Patent Publication Number: US-11048121-B2

Title: Lighting device and display device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. Provisional Patent Application No. 62/814,48 flied on Mar. 6, 2019. The entire contents of the priority application are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present technology relates to a lighting device and a display device. 
     BACKGROUND ART 
     A backlight unit mounted in a display device including a display panel that does not emit light and supplying light to the display panel has been known as one example of the lighting units. For example, Japanese Patent No. 5026620 discloses a planar light source that can be used in such a backlight unit. The planar light source includes: a plurality of light emitting elements that emit first colored light (primary light); a first reflecting member disposed behind the light emitting elements and reflecting the light; a diffusing member disposed in front of the light emitting elements and diffusing the light; a second reflecting member disposed in front of the diffusing member allowing a part of the light to reflect and pass therethrough; and a phosphor layer disposed between the first reflecting member and the second reflecting member and allowing a part of the first colored light to pass therethrough and converting another part of the first colored light into second colored light (secondary light) (converting a wavelength). The first colored light that has passed through the phosphor layer and the second colored light that has passed through the phosphor layer with wavelength conversion are mixed to emit white light. In such a configuration, a part of the light rays that have emitted by the light emitting elements is reflected by the first reflecting member and the second reflecting member multiple times repeatedly (so-called multiple reflection) and thereafter the light exits the planar light source. A part of the first colored light rays included in the light rays that have reflected multiple times is converted to the second colored light (so-called multiple wavelength conversion) every time passing through the phosphor layer. Therefore, the wavelength conversion amount of light rays converted from the first colored light to the second colored light in the exit light rays changes according to the number of passing times of the light passing through the phosphor layer or the passing distance of the phosphor layer through which the light passes. The light that has reflected multiple times normally travels farther away from the optical axis of the light emitting element. Therefore, the chromaticity of the planar light source becomes closer to the second colored light as the position is farther away from the optical axis of the light emitting element and, for example, color unevenness in a concentric ring shape may be caused. In the planar light source, the phosphor layer is configured in such a manner that the conversion rate of the colored light per a unit area is decreased as the position is farther away from the optical axis of each light emitting element. Accordingly, the wavelength conversion amount of the light rays that have reflected multiple times and exit the portion away from the optical axis is less likely to increase and the wavelength conversion amount of the light rays that do not reflect and directly exit the portion near the optical axis can be maintained. As a result, the change in the chromaticity caused by the multiple wavelength conversion is cancelled and the unevenness in the whole planar light source is less likely to be caused. 
     Furthermore, for example, Japanese Patent No. 6021967 discloses light source device that emits light through a light emitting surface and the light source device includes: a plurality of light sources provided respectively in a plurality of first division regions that configure region of the light emitting surface; a first suppression member for suppressing the light ted by the light source disposed in each of the first division regions from spreading into a direction parallel to the light emitting surface; a conversion member provided closer to the light emitting surface than the plurality of light sources and the first suppression member and for converting the color of the light emitted by the plurality of light sources and outputting the light of the converted color; a second suppression member provided closer to the light emitting surface than the conversion member and for suppressing the light output from the conversion member from spreading into a direction parallel to the light emitting surface for each of second division regions, each second division region including at least one first region; and a diffusion member provided closer to the light emitting surface than the conversion member while having a predetermined distance from the conversion member and for diffusing the light emitted from the conversion member. In the light source device, the light rays emitted by the light sources is suppressed from spreading and the light emitting region restricted within each division region where each light source is disposed to reduce brightness unevenness and color unevenness. 
     However, in the configuration described in Japanese Patent No. 5026620, the amount of light rays that are reflected multiple times through the phosphor layer and the number of passing times which the light passes through the phosphor layer are almost same as those in the prior art configuration. Therefore, the color unevenness is not sufficiently suppressed and can be further suppressed. In the configuration described in Japanese Patent No. 6021967, the directivity of the light is strong in each division region. Therefore, it is difficult to design the device in such a manner that borders between the division regions are not recognized and a thick diffuser member needs to used to obtain uniform planar light. Therefore, development of a lighting unit that can effectively suppress color unevenness with a simple structure has been demanded. 
     SUMMARY 
     The present technology was made in view of the above circumstances. An object of the technology described herein is to effectively suppress color unevenness in a lighting device and a display device. 
     A lighting device according to the technology described herein includes a light source emitting primary light rays that are included in a certain wavelength region, a wavelength conversion member disposed in a light exit direction of the primary light rays with respect to the light source, and a reflection layer disposed on an opposite side from the light source with respect to the wavelength conversion member. The wavelength conversion member has a function of converting some of the primary light rays that have passed through wavelength conversion member into secondary light ray that are included in another wavelength region that is different from the certain wavelength region. The reflection layer has a function of reflecting light rays that reach a first surface on an opposite side from the light source, The reflection layer includes light transmission section in a portion thereof, and light rays that reach a second surface on a light source side pass through the light transmission section to the first surface at a higher ratio than other section of the reflection layer. 
     A display device according to the technology described herein includes a display panel including an image display surface displaying an image and the lighting device. 
     According to the present technology, a lighting device and a display device in which color unevenness is effectively suppressed are obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view illustrating a general configuration of a liquid crystal display device according to a first embodiment. 
         FIG. 2  is a cross-sectional view illustrating the general configuration of the liquid crystal display device. 
         FIG. 3  is a schematic view illustrating a backlight unit with travelling images of light rays. 
         FIG. 4A  is a plan view schematically illustrating a configuration of a light source unit model. 
         FIG. 4B  is a cross-sectional view schematically illustrating a configuration of the light source unit model. 
         FIG. 5  is graphs representing relations between an angle between an optical axis and a line extending from a LED to an edge of a light transmission section (θ) and use efficiency of light emitted by the LED represented by (Φf /4πI 0 ) with various arrangement intervals of the LEDs. 
         FIG. 6  is graphs representing relations between the angle between the optical axis and the line extending from the LED to the edge of the light transmission section (θ) and the use efficiency of light emitted by the LED represented by (Φf /4πI 0 ) with various thicknesses of a wavelength conversion sheet. 
         FIG. 7A  is a plan view schematically illustrating an layout of a reflection sheet and LED packages in a liquid crystal display device according to a second embodiment. 
         FIG. 7B  is a cross-sectional view schematically illustrating the layout of the reflection sheet and the LED packages. 
         FIG. 8  is a cross-sectional view illustrating a general configuration of a liquid crystal display device according to a third embodiment. 
         FIG. 9  is an exploded perspective view illustrating a general configuration of an optical member disposed on an edge section of the backlight unit. 
         FIG. 10  is a cross-sectional view illustrating a general configuration of a liquid crystal display device  4  according to other configuration. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     A first embodiment will be described with reference to  FIGS. 1 to 6 . 
     In the section, a backlight unit  20  (one example of lighting unit) that is included in a liquid crystal display device  1  (one example of a display device) and mounted on a liquid crystal panel  10  (one example of a display panel) will be described as an example. X-axis, Y-axis and Z-axis may be present in the drawings and each of the axial directions represents a direction represented in each drawing. An upper side in  FIG. 1  corresponds to a front side (a lower side corresponds to a back side). One of the same components is provided with a symbol and other ones may not be provided with the symbol. 
     The liquid crystal display device  1  according to the present embodiment is particularly suitable for display devices that are classified into a middle size to a large (extra-large) size and that have been demanded to increase image quality such as a note book personal computer (including a tablet-type note personal computer) and a television receiver. However, the present technology is not limited to such display devices and can be applied to display devices that are classified into a small-size display device or a medium-size display device having a screen size of several inches to some dozen centimeters. Recently, the image display devices have been demanded to improve image quality and the High Dynamic Range (HDR) technology has been focused on. To achieve the HDR in the liquid crystal display device, the local-dimming control of locally controlling the brightness level of the backlight unit is necessary. The present technology is not limited to but may be particularly and preferably applied to the liquid crystal display device  1  that performs the local-dimming technology to locally adjust the brightness level of the backlight device  20 . 
     As illustrated in  FIG. 1 , the liquid crystal display device  1  includes the liquid crystal panel  10  displaying an image and a backlight unit  20  that is disposed on a back side with respect to the liquid crystal panel  10  and supplies light to the liquid crystal panel  10  for displaying. The liquid crystal panel  10  and the backlight unit  20  are integrally held by a bezel  30  of a frame shape. The liquid crystal display device  1  has a front side plate surface as an image display surface  10 A displaying an image (see  FIG. 2  and  FIG. 3 ) and light exits the backlight unit  20  toward the front side where the liquid crystal panel  10  is arranged. 
     The liquid crystal panel  10  is not limited to particular ones and a liquid crystal panel having a known configuration can be used. Details of the liquid crystal panel  10  are not illustrated and described. For example, the liquid crystal panel  10  includes a pair of rectangular glass substrates that are bonded to each other while having a certain gap therebetween and a liquid crystal layer that is disposed between the substrates. The pair of glass substrates include an array substrate (an active matrix substrate) and a CF substrate (an opposing substrate). Switching components (for example, TFTs), pixel electrodes that are connected to the switching components, and an alignment film are disposed on the array substrate. The switching components are connected to gate lines and source lines that are perpendicular to each other. Color filters including color portions of red (R), green (G), and blue (B) that are arranged in certain arrangement, an opposing electrode, and an alignment film are disposed on the CF substrate. Polarizing plates are disposed on outer surfaces of the glass substrates, respectively. 
     As illustrated in  FIG. 1 , the backlight unit  20  includes LEDs  51  (light emitting diodes, one example of light sources), a LED board  22  (one example of a light source board), an optical member  40  including a multiple sheets or a plate member, and a frame  23 . The optical member  40  in the present embodiment includes a phosphor sheet  41  (one example of a wavelength conversion sheet) and a reflection sheet  42  (one example of a reflection layer). The optical member  40  has a rectangular shape that is similar to a plan view shape of the liquid crystal panel  10 . As illustrated in  FIG. 2 , the optical member  40  is disposed to cover an opening of the frame  23  and disposed on a lower surface of the liquid crystal panel  10 . The LEDs  51  are dispersedly arranged over an entire area of a plate surface of the LED board  22  that is disposed opposite the back surface of the optical member  40 . As illustrated in  FIGS. 2 and 3 , in the backlight unit  20  according to the present embodiment, the LEDs  51  are arranged directly below the image display surface  10 A of the liquid crystal panel  10  of the liquid crystal display device  1  and light emitting surfaces  51 A (see  FIG. 3 ) are opposite the liquid crystal panel  10 . Namely, the backlight unit  20  is a so-called direct-type lighting unit. The bezel  30  is not illustrated in  FIG. 2 . 
     Components of the backlight unit  20  will be described in sequence. 
     The LEDs  51  are light sources that emit primary light included in a certain wavelength region and are arranged on a surface of the LED board  22  in such a manner that each optical axis matches a normal direction of the image display surface of the liquid crystal panel  10  (a normal direction of plate surface of the optical member  40 ). Here, “the optical axis” is an axis that matches a traveling direction of light rays having highest light emission intensity among the light rays emitted by the LEDs  51 . As illustrated in  FIGS. 2 and 3 , in this embodiment, the light emitting surfaces  51 A faces an opposite side from the LED board and so-called top-surface light emission type LEDs are used as the LEDs  51 . Namely, in the backlight unit  20  according to the present embodiment, a front direction is an exit direction L 1  of the primary light. 
     In the present embodiment, the LED  51  includes a unit member of a LED component chip that is a light emitting source. For example, the LED  51  is a so-called mini LED and has a cube shape having each side of about 0.1 mm to 0.3 mm. The present technology can be preferably applied to the lighting unit including the mind LEDs as the light source; however, the light sources are not limited to the ones having such a size. For example, the present technology may be applied to a lighting unit including normal LED chips of a cube shape having one side of several mm or more. In this embodiment, the LED  51  includes a blue LED chip (a blue light emitting component), a transparent sealant that seals the blue LED component, and a box casing in which the blue LED component and the sealant are arranged. The LED  51  is configured to emit blue light. The blue LED component is, for example, a semiconductor made of InGaN and is configured to emit light (blue light) in the wavelength region of blue light (about 420 nm to about 500 nm) as the primary light in response to the application of the forward voltage. 
     In this embodiment, the LED board  22  includes a base member and wiring. The base member is a rectangular plate and made of metal such as aluminum material. The wiring is formed on the surface of the base member via an insulation layer and is made of a metal film such as a copper foil. The base member of the LED board  22  may be made of insulating material such as glass epoxy and ceramics. The LED board  22  has a plate surface facing the front side (the optical member  40  side, the light exit direction) as a mounting surface  22 A and the LEDs  51  are surface-mounted on the mounting surface  22 A. The LEDs  51  are arranged in rows and columns (in a matrix, in a grid) within a surface area of the mounting surface  22 A of the LED board  22  and are electrically connected to each other by the wiring that is arranged within the surface area of the mounting surface  22 A. The intervals between the LEDs  51  are substantially same and the LEDs  51  are arranged at substantially equal intervals. The optical member  40 , which covers the opening of the frame  23 , is disposed opposite all of the LEDs  51  that are arranged as described above. Connectors to which the cables are connected are disposed on the LED board  22  and the LED board  22  is connected to an external power source via the cables and the driving power is supplied to the LED board  22 . The number of LEDs  51  and the wiring formed on the LED board  22  are not particularly limited but may be preferably configured to perform the local dimming control. Namely, the LED board  22  is divided into multiple areas each including at least one light source, and an LED driving board (a light source driving board) is controlled to apply a specific current flow to each LED for every area and to locally adjust the brightness level. 
     A low reflecting layer is formed on an outermost surface and the mounting surface  22 A of the LED board  22  in this embodiment (refer  FIGS. 2 and 3 ) is a low reflecting surface. The low reflecting layer is less likely to reflect light. The mounting surface  22 A is subjected to an antiglare (non-glossy) treatment to reduce the amount of light rays that are to be reflected compared to a mounting surface of a general light source board to obtain the low reflecting surface. For example, the mounting surface  22 A is coated with a low reflecting resin layer including a light absorber or the outermost surface is subjected to the roughing treatment. The mounting surface  22 A has the low reflecting surface over an entire surface thereof; however, the mounting surface  22 A preferably has the low reflecting surface at least in an area except for the sections where the LEDs  51  are mounted. The mounting surface  22 A is preferably configured such that 20% or less of the light rays that are supplied to the mounting surface  22 A is to be reflected by the mounting surface  22 A, more preferably 10% or less, and particularly preferably 5% or less. 
     The frame  23  illustrated in  FIGS. 1 and 2  may be an injection molded object molded with resin, for example, a molded object molded with white polycarbonate resin. As illustrated in  FIG. 1 , the frame  23  in this embodiment has a frame shape that follows outer edges or the LED board  22  and the optical member  40 . As illustrated in  FIG. 2 , the outer edge portion of the optical member  40  is held by the frame  23  and the outer edge portion of the LED board  22  is fixed to a back surface of the frame  23 . This keeps the optical member  40  and the light emitting surfaces  51 A of the LEDs  51  mounted on the LED board  22  in the predefined relative arrangement. 
     As illustrated in  FIGS. 2 and 3 , the optical member  40  is arranged on a front side of the LEDs  51  that are mounted on the LED board  22  while the light emitting surfaces  51 A facing the front side, that is, on the exit direction L 1  side of the primary light. The optical member  40  is arranged between the liquid crystal panel  10  and the LEDs  51  and adds predetermined optical effects to the light emitted by the LEDs  51 . The optical member  40  includes multiple sheets or plates. In this embodiment, the optical member  40  includes the phosphor sheet  41 , the reflection sheet  42 , a diffuser sheet  43  (a light transmissive sheet), and a brightness enhancement sheet  44 . The diffuser sheet  43  and the brightness enhancement sheet  44  may not be included and the optical member  40  is not limited to the one including such sheets. The optical member  40  may include other kinds of optical sheets such as a micro lens sheet and a polarizing reflection sheet instead of or in addition to the above sheets  43 ,  44 . The optical member  40  may include multiple brightness enhancement sheets  44  or include the diffuser sheet  43  between the brightness enhancement sheets  44 . To obtain different effects, the optical member  40  may further include an optical sheet (a dichroic filter) that provides effects of a Band-Pass filter. As illustrated in  FIGS. 1 to 3 , the optical member  40  in this embodiment includes the phosphor sheet  41 , the reflection sheet  42 , the diffuser sheet  43 , and the brightness enhancement sheet  44  that are disposed on top of each other in this sequence from the back surface side to the front side, that is, from the LED  51  side to the exit direction L 1  of the primary light (toward the liquid crystal panel  10 ). 
     Each of the components included in the optical member  40  will be explained. The brightness enhancement sheet  44  that is disposed on the uppermost side (the liquid crystal panel  10  side) of the optical member  40  has a function of enhancing brightness of the backlight unit  20 . For example, the brightness enhancement sheet  44  is configured to include unit prisms that have an apex angle of 90 degrees and extend along one side and are arranged along another side that is perpendicular to the side without having any space therebetween. The brightness enhancement sheet  44  having such a configuration has an action of collecting light (an anisotropic light collecting action) selectively with respect to the direction along the other side (the arrangement direction of the unit prisms, the direction perpendicular to the extending direction of the unit prism). Brightness Enhancement film (BEF) (registered trademark) or Dual Brightness Enhancement film (DBEF) (registered trademark) produced by 3M may be used as the brightness enhancement sheet  44 . In this embodiment, the front side plate surface of the brightness enhancement sheet  44  is a light exit surface  20 A of the backlight unit  20  (refer  FIGS. 2 and 3 ) and the light exits through the light exit surface  20 A toward the liquid crystal panel  10 . 
     The diffuser sheet  43  that is disposed on the back side of the brightness enhancement sheet  44  is one kind of the light transmissive sheets that transmit light. The light enters the diffuser sheet  43  through the back surface thereof (on the LED  51  side) and is diffused therein and exits the diffuser sheet  43  toward the front side (the liquid crystal panel  10  side). The diffuser sheet  43  has a function of uniformizing the amount of light rays emitted by the light source and outputting the light. The diffuser sheet  43  may include a base member made of substantially transparent resin and having a predefined thickness and a large number of diffuser particles that are diffused in the base member. The transparent resin base member is not limited to particular one but may be made of (meth)acrylic resin, polycarbonate resin, polystyrene resin, and polyvinyl chloride resin. Particularly, a resin sheet that is made of acrylic resin or polycarbonate resin and is good in transparency and shock resistance is preferably used. A relatively thick resin plate may be used as the base member. For example, Sumipex Opal plate (registered trademark) produced by Sumitomo Chemical Company, Limited may be used as the diffuser sheet  43 . 
     The phosphor sheet  41  is disposed on the lowest side (on the back surface side, the LED  51  side) of the optical member  40  and adjacent to the LEDs  51 . Some of the light rays emitted by the LEDs  51  pass through the phosphor sheet  41  in the thickness direction thereof and some of the light rays emitted by the LEDs  51  are absorbed by the phosphor sheet  41  and converted into secondary light included in another wavelength region and the converted light exits the phosphor sheet  41 . The phosphor sheet  41  is preferably disposed so as to have substantially no space with respect to the light emitting surfaces  51 A of the LEDs  51 . Hereinafter, the phosphor sheet  41  has a back surface (on the LED  51  side) through which the primary light emitted by the LEDs  51  enters and a front surface (on the liquid crystal panel  10  side) through which the secondary light having a converted wavelength exits (refer  FIGS. 2 and 3 ). The back surface is referred to as a primary light entering surface  41 A and the front surface is referred to as a secondary light exit surface  41 B. The configuration and the shape of the phosphor sheet  41  are not particularly limited; however, the phosphor sheet may include, for example, a wavelength conversion layer, a pair of support layers sandwiching the wavelength conversion layer, and a pair of barrier layers that are disposed on an outer side of the respective support layers and sandwich the wavelength conversion layer and the pair of support layers. The thickness of the phosphor sheet (the wavelength conversion sheet) will be described later. 
     The wavelength conversion layer of the phosphor sheet  41  includes acrylic resin as binder resin and quantum dot phosphors (one example of the phosphor) that are dispersed in the acrylic resin. The acrylic resin is transparent and has light transmissivity and adhering properties with respect to the support layer, which will be described later. 
     In this embodiment, the wavelength conversion layer includes green quantum dot phosphors and red quantum dot phosphors as the quantum dot phosphors. The green quantum dot phosphors are excited by absorbing the light emitted by the LEDs  51  (blue light, the primary light, excitation light) and emits green light (the wavelength range from about 500 nm to about 570 nm). The red quantum dot phosphors are excited by absorbing the light emitted by the LEDs  51  (blue light, the first light, excitation light) and emits red light (the wavelength range from about 600 nm to about 780 nm). Materials used for the quantum dot phosphors include a material prepared by combining elements that could be divalent cations such as Zn, Cd, and Pb and elements that could be divalent anions such as O, S, Se, and Te (e.g., cadmium selenide (CdCe), zinc sulfide (ZnS), a material prepared by combining elements that could be trivalent cations such as Ga and In and elements that could be trivalent anions such as P, As, and Sb (e.g., indium phosphide (InP), gallium arsenide (GaAs), and chalcopyrite-type compounds (CuInSe2). 
     In the present embodiment, the quantum dot phosphors (the green quantum dot phosphors and the red quantum dot phosphors) include color conversion components and the ratio of the color conversion components is adjusted such that white light is obtained by mixing the secondary light rays having wavelengths (colors) converted by the quantum dot phosphors. The quantum dot phosphors are evenly dispersed in the acrylic resin included in the wavelength conversion layer. The phosphors included in the phosphor sheet may be any phosphors that can covert the wavelength of the primary light in the certain wavelength region into the secondary light in a different wavelength region and are not limited to the quantum dot phosphors. The wavelength conversion layer may include other components such as a scattering agent. 
     The support layer of the phosphor sheet  41  is a sheet (a film) made of polyester resin such as polyethylene terephthalate (PET), for example. The quantum dot phosphors are phosphors that have high quantum efficiency. The quantum dot phosphors include semiconductor nanocrystals (e.g., diameters in a range from 2 nm to 10 nm) that tightly confine electrons, electron holes, or excitons with respect to all direction of a three dimensional space to have discrete energy levels. A peak wavelength of emitting light (a color of emitting light) is freely selectable by changing the dot size. 
     In the present embodiment, the barrier layer of the phosphor sheet  41  is a metal oxide film made of aluminum or silicon oxide. The barrier layer protects the quantum dot phosphors included in the wavelength conversion layer from coming into contact with moisture (humidity) or oxygen. The barrier layer is formed on the support layer with the vacuum deposition method, for example. 
     In the present embodiment, the reflection sheet  42  is disposed on top of the phosphor sheet  41  on a front side thereof (on an opposite side from the LEDs  51  with respect to the phosphor sheet  41 ). The reflection sheet  42  is preferably disposed to be in contact with the secondary light exit surface  41 B of the phosphor sheet  41  and cover the secondary light exit surface  41 B. The reflection sheet  42  is preferably disposed to have substantially no space with respect to the phosphor sheet  41 . The reflection sheet  42  has a first surface  42 A on the front side (on an opposite side from the phosphor sheet  41 , opposite the diffuser sheet  43 ) and has a function of reflecting light that has reached the first surface  42 A (refer  FIGS. 2 and 3 ). The material of the reflection sheet  42  is not limited as long as the reflection sheet  42  has such a function. A known light reflecting member of a sheet or a plate such as a metal thin film sheet, an inductor multilayer film sheet, or a sheet having good light reflectivity and made of white foamed polyethylene terephthalate (one example of a white plastic sheet) may be used as the reflection sheet  42 . 
     The reflection sheet  42  includes a light transmission section in a portion thereof. The light that has reached the second surface  42 B, which is a back surface (on the phosphor sheet  41  side or the LED  51  side), of the reflection sheet  42  passes through the light transmission section at a higher ratio than other sections toward the first surface  42 A. In this embodiment, the reflection sheet  42  includes through holes  42 H (one example of the light transmission section) therein as the light transmission section. The reflection sheet  42  includes a non-transmission section  42 N where no through holes  425  are formed. Light does not substantially pass through and is reflected by the non-transmission section  42 N. The non-transmission section  42 N is preferably configured to reflect 90% or more of the light rays that have reached the first surface  42 A, and more preferably 95% or more, and much more preferably 98% or more. The light transmission section such as the through hole  42 H is preferably configured to transmit 90% or more of the light rays that have reached the second surface  42 B, and more preferably 95% or more, and much more preferably 98% or more. 
     In this embodiment, the through hole  42 H is formed to overlap the light emitting surface  51 A of the LED  51  with a view in a normal line of the first surface  42 A (the front-back direction). The LEDs  51  in this embodiment are arranged in rows and columns on the mounting surface  22 A of the LED board  22 , as described earlier. The through holes  42 H are formed in rows and columns corresponding to the respective LEDs  51 . The LEDs  51  in this embodiment are arranged in such a manner that the optical axis of each LED  51  matches the normal direction of the plate surface of the optical member  40  including the reflection sheet  42 , as described earlier. Therefore, an incident angle of the light rays that have been emitted by the LED  51  and reached the second surface  42 B of the reflection sheet  42  is smallest in the section that overlaps the light emitting surface  51 A of the LED  51  with a view in the normal direction of the first surface  42 A (the front-back direction). The through hole  42 H is formed in an area including the above section. To increase evenness of the light rays exiting the backlight unit  20 , the through hole  42 H may be formed in other sections in addition to the section that overlaps the light emitting surface  51 A of the LED  51  with a view in the normal direction of the first surface  42 A (the front-back direction). 
     The through holes  42 H each of which is a single unit and has a predefined shape are included repeatedly in a planar form. A unit shape of the through hole  42 H may be any shape defined by a curved line such as a circle, an oval, and a cloud shape, or a polygon defined by straight lines such a triangle and a square, or combination thereof. The unit shapes of all the through holes  42 H may be same but may be different in shape and size according to the position on the reflection sheet  42  (so as to be in gradation, for example). The through holes  42 H may be formed in a continuous form, for example, in a mesh connecting the sections above the respective LEDs  51 . The shape of the through hole  42 H depends on an outline of the LED  51  but is not necessarily the same as that of the LED  51 . For example, the present embodiment includes mini LEDs that have a very small outline as the LEDs  51 . As illustrated in  FIG. 1 , each LED  51  has a cubic shape and the light emitting surface  51 A has a square plan view shape and the through holes  42 H that are formed directly above the respective LEDs  51  have a circular shape and a same size as that of the LED such that the whole light emitting surface  51 A overlaps the through hole  42 H in a plan view. 
     The method of forming the through holes  42 H is not particularly limited but may be any method. For example, after the reflection sheet without having holes is formed, the portions where the through holes are to be formed are removed with punching or photo-process. The reflection sheet  42  including the through holes  42 H may be formed with using a screen. 
     Travelling of the light in the backlight unit  20  having the above configuration will be described. As illustrated in  FIG. 3 , the primary blue light that is emitted by the LED  51  through a top surface thereof toward the front side (in the exit direction L 1  of the primary light) enters the phosphor sheet  41  through the primary light entering surface  41 A. While the light passes through the phosphor sheet  41 , some of the light rays are converted to green secondary light and red secondary light through the wavelength conversion by the quantum dot phosphors and another of the primary light rays that are not converted through the wavelength conversion pass through the phosphor sheet  41  as the blue light. As a result, the blue light, the green light, and the red light are mixed and substantially white secondary light is obtained. The white secondary light exits the phosphor sheet  41  through the front side secondary light exit surface  41 B. 
     The secondary light that has exited the phosphor sheet  41  through the secondary light exit surface  41 B reaches the second surface  42 B, which is a back surface, of the reflection sheet  42  that is disposed on top of the phosphor sheet  41 . Some of the light rays that have reached the section of the second surface  42 B having the through hole  42 H only pass through the through hole  42 H to the first surface  42 A side at a high rate. The light rays that have exited the reflection sheet  42  to the first surface  42 A side reach the diffuser sheet  43  disposed on the front side. The light rays pass through the diffuser sheet  43  while being diffused and reach the brightness enhancement sheet  44  disposed on the front side. The light rays further pass through the brightness enhancement sheet  44  and exit through the light exit surface  20 A toward the liquid crystal panel  10 . 
     In such a process, for example, some of the light rays may be reflected by an interface between the diffuser sheet  43  and the brightness enhancement sheet  44 . The reflected light rays reach the first surface  42 A and try to enter the reflection sheet  42  but are reflected by the non-transmission section  42 N of the first surface  42 A. The reflected light rays do not pass through the phosphor sheet  41  that is disposed on the back surface side of the reflection sheet  42  and change the traveling direction thereof to travel toward the front side (the diffuser sheet  43 ) again. Then, the light rays pass through the diffuser sheet  43  and the brightness enhancement sheet  44  sequentially and exit through the light exit surface  20 A toward the liquid crystal panel  10 . During the procedure, if the light rays are reflected by the interface between the diffuser sheet  43  and the brightness enhancement sheet  44  again, most of the reflected light rays are reflected by the non-transmission section  42 N of the first surface  42 A of the reflection sheet  42  and such travelling procedures are performed repeatedly. Thus, most of the reflected light rays exit through the light exit surface  20 A without passing through the phosphor sheet  41 . Therefore, the number of times most of the secondary light rays that have exited the reflection sheet  42  to the first surface  42 A side once pass through the phosphor sheet  41  before exiting through the light exit surface  20 A is much smaller than the number of times obtained in a prior art backlight unit without including the reflection sheet  42 . As a result, color unevenness caused by the multi-wavelength conversion is suppressed in the light rays exiting through the light exit surface  20 A. 
     Influences of the layout of the through holes  42 H in the reflection sheet  42  acting on the brightness (light use efficiency) of the backlight unit  20  will be explained with reference to a virtual light source unit model  100  having a similar basic configuration.  FIGS. 4A and 4B  schematically illustrate the configuration of the light source unit model  100 . 
     As illustrated in  FIGS. 4A and 4B , the light source unit model  100  includes a light source board  122 , a top-surface light-emitting type light source  151  that is mounted on the light source board  122  and emits the primary light, a wavelength conversion sheet  141  disposed to be in contact with a light emitting surface  151 A of the light source  151  without having a space therebetween, and a reflection layer  142  that is disposed to be in contact with the wavelength conversion sheet  141  without having a space therebetween. The mounting surface of the light source board  122 , a primary light entering surface  141 A and a secondary light exit surface  141 B of the wavelength conversion sheet  141 , a second surface and a first surface  142 A of the reflection layer  142  are parallel to each other and the normal directions of the surfaces match each other. The primary light entering surface  141 A is opposite the light source  151  and the secondary light exit surface  141 B is on an opposite side from the light source  151 . The second surface is opposite the wavelength conversion sheet  141  and the first surface  142 A an opposite side from the wavelength conversion sheet  141 . A liquid crystal panel is disposed on the first surface  142 A side of the reflection layer  142  via an optical member, and light exits the light source unit model  100  toward the liquid crystal panel. 
     In the light source unit model  100 , it is supposed that the light source  151  mounted on the light source board  122  is a minute surface light source and has a uniform distribution (an index indicating direction of the light from the light source and intensity (luminous intensity) of the light) in which the light spreads uniformly, and the uniform distribution is a so-called Lambertian distribution. As illustrated in  FIG. 4B , the wavelength conversion sheet  141  has a thickness d and the light sources  151  are arranged at an arrangement interval P, and the thickness of the reflection layer  142  has no influence. The reflection layer  142  includes light transmission sections  142 H. The light transmission section  142 H is formed in a section of the first surface  142 A that is defined as follows. A normal line of the first surface  142 A that passes a center of the light source  151  (an optical axis of the light source  151  with respect to the reflection layer  142 ) is defined as an axis X 1  and an angle between the axis X 1  and a line extending from the light source  151  to the first surface  142 A is θ or smaller. Namely, some of the secondary light rays that are emitted by the light source  151  and converted through the wavelength conversion sheet  141  and exit the sheet at the angle θ or smaller with respect to the axis X 1  are supplied to the light transmission section  142 H. Hereinafter, a radius of the light transmission section  142 H may be represented by r (r=d×tan θ). It is supposed that 100% of the light rays that have reached the non-transmission section  142 N except for the light transmission sections  142 H are reflected by the first surface  142 A and the second surface  142 B of the reflection layer  142  and 100% of the light rays that have reached the light transmission sections  142 H pass therethrough. 
     Based on the above condition, the illuminance of the primary light emitted by the light source  151  on the axis X 1  (namely, θ=0°) is represented by E 0 , and the illuminance of the light on a circumference of a circle that is obtained by forming an angle θ with respect to the axis X 1  is represented by E θ , and the following formula (1) is obtained based on the cosine fourth law. It is obvious from the formula (1) that the illuminance of the primary light that is emitted by the light source  151  and supplied to the wavelength conversion sheet  141  is a half or more at the position of θ=30° and a ¼ at the position of θ=45° with reference to the position of θ=0°.
 
 E   θ   =E   0 ×cos 4  δ  (1)
 
     On the other hand, the reflection efficiency on the first surface  142 A of the reflection layer  142  depends on an area ratio of the light transmission sections  142 H to the non-transmission section  142 N of the reflection layer  142 . An area A of the light transmission section  142 H within a unit area is obtained by the following formula (2). 
     
       
         
           
             
               
                 
                   
                     
                       
                         A 
                         = 
                         
                           Π 
                           × 
                           
                             r 
                             2 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           Π 
                           × 
                           
                             
                               ( 
                               
                                 d 
                                 × 
                                 tan 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 θ 
                               
                               ) 
                             
                             2 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           Π 
                           × 
                           
                             d 
                             2 
                           
                           × 
                           
                             tan 
                             2 
                           
                           ⁢ 
                           θ 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Based on the formula (2), when the angle θ becomes greater, an increase dA/dθ of the area A of the light transmission section  142 H is obtained by the following formula (3). In the formula (3), the value of (sin θ/cos 3  θ) abruptly increases as the angle θ increases within the range of 0°≤θ≤90° ((sin θ/cos 3  θ)≈2, when θ=45°, and (sin θ/cos 3  θ)≈7, when θ=60°). Therefore, it is obvious that the reflection area (the area of the non-transmission section  142 N) on the first surface  142 A decreases as the angle θ increases, and among the light rays that have reached the first surface  142 A from an outside (on an opposite side from the light sources  151 ) of the reflection layer  142 , the ratio of the light rays that are reflected by the first surface  142 A and exit the light source unit model  100  to be used is decreased.
 
 dA (θ)/ dθ= 2π× d   2 ×(sin θ/cos 3  θ)  (3)
 
     When the luminous intensity of light that is emitted by the light source  151  evenly in each direction is represented by I 0 , the illuminance E 0  at the position of θ=0° is obtained by the following formula (4).
 
 E   0   =I   0   /d   2   (4)
 
     Based on the above formulae (1) and (4), the following formula (5) is obtained.
 
 E   θ   =I   0 ×cos 4    θ/d   2   (5)
 
     To simplify the calculation, the diffusing properties and the wavelength conversion efficiency of the wavelength conversion sheet  141  are not taken into consideration and it is supposed that the light transmittance of the wavelength conversion sheet  141  is 100%. The luminous flux Φθ that passes through the light transmission section  142 H of the reflection layer  142  is obtained by integrating the illuminance by the area of the light transmission section  142 H as indicated by Formula. 1 and the following formula (6) is obtained. 
     
       
         
           
             [ 
             
               Formula 
               . 
               
                   
               
               ⁢ 
               1 
             
             ] 
           
         
       
       
         
           
             
               
                 
                   
                     
                       
                         
                           Φθ 
                           = 
                           
                             
                               ∫ 
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                             ⁢ 
                             
                               
                                 { 
                                 
                                   
                                     E 
                                     0 
                                   
                                   × 
                                   
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                                   ⁢ 
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                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
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                                   ⁢ 
                                   
                                     / 
                                   
                                   ⁢ 
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                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
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                                 } 
                               
                               ⁢ 
                               d 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               θ 
                             
                           
                         
                         ⁢ 
                         
                             
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           2 
                           × 
                           π 
                           × 
                           
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                             0 
                           
                           × 
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                           × 
                           
                             
                               ∫ 
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                             ⁢ 
                             
                               
                                 { 
                                 
                                   
                                     cos 
                                     3 
                                   
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                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
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                                 } 
                               
                               ⁢ 
                               d 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               θ 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             ( 
                             
                               π 
                               ⁢ 
                               
                                 / 
                               
                               ⁢ 
                               2 
                             
                             ) 
                           
                           × 
                           
                             E 
                             0 
                           
                           × 
                           d 
                           × 
                           
                             ( 
                             
                               1 
                               - 
                               
                                 
                                   cos 
                                   3 
                                 
                                 ⁢ 
                                 θ 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             ( 
                             
                               π 
                               ⁢ 
                               
                                 / 
                               
                               ⁢ 
                               2 
                             
                             ) 
                           
                           × 
                           
                             I 
                             0 
                           
                           × 
                           
                             ( 
                             
                               1 
                               - 
                               
                                 
                                   cos 
                                   3 
                                 
                                 ⁢ 
                                 θ 
                               
                             
                             ) 
                           
                           ⁢ 
                           
                             / 
                           
                           ⁢ 
                           d 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     Hereinafter, the light use efficiency will be considered for a unit area including one light source  151  and one light transmission section  142 H in a plan view of the light source unit model  100 . Regarding the reflection from an optical member (for example, the diffuser sheet  43  and the brightness enhancement sheet  44  in the first embodiment) that is disposed on a front side (on the light exit side, on the liquid crystal panel side) of the reflection, it is supposed that s % of the light rays that have passed through the light transmission section  142 H is reflected and α % thereof is lost, that is, (100−s−α) % of the light rays exits toward the liquid crystal panel per one incident of light. Among the s % light rays that have been reflected by the optical member and reached the first surface  142 A of the reflection layer  142 , the ratio of the light rays that are reflected by the first surface  142 A again depends on a ratio of the light transmission section  142 H and the non-transmission section  142 N in a unit area of the reflection layer  142 . Therefore, the ratio of light rays that are reflected again to the light rays that have passed through the light transmission section  142 H is obtained by (s/100)×(P 2 −πr 2 )/P 2 . The light rays that are reflected again are supplied to the optical member on the front side of the reflection layer  142 . Some of the light rays that have reflected again are reflected further again similarly to the light rays that have passed through the light transmission section  142 H first time and travel toward the first surface  142 A of the reflection layer  142  again. The ratio of the light rays that are reflected further again toward the first surface  142 A of the reflection layer  142  is obtained by (s/100)×(P 2 −πr 2 )/P 2 ×(s/100). Such reflections will be repeated (multi-reflection). 
     When the luminous flux that passes through the light transmission section  142 H is represented by Φθ, the luminous flux Φf that passes through and exits the optical member toward the liquid crystal panel is represented by the following formula (7) with considering the above-described multi-reflection sum of geometric progression).
 
Φ f=Φθ×a /(1− b )  (7)
 
In the formula (7), a represents light transmittance (%) of light that passes through the optical member at one incident, and b represents a re-entering ratio (%) of light that re-enters the optical member that is obtained by multiplying the reflectance of the optical member and the reflectance of the reflection layer  142 . a and b are represented as follows.
 
             a   =       (     100   -   s   -   α     )     ⁢     /     ⁢   100                       b   =     s   ⁢     /     ⁢   100   ×     (       P   2     -     π   ⁢           ⁢     r   2         )     ⁢     /     ⁢     P   2                   =     s   ⁢     /     ⁢   100   ×     (     1   -     Π   ×       (     d   ⁢     /     ⁢   P     )     2     ×     tan   2     ⁢   θ       )                   
When s′=s/100 and α′=α/100, the above a and b are represented as follows.
 
 a= 1− s′−α′ 
 
 b=s′× (1−π×( d/P ) 2 ×tan 2  θ)
 
     When a and b, and the formula (6) are substituted for the formula (7), the following formula (8) is obtained. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           Φ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           f 
                         
                         ⁢ 
                           
                         = 
                       
                     
                     
                       
                           
                         ⁢ 
                         
                           Φθ 
                           × 
                           a 
                           ⁢ 
                           
                             / 
                           
                           ⁢ 
                           
                             ( 
                             
                               1 
                               - 
                               b 
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         
                             
                           = 
                         
                       
                       
                         
                             
                           ⁢ 
                           
                             
                               ( 
                               
                                 π 
                                 ⁢ 
                                 
                                   / 
                                 
                                 ⁢ 
                                 2 
                               
                               ) 
                             
                             × 
                             
                               I 
                               0 
                             
                             × 
                             
                               ( 
                               
                                 1 
                                 - 
                                 
                                   
                                     cos 
                                     3 
                                   
                                   ⁢ 
                                   θ 
                                 
                               
                               ) 
                             
                             ⁢ 
                             
                               / 
                             
                             ⁢ 
                             d 
                             × 
                             a 
                             ⁢ 
                             
                               / 
                             
                             ⁢ 
                             
                               ( 
                               
                                 1 
                                 - 
                                 b 
                               
                               ) 
                             
                           
                         
                       
                     
                     
                       
                         
                             
                           = 
                         
                       
                       
                         
                             
                           ⁢ 
                           
                             
                               { 
                               
                                 
                                   ( 
                                   
                                     π 
                                     ⁢ 
                                     
                                       / 
                                     
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                                   ) 
                                 
                                 × 
                                 
                                   I 
                                   0 
                                 
                                 × 
                                 
                                   ( 
                                   
                                     1 
                                     - 
                                     
                                       
                                         cos 
                                         3 
                                       
                                       ⁢ 
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                                   ) 
                                 
                                 × 
                                 
                                   ( 
                                   
                                     1 
                                     - 
                                     
                                       s 
                                       ′ 
                                     
                                     - 
                                     
                                       α 
                                       ′ 
                                     
                                   
                                   ) 
                                 
                               
                               } 
                             
                             ⁢ 
                             
                               / 
                             
                           
                         
                       
                     
                     
                       
                           
                       
                       
                         
                             
                           ⁢ 
                           
                             
                               { 
                               
                                 ( 
                                 
                                   1 
                                   - 
                                   
                                     
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                                         ( 
                                         
                                           d 
                                           ⁢ 
                                           
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                                           ⁢ 
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                                         ) 
                                       
                                       2 
                                     
                                     × 
                                     
                                       tan 
                                       2 
                                     
                                     ⁢ 
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                                 ) 
                               
                               ) 
                             
                             × 
                             d 
                           
                           } 
                         
                       
                     
                     
                       
                         
                             
                           = 
                         
                       
                       
                         
                             
                           ⁢ 
                           
                             
                               { 
                               
                                 
                                   ( 
                                   
                                     π 
                                     ⁢ 
                                     
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                                 × 
                                 
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                                   0 
                                 
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                                     1 
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                                         3 
                                       
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                                   ) 
                                 
                                 × 
                                 
                                   ( 
                                   
                                     1 
                                     - 
                                     
                                       s 
                                       ′ 
                                     
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                                       ′ 
                                     
                                   
                                   ) 
                                 
                               
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                             ⁢ 
                             
                               / 
                             
                           
                         
                       
                     
                     
                       
                           
                       
                       
                         
                             
                           ⁢ 
                           
                             { 
                             
                               ( 
                               
                                 d 
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                                         ′ 
                                       
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                                             × 
                                             
                                               
                                                 ( 
                                                 
                                                   d 
                                                   ⁢ 
                                                   
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                                                   ⁢ 
                                                   P 
                                                 
                                                 ) 
                                               
                                               2 
                                             
                                             × 
                                             
                                               tan 
                                               2 
                                             
                                             ⁢ 
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                                         ) 
                                       
                                     
                                   
                                   ) 
                                 
                               
                               } 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
       FIG. 3  illustrates graphs representing relations between the angles θ in the light transmission section  142 H and the values of Φf/(4πI 0 ) obtained when d=200 μm, s′=0.5, α′=0.1 and the arrangement interval P of the light sources  151  is varied between 0.9 mm, 1 mm, 2 mm, 5 mm, and 10 mm. The luminous intensity I 0  represents luminous flux that exits in a certain direction and the luminous flux that is emitted by the light source  151  is calculated by multiplying the luminous intensity I 0  by a solid angle. It is supposed trial the light source  151  basically emits light in all directions. Since the solid angle is 4π, the luminous flux that is emitted by the light source  151  is represented by 4πI 0 . Φf/(4πI 0 ) is a value that is obtained by dividing the luminous flux Φf that passes through the optical member and exits toward the liquid crystal panel by the luminous flux (4πI 0 ) that is emitted by the light source  151  in all directions and represents use efficiency of the light that is emitted by the light source  151 . If the value of Φf/(4πI 0 ) is low, it is necessary to increase the number of light sources  151  to reduce the arrangement interval between the light sources  151 . However, if the arrangement interval becomes smaller, the heat generated by the light source  151  needs to be dissipated, but otherwise the light emission efficiency of the light source  151  may be lowered. Therefore, to effectively use the light from the light source  151  in the lighting device that is mounted in an image display device, for example, the value of Φf/(4πI 0 ) is preferably 0.3 or more. With reference to  FIG. 5 , if the arrangement interval P between the light sources  151  is 0.9 mm or less, it may be difficult to obtain 0.3 or more for the value of Φf/(4πI 0 ). Therefore, the arrangement interval is preferably 1 mm or more. With reference to  FIG. 5 , the angle θ that defines the light transmission section  142 H is preferably from 40° or greater to 90° or less, more preferably from 45° or greater to 80° or less, and particularly preferably from 50° or greater to 60° or less. The preferable angle θ is changed depending on the arrangement interval P. Therefore, more particularly, when the arrangement interval is about 10 mm, the angle θ is preferably from 40° or greater to 90° or less, more preferably from 55° greater to 85° or less, and particularly preferably from 70° or greater to 80° or less. When the arrangement interval P is about 5 mm, the angle θ is preferably from 40° or greater to 85° or less, more preferably from 55° or greater to 85° or less, and particularly preferably from 65° or greater to 75° or less. When the arrangement interval P is about 2 mm, the angle θ is preferably from 42° or greater to 78° or less, and more preferably from 60° or greater to 70° or less. When the arrangement interval P is about 1 mm, the angle θ is preferably from 47° or greater to 65° or less. Within such a range, the value of Φf/(4πI 0 ) can be 0.3 or more and the light use efficiency can be increased. 
       FIG. 6  illustrates graphs representing relations between the angles θ in the light transmission section  142 H and the values of Φf/(4πI 0 ) obtained when P=1 mm, s′=0.5, α′=0.1 and the thickness d of the wavelength conversion sheet  141  is varied between 200 μm, 2.10 μm, and 230μm. As illustrated in  FIG. 6 , the light use efficiency is varied depending on the thickness d. As the thickness d increases from 200 μm, the use efficiency of the light with respect to I 0  of the light source  151  is lowered. If the thickness d is 230 μm or more, it may be difficult to obtain 0.3 or more for the value of Φf/(4πI 0 ) and to achieve brightness that is necessary for the lighting unit mounted in the image display device. Therefore, it is assumed that the thickness d of the wavelength conversion sheet  141  is preferably less than 230 μm, more preferably 210 μm or less, and particularly preferably 200 μm or less. The preferable angle θ is different depending on the thickness d. When the thickness d is about 210 μm, the angle θ is preferably from 40° or greater to 65° or less and more preferably from 45° or greater to 60° or less. When the thickness d is about 200 μm, the angle θ is preferably prom 40° or greater to 65° or less and more preferably from 45° or greater to 60° or less. Within such a range, the value of Φf/(4πI 0 ) can be 0.3 or more and the light use efficiency can be further increased. 
     (1) As described above, the backlight unit  20  (the lighting unit) according to the first embodiment includes the LEDs  51  (the light source) that emits primary light (blue light) included in a certain wavelength range, the phosphor sheet  41  (the wavelength conversion member) that is disposed on a light emitting direction side of the primary light with respect to the LEDs  51 , and the reflection sheet  42  (the reflection layer) that is disposed on an opposite side from the LEDs  51  with respect to the phosphor sheet  41 . The phosphor sheet  41  has a function of converting some of the first primary light rays that have passed through the phosphor sheet  41  into secondary light rays (green light or red light) included in another wavelength region that is different from the certain wavelength region. The reflection sheet  42  has a function of reflecting light that reaches the first surface  42 A on an opposite side from the LEDs  51 . The reflection sheet  42  includes through holes  42 H (the light transmission section) and the light that reaches the second surface  42 B on a LED  51  side passes through the through hole  42 H at a higher rate than other sections. 
     In the backlight unit  20  having the above configuration, the primary light (blue light) that is emitted by the LEDs  51  reaches the primary light entering surface  41 A on the LED  51  side (back surface side) of the phosphor sheet  41  and enters the phosphor sheet  41  through the primary light entering surface  41 A. Some of the primary light rays are converted into secondary light (green light or red light) with wavelength conversion while the primary light rays passing through the phosphor sheet  41 . Then, the converted light rays exit the phosphor sheet  41  through the secondary light exit surface  41 B on an opposite side from the LEDs  51  (the front side). The secondary light rays that have exited the phosphor sheet  41  and reached the second surface  42 B of the reflection sheet  42  pass through the through holes  42 H, which are formed in portions of the reflection sheet  42 , and exit the reflection sheet  42  through the first surface  42 A. On the other hand, the reflection sheet  42  that is disposed on an opposite side from the LEDs  51  with respect to the phosphor sheet  41 , that is, on the secondary light exit surface  41 B side reflects the light that has reached the non-transmission section  42 N of the first surface  42 A. Therefore, most of the light rays that are to travel toward the phosphor sheet  41  from an outside of the first surface  42 A of the reflection sheet  42  are blocked by the reflection sheet  42 . Accordingly, among the light rays that have passed the phosphor sheet  41  once and exited the reflection sheet  42  through the first surface  42 A, the amount of the light rays that enter the phosphor sheet  41  through the secondary light exit surface  41 B again is much smaller than that in a configuration without including the reflection sheet  42 . The light rays that have reflected by the first surface  42 A of the reflection sheet  42  do not pass through the phosphor sheet  41  and multi-reflected repeatedly by the reflection sheet  42  and the optical member  40  that is disposed on the front side (on the opposite side from the LEDs  15 ) of the reflection sheet  42 . Thereafter, most of the reflected light rays exit the backlight unit  20 . According to the above configuration, the amount of light rays that are multi-reflected in the backlight unit  20  is reduced and the number of times the light passes through the phosphor sheet  41  is greatly reduced until the light emitted by the LEDs  51  exits the backlight unit  20 . As a result, color unevenness caused by the light rays that are multi-reflected and converted with multiple wavelength conversion is effectively suppressed in the backlight unit  20 . The reflection sheet  42  preferably reflects 90% or more of the light rays that have reached the non-transmission section  42 N except for the through holes  42 H in the first embodiment. Further, the reflection sheet  42  more preferably reflects 95% or more of the light rays, and much more preferably 98% or more of the light rays. The light transmission sections such as the through holes  42 H preferably transmits 90% or more of the light rays that have reached the second surface  42 B, more preferably 95% or more, and much more preferably 98% or more. 
     (2) In the backlight unit  20  according to the first embodiment, the reflection sheet  42  disposed adjacent to the phosphor sheet  41 , which means no other components are between the reflection sheet  42  and the phosphor sheet  41 . The reflection sheet  42  and the phosphor sheet  41  may be disposed to have a space therebetween; however, the two sheets are preferably disposed adjacent to each other without having a space therebetween. According to such a configuration, the reflection sheet  42  that is disposed quite close to the secondary light exit surface  41 B of the phosphor sheet  41  reflects light. This surely reduces the amount of light rays that reach the secondary light exit surface  41 B and the wavelength conversion amount of the light that may be increased by the multi-wavelength conversion. As a result, color unevenness in the backlight unit is suppressed more effectively. The reflection sheet  42  is preferably disposed to cover the secondary light exit surface  41 B of the phosphor sheet  41 . According to such a configuration, most of the light rays that try to enter the phosphor sheet  41  through the secondary light exit surface  41 B again are blocked by the reflection sheet  42  and the amount of light rays that are to be multi-reflected is decreased. As a result, occurrence of color unevenness is effectively suppressed in the backlight unit  20 . As the distance between the reflection sheet  42  and the phosphor sheet  41  becomes smaller, it is more preferable. Furthermore, it is particularly preferable that the reflection sheet  42  is disposed on top of the phosphor sheet  41  to be in contact with the secondary light exit surface  41 B or the reflection sheet  42  is formed on the secondary light exit surface  41 B of the phosphor sheet  41 . According to such a configuration, occurrence of the color unevenness is effectively suppressed and also the light use efficiency of the light emitted by the LEDs  51  is improved and the backlight unit  20  can be reduced in thickness and size (frame width). 
     (3) In the backlight unit  20  according to the first embodiment, the phosphor sheet  41  is disposed adjacent to the LEDs  51 . Normally, in the lighting unit, the light emitted by the light source passes through optical members providing various kinds of optical effects such as uniform diffusion or brightness enhancement and subsequently exits the lighting unit. According to the above-described configuration, the primary light emitted by the LED  51 , which is the light source, enters the phosphor sheet  41  first and converted into secondary light with the wavelength conversion. Then, the converted light passes through the optical member  40  except for the phosphor sheet  41 . Accordingly, the optical effects similar to those in the prior art can be provided to the light exiting the backlight unit  20  while suppressing the multi-wavelength conversion. The distance between the phosphor sheet  41  and the LEDs  51  is more preferable as it is smaller. Furthermore, the phosphor sheet  41  is preferably disposed on the LEDs  51  while having substantially no space therebetween. According to such a configuration, the light use efficiency of the light emitted by the LEDs  51  is increased and the backlight unit  20  can be reduced in thickness and size (frame width). 
     (4) In the backlight unit  20  according to the first embodiment, the through hole  42 H included in a section of the reflection sheet  42  is the light transmission section. According to such a configuration, with a simple configuration including the through hole  42 H in the reflection sheet  42 , the amount of light rays that enter the phosphor sheet  41  through the secondary light exit surface  41 B can be reduced and some of the light rays emitted by the LED  51  pass through the reflection sheet  42  from the second surface  42 B side to the first surface  42 A side. Thus, the light exit amount of the light rays exiting the backlight unit  20  can be maintained. 
     (5) In the backlight unit  20  according to the first embodiment, the through hole  42 H is formed in the reflection sheet  42  so as to include an area overlapping the LED  51  seen from the normal direction of the first surface  42 A. The light emitted the LED  51  and reaches the reflection sheet  42  and exits toward the first surface  42 A normally has a higher density of the luminous flux and the incident angle is small at a position overlapping the LED  51  seen from the normal direction of the first surface  42 A. Therefore, the light exiting toward the first surface  42 A is not reflected at each interface and a higher ratio of the light rays exit toward the first surface  42 A. According to the above configuration, by providing the through hole  42 H to include such section, the re-entry of the light from the secondary light exit surface  41 B side to the phosphor sheet  41  is suppressed and the amount of light rays exiting the reflection sheet  42  through the first surface  42 A can be ensured. This increases a light exit ratio from the backlight unit  20  and increases light use efficiency and the backlight unit  20  that can suppress color unevenness and exert high brightness can be provided. 
     (6) In the backlight unit  20  according to the first embodiment, the through hole  42 H is formed in the reflection sheet  42  so as to include a position where the light emitted by one LED  51  reaches the second surface  42 B at the smallest incident angle. The light emitted by the LED  51  and reaches the reflection sheet  42  normally has a high density of the luminous flux and the incident angle is small at the position where the light reaches the second surface  42 B at the smallest incident angle. Therefore, the light reaching the reflection sheet  42  is not reflected at each interface and a higher ratio of the light rays exit toward the first surface  42 A. According to the above configuration, by providing the through hole  42 H to include such a section, the re-entry of the light from the secondary light exit surface  41 B side to the phosphor sheet  41  is suppressed and the amount of light rays exiting the reflection sheet  42  through the first surface  42 A can be ensured. This increases a light exit ratio from the backlight unit  20 , that is light use efficiency, and the backlight unit  20  that can suppress color unevenness and exert high brightness can be provided. 
     (7) In the backlight unit  20  according to the first embodiment, the LEDs  51  are mounted on the LED board  22  (the light source board) and the mounting surface  22 A of the LED board  22  where the LEDs  51  are mounted is a low reflection surface that causes less light reflection. The mounting surface of the light source board where the light source is mounted has been generally a high reflection surface that accelerates light reflection to diffuse light and increase light use efficiency. However, if the light is reflected by the mounting surface of the light source board, the light is likely to be multi-reflected by the reflection layer and the mounting surface of the light source board and the light is converted with multi-wavelength conversion and this may cause color unevenness. According to the above configuration, since the mounting surface  22 A of the LED board  22  is a low reflection surface, the amount of light rays that have reached the mounting surface  22 A and is reflected toward the phosphor sheet  41  is reduced and this reduces multi-reflection of the light and multi-wavelength conversion. As a result, color unevenness is less likely to be caused in the backlight unit  20 . The low reflection surface may be a surface that is formed to reduce the amount of the reflected light rays compared to the mounting surface of a general light source board. For example, preferably 20% or less of the light rays that are supplied to the low reflection surface reflected, 10% or less is more preferable, and 5% or less is particularly preferable. The low reflection surface is formed as follows, for example. A target surface is coated with a low reflection resin layer including a light absorber or a target surface is processed with a surface roughing treatment. 
     (8) In the backlight unit  20  according to the first embodiment, the LEDs  51  (light emitting diodes) are included as the light source. The LEDs (light emitting diodes) that have high light emission efficiency and small power consumption have been widely used as a light source in a lighting unit. Since the LEDs have high directivity of light, the configurations described in (1) to (7) are particularly effective for reducing color unevenness in the backlight unit  20  including the LEDs  51  as the light source. Particularly, a local-dimming type lighting unit in which a light exit area is divided into multiple sections and each section driven separately and having a following configuration has been greatly expected. Like the backlight unit  20  according to the present embodiment, the mini LEDs  51  having a cubic outer shape of 0.3 mm or less and emitting primary light are used as the light source and the primary light is converted with wavelength conversion into white secondary light and the backlight unit exits white light. When the light emission brightness is varied in each light source or each section like in the local dimming control, color of the chromaticity of display is shifted for every pixel depending on the distance between the surrounding of the pixel from the light source. The present technology is particularly useful for the lighting unit having such a configuration. 
     (9) The backlight unit  20  according to the first embodiment includes multiple LEDs  51 . To suppress color unevenness in the backlight unit  20  including the LEDs  51  like the local dimming type lighting unit described above, the configurations of (1) to (8) are particularly useful. 
     (10) The liquid crystal display device  1  (the display device) according to the first embodiment includes the liquid crystal panel  10  (the display panel) having the image display surface  10 A displaying an image, and the backlight unit  20  described in (1) to (9). According to such a configuration, the liquid crystal display device  1  having less occurrence of color unevenness and good image display quality can be obtained. 
     (11) In the liquid crystal display device  1  according to the first embodiment, the LEDs  51  are disposed directly below the image display surface  10 A. According to such a configuration, the liquid crystal display device  1  including the direct type backlight unit  20  and having good image display quality can be obtained. Such a liquid crystal display device  1  can be particularly and preferably used in performing the local dimming control. 
     Second Embodiment 
     A second embodiment will described with reference to  FIGS. 7A and 7B . The present embodiment differs from the backlight unit  20  according to the first embodiment in that LEDs  251  with a chip scale package (CSP) are used as a light source of a backlight unit  220 . Other basic configurations of the backlight unit  220  are similar to those of the backlight unit  20  in the first embodiment. Hereinafter, the configurations same as those in the first embodiment are provided with the same symbols and will not be described (similar in a third embodiment). 
     As illustrated in  FIGS. 7A and 7B , the LED  251  in the present embodiment is installed in a package  250  that has an outer shape of a truncated cone. A diameter of the package  250  increases as the package  250  extends to the front side. The package  250  has a side surface and a bottom surface (a back surface, a surface that is mounted on the LED board  22 ) that provide an outline thereof. At least inner surfaces of the side surface and the bottom surface are configured with a reflecting member  252  having good light reflectivity. In the present embodiment, the package  250  is open at a top surface (a front surface, a surface that is opposite the primary light entering surface  41 A of the phosphor sheet  41 ) and the inside of the package  250  is a hollow space. The hollow space of the package  250  may be filled with a material having light transmissivity and a refractive index that is uniform and greater than the refractive index of the phosphor sheet  41 . The package  250  is configured in such a manner that the primary light (for example, blue light) emitted by the top-surface light emitting type LED  251  through a light emitting surface  251 A is supplied to the primary light entering surface  41 A of the phosphor sheet  41  through a front side opening of the package  250 . 
     The side surface of the package  250  that is defined by the reflecting member  252  and surrounds the light emitting surface  251 A is set so as to form an angle θ with respect to the normal direction of the bottom surface. The reflecting member  252  suppresses the light emitted by the LED  251  from spreading in the direction parallel to the light emitting surface  251 A, and the light from the LED  251  is supplied to an area on the first surface  42 A of the reflection sheet  42  defined by the angle θ between an edge surface of the LED  251  and the normal direction of the bottom surface. The light emitted by the LED  251  can effectively exit toward the first surface  42 A side of the reflection sheet  42  by forming the through hole  42 H in the reflection sheet  42  so as to include the area. The through hole  42 H is preferably formed to include the area and not to be greater than the area. Since the rest of the area of the reflection sheet  42  except for the above area is the non-transmission section  42 N, the light rays that try to travel toward the phosphor sheet  41  from the outside of the first surface  42 A are reflected by the non-transmission section  42 N. This suppresses color unevenness caused by the multi-wavelength conversion and increases the light use efficiency. 
     (12) As described above, the backlight unit  220  (the lighting unit) according to the second embodiment further includes the reflecting member  252  (a light diffusion suppressing member) that is disposed to surround the light emitting surface  251 A of the LED  251  (the light source) through which the primary light is emitted. The reflecting member  252  surrounds the light emitting surface  251 A except for an opening that opens toward the phosphor sheet  41  and suppresses the light from spreading in the direction parallel to the light emitting surface  251 A. 
     According to the above configuration, the light emitted by the LED  251  is reflected by the reflecting member  252  toward the specific area of the phosphor sheet  41  (the wavelength conversion member). Accordingly, the incident angle of the light at which the light enters the phosphor sheet  41  is restricted to reduce the amount of light rays to be multi-reflected. As a result, color unevenness caused by the multi-wavelength conversion is suppressed. With the configuration of the reflecting member  252  having the opening such that the light is supplied toward the through hole  42 H (the light transmission area) in the reflection sheet  42  (the reflection layer), the light exit efficiency of the backlight unit is increased and brightness is increased. The increase in the amount of light rays that exit through the through holes  42 H and a steep light distribution are particularly useful to obtain the display device that performs the local dimming control. Specifically, as the light distribution becomes steep, a certain pixel of the liquid crystal panel  10  is less likely to be influenced by the light sources near the certain pixel and a calculation burden of calculation for correction estimation of pixel data can be reduced. As a result, the display device that can perform the local dimming control and display high quality images can be produced at cost while suppressing a required burden of the calculating means for the local dimming control. 
     Third Embodiment 
     A third embodiment will be described with reference to  FIGS. 8 and 9 . A liquid crystal display device  3  according to the present embodiment differs from the backlight unit  20  according to the first embodiment in that an edge-light type backlight unit  320  is included and the LEDs  251  with a chip scale package (CSP) are used as the light source. The package  250  including the LED  251  therein as the light source has the configurations similar to those in the second embodiment. 
       FIG. 8  is an enlarged view illustrating an edge section of a backlight unit  320 . The backlight unit  320  may be any edge-light type backlight unit that includes a known basic configuration of the edge-light type backlight unit without any limitation. For example, the backlight unit  320  illustrated in  FIG. 8  includes the brightness enhancement sheet  44 , a light guide plate  345  disposed on a back surface side of the diffuser sheet  43 , and the packages  250 . The brightness enhancement sheet  44  is disposed directly below the image display surface  10 A of the liquid crystal panel  10 . The packages  250  including the respective LEDs  251 , which is the light source, are disposed opposite an edge surface of the light guide plate  345 . The packages  250  are disposed such that the light exits toward the edge surface of the light guide plate  345 . Namely, in the backlight unit  320 , the exit direction L 1  of the primary light is parallel to the image display surface  10 A. The packages  250  are mounted on a LED board  322  that is disposed substantially vertical to the image display surface  10 A and along the side wall of the frame  23 . A bottom surface reflection sheet  346  that reflects light is mounted on a back surface side of the light guide plate  345  to cover the opening of the frame  23  on the back surface side. The packages  250  are disposed opposite at least one of the four edge surfaces of the light guide plate  345  and may be disposed opposite multiple edge surfaces. 
     A known light guide plate can be used for the light guide plate  345  without any limitation. The light that has entered the light guide plate  345  through the edge surface that is opposite the packages  250  travels therein farther away from the light sources and toward the front side (the light exit side, the liquid crystal panel  10  side) and planar light exits the light guide plate  345 . The light guide plate  345  may be configured to become thicker as it extends farther away from the edge surface that is opposite the packages  250 . The light guide plate  345  is made of synthetic resin (acrylic resin such as PMMA or polycarbonate resin) that has a refractive index sufficiently greater than that of air and substantially transparent (highly transmissive). The light that has exited the light guide plate  345  through the front surface passes through the diffuser sheet  43  and the brightness enhancement sheet  44  while providing the certain optical effects to the light. Then, the light exits through the light exit surface  20 A. 
     A known reflection sheet can be used for the bottom surface reflection sheet  346  without any limitation. The bottom surface reflection sheet  346  reflects light that has exited the light guide plate  345  through the back side surface to enter the light guide plate  345  again. The bottom surface reflection sheet  346  can increase the amount of light rays that exit toward the liquid crystal panel  10  and increase the light use efficiency and increase screen brightness of the liquid crystal display device  3 . The bottom surface reflection sheet  346  may be an insulation synthetic resin sheet. The bottom surface reflection sheet  346  preferably has a front surface that is white and has good light reflectivity. The bottom surface reflection sheet  346  is preferably disposed on a back surface side of each of a reflection sheet  342 , a phosphor sheet  341 , the package  250 , and the LED board  322  in addition to the back surface side of the light guide plate  345 . According to such a configuration, the amount of light rays that exit through the back surface of the backlight unit  320  or are lost on the back surface side thereof can be reduced. 
     As illustrated in  FIG. 9 , in the edge section of the backlight unit  320 , the phosphor sheet  341  and the reflection sheet  342  are disposed between the packages  250  and the edge surface of the light guide plate  345 . The phosphor sheet  341  and the reflection sheet  342  have the functions similar to those of the phosphor sheet  41  and the reflection sheet  42  in the first embodiment, respectively. The shape and the arrangement of the phosphor sheet  341  and the reflection sheet  342  differ from those in the first embodiment. As illustrated in  FIG. 8 , the phosphor sheet  341  is disposed in such a manner that a primary light entering surface  341 A thereof opposite the LEDs  251  closes the openings of the packages  250  mounted on the LED board  322  without having any space therebetween. Furthermore, the reflection sheet  342  is disposed on top of the phosphor sheet  341  such that a second surface  342 B is closely in contact with a secondary light exit surface  341 B of the phosphor sheet  341  and the first surface  342 A is disposed opposite the edge surface (the light entering surface) of the light guide plate  345 . The reflection sheet  342  includes through holes  342 H corresponding to the respective packages  250  that are mounted on the LED board  322 . An area other than the through holes  342 H is a non-transmission section  342 N. 
     The primary light that is emitted by the packages  250  is converted to the secondary light with wavelength conversion while passing through the phosphor sheet  341  and passes through the through holes  342 H in the reflection sheet  342  and enter the light guide plate  345  through the edge surface of the light guide plate  345 . Most of the light rays that have been reflected by the light guide plate  345  toward the phosphor sheet  341  are reflected again and blocked by the non-transmission section  342 N of the first surface  342 A of the reflection sheet  342 . This suppresses the multi-wavelength conversion that is caused when the light passes through the phosphor sheet  341  multiple times. The through hole  342 H is preferably formed according to the angle θ of the reflecting member  252  that defines an outline of the package  250  similarly to that in the second embodiment. 
     (13) As described above, the backlight unit  320  (the lighting device) according to the third embodiment includes the light guide plate  345  (a light guide member) and the LEDs  251  (the light source) that are disposed opposite the edge section of the light guide plate  345 . The light emitted by the LEDs  251  travels through the light guide plate  345  toward the liquid crystal panel  10  (the display panel). 
     According to the above configuration, the liquid crystal display device  3  (the display device) that includes the edge-light type backlight unit  320  and has good image display quality can be obtained. Particularly, such a liquid crystal display device  3  is preferably used to perform the power-saving local dimming control and useful for reducing the thickness. 
     Other Embodiments 
     The present technology is not limited to the embodiments described in the above descriptions and drawings. The following embodiments may be included in the technical scope. 
     (1) The above embodiments include the reflection sheet that is an isolated reflecting member as one example of the reflection layer. However, the reflection sheet is not limited to the configuration. For example, the reflection layer may be formed with coating or printing resin or metal on the secondary light exit surface of the wavelength conversion member. In such a configuration, the reflection layer may be a white ink layer including a white pigment such as titanium oxide, barium sulfate, and zinc oxide or a metal layer. 
     (2) The above embodiments include the through hole as the light transmission section of the reflection layer. However, the light transmission section is not limited to such a configuration. For example, the reflection layer or the reflection sheet  42  that is a white ink layer may include a section where the light transmittance thereof differs from that in another section and for example, the section may be a substantially transparent section. 
     (3) In the above embodiments, each of the first surface and the second surface of the reflection layer is defined into two sections of the light transmission section and the non-transmission section. However, the configuration of the reflection layer is not limited to such a configuration. For example, the reflection layer may further include a semi-transmission section where the light transmittance through the second surface and the light reflectance on the first surface of the reflection layer have an intermediate value between those of the light transmission section and those of the non-transmission section. Thus, the reflection layer may include multiple sections having different light transmittances that are varied in a stepwise manner. The light transmittance of the reflection layer can be adjusted by changing a material in a portion of the reflection layer, changing a density or a distribution of the light diffuser that is mixed in the reflection layer, or changing a thickness in a portion of the reflection layer. 
     (4) In the above embodiments, the reflection layer includes the light transmission section that is defined in such a manner that the incident angle of the light rays that have been emitted by the light source and reached the second surface of the reflection layer is smallest. However, the configuration of the reflection layer is not limited to the above one. For example, the reflection layer may include the non-transmission section or the semi-transmission section at a position having the smallest incident angle. The liquid crystal display device  4  (the display device) illustrated in  FIG. 10  includes backlight unit  420  (the lighting device). The backlight unit  420  includes a semi-transparent section  442 C at a position on the reflection layer  442  having the smallest incident angle. The reflection layer  442  is disposed on the secondary light exit surface  41 B of the phosphor sheet  41  (the wavelength conversion member) and includes a light transmission section  442 H in a certain area around the semi-transparent section  442 C and the non-transmission section  442 N that is an area outside the light transmission section  442 H. At the position of the reflection layer having the smallest incident angle, a density of light rays that are emitted by the LED  51  (the light source) and pass through the phosphor sheet  41  and reach the reflection layer  442  is highest and the ratio of light rays that are not reflected by each of the interfaces due to the small incident angle and exit through the first surface  442 A is highest. Therefore, the light that emits through the position may locally increase the brightness of the lighting device. According to the configuration of the reflection layer  442 , the light exit amount of the light rays that exit the reflection layer  442  through the first surface is maintained while suppressing brightness unevenness. 
     The above embodiments include the LEDs as the light source; however, the light source is not limited to the LEDs. For example, the light source may be fluorescent tubes. However, the present technology is preferably applied to the lighting device including the light source having strong directivity such as the LEDs. Particularly, since the LEDs have low power consumption properties, long-life properties, and are suitable for reducing a size, the LEDs are widely used for the backlight unit. On the other hand, since the LED has strong directivity, illuminance unevenness or chromaticity unevenness is likely to be caused. Particularly, the present technology is preferably applied to lighting devices including the LEDs as the light source.