boards  20   a  and the second LED boards  20   b  are arranged in the alternate rows. 
     Furthermore, the adjacent LEDs  17 ,  17  on the respective adjacent first LED boards  20   a ,  20   a  connected in series in the X-axis direction are in the adjacent color ranges (A and C). The adjacent LEDs  17 ,  17  on the respective adjacent second LED boards  20   b ,  20   b  connected in series in the X-axis direction are in the adjacent color ranges (A and B). The LEDs  17 ,  17  adjacently arranged with respect to the X-axis direction are all in the adjacent color ranges (A and B, or A and C). Namely, the LEDs  17  that are two color ranges apart (B and C) are not adjacently arranged. 
     When the LED boards  20  are viewed with respect to the column direction (the Y-axis direction, the short-side direction of the chassis  14 , the arrangement direction of the LED boards  20   a ,  20   b ), the first LED boards  20   a  and the second LED boards  20   b  are alternately arranged. The first column at the leftmost in  FIG. 12  includes the LEDs  17  in the color ranges A, B, A, B, . . . arranged in this sequence. The second column includes the LEDs  17  in the color ranges C, A, C, A, . . . arranged in this sequence. The rest of columns are formed by repeating the above arrangements. Among the first LED boards  20   a  and the second LED boards  20   b  arranged parallel to one another, the adjacent LEDs  17 ,  17  with respect to the row direction (the Y-axis direction) are in the adjacent color ranges (A and B, or A and C). Namely, the LEDs  17  that are two color ranges apart (B and C) are not adjacently arranged. 
     On each first LED board  20   a , the LEDs  17  with the color ranges A and C are alternately arranged. An average color of the LEDs  17  on the first LED board  20   a  is on the border between the color ranges A and C, or in the color range A. On each second LED board  20   b , the LEDs  17  with the color ranges A and B are alternately arranged. An average color of the LEDs  17  on the second LED board  20   b  is on the boarder between the color ranges A and B, or in the color range B. The equivalent color range H is included in the color range A. Two sides of the equivalent color range H are the border between the color range A and the color range C and the boarder between the color range A and the color range B. The average color of the LEDs  17  on the first LED board  20   a  and the average color of the LEDs  17  on the second LED board  20   b  are in the equivalent color range H. 
     As described above, the LEDs  17  in this embodiment are classified into the color ranges A, B, and C according to the colors. The color range A is defined by a square having 0.015-long sides in the CIE 1931 diagram and includes the equivalent color range H. Each of the color ranges C and B is defined by a square having a 0.015-long side and located next to the color A. The LED boards  20  include the first LED boards  20   a  and the second LED boards  20   b . On each first LED board  20   a , the LEDs  17  in the color ranges A and B are mounted. On each second LED board  20   b , the LEDs  17  in the color ranges A and B are mounted. The first LED boards  20   a  and the second LED boards  20   b  are alternately arranged. 
     With this configuration, the average colors do not significantly differ from one another among the alternately arranged first LED boards  20   a  and second LED boards  20   b . Therefore, the uneven color is less likely to occur. 
     In this embodiment, the LEDs  17  in the color ranges A and C are alternately arranged on each first LED board  20   a . The LEDs  17  in the color ranges A and B are alternately arranged on each second LED board  20   b.    
     With this configuration, the adjacent LEDs  17 ,  17  on each of the first LED boards  20   a ,  20   b  are in the adjacent color ranges (A and B, or A and C). Therefore, their colors do not significantly differ from one another and thus the uneven color is further less likely to occur. 
     The second embodiment has been explained above. However, the present invention is not limited to the above embodiment. For example, the following various modifications can be included in the scope of the present invention. In the following modifications, the same components and members as those in the second embodiment will be indicated by the same symbols and will not be explained. 
     &lt;First Modification of the Second Embodiment&gt; 
     As a modification of the arrangement of the LEDs  17 , an arrangement illustrated in  FIG. 13  may be used.  FIG. 13  is a schematic view illustrating a different arrangement of the LEDs in different color ranges on LED boards. 
     In  FIG. 13 , when the LED boards are viewed with respect to the X-axis direction (the row direction, the longitudinal direction of the third LED boards  20   d ), three third LED boards  20   d ,  20   d ,  20   d  are arranged in the first row at the uppermost of the arrangement are electrically and physically connected by the connectors  22 . The LEDs  17  in the colors A, B, A, B, A, and B in this sequence from the left in  FIG. 13  are arranged. The adjacent LEDs  17 ,  17  on the third LED boards  20   d  are in the adjacent color ranges (A and B). In each of the second row, the third row, the fourth row, . . . , three LED boards  20   d  are connected as in the first row. When the LED boards are viewed with respect to the Y-axis direction (the arrangement direction of the third LED boards  20   d ), the LEDs  17  in the color ranges A, A, A, A, . . . are arranged in the first column. The LEDs  17  in the color ranges B, B, B, B, . . . are arranged in the second column. The LEDs  17 ,  17  arranged adjacently with respect to the arrangement direction are in the same color range (A and A, or B and B). The average color on each third LED board  20   d  is on the border between the color ranges A and B, or in the color range A, namely, in the equivalent color range H. 
     With this configuration, the colors of the adjacent LEDs  17 ,  17  do not significantly differ from each other, and thus the uneven color is less likely to occur. Especially in this example, kinds of the prepared LED boards  20  (the third LED boards  20   d ) can be reduced. This contributes to a cost reduction. 
     &lt;Second Modification of the Second Embodiment&gt; 
     As a modification of the arrangement of the LED boards  17 , the arrangement illustrated in  FIG. 14  can be used.  FIG. 14  is a schematic view illustrating a different arrangement of the LEDs in different color ranges. 
     In  FIG. 14 , when the LED boards are viewed with respect to the X-axis direction (the row direction, the longitudinal direction of the LED boards  20   e ,  20   f ), three fourth LED boards  20   e ,  20   e ,  20   e  arranged in the first row at the uppermost of the arrangement are electrically and physically connected by the connectors  22 . The LEDs  17  in the color ranges A, B, A, A, A, B are arranged in this sequence from the left in  FIG. 14  on each fourth LED board  20   e . The adjacent LEDs  17 ,  17  on the fourth LED board  20   e  are in the same color range (A and A), or in the adjacent color ranges (A and B). In the second row, three fifth LED boards  20   f ,  20   f ,  20   f  arranged in the second row are electrically and physically connected by the connectors  22 . On each fifth LED board  20   f , the LEDs  17  in the color ranges C, A, A, A, C, A are arranged in this sequence from the left in  FIG. 14 . The adjacent LEDs  17 ,  17  on the fifth LED board  20   f  are in the same color range (A and A), or in the adjacent color ranges (A and C). The average color on the fourth LED board  20   e  is in the color range A. The average color on the fifth LED board  20   f  is in the color range A. Namely, the average colors on the fourth LED board  20   e  and the fifth LED board  20   f  are in the equivalent color range H. 
     With this configuration, the colors of the LEDs  17 ,  17  arranged adjacently with respect to the column direction and the row direction do not significantly differ from one another. Therefore, uneven color is less likely to occur. This example is especially preferable in the case that the number of LEDs  17  in the color range A, which is the target range, is significantly larger than the number of the LEDs  17  in the color ranges B and C. 
     &lt;Third Modification of the Second Embodiment&gt; 
     As a modification of the arrangement of the LEDs  17 , an arrangement illustrated in  FIG. 15  may be used.  FIG. 15  is a schematic view illustrating a different arrangement of the LEDs in different color ranges on the LED boards. 
     In  FIG. 15 , when the LED boards are viewed with respect to the X-axis direction (the row direction, the longitudinal direction of the LED boards  20   a ,  20   g ), three first LED boards  20   a ,  20   a ,  20   a  arranged in the first row at the uppermost of the arrangement are electrically and physically connected by the connectors  22 . On each first LED board  20   a , the LEDs  17  in the color ranges A, C, A, C, A, C are arranged in this sequence from the left in  FIG. 15 . The adjacent LEDs  17 ,  17  on the first LED board  20   a  are in the adjacent color ranges (A and C). In the second row, three sixth LED boards  20   g ,  20   g ,  20   g  are electrically and physically connected by the connectors  22 . On the sixth LED board  20   g , the LEDs  17  in the color ranges A, A, A, A, A, A are arranged in this sequence from the left in  FIG. 15 . Namely, the adjacent LEDs  17 ,  17  on the sixth LED board  20   g  are in the same color range (A). 
     With this configuration, the LEDs  17  with the adjacent color ranges (A and C) are adjacently arranged and mounted on the first LED board  20   a . Therefore, the colors of the adjacent LEDs  17 ,  17  do not significantly differ from each other and thus uneven color is less likely to occur. Furthermore, the LEDs  17  in the color range A are adjacently arranged on the sixth LED board  20   g  and thus the uneven color is further less likely to occur. This example is especially preferable in the case that the number of the LEDs  17  in the color range A, which is a target range, is significantly larger than the numbers of the LEDs  17  in the color ranges B and C. 
     &lt;Third Embodiment&gt; 
     A third embodiment of the present invention will be explained with reference to  FIGS. 16 and 17 . In this embodiment, an arrangement of the LEDs in different color ranges on each LED board. Other configurations are the same as the first embodiment. The same parts as those in the first embodiment will be indicated by the same symbols and will not be explained. 
       FIG. 16  is a partial magnified view illustrating color ranges of LEDs in a backlight unit, the color ranges being defined in the color space chromaticity diagram created by the International Commission on Illustration (CIE) in 1931.  FIG. 17  is a schematic view illustrating arrangements of the LEDs in different color ranges on the LED boards. 
     The color ranges of the LEDs  17  in this embodiment vary within a range of a use area W defined by solid lines in the CIE 1931 diagram in  FIG. 16 . The use area W is divided into two ranges: a color range A and a color range B. Each range is defined by a square, each side of which is 0.015 coordinate length. Each side of the square area has a length of 0.015 coordinate distance, which means an actual distance between two adjacent corners of the square, that is, the actual distance between ends of one side is 0.015. More specifically, the color range A (a first color range) corresponds to the target color. The range above the color range A is the color range C (a second color range). The LEDs  17  having the colors off the target color are in the color range C. The color ranges A and C are the adjacent color ranges. Each color range A or C, which is a square having 0.015-long sides, is a color range of the LEDs  17  in which colors are not recognized as different colors. The color range A includes the equivalent color range H. A border between the color range A and the color range C is one of the sides of the equivalent color range H. 
     Next, the arrangements of the LEDs  17  on the LED boards  20  according to the color ranges will be explained with reference to  FIG. 17 . 
     In  FIG. 17 , when the LED boards area viewed with respect to the X-axis direction (the row direction, the longitudinal direction of the first LED boards  20   h ,  20   j ), three seventh LED boards  20   h ,  20   h ,  20   h  are electrically and physically connected by the connectors  22  in the first row at the uppermost of the arrangement. The LEDs  17  with the color ranges A, A, A, A, A, A are arranged in this sequence from the left in  FIG. 17  on each seventh LED board (a third light source board)  20   h . Namely, the adjacent LEDs  17 ,  17  on the seventh LED board  20   h  are in the color range A. In the second row, three eighth LED boards (a fourth light source board)  20   j ,  20   j ,  20   j  are electrically and physically connected by the connectors  22 . On the eighth LED board  20   j , the LEDs  17  with the color ranges C, A, C, A, C, A are arranged in this sequence from the left in  FIG. 17 . Namely, the adjacent LEDs  17 ,  17  on the eighth LED board  20   j  are in the adjacent color ranges (A and C). 
     Furthermore, when the arrangement of the LEDs is viewed with respect to the column direction (the Y-axis direction, the short-side direction of the chassis  14 , the arrangement direction of the LED boards  20   h ,  20 ), the seventh LED boards  20   h  and the eighth LED boards  20   g  are alternately arranged. The LEDs  17  in the color ranges A, C, A, C, . . . are arranged in this sequence from the left in  FIG. 17  in the first row. In the second row, the LEDs  17  with the colors A, A, A, A, . . . are arranged in this sequence. The rest of rows are formed by repeating the above arrangements. Among the seventh LED boards  20   h  and the eighth LED boards  20   j  arranged parallel to one another, the adjacent LEDs  17 ,  17  with respect to the column direction (the Y-axis direction) are in the adjacent color ranges (A and C) or in the same color range A. The average color on each seventh LED board  20   h  and the average color on each eighth LED board  20   j  are both in the equivalent color range H. 
     In the configuration of this embodiment, the seventh LED boards  20   h  and the eighth LED boards  20   j  are alternately arranged and the average colors thereof do not significantly differ from one another. Therefore, uneven color is less likely to occur. 
     In this embodiment, the LEDs  17  in the color range A and the LEDs  17  in the color C are alternately arranged on the eighth LED boards  20   j.    
     With this configuration, the adjacent LEDs  17 ,  17  on each eighth LED board  20   j  are in the adjacent color ranges (A and C). Therefore, the colors of the LEDs  17  do not significantly differ from one another and thus the uneven color is further less likely to occur. 
     &lt;Other Embodiments&gt; 
     The embodiments according to the present invention have been described. The present invention is not limited to the embodiments explained in the above description with reference to the drawings. The following embodiments may be included in the technical scope of the present invention, for example. 
     (1) In the second embodiment, three color ranges are used. However, the number of color ranges is not limited to three. Four or more color ranges may be used. 
     (2) In the second embodiment, the LED boards on which the LEDs are arranged in the same layout according to the color ranges with respect to the longitudinal direction of the chassis (the X-axis direction). However, LED boards on which the LEDs are arranged in different layout according to the colors may be connected. 
     (3) In the above embodiments, three LED boards are arranged along the longitudinal direction of the chassis (the X-axis direction) and connected. However, the number of the LED boards may be one or two, or more than three. Furthermore, the number of the LEDs arranged on each LED board is not limited to six. Any number of the LEDs can be arranged on each LED board. 
     (4) In the above embodiments, the white connectors are used. However, the connectors can be made of materials in different colors, for instance, in ivory color, as long as they have high light reflectivities. 
     (5) In the above embodiments, the LEDs are arranged in a grid. However, the LEDs may be arranged in a honeycomb structure. Namely, the LEDs may be arranged at equal intervals or in staggered layout. 
     (6) In the above embodiments, the diffuser lenses are arranged so as to cover the respective LEDs. However, the diffuser lenses may not be required. By closely arranging the LEDs, dot-like lamp images are less likely to appear. 
     (7) In the above embodiments, the white LEDs are used. However, the color of light is not limited to white. LEDs that emit any color of light may be used. 
     (8) In the above embodiments, the LEDs, each prepared by applying a phosphor having a light emitting peak in an yellow range to a blue light emitting chip to emit white light, are used as light sources. However, a light source may be constructed of an ultraviolet light emitting chip having a light emitting peak around a wavelength of 380 nm and a phosphor that absorbs the ultraviolet light and produces fluorescence. With phosphors having light emitting peak in blue, green, and red ranges, respectively, white light can be achieved. The white light produced by the lighting device in the above configuration has smooth spectrum in a wide visible light range and thus has high color rendering properties. Color variation may be produced due to variations in distributed amount of the phosphors. However, the colors can be evened with the lighting device in the above configuration. Namely, the lighting device having high color rendering properties and fewer tendencies to produce color variations can be provided. 
     (9) In the above embodiments, the LEDs are used as point light sources. However, other types of light sources can be used. 
     (10) In the above embodiments, the optical sheet set includes the diffuser plate, the diffuser sheet, the lens sheet, and the reflection-type polarizing sheet. However, the optical may include two diffuser plates that are layered.