Patent Publication Number: US-2022221758-A1

Title: Display apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of PCT/CN2021/081640, filed on Mar. 18, 2021, which claims priorities to Chinese patent applications No. 202010221021.1 filed on Mar. 25, 2020, No. 202010351591.2 filed on Apr. 28, 2020, No. 202020687645.8 filed on Apr. 28, 2020, No. 202010453658.3 filed on May 26, 2020, No. 202010522067.7 filed on Jun. 10, 2020, No. 202010522571.7 filed on Jun. 10, 2020, No. 202010570713.7 filed on Jun. 19, 2020, No. 202010756556.9 filed on Jul. 31, 2020, No. 202010855892.9 filed on Aug. 24, 2020, No. 202010791424.X filed on Aug. 7, 2020, No. 202010791451.7 filed on Aug. 7, 2020, No. 202011182703.2 filed on Oct. 29, 2020, No. 202022825588.8 filed on Nov. 30, 2020, and No. 202011508504.6 filed on Dec. 18, 2020, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The present application relates to the display technology, in particular to a display apparatus. 
     BACKGROUND 
     As the mainstream panel at present, a liquid crystal panel has the advantages of low power consumption, small size, low radiation and the like. A liquid crystal panel is not self-lit panel, and needs to work with a backlight module together. At present, the backlight module can be divided into a direct backlight module and an edge lit backlight module. The direct backlight module is widely used because of its advantages of high brightness, efficient light utilization, simple structure and the like. An existing direct backlight module usually uses a light emitting diode (LED) as a backlight source, which has the advantages that backlight brightness is high and will not decrease after long-term use. Light emitting from the LED is distributed like a Lambert body, and emitted light rays has high intensity at a small angle and low intensity at a large angle, resulting in uneven light distribution. In order to meet the requirements of production cost and ultra-thin appearance, how to realize the uniformity of backlight to meet the requirements of image quality is an urgent issue. 
     SUMMARY 
     A display apparatus according to an present application includes: a display panel, configured to display an image; a micro light emitting diode light board, used as a backlight source; wherein the panel is on a light emitting side of the micro light emitting diode light board; the micro light emitting diode light board includes a circuit board, micro light emitting diodes and a reflective layer; the circuit board is configured to provide a driving signal; the micro light emitting diodes is on the circuit board; and the reflective layer is on a surface of a side of the circuit board close to the micro light emitting diodes, the reflective layer includes an opening for one of exposing the micro light emitting diode, and the reflective layer is configured to perform diffuse reflection on incident light rays; an angle selection layer on the light emitting side of the micro light emitting diode light board, configured to reflect light rays with a first incident angle range and transmit light rays with a second incident angle range; wherein an incident angle value corresponding to the first incident angle range is smaller than an incident angle value corresponding to the second incident angle range; and the reflective layer and the angle selection layer are configured for improving light emitting uniformity of the micro light emitting diode light board; and a diffusion layer on a side of the angle selection layer away from the micro light emitting diode light board, or, between the angle selection layer and the micro light emitting diode light board. 
     In some embodiments, a vertical distance from the circuit board to the diffusion layer and a distance between every two adjacent micro light emitting diodes meet a following relationship: 0.15≤h/p&lt;0.67; wherein h represents the vertical distance from the circuit board to the diffusion layer, and p represents the distance between every two adjacent micro light emitting diodes. 
     In some embodiments, the angle selection layer further includes: a plurality of film layers, disposed in a laminated mode, wherein every two adjacent film layers of the plurality of film layers have different refraction indexes; wherein the refraction indexes and thicknesses of the plurality of film layers meet a condition of reflecting the light rays with the first incident angle range and transmitting the light rays with the second incident angle range. 
     In some embodiments, the first incident angle range is 0° to 70°, and the second incident angle range is greater than 70°. 
     In some embodiments, a reflectivity of the angle selection layer to the light rays with the first incident angle range is decreased with increasing of an incident angle; and the reflectivity of the angle selection layer to the light rays with the first incident angle range is 10% to 80%, and the reflectivity of the angle selection layer to the light rays with the second incident angle range is less than 10%. 
     In some embodiments, the micro light emitting diode light board further includes: a packaging layer on a surface of a side of the micro light emitting diode away from the circuit board. 
     In some embodiments, wherein the angle selection layer is attached to a surface of the diffusion layer. 
     In some embodiments, the display apparatus further includes a transparent substrate between the micro light emitting diode light board and the diffusion layer; wherein the angle selection layer is attached to a surface of a side of the transparent substrate away from the micro light emitting diode light board. 
     In some embodiments of the present application, the display apparatus further includes a transparent support on the micro light emitting diode light board, configured to support the diffusion layer. 
     In some embodiments of the present application, the display apparatus further includes a base, wherein the film layers disposed in the laminated mode are disposed on the base. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of a display apparatus according to an embodiment of the present application. 
         FIG. 2  is a first schematic structural diagram of a backlight module according to an embodiment of the present application. 
         FIG. 3A  is an emergent light intensity distribution diagram of a backlight module without an angle selection layer. 
         FIG. 3B  is an emergent light intensity distribution diagram of a backlight module with an angle selection layer. 
         FIG. 4  is a schematic structural diagram of a backlight module according to some embodiments of the present application. 
         FIG. 5  is a schematic structural diagram of a backlight module according to some embodiments of the present application. 
         FIG. 6  is a schematic structural diagram of a backlight module according to some embodiments of the present application. 
         FIG. 7  is a schematic structural diagram of a backlight module according to some embodiments of the present application. 
         FIG. 8  is a schematic structural diagram of a backlight module according to some embodiments of the present application. 
         FIG. 9  is a first schematic cross-sectional view of a backlight module according to an embodiment of the present application. 
         FIG. 10  is a first schematic cross-sectional view of an angle selection layer according to an embodiment of the present application. 
         FIG. 11  is a schematic diagram of a working principle of an angle selection layer according to an embodiment of the present application. 
         FIG. 12  is a second schematic cross-sectional view of an angle selection layer according to an embodiment of the present application. 
         FIG. 13  is a second schematic cross-sectional view of a backlight module according to an embodiment of the present application. 
         FIG. 14A  is a light emitting brightness distribution effect diagram of a backlight module in related art. 
         FIG. 14B  is a light emitting brightness distribution effect diagram of a backlight module according to an embodiment of the present application. 
         FIG. 15  is a third schematic cross-sectional view of a backlight module according to an embodiment of the present application. 
         FIG. 16  is a fourth schematic cross-sectional view of a backlight module according to an embodiment of the present application. 
         FIG. 17  is a fifth schematic cross-sectional view of a backlight module according to an embodiment of the present application. 
         FIG. 18  is a sixth schematic cross-sectional view of a backlight module according to an embodiment of the present application. 
         FIG. 19  is a schematic structural diagram of a micro light emitting diode according to an embodiment of the present application. 
         FIG. 20  is a schematic cross-sectional view of a backlight module according to some embodiments of the present application. 
         FIG. 21  is a schematic cross-sectional view of a backlight module according to some embodiments of the present application. 
         FIG. 22  is a schematic cross-sectional view of a backlight module according to some embodiments of the present application. 
         FIG. 23  is a light emitting intensity distribution effect diagram of a backlight module in related art. 
         FIG. 24  is a light emitting intensity distribution effect diagram of a backlight module according to an embodiment of the present application. 
         FIG. 25  is a schematic cross-sectional view of a backlight module according to some embodiments of the present application. 
         FIG. 26  is a graph of a reflectivity of a first functional layer according to an embodiment of the present application. 
         FIG. 27  is a schematic diagram of emergent light rays of a wavelength conversion layer. 
         FIG. 28  is a diagram of a working principle of a second functional layer according to an embodiment of the present application. 
         FIG. 29  is a transmittance graph of a second functional layer according to an embodiment of the present application. 
         FIG. 30  is a reflectivity graph of a second functional layer according to an embodiment of the present application. 
         FIG. 31  is a transmittance graph of a second functional layer to blue light according to an embodiment of the present application. 
         FIG. 32  is a schematic cross-sectional view of a backlight module according to some embodiments of the present application. 
         FIG. 33  is a schematic cross-sectional view of a backlight module according to some embodiments of the present application. 
         FIG. 34  is a schematic diagram of film interference according to some embodiments of the present application. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In order to make the objectives, features and advantages of the present application obvious and easy to understand, the present application will be further described below in combination with the accompanying drawings and embodiments. However, example implementations can be implemented in a variety of forms and should not be construed as limited to the implementations set forth herein. 
     A liquid crystal display apparatus is mainly includes a backlight module and a liquid crystal panel. The liquid crystal panel does not emit light itself, and needs to use a light source according to a backlight module to achieve brightness display. 
     The work principle of the liquid crystal display apparatus is that liquid crystals are placed between two pieces of conductive glass, the electric field effect which is driven by an electric field between two electrodes causes distortion of liquid crystal molecules, so as to control transmission or shielding for light emitting from a backlight source, thereby displaying images. If color light filters are added, color images may be displayed. 
       FIG. 1  is a schematic cross-sectional view of a display apparatus according to an embodiment of the present application. 
     Referring to  FIG. 1 , the display apparatus includes: a backlight module  100  and a panel  200 . The backlight module  100  is configured to provide a backlight source for the panel  200 , and the panel  200  is configured to display images. 
     The backlight module  100  is usually at the bottom of the display apparatus, with its shape and size being adaptive to those of the display apparatus. When applied to devices such as a television or a mobile terminal, the backlight module is usually in a rectangular shape. 
     The backlight module in the embodiments of the present application adopts a direct backlight module which is configured to uniformly emit light rays on a whole light emitting surface to provide light rays full in brightness and uniform in distribution for the panel, so that the panel can normally display images. 
     The panel  200  is located on a light emitting side of the backlight module  100 , and a shape and size of the panel are usually matched with those of the backlight module. Usually, the panel  200  may be rectangular, including a top side, a bottom side, a left side and a right side. The top side and the bottom side are opposite, the left side and the right side are opposite, the top side is connected with one end of the left side and one end of the right side, and the bottom side is connected with the other end of the left side and the other end of the right side. 
     The panel  200  is a panel which is able to transmit light and adjust transmittance of light, but the panel does not emit light itself. The panel  200  has a plurality of pixel units arranged in an array, and each pixel unit may independently control a transmittance of and color of light entering into the pixel unit from the backlight module  100  to make light rays transmitted through all the pixel units form a display image. 
     The structure of the direct type backlight module is described below. In view of backlight uniformity issue, the present application provides a structure of a backlight module. 
     As shown in  FIG. 2 , the backlight module according to the embodiment of the present application includes: a plurality of light sources  21  arranged in an array, an angle selection layer  22  and a reflective layer  23 . In some embodiments, the light sources  21  are ordinary LED lamp beads, a single LED lamp bead is a light emitting device with an LED chip encapsulated, and the plurality of LED lamp beads are arranged on a circuit board. Usually, the circuit board is in a strip shape and in the form of an LED light bar. In order to expand a light spot range of LEDs, matching the LEDs with lens is also usually adopted to increase the brightness of large-angle emitting light from the LEDs. In some embodiments, the light sources  21  may be micro light emitting diodes or sub-millimeter light emitting diodes, also known as mini-LEDs. The light source of that type will be illustrated in detail in subsequent embodiments. 
     An angle selection layer  22  is located on a light emitting side of the light sources  21 . The angle selection layer  22  is configured to reflect light rays with a first incident angle range and transmit light rays with a second incident angle range. An incident angle value corresponding to the first incident angle range is smaller than an incident angle value corresponding to the second incident angle range. That is, the angle selection layer is configured that: the larger an angle of incident light rays, the smaller a reflectivity to the incident light rays; and the larger the angle of the incident light rays, the larger a transmittance to the incident light rays. 
     The reflective layer  23  is located on a side of the light sources  21  away from the angle selection layer  22 , and configured to do scattering or diffuse reflection on the light rays reflected from the angle selection layer to emit the light rays to the panel. In some embodiments, the reflective layer  23  is a reflective sheet. The reflective sheet is located on the circuit board and has holes for exposing the light sources  21 . It is noted that the reflective layer  23  is not limited to the sheet-like reflective sheet, and also refer to structure arrangements with a reflecting effect, such as a surface of the circuit board having a reflecting function. 
     In the embodiment of the present application, by disposing the angle selection layer  22  on the light emitting side of the light sources  21 , the angle selection layer  22  may enhance reflection for light rays at a particular angle(s) within the light rays with the first incident angle range, meanwhile, and enhance transmission for the light rays at a particular angle(s) within the light rays with the second incident angle range. The first incident angle range corresponds to emitting angles with high light intensity and the second incident angle range corresponds to emitting angles with low light intensity, light rays with small emitting angles may be transmitted only partially, a part of the light rays at the particular angle are reflected to the direction of the light sources, and light rays with large emitting angles are emitted in an transmittance-enhancing mode; and the light rays with the small angles reflected to the direction of the light sources are subjected to scattering or diffuse reflection by the reflective layer  23  to form light rays with large emitting angles so as to be emitted from the angle selection layer in an transmittance-enhancing mode, so that emitting intensity of the small-angle light rays is reduced, emitting intensity of the large-angle light rays is increased, final emitting illuminance is made uniform, and the uniformity of light emitted from the light sources is improved. 
     The angle selection layer is configured that: the larger the angle of the incident light rays, the smaller the reflectivity to the incident light rays; and the larger the angle of the incident light rays, the larger the transmittance to the incident light rays. Characteristics of the angle selection layer decrease the emitting intensity of the small-angle light rays and increase the emitting intensity of the large-angle light rays. A specific principle and structure of the angle selection layer will be illustrated in detail in subsequent embodiments. 
     According to light intensity distribution of the light sources, generally, the emitting light intensity at an area close to an emitting center is high, and the light intensity at an edge area away from the emitting center is low, and therefore when the light sources emit to a certain plane, brightness corresponding to the area of the emitting center is high, while brightness corresponding to the area away from the emitting center is low, so that light intensity distribution at a junction between two adjacent light sources in the backlight module is weak, resulting in poor uniformity, that is, emitting surface illuminance is inconsistent. The display apparatus according to the embodiments of the present application can make emitting surface illuminance of the light sources consistent, decrease light intensity close to the emitting center of the light sources and increase light intensity at edges. 
       FIG. 3A  and  FIG. 3B  show a comparison of light intensity distribution of a single light source of the backlight module without the angle selection layer  22  and a single light source with light passing the angle selection layer. According to the schematic diagram of light intensity distribution of the light source without the angle selection layer as shown in  FIG. 3A , emitting light intensity of the light rays of the light source close to the emitting center (close to 0°) is far greater than light intensity of the light rays of the light source away from the emitting center (approaching 90°), and thus fewer light rays are distributed at a junction region of the light sources, and light uniformity is poor. After the angle selection layer  22  is disposed in the backlight module, light intensity distribution of light rays passing the angle selection layer is as shown in  FIG. 3B . Original small-angle emitting light rays are reflected by the angle selection layer, after a scattering or diffuse reflection effect of the reflective layer, a part of light rays are transmitted at a large angle, and thus emitting light intensity at the edge areas is increased, and light intensity at the center area is decreased, so that final emitting illuminance of the light sources is substantially equal at all areas, and uniformity of the light rays emitted from the light sources is improved. 
     A specific arrangement for the angle selection layer  22  in the backlight module is specifically described below. 
     As shown in  FIG. 4  and  FIG. 5 , the backlight module according to the embodiment of the present application further includes a diffusion layer  26 . 
     The diffusion layer  26  is located on a side of the light sources  21  away from the reflective layer  23 , namely located on the light emitting side of the light sources  21 , and the diffusion layer  26  is configured for uniformizing light. 
     As shown in  FIG. 4 , the angle selection layer  22  is located on a side of the diffusion layer  26  close to the light sources  21 , and specifically, the angle selection layer  22  may be located between the diffusion layer  26  and the light sources  21 . 
     As shown in  FIG. 5 , the angle selection layer  22  is located on a side of the diffusion layer  26  away from the light sources  21 , and specifically, the diffusion layer  26  carries the angle selection layer  22 . The arrangement may guarantee that the angle selection layer  22  has an enough distance to reflect the small-angle light rays. 
     When the backlight module according to the embodiment of the present application is applied to a small-size display apparatus, the structure as shown in  FIG. 4  or  FIG. 5  may be adopted. When the backlight module is applied to a large-size display apparatus, since a back frame of the backlight module cannot play a complete supporting role for the angle selection layer  22  and the diffusion layer  26  thereon, as shown in  FIG. 6  and  FIG. 7 , a glass substrate  27  may be further disposed in the backlight module to support all functional films or sheets in the backlight module. 
     Specifically, as shown in  FIG. 6 , the glass substrate  27  is located on the light emitting side of the light sources  21 , the angle selection layer  22  may be located on a surface of a side of the glass substrate  27  facing the light sources  21 , and the diffusion layer  26  may be located on a surface of a side of the glass substrate  27  away from the light sources  21 ; or, as shown in  FIG. 7 , the diffusion layer  26  may be located on the surface of the side of the glass substrate  27  facing the light sources  21 , and the angle selection layer  22  may be located on the surface of the side of the glass substrate  27  away from the light sources  21 . When the glass substrate is disposed in the backlight module, a layer of diffusion material may be formed on a surface of a side of the glass substrate to form a diffusion plate of an integrated structure, and the diffusion plate may replace a diffusion plate made of resin base materials such as PC in related art. 
     In another embodiment, the surface of the side of the glass substrate  27  facing the light sources  21  may also be sanded to form a sanded surface, which may replace the effect of the diffusion layer shown in  FIG. 7 , so that a manufacturing process is simplified. 
     According to the backlight module according to the embodiment of the present application, the glass substrate is used as a base material for the diffusion material, compared with that a resin material is used as the base material for the diffusion material, since the glass substrate has high rigidity, a thickness may be 1.5 mm and even smaller. Besides, the glass substrate has a smaller expansion coefficient, so that there is no need of reserving a large expansion space for the glass substrate when the backlight module is designed, and ultra-narrow bezel design may be achieved. In related art, base materials (usually PET base materials) need to be disposed on two sides of a quantum dot layer when the quantum dot layer is manufactured, while in the embodiments of the present application, a quantum dot layer  24  may be directly manufactured on the surface of the angle selection layer  22  or the diffusion layer  26 , only a protective layer needs to be disposed on one side, and thus the thickness of the backlight module may be further reduced. 
     Further, as shown in  FIG. 8 , the backlight module according to the embodiment of the present application further includes: an optical film  28  located on a side of the protective layer  25  away from the quantum dot layer  24 . During implementation, the optical film  28  may include a brightness enhancement film which is configured to enhance the brightness of the light rays emitted from the front face of the backlight module to improve light ray using efficiency. In addition, the optical film may further include a diffusion sheet which is configured to diffuse the light rays a second time; or, when the backlight module is used together with the liquid crystal panel, the optical film may further include a polarizer located on the outermost side, which is not limited herein. 
     Next, description is made in detail by taking that the light sources  21  are the micro light emitting diodes or sub-millimeter light emitting diodes (also known as mini-LED) as an example. 
       FIG. 9  is a schematic cross-sectional view of the backlight module according to an embodiment of the present application. 
     Referring to  FIG. 9 , in a light emitting direction of the light rays in the backlight module, the backlight module includes: a back plate  11 , a micro light emitting diode light board  12  and a diffusion layer  13 . 
     The back plate  11  is located at the bottom of the backlight module and configured to support. Usually, the back plate  11  is of a square structure, and when the back plate is applied to a special-shaped display apparatus, a shape of the back plate is adaptive to a shape of the display apparatus. The back plate  11  includes a top side, a bottom side, a left side and a right side. The top side and the bottom side are opposite, the left side and the right side are opposite, the top side is connected with one end of the left side and one end of the right side, and the bottom side is connected with the other end of the left side and the other end of the right side. 
     In the embodiment of the present application, the backlight module is a direct type backlight module, and the micro light emitting diode light board  12  is located on the back plate  11 . Usually, the whole micro light emitting diode light board  12  may be square or rectangular, with a length of 200 mm to 800 mm and a width of 100 mm to 500 mm. 
     A plurality of micro light emitting diode light boards  12  may be disposed according to a size of the display apparatus, and the micro light emitting diode light boards  12  are spliced to collectively provide backlight. In order to avoid optical problems caused by splicing of the micro light emitting diode light boards  12 , splicing seams between the adjacent micro light emitting diode light boards  12  are made as small as possible, and uniform seamless splicing is achieved. 
     As a backlight source, compared with a traditional light emitting diode, the micro light emitting diode light board  12  has a smaller size and can achieve finer dynamic control and improve a dynamic contrast of the display apparatus. 
     The micro light emitting diode light board  12  includes micro light emitting diodes  122 , and sizes of chips of the micro light emitting diodes in the micro light emitting diode light board  12  are at a micron level. In some embodiments, the micro light emitting diode light board  12  is a mini-LED light board. 
     The micro light emitting diode light board may be formed through two surface mounted manners: POB and COB. POB is short for package on board, and means that LED chips are packaged (large-size bonding pad) and then mounted to a circuit board; and COB is short for chip on board, and means that LED chips are directly mounted on a circuit board. 
     The two surface mounted manners both can apply to the micro light emitting diode light board in the present application. 
     Next, a structure of the micro light emitting diode light board formed through COB manner is taken as an example for description in detail. 
     The micro light emitting diode light board  12  specifically includes: a circuit board  121 , micro light emitting diodes  122 , a reflective layer  123  and a packaging layer  124 . 
     The circuit board  121  is located on the back plate  11 , and a shape of the circuit board  121  is substantially the same as an overall shape of the micro light emitting diode light board  12 . Usually, the circuit board  121  is in a plate shape and is rectangular or square as a whole. The circuit board  121  has a length of 200 mm to 800 mm and a width of 100 mm to 500 mm. 
     In the embodiments of the present application, the circuit board  121  may be a printed circuit board (PCB), the PCB includes an electronic circuit and an insulating layer, and the insulating layer exposes one or more bonding pads in the electronic circuit for welding the micro light emitting diodes and covers remaining parts. 
     Or, the circuit board  121  may also be an array substrate formed by manufacturing a thin film transistor driving circuit on a base substrate, and a surface of the array substrate has electrodes connected to the thin film transistor driving circuit for welding the micro light emitting diodes. 
     A base or base substrate of the above circuit board  121  may be made of a flexible material to form a flexible display apparatus. 
     The circuit board  121  is configured to provide a driving electric signal for the micro light emitting diodes  122 . The micro light emitting diodes  122  and the circuit board  121  are separately manufactured, a surface of the circuit board  121  includes a plurality of bonding pads for welding the micro light emitting diodes  122 , the micro light emitting diodes  122  are transferred above the bonding pads after being manufactured, the micro light emitting diodes  122  are welded to the circuit board  121  through processes such as reflow soldering, and thus the micro light emitting diodes  122  may be driven to emit light by controlling an input signal of the circuit board  121 . 
     The micro light emitting diodes  122  are located on the circuit board. Electrodes of the micro light emitting diodes  122  are welded to the bonding pads exposed on the circuit board  121  to achieve electric connection therebetween. 
     In this embodiment, the micro light emitting diodes  122  are different from ordinary light emitting diodes, and specifically refer to micro light emitting diode chips. Since the micro light emitting diodes  122  have small sizes, dynamic light emitting of the backlight module can be controlled to smaller partitions, which contributes to increase picture contrast. In the embodiments of the present application, the size of the micro light emitting diodes  122  is 50 μm to 300 μm. 
     The micro light emitting diode light board may only include micro light emitting diodes  122  of one color, or micro light emitting diodes of various colors, which is not limited herein. 
     The reflective layer  123  is located on a surface of a side of the circuit board  121  close to the micro light emitting diodes  122 . The reflective layer  123  and the circuit board  121  are substantially same in shape, and the reflective layer  123  includes a plurality of openings for exposing the micro light emitting diodes  122 . 
     The reflective layer  123  is a protective layer located above the circuit board and configured for protecting the circuit board and performing diffuse reflection on the incident light rays. In the embodiments of the present application, the reflective layer  123  may be formed in the way that the surface of the circuit board  121  is coated with white oil or other materials having light reflecting properties and then the areas of the bonding pads for welding the micro light emitting diodes  122  are exposed through processes such as etching. 
     The reflective layer  123  has reflecting light property, so that when the light rays emitted from the micro light emitting diode light board  122  are reflected to one side of the back plate by elements in the backlight module, the light rays may be reflected to the light emitting side again by the reflective layer  123 , thereby improving the efficiency of the light sources. 
     The packaging layer  124  is located on surfaces of a side of the micro light emitting diodes  122  away from the circuit board  121 . The packaging layer  124  may be disposed individually or as a whole layer. When being disposed individually, the packaging layer  124  only covers the surface of the micro light emitting diodes  122 , while no layer is disposed in other regions of the circuit board; and when being disposed as the whole layer, the packaging layer  124  covers the whole circuit board  121  and the surfaces of the micro light emitting diodes  122 . 
     The packaging layer  124  is configured to protect the micro light emitting diodes  122  and prevent foreign items from entering the micro light emitting diodes  122 . In the embodiment of the present application, the packaging layer  124  may be made of a transparent colloid material, such as silica gel or epoxy resin. The packaging layer  124  may be manufactured in a point coating or whole-face coating mode. 
     It is noted that, although the reflective layer  123  in this embodiment has the reflecting effect, in some embodiments, when high reflection is required, a reflective layer such as a reflective sheet may be further disposed on the light board  12 , and similarly, the reflective sheet is provided with openings for exposing the micro light emitting diodes. 
     The diffusion layer  13  is located on the light emitting side of the micro light emitting diode light board  12 . The diffusion layer  13  is disposed on the light emitting side of the micro light emitting diode light board  12  as a whole layer, and a shape of the diffusion layer  13  is substantially same as the shape of the micro light emitting diode light board  12 . Usually, the diffusion layer  13  may be rectangular or square. 
     The diffusion layer  13  is configured to scatter the incident light rays to make the light rays passing the diffusion layer  13  more uniformly. Scattering particle materials are disposed in the diffusion layer  13 , and the light rays will be refracted and reflected continuously after entering the scattering particle materials, so that the effect of dispersing the light rays is achieved to achieve light uniformizing. 
     The diffusion layer  13  may adopt two forms, a diffusion plate or a diffusion sheet. The diffusion plate may be adopted when applied to a large display apparatus such as a television; while the diffusion sheet may be adopted when applied to a small display apparatus such as a mobile phone and a smart watch. 
     A thickness of the diffusion plate is larger than that of the diffusion sheet and is 1.5 mm to 3 mm. The diffusion plate has the larger haze and better uniformizing effect, and usually may be processed through an extrusion process. A material for the diffusion plate is generally selected from at least one of polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS) or polypropylene (PP). 
     A thickness of the diffusion sheet is 0.3 mm or less, and the diffusion sheet is relatively thin and more applicable to small and light display apparatuses. According to the diffusion sheet, a base material is usually coated with diffusion particles, the base material may adopt polyethylene terephthalate (PET) or glass, and the diffusion particles may adopt titanium dioxide, zinc oxide, calcium oxide and the like. 
     Referring to  FIG. 9 , a vertical distance h between the diffusion layer  13  and the circuit board  121  is also called an optical distance (OD), a ratio h/p of the vertical distance h between the diffusion layer  13  and the circuit board  121  to a distance p between every two adjacent micro light emitting diodes  122  may indicate the overall thickness of the backlight module and a relative quantity of the micro light emitting diodes  122 . The smaller the h/p value, the smaller the optical distance, and the thinner the whole device; and the larger the distance between the adjacent micro light emitting diodes, the fewer micro light emitting diodes required, so the cost is lowered. 
     In a backlight module with light emitting diodes as light sources used in related art, lens need to be used together with the light emitting diodes, a height of the lens reaches about 5 mm, and the h/p value is about 0.3, but design of the OD being 5 mm or less cannot be achieved. 
     In the embodiments of the present application, in order to reduce the thickness of the backlight module, the micro light emitting diode light board  12  is adopted, no lens is disposed on the light emitting side of the micro light emitting diodes  122 , light intensity emit from the micro light emitting diodes  122  is distributed according to Lamber body, and its property is that the brightness is high over the micro light emitting diodes  122 , while the brightness is low at junctions of adjacent micro light emitting diodes. If the uniformity of backlight is required, the h/p value needs to reach 0.6 or above, for example, about 40,000 micro light emitting diodes are required by a 65-inch display, and apparently, the cost is high. 
     In view of the above issue, referring to  FIG. 9 , the display apparatus according to the embodiments of the present application further includes an angle selection layer  14 . 
     The angle selection layer  14  is located on the light emitting side of the micro light emitting diode light board  12 . In the embodiment of the present application, the angle selection layer  14  is disposed as a whole layer to be formed on the light emitting side of the micro light emitting diode light board  12 . The angle selection layer  14  may be prepared through an optical coating, and its specific form may be an optical film. 
     The angle selection layer  14  is configured to reflect the light rays with the first incident angle range and transmit the light rays with the second incident angle range. The incident angle value corresponding to the first incident angle range is smaller than the incident angle value corresponding to the second incident angle range. 
     The incident angle of the light rays entering into the angle selection layer  14  is equal to an angle of the light rays emitted from the micro light emitting diodes  122 , and thus the first incident angle range corresponds to an emitting angle range in which the emitting light intensity of the micro light emitting diodes  122  is high, and the second incident angle range corresponds to an emitting angle range in which the emitting light intensity of the micro light emitting diodes  122  is low. 
     The angle selection layer  14  may select to reflect the light rays with a small incident angle and transmit the light rays with a large incident angle. Meanwhile, the reflective layer  123  on the micro light emitting diode light board may conduct diffuse reflection on the light rays reflected by the angle selection layer  14  and the light rays re-enter the angle selection layer  14 , so that light rays of a second incident angle subjected to the diffuse reflection are transmitted while light rays of a first incident angle continue to repeat the described reflection operation. 
     Through the reflecting effect of the angle selection layer  14  and the reflective layer  123  to the light rays, the light intensity of a small angle range over the micro light emitting diodes  122  may be finally weakened, while the light intensity of a large angle range at junction areas of the micro light emitting diodes  122  may be finally enhanced, so that the light rays at all emitting angles of the micro light emitting diodes  122  are relatively uniform, and the light emitting uniformity of the micro light emitting diode light board  12  is improved. 
     In the embodiments of the present application, the angle selection layer  14  is disposed on the light emitting side of the micro light emitting diode light board  12 , by adjusting the distance between the micro light emitting diode light board and the angle selection layer  14 , the hip value may be in a range from 0.15 to 0.67, and thus requirements of display apparatuses of different specifications are met. 
     In the embodiments of the present application, since the light intensity of the micro light emitting diodes  122  is high at an area close to a light emitting center and is low at an area away from the light emitting center, the first incident angle range corresponds to 0° to 70°, and the second incident angle range corresponds to 70° or above. In this way, the angle selection layer  14  may achieve the effects of reflection enhancement to incident light rays of 0° to 70° and transmittance enhancement to incident light rays of 70° or above, so that the incident light rays within the angle range of the higher light intensity are reflected, the incident light rays within the angle range of the lower light intensity are transmitted, finally uniform light intensity distribution is achieved, and a light intensity difference of the emitting center and the junction areas of the micro light emitting diodes is reduced. 
     Since the closer to the emitting center, the higher the light intensity of the micro light emitting diodes, in the embodiments of the present application, the reflectivity of the angle selection layer  14  to the light rays with the first incident angle range is decreased with increasing of the incident angle, that is, the angle selection layer  14  has the more obvious reflecting effect to the emitting light rays closer to the area of the light emitting center, the angle selection layer  14  has the more obvious transmitting effect to the emitting light rays closer to edge areas, after the reflected light rays are subjected to the circulating reflecting effect of the angle selection layer  14  and the reflective layer  123 , transmittance of small-angle light rays will be decreased, transmittance of large-angle light rays will be increased, and finally the light intensity is uniformized. 
     Therefore, in the embodiments of the present application, the angle selection layer  14  is configured that: the larger the angle of the incident light rays, the smaller the reflectivity to the incident light rays; and the larger the angle of the incident light rays, the larger the transmittance to the incident light rays. 
     In the embodiments of the present application, the reflectivity of the angle selection layer  14  to the light rays with the first incident angle range is 10% to 80%, and the reflectivity of the angle selection layer  14  to the light rays with the second incident angle range is less than 10%. For the incident light rays with the first incident angle range, the angle selection layer  14  is disposed to have the highest reflectivity to light rays entering perpendicular to the light emitting center, and with increasing of the incident angle, the reflectivity of the angle selection layer  14  to the incident light rays is lowered; and for the incident light rays with the second incident angle range, the transmittance of the angle selection layer  14  is increased with increasing of the incident angle. 
       FIG. 10  is a schematic cross-sectional view of the angle selection layer according to an embodiment of the present application. 
     The angle selection layer includes a plurality of film layers  141  disposed in a laminated mode, and two adjacent film layers  141  has different refraction indexes. The film layers  141  in the angle selection layer may adopt optical films and be manufactured through an optical coating process with polymer materials such as polyhexafluoropropylene oxide, polytrifluoroethyl methacrylate and polymethylhydrosiloxane. 
     A thickness of the angle selection layer is 50 μm to 60 μm, and the thickness is small relative to other optical film layers in the backlight module, so that the impact on the overall thickness of the backlight module is little. 
     Next, the work principle of transmittance and reflection enhancement of the angle selection layer  14  to the incident light rays is specifically described. 
       FIG. 11  is a schematic diagram of the work principle of the angle selection layer according to an embodiment of the present application. 
     Referring to  FIG. 11 , when light rays enter a surface of a thin film with a refraction index n 2  from a medium with a refraction index n 1  with an incident angle i, light reflection and refraction occur at an interface of two media with indexes n 1  and n 2 , a reflection angle and the incident angle are equal and are still i, and a refraction angle is γ; and when refracted light rays enter a lower surface of the thin film, light reflection and refraction also occur on the lower surface, wherein reflected light rays will pass an upper surface of the thin film to be refracted in the medium with an index n 1 , and thus two beams of reflected light rays (1) and (2) are formed on the upper surface and the lower surface of the thin film. An optical path difference δ′ between the reflected light ray (1) and the reflected light ray (2) is: 
       δ′= n   2 (   AB + BC   )− n   1     AD .  
 
     If a thickness of the thin film with the refraction index being n 2  is d and the thickness of the thin film is uniform, due to  AB = BC =d/cos γ and  AD = AC  sin i=2d tan γ×sin i, the following may be obtained: 
     
       
         
           
             
               δ 
               ′ 
             
             = 
             
               
                 
                   
                     n 
                     2 
                   
                   ⁢ 
                   2 
                   ⁢ 
                   
                     AB 
                     _ 
                   
                 
                 - 
                 
                   
                     n 
                     1 
                   
                   ⁢ 
                   
                     AD 
                     _ 
                   
                 
               
               = 
               
                 
                   
                     
                       2 
                       ⁢ 
                       
                         n 
                         2 
                       
                       ⁢ 
                       d 
                     
                     
                       cos 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       γ 
                     
                   
                   - 
                   
                     2 
                     ⁢ 
                     
                       n 
                       1 
                     
                     ⁢ 
                     d 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     tan 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     γ 
                     × 
                     sin 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     i 
                   
                 
                 = 
                 
                   
                     
                       2 
                       ⁢ 
                       d 
                     
                     
                       cos 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       γ 
                     
                   
                   ⁢ 
                   
                     
                       ( 
                       
                         
                           n 
                           2 
                         
                         - 
                         
                           
                             n 
                             1 
                           
                           ⁢ 
                           sin 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           i 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           sin 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           γ 
                         
                       
                       ) 
                     
                     . 
                   
                 
               
             
           
         
       
     
     It can be known from the refraction law that: 
     
       
         
           
             
                 
             
             ⁢ 
             
               
                 
                   
                     n 
                     1 
                   
                   ⁢ 
                   sin 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   i 
                 
                 = 
                 
                   
                     n 
                     2 
                   
                   ⁢ 
                   sin 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   γ 
                 
               
               ; 
             
           
         
       
       
         
           
             
               δ 
               ′ 
             
             = 
             
               
                 
                   
                     2 
                     ⁢ 
                     d 
                     ⁢ 
                     
                       n 
                       2 
                     
                   
                   
                     cos 
                     ⁢ 
                     r 
                   
                 
                 ⁢ 
                 
                   ( 
                   
                     1 
                     - 
                     
                       
                         sin 
                         2 
                       
                       ⁢ 
                       γ 
                     
                   
                   ) 
                 
               
               = 
               
                 
                   
                     
                       2 
                       ⁢ 
                       
                         n 
                         2 
                       
                       ⁢ 
                       d 
                     
                     
                       cos 
                       ⁢ 
                       γ 
                     
                   
                   ⁢ 
                   
                     cos 
                     2 
                   
                   ⁢ 
                   γ 
                 
                 = 
                 
                   
                     2 
                     ⁢ 
                     
                       n 
                       2 
                     
                     ⁢ 
                     d 
                     ⁢ 
                     cos 
                     ⁢ 
                     γ 
                   
                   = 
                   
                     
                       2 
                       ⁢ 
                       
                         n 
                         2 
                       
                       ⁢ 
                       d 
                       ⁢ 
                       
                         
                           1 
                           - 
                           
                             
                               sin 
                               2 
                             
                             ⁢ 
                             γ 
                           
                         
                       
                     
                     = 
                     
                       2 
                       ⁢ 
                       d 
                       ⁢ 
                       
                         
                           
                             
                               n 
                               2 
                               2 
                             
                             - 
                             
                               
                                 n 
                                 1 
                                 2 
                               
                               ⁢ 
                               
                                 sin 
                                 2 
                               
                               ⁢ 
                               i 
                             
                           
                         
                         . 
                       
                     
                   
                 
               
             
           
         
       
     
     so: 
     It can be seen from the above formula that, if a multi-layer film structure is disposed, an optical path difference between reflected light of the light rays on the upper and lower surfaces of each layer of medium is only related to a refraction index and a thickness of this layer and an incident angle. In practical applications, light rays usually enter a thin film from an air medium, light reflection occurs on an upper surface and a lower surface of the thin film, that is, the refraction index in the above formula is n 1 =1, and thus the above formula may be simplified as: 
       δ′=2 d √{square root over ( n   2   2   −n   1   2  sin 2    i )}=2 d √{square root over ( n   2   2 −sin 2    i )}.
 
     It can be known from the Thin-film interference law that, when the optical path difference between the reflected light rays on the upper surface and the lower surface of the thin film is integer times of a wavelength, the two beams of light rays are coherently added; and when the optical path difference between the reflected light rays on the upper surface and the lower surface is odd times of a half-wavelength, the two beams of light rays are coherently subtracted. According to the law of conservation of energy, if the reflected light is coherently added, energy of the reflected light is enhanced, and energy of transmission light is weakened; and if the reflected light is coherently subtracted, the energy of the reflected light is weakened, and the energy of the transmission light is enhanced. 
     When the above principle is applied to the embodiments of the present application, for any film layer  141  in the angle selection layer  14 , an incident angle of reflection enhancement is set as θ 1  and an incident angle of transmittance enhancement is set as θ 2 , so that when emitting light of the micro light emitting diodes  122  enter the angle selection layer  14 , light rays with the incident angle θ 1  may be subjected to reflection enhancement, and light rays with the incident angle θ 2  may be subjected to transmittance enhancement. 
     It can be seen that as long as the refraction indexes and thicknesses of the film layers  141  meet a condition of reflecting the light rays with the first incident angle range and transmitting the light rays with the second incident angle range, the same film layer  141  may have the effects of reflection enhancement and transmittance enhancement to different incident angles. 
     The angle selection layer  14  includes the plurality of film layers  141  disposed in the laminated mode, and each film layer  141  may have the effect of reflection enhancement for different first incident angles and the effect of transmittance enhancement for the second incident angles. By disposing the plurality of film layers  141 , the effect of reflection enhancement is achieved for the light rays within the first incident angle range, and the effect of transmittance enhancement is achieved for the light rays within the second incident angle range. 
     In the embodiments of the present application, the angle selection layer includes multiple groups of film layers, wherein each group includes a plurality of film layers, and the film layers has different refraction indexes and thicknesses. If the refraction index of a certain film layer in the film layer group is n1, a thickness thereof is d1, and the film layer is configured to reflect 0° incident light rays and transmit 70° incident light rays, a following relation may be concluded from the above formulas: 
       2 d   1 √{square root over ( n   1   2 −sin 2  0°)}= mλ;  
 
       2 d   1 √{square root over ( n   1   2 −sin 2  70°)}=( m− 0.5)λ.
 
       The following may be obtained by dividing the above two formulas: 
         n   1 /√{square root over ( n   1   2 −sin 2  70°)}= m /( m −0.5).
 
     Wherein m is a positive integer, and λ is a wavelength of the incident light rays. 
     In a case where a material of the film layers  141  has a determined refraction index, the thickness of the film layers  141  may be figured out according to the above, so that the film layers may have the effect of reflection enhancement to the 0° incident light rays and the effect of transmittance enhancement to the 70° incident light rays. 
     Similarly, another film layer may be disposed in the above film layer group to achieve the effect of reflection enhancement to 30° incident light rays and the effect of transmittance enhancement to 80° incident light rays, and another film layer may be disposed to achieve the effect of reflection enhancement to 60° incident light rays and the effect of transmittance enhancement to 90° incident light rays, so that the film layer group have the effects of reflection enhancement to the incident light rays of 0° to 70° and transmittance enhancement to the incident light rays of 70° or above. 
     By disposing the plurality of film layer groups, the effect of reflection enhancement for the light rays within the first incident angle range and the effect of anti-reflection for the light rays within the second incident angle range by the angle selection layer  14  may be enhanced. The effect of adjusting the reflectivity and the transmittance may also be achieved by adjusting the quantity of the film layers. 
     In some embodiments, the light sources of the backlight module according to the embodiment of the present application may be white light sources, so film layers for reflection enhancement for the first incident angle and transmittance enhancement for the second incident angle need to be disposed for three components, namely red, green and blue, in white light respectively. 
     In some embodiments, the light sources of the backlight module according to the embodiments of the present application are single-color light sources, and the single-color light sources need to be matched with a color conversion layer for use. 
     In some embodiments, the light sources are blue light sources, so in this case, a wavelength conversion layer such as a quantum dot layer may be used together, and red quantum dot materials and blue quantum dot materials are mixed in the quantum dot layer, so that transmitted blue light as well as red light and green light emitted by excitation for three primary lights to achieve full-color display. 
     When the blue light sources are adopted, incident light entering the film layers in the angle selection layer is fixed in wavelength which is in a wavelength range corresponding to blue light, and thus the film layers only need to be disposed for the wavelength of the blue light to perform reflection enhancement on a plurality of first incident angle ranges and transmittance enhancement on a plurality of second incident angle ranges at the same time. A value range of the first incident angle is smaller than a value range of the second incident angle. 
       FIG. 12  is a second schematic cross-sectional view of the angle selection layer according to an embodiment of the present application. 
     Referring to  FIG. 12 , the backlight module further includes a base material  140  configured to support the film layers disposed in the laminated mode. 
     The base material  140  and the film layers  141  have substantially the same shape and size, usually, the shape may be a rectangle, and the size is matched with the size of the micro light emitting diode light board  12 . 
     The base material  140  has a support effect, the film layers  141  in the angle selection layer  14  are mostly optical films with the thickness being at a nanometer to micron scale, if the film layers are separately formed, mounting is relatively difficult in an mounting process of the module, and therefore the film layers  141  are formed on a surface of the base material  140  and then the base material  140  and the film layers  141  are transferred to a corresponding area in the backlight module together, so that the base material  140  also has a certain protecting effect for the film layers  141 . 
     A material of the base material  140  may be polyethylene terephthalate (PET) and the like, which is not limited here. 
       FIG. 13  is a second schematic cross-sectional view of the backlight module according to an embodiment of the present application. 
     Referring to  FIG. 9  and  FIG. 6 , the positions of the diffusion layer  13  and the angle selection layer  14  in the embodiment of the present application may be flexibly set. 
     As shown in  FIG. 9 , the angle selection layer  14  is located on a side close to the micro light emitting diode light board  12 , and the diffusion layer  13  is located on a side of the angle selection layer  14  away from the micro light emitting diode light board  12 . 
     Disposing the angle selection layer  14  between the diffusion layer  13  and the micro light emitting diode light board  12  contributes to increase the vertical distance between the micro light emitting diodes  122  and the diffusion plate  13 , namely increasing the OD, so that the light mixing effect of the micro light emitting diodes  122  can be improved. 
     As shown in  FIG. 12 , the diffusion layer  13  is located on a side close to the micro light emitting diode light board  12 , and the angle selection layer  14  is located on a side of the diffusion layer  13  away from the micro light emitting diode light board  12 . 
     Disposing the diffusion layer  13  between the micro light emitting diode light board  12  and the angle selection layer  14  facilitates to increase the distance between the angle selection layer  14  and the micro light emitting diode light board  12 , and the larger the distance therebetween, the farther the position of light rays re-entering the angle selection layer  14  after being reflected, so that a light illumination range of the micro light emitting diodes  122  is expanded. 
     However, in the embodiment shown  FIG. 12 , a minimum h/p value achieving good backlight uniformity is greater than the h/p value in the embodiment where the angle selection layer is disposed on an incident side of the diffusion layer (the diffusion plate, or the diffusion sheet or a quantum dot film). 
     The backlight module in the embodiment of the present application may achieve the small h/p value on the premise of guaranteeing uniform backlight, so that the overall thickness of the backlight module is reduced, the using quantity of the micro light emitting diodes is reduced under the same size, and the cost is controlled. 
     In the present application, brightness distribution conditions of the backlight module without an angle selection layer in the related art and the backlight module adopting the angle selection layer in the embodiment of the present application are further subjected to comparison testing. When the h/p value is 0.22, brightness distribution uniformity of the backlight module in the embodiment of the present application is remarkably improved. 
       FIG. 14A  shows a schematic diagram of brightness distribution of the backlight module without an angle selection layer in the related art. It can be seen from  FIG. 14A  that many discrete bright spots occur in the backlight module, a circle of dark region is formed around the bright spots, and brightness distribution is not uniform. 
       FIG. 14B  shows a schematic diagram of brightness distribution of the backlight module adopting the angle selection layer in the embodiment of the present application. It can be seen from  FIG. 14B  that through the circulating reflecting effect of the angle selection layer and the reflective layer in the micro light emitting diode light board in the embodiment of the present application, brightness spots are eliminated, and brightness distribution is uniform, which meets the backlight requirement. 
     The backlight module shown in  FIG. 9  and  FIG. 13  may achieve backlight design of a small OD value. Directly disposing the angle selection layer  14  and the diffusion layer  13  on the micro light emitting diode light board  12  may reduce the OD value to 1 mm or below to achieve the design of an ultra-thin module. 
     The angle selection layer  14  may be directly attached to the surface of the micro light emitting diode light board  12 , so that the base material  140  is omitted and the thickness is reduced on the whole. 
     Or, when the backlight module is applied to a display apparatus such as a large-size television, the diffusion layer  13  may adopt the diffusion plate, and the angle selection layer  14  may be directly attached to the surface of the diffusion plate, so that the base material  140  is omitted. The diffusion plate has the effect of diffusion and the effect of supporting the angle selection layer  14  at the same time. 
     Or, when the backlight module is applied to a display apparatus such as a small-size mobile terminal, the diffusion layer  13  may adopt the diffusion sheet, and the angle selection layer may be directly attached to the base material of the diffusion plate without separately disposing the base material for the angle selection layer  14 , so that one base material may be omitted, and the diffusion sheet has the effect of diffusion and the effect of supporting the angle selection layer  14  at the same time. 
     Or, the angle selection layer  14  may be disposed on the base material  140  and then transferred with the base material to the corresponding position of the backlight module together. The angle selection layer  14  with the base material  140  is easier to mount to avoid damage during mounting. 
       FIG. 15  is a third schematic cross-sectional view of the backlight module according to an embodiment of the present application. 
     Referring to  FIG. 15 , in another embodiment of the present application, the backlight module further includes a transparent substrate  15 , and the transparent substrate  15  is located between the micro light emitting diode light board  12  and the diffusion layer  13 . 
     The transparent substrate  15  and the micro light emitting diode light board  12  are substantially the same in shape, the micro light emitting diode light board  12  is coated with the whole packaging layer, and the transparent substrate  15  is directly placed on the packaging layer of the micro light emitting diode light board  12 . The transparent substrate adopts a material with a high transmittance such as polymethyl methacrylate (PMMA) or glass. 
     As a supporting structure of the diffusion layer  13 , the transparent substrate  15  makes the micro light emitting diode light board  12  and the diffusion layer  13  have a certain distance, so that light emitted from the micro light emitting diodes  122  is fully mixed before reaching the diffusion layer  13 , and the backlight brightness uniformity is improved. 
     The structure that the transparent substrate  15  is disposed on the micro light emitting diode light board  12  is more suitable for design of a backlight module with a large OD value. 
     The angle selection layer  14  may be directly attached to the transparent substrate  15 , so that the base material  140  may be omitted, components used in the backlight module are reduced, and the thickness is reduced. 
       FIG. 16  is a fourth schematic cross-sectional view of the backlight module according to an embodiment of the present application. 
     Referring to  FIG. 16 , in another embodiment of the present application, the backlight module further includes transparent supports  15 ′, and the transparent supports  15 ′ are located on the micro light emitting diode light board  12  and are configured to support the diffusion layer  13 . 
     The micro light emitting diode light board  12  is spot-coated with a packaging material, there is a gap between adjacent micro light emitting diodes, and the transparent supports  15 ′ are disposed at the positions of these gaps to support the diffusion layer  13  so as to make a certain distance between the diffusion plate  13  and the micro light emitting diodes  122  to increase the OD value. 
     The angle selection layer  14  may be directly attached to the surface of the diffusion layer  13 , so that the base material  140  is omitted, and the diffusion layer may achieve the supporting effect for the angle selection layer. 
       FIG. 17  is a fifth schematic cross-sectional view of the backlight module according to an embodiment of the present application. 
     Referring to  FIG. 17 , the backlight module in the embodiment of the present application further includes a quantum dot layer  16  and an optical film  17 . The quantum dot layer  16  functions as wavelength conversion layer, and the wavelength conversion layer in the embodiment of the present application is not limited to the quantum dot layer and may also be a fluorescent powder layer and the like. 
     The quantum dot layer  16  is located on a side of the diffusion layer  13  away from the micro light emitting diode light board  12 . The quantum dot layer  16  is disposed as a whole layer, and a shape of the quantum dot layer  16  is substantially same as that of the micro light emitting diode light board  12  and usually may be a rectangle or a square. 
     The quantum dot layer  16  is used together with single-color micro light emitting diodes. In the embodiment of the present application, the micro light emitting diodes are blue light micro light emitting diodes. The quantum dot layer  16  has two quantum dot materials, wherein one is red quantum dot material, with a wavelength of light excited by blue light being about 620 nm to 640 nm; and the other is green quantum dot material, with a wavelength excited by the blue light being about 520 nm to 540 nm. Red light and green light emitted by excitation from the quantum dot layer  16  are mixed with transmitted blue light to form white light so as to provide backlight for the panel. 
     The optical film  17  is located on a side of the quantum dot layer  16  away from the diffusion layer  13 . The optical film  17  is disposed as a whole layer, and a shape of the optical film  17  is substantially same as that of the micro light emitting diode light board  12  and usually may be a rectangle or a square. 
     Disposing the optical film  17  may make the backlight module adaptive to various practical applications. 
     The optical film  17  may include a prism sheet, and the prism sheet may change an emitting angle of light rays to change a viewing angle of the display apparatus. 
     The optical film may further include a reflective polarizer. As a brightness enhancement sheet, the reflective polarizer may increase the brightness of the backlight module, improve efficiency of light rays, and make emitting light rays have a polarizing property, so use of a polarizer in the liquid crystal panel is omitted. 
       FIG. 18  is a sixth schematic cross-sectional view of the backlight module according to an embodiment of the present application. 
     Referring to  FIG. 18 , in another embodiment of the present application, the backlight module further includes an anti-reflection film  18  which is located on a side of the quantum dot layer  16  facing the micro light emitting diode light board  12 . 
     The transmittance-enhancing film  18  is configured to increase transmittance of blue light and enhance reflection of red light and green light, so that light rays entering the quantum dot layer  16  may all be blue light, and an excitation rate of the quantum dot layer  16  is increased. Meanwhile, it is guaranteed that red light and green light emitted to one side of the panel are both excited by the quantum dot layer  16 , so that a high color gamut is achieved. 
     Next, a structure of the micro light emitting diode light board formed through a POB packaging is described. 
     The micro light emitting diode light board includes a circuit board and micro light emitting diodes  122 ′ located on the circuit board. The micro light emitting diodes  122 ′ are devices with micro light emitting diode chips  1221 ′, and see  FIG. 19  for the specific structure. 
     As shown in  FIG. 19 , the micro light emitting diodes  122 ′ include the micro light emitting diode chips  1221 ′ and individual packaged supports  1222 ′, and the micro light emitting diode chips  1221 ′ are placed at the bottoms of the encapsulation supports  1222 ′. 
     To further lower the OD value, the micro light emitting diodes  122 ′ further include top shielding layers  1223 ′ located on a light emitting side of the micro light emitting diode chips  1221 ′. 
     The top shielding layers  1223 ′ are formed by mixing scattering particles, such as titanium dioxide, in glue. The existence of the top shielding layers  1223 ′ can increase a light emitting angle of the micro light emitting diode chips  1221 ′. In a case where the quantity and distance of the micro light emitting diodes  122 ′ are not changed, an illumination range of the micro light emitting diodes  122 ′ may be expanded, and the OD value is further reduced. 
     When the micro light emitting diode light board in this embodiment is used, a reflective sheet is often required to be used together as a reflective layer to achieve the effect jointly. 
     The angle selection layer in the present application can also apply to an scenario where a lens is disposed on the light sources. Description is made in combination with the structure of the micro light emitting diode light board with COB packaging below, and it is noted that it is not limited to the micro light emitting diode light board with COB packaging. 
       FIG. 20  is a schematic cross-sectional view of a backlight module according to an embodiment of the present application. 
     Referring to  FIG. 20 , the backlight module includes: a back plate  331 , a micro light emitting diode light board  32 , a functional layer  33 , an angle selection layer  34  and an optical film  35 . 
     In the embodiment of the present application, the micro light emitting diode light board  32  includes: a circuit board  321 , micro light emitting diodes  322 , a reflective layer  323  and one or more light uniformizing components  324 . 
     The micro light emitting diode light board according to an embodiment of the present application further includes a packaging layer not shown in the figure, and the packaging layer is located on surfaces of a side of the micro light emitting diodes  322  away from the circuit board  321 . The packaging layer has individual patterns, the surfaces of the micro light emitting diodes  322  are spot-coated with the packaging layer, and no pattern is disposed in other regions of the circuit board  321 . 
     The packaging layer is configured to protect the micro light emitting diodes  322  and prevent foreign items from entering the micro light emitting diodes  322 . In the embodiments of the present application, the packaging layer may be made of a transparent material, such as silica gel or epoxy resin. 
     The one or more light uniformizing component  324  is located on a light emitting side of the micro light emitting diodes  322 . The light uniformizing components  324  have one to one correspondence with the micro light emitting diodes, and one light uniformizing component  324  is disposed on the light emitting side of each micro light emitting diode  322  for uniformizing light rays emitting from the micro light emitting diodes  322 . 
     Since the micro light emitting diodes  322  are used as backlight sources in the embodiment of the present application, energy distribution of emitting light of the micro light emitting diodes  322  meets Lambertian distribution, energy over the micro light emitting diodes  322  is high, while energy at junction areas of the adjacent micro light emitting diodes  322  is weak. 
     In the embodiments of the present application, the light uniformizing components  324  are disposed on the light emitting side of the micro light emitting diodes  322  to uniformize the light rays emitted from the micro light emitting diodes  322 , and thus an energy difference within a small-angle emitting range and a large-angle emitting range of the micro light emitting diodes  322  is reduced. 
     The uniformized light rays will enter the angle selection layer  33 , and a reflectivity of the angle selection layer  33  to the incident light rays is decreased with angle increase of the incident light rays. That is, the larger the angle of the incident light rays, the smaller the reflectivity of the angle selection layer  33  to the incident light rays; and the larger the angle of the incident light rays, the larger a transmittance of the angle selection layer to the incident light rays. Thus, most small-angle light rays entering the angle selection layer  33  will be reflected by the angle selection layer  33 , while most large-angle light rays entering the angle selection layer  33  will be transmitted by the angle selection layer  33 . The reflected small-angle light rays re-enter the reflective layer  323  and re-enter the angle selection layer  33  after being subjected to the diffuse reflection effect of the reflective layer  323 , and after multiple times of reflection between the angle selection layer  33  and the reflective layer  323 , finally emitting light rays are further uniformized. 
     The light uniformizing components  324  and the angle selection layer  33  are utilized to uniformize the emitting light rays of the micro light emitting diodes  322  in the embodiments of the present application, so that a vertical distance from the micro light emitting diode light board  32  to the diffusion layer  34  and a distance between every two adjacent micro light emitting diodes  322  meet a following relationship: H/P≤0.2. 
     Referring to  FIG. 20 , H represents the vertical distance from the micro light emitting diode light board  32  to the diffusion layer  34 , and P represents the distance between every two adjacent micro light emitting diodes  322 . 
     The vertical distance H between the micro light emitting diode light board  32  and the diffusion layer  34  is also called an optical distance (OD), and the ratio H/P of the vertical distance H between the micro light emitting diode light board  32  and the diffusion layer  34  to the distance P between every two adjacent micro light emitting diodes  322  may indicate an overall thickness of the backlight module. The smaller the H/P value of the quantity of the micro light emitting diodes  322 , the smaller the optical distance, and the thinner the whole device. The larger the distance between the adjacent micro light emitting diodes, the fewer the micro light emitting diodes required for use, so that the cost may be lowered. 
     The structure that the light uniformizing components are combined with the angle selection layer according to an embodiment of the present application may control the H/P ratio to be 0.2 or below, and compared with a structure in the related art that an H/P ratio is 0.3 or above, the backlight module according to an embodiment of the present application may have the smaller thickness, which meets the ultra-thin design of the display apparatus. The quantity of the micro light emitting diodes used is reduced, and the production cost is lowered. 
     In the embodiments of the present application, as shown in  FIG. 20 , the light uniformizing components  324  may be disposed as lenses located on the light emitting side of the micro light emitting diodes  322 . The lenses correspond to the micro light emitting diodes one to one, and one lens is disposed on the light emitting side of each micro light emitting diode  322 . 
     The lenses include incident surfaces facing a side of the micro light emitting diodes and emitting surfaces away from the side of the micro light emitting diodes, the incident surfaces protrude towards the side away from the micro light emitting diodes to form chambers, and the micro light emitting diodes are located in the chambers, Packaging layers are generally disposed on the surfaces of the micro light emitting diodes, and the micro light emitting diodes and the packaging layers on their surfaces are located in the chambers of the incident surfaces of the lenses. 
     Through appropriate optical design, surface types of the incident surfaces and the emitting surfaces of the lenses may enable light emitting from the light emitting diodes to enter the lenses first, and optical field distribution of transmitted light rays is adjusted. After the lenses are disposed on the light emitting side of the micro light emitting diodes, light intensity over the micro light emitting diodes and light intensity at junction areas of the adjacent micro light emitting diodes are relatively uniform. 
       FIG. 21  is a schematic cross-sectional view of the backlight module according to some embodiments of the present application. 
     Referring to  FIG. 21 , in other embodiments of the present disclosure, the light uniformizing components  324  may be disposed as half-transmittance and half-reflection layers located on the light emitting side of the micro light emitting diodes. 
     When receiving light rays emitting from the micro light emitting diodes, the half-transmittance and half-reflection layers will transmit a part of the light rays and reflect remaining light rays, and the reflected light rays re-enter the reflective layer  323  and then are emitted to one side of the angle selection layer  33  after subjected to diffuse reflection of the reflective layer  323 . 
     Disposing the half-transmittance and half-reflection layers on the light emitting side of the micro light emitting diodes may reduce the intensity of emitting light over the micro light emitting diodes to make the light rays distributed towards regions away from the region over the micro light emitting diodes, so that the emitting light rays of the micro light emitting diodes are relatively uniform. 
     As shown in  FIG. 21 , the micro light emitting diodes  322  are micro light emitting diode chips which are usually of a square structure, and the half-transmittance and half-reflection layers ( 324 ) may be directly disposed on light emitting surfaces, namely upper surfaces, of the micro light emitting diodes  322 . In this way, all the light rays emitted upwards from the micro light emitting diodes  322  are subjected to the effect of the half-transmittance and half-reflection layers, so that the light intensity of the emitting light rays is relatively uniform after the reflecting effect of the half-transmittance and half-reflection layers and the reflective layer  323 . 
       FIG. 22  is a schematic cross-sectional view of the backlight module according to some embodiments of the present application. 
     Referring to  FIG. 22 , in other embodiments of the present application, protective components  325  are disposed on the surfaces of the micro light emitting diodes  322 , and the half-transmittance and half-reflection layers ( 324 ) are located on surfaces of a side of the protective components  325  away from the micro light emitting diodes  322 . 
     The protective components  325  on the surfaces of the micro light emitting diodes  322  may be the packaging layers above, and the surfaces of the micro light emitting diodes  322  may be spot-coated with a light transmitting material to form a protective layer. 
     The protective components may configured for protecting the micro light emitting diodes  322  and may also form a certain distance between the half-transmittance and half-reflection layers ( 324 ) and the micro light emitting diodes  322 . In this way, the light rays emitted from the micro light emitting diodes  322  enter the half-transmittance and half-reflection layers after passing a certain distance, light rays reflected by the half-transmittance and half-reflection layers are reflected again after entering the reflective layer  323 , a path of the reflected light rays is lengthened, and the light rays may be reflected to farther regions, so that the light rays emitted upwards from the micro light emitting diodes can be converted to the junction areas of the adjacent micro light emitting diodes, thereby achieving uniformity of the light rays emitted from the micro light emitting diodes. 
     The structure that the light uniformizing components  324  and the angle selection layer  33  are used together in the backlight module of the embodiment of the present application may improve the light emitting uniformity of the backlight module. 
       FIG. 23  shows a schematic diagram of light intensity distribution of the backlight module without the light uniformizing components  324  or the angle selection layer  33  in the related art. It can be seen from  FIG. 23  that many discrete bright spots occur in the backlight module, a circle of dark region is formed around the bright spots, and brightness distribution is not uniform. 
       FIG. 24  shows a schematic diagram of light intensity distribution of the backlight module adopting the light uniformizing components  324  and the angle selection layer  33  in the embodiments of the present application. It can be seen from  FIG. 24  that in the embodiments of the present application, through the light uniformizing components  324  and the angle selection layer  33 , when the H/P value is reduced to 0.15, light intensity distribution uniformity is still good, which meets requirements like thin backlight module and less micro light emitting diodes. 
     In order to meet requirements of the production cost and ultra-thin appearance and the like, the present application further provides a display apparatus, and two functional layers are introduced into the display apparatus. 
       FIG. 25  is a schematic cross-sectional view of a backlight module according to some embodiments of the present application. 
     Referring to  FIG. 25 , the backlight module according to an embodiment of the present application includes: a back plate  41 , a circuit board  42 , light sources  43 , a wavelength conversion layer  44 , a reflective layer  45 , a first functional layer  46 , a second functional layer  47 , a diffusion layer  48  and an optical film  49 . 
     The back plate  41  is located at the bottom of the backlight module and configured for supporting. Usually, the back plate  41  is of a square structure or a rectangular structure, and when the back plate is applied to a special-shaped display apparatus, a shape of the back plate is adapted to a shape of the display apparatus. The back plate  41  includes a top side, a bottom side, a left side and a right side. The top side and the bottom side are opposite, the left side and the right side are opposite, the top side is connected with one end of the left side and one end of the right side, and the bottom side is connected with the other end of the left side and the other end of the right side. 
     A material of the back plate  41  is aluminum, iron, aluminum alloy or iron alloy. The back plate  41  is configured to fix and support edge areas of components such as the optical film and the diffusion layer, and the back plate  41  is also configured to dissipate heat. 
     The circuit board  42  is located on the back plate  41 , and a shape of the circuit board  42  is substantially same as an overall shape of the back plate  41 . Usually, the circuit board  42  is in a plate shape and is rectangular or square as a whole. 
     In the embodiments of the present application, the circuit board  42  may be a printed circuit board (PCB), the PCB includes a driving circuit and an insulating layer, and the insulating layer exposes a bonding pad in the driving circuit for welding the light sources and covers remaining parts. 
     Or, the circuit board  42  may also be an array substrate formed by manufacturing a thin film transistor driving circuit on a base substrate, and a surface of the array substrate has electrodes connected to the thin film transistor driving circuit for welding the light sources. 
     A material of the circuit board  42  may be an aluminum substrate, BT or FR4, which is not limited here. Or, a base or base substrate of the circuit board  42  may adopt a hard material or adopt a flexible material to form a flexible display apparatus. 
     The circuit board  42  provides a driving electric signal for the light sources. The light sources  43  are welded on the circuit board  42  to electrically connect the light sources  43  with the driving circuit in the circuit board  42 , and controlling the driving signal of the circuit board  42  may drive the light sources  43  to emit light. 
     The backlight module according to an embodiment of the present application is a direct backlight module, and the light sources  43  are distributed on the circuit board  42  to emit light rays to the upper side so as to provide backlight. The light sources  43  on the circuit board  42  are partitioned, light emitting brightness in each partition may be independently controlled, and therefore backlight brightness in each partition is regulated according to displayed images to achieve dynamic control over backlight so as to increase the contrast of the displayed images. 
     In the embodiments of the present application, the light sources  43  may adopt blue light emitting diodes to emit blue light, and a wavelength of light rays emitted from the blue light emitting diodes is 440 nm to 450 nm. 
     The wavelength conversion layer  44  is disposed on a light emitting side of the light sources  43 , the wavelength conversion layer  44  is disposed as a whole layer with a shape being substantially same as the shape of the back plate  41 , which may be square or rectangular usually. 
     The wavelength conversion layer  44  includes a red light conversion material and a green light conversion material, and under irradiation of the blue light, the red light conversion material is excited to emit red light (620 nm to 660 nm) and the green light conversion material is excited to emit green light (525 nm to 545 nm). Therefore, the wavelength conversion layer  44  is excited by the blue light to emit the red light and the green light, and the blue light, the red light and the green light are mixed to form white light so as to provide backlight for the display panel. 
     In the embodiments of the present application, the wavelength conversion layer  44  may be a quantum dot layer, the quantum dot layer includes a red quantum dot material and a green quantum dot material, the red quantum dot material is excited by the blue light to emit red light, the green quantum dot material is excited by the blue light to emit green light, and the red light and the green light which are emitted by excitation and the transmitted blue light are mixed to form white light to be emitted. 
     In other embodiments of the present application, the wavelength conversion layer  44  may be a fluorescent layer, the fluorescent layer includes a red light conversion material and a green light conversion material, the red light conversion material is excited by the blue light to emit red light, the green light conversion material is excited by the blue light to emit green light, and the red light and the green light which are emitted by excitation and the transmitted blue light are mixed to form white light to be emitted. 
     The reflective layer  45  is located on a side of the circuit board  42  close to the light sources  43 . A shape of the reflective layer  45  is substantially same as that of the circuit board  42  and is usually a square or a rectangle. The reflective layer  45  includes a plurality of openings for exposing the light sources  43 . 
     The reflective layer  45  is configured for scattering or diffuse reflection on incident light rays, light rays emitted from the light sources  43  to one side of the circuit board  42  or light rays reflected to one side of the circuit board  42  may be reflected again by the reflective layer  45  to the light emitting side of the backlight module, and thus use efficiency of the light sources  43  is improved. 
     When the light sources  43  are light emitting diodes, the reflective layer  45  may be disposed as a reflective sheet or as a white oil coating on the surface of the circuit board. 
     The first functional layer  46  is located between the light sources  43  and the wavelength conversion layer  44 . The first functional layer  46  is disposed as a whole layer with a shape being substantially same as the shape of the wavelength conversion layer  44 , which may be square or rectangular usually. 
     An angle of the light rays emitted from the light sources is related to an incident angle of the light rays entering the first functional layer, when small-angle light rays emitted from the light sources enter into the first functional layer, the incident angle is small, and when large-angle light rays emitted from the light sources enter into the first functional layer, the incident angle is large. In the embodiments of the present application, the first functional layer  46  is configured to reflect the small-angle light rays emitted from the light sources  43  and transmit the large-angle light rays emitted from the light sources  43 . A reflectivity of the first functional layer  46  to the incident light rays is decreased with increasing of the angle of the incident light rays, that is, the larger the incident angle of the incident light rays, the smaller the reflectivity of the first functional layer to the incident light rays, and the larger a transmittance to the incident light rays; and the smaller the incident angle of the incident light rays, the larger the reflectivity of the first functional layer to the incident light rays, and the smaller the transmittance. 
     The first functional layer  46  in the present application may be the above angle selection layer. 
     Since the light sources  43  adopt the light emitting diodes (LED) and an emitting light pattern of the LEDs meets Lambertian distribution, energy of emitting light is concentrated in a small angle, and energy of the light rays is distributed less with increasing of the emitting angle of the light rays. Therefore, if the quantity of the light sources used in the backlight module is reduced, when the distance between the light sources is increased, brightness over the LEDs will be high, while brightness at junction areas of the adjacent LEDs will be low, resulting in the non-uniform backlight brightness. 
     In the embodiments of the present application, the first functional layer  46  is disposed on the light emitting side of the light sources  43 , so that when the light rays emitted from the light sources  43  enter into the first functional layer  46 , the reflectivity of the first functional layer  46  to the incident light rays is decreased with increasing of the angle of the incident light rays. In this way, when the large-angle light rays emitted from the light sources  43  enter the first functional layer  46 , most of the light rays are transmitted by the first functional layer  46 ; while when the small-angle light rays emitted from the light sources  43  enter the first functional layer  46 , most of the light rays are reflected by the first functional layer  46 , and the reflected light rays are subjected to scattering or diffuse reflection after entering the reflective layer  45 , so that large-angle light rays are generated again to be reflected to the first functional layer  46  so as to be transmitted by the first functional layer  46 . By means of the above reflection for several times, the energy of the light rays emitted from the light sources  43  may be not concentrated in the small emitting angle any more, so that the light rays emitted from the light sources  43  are relatively uniform. 
     The reflectivity of the first functional layer  46  to the incident light rays is 10% to 90%. The reflectivity of the first functional layer  46  to the incident light rays may be lowered from 90% to 10% with increasing of the incident angle, that is, the smaller the angle of the light rays emitted from the light sources, the smaller the incident angle of the light rays entering the first functional layer, and the more obvious a reflecting effect of the first functional layer  46  to the light rays; and the larger the angle of the light rays emitted from the light sources, the larger the incident angle of the light rays entering the first functional layer, and the more obvious a transmitting effect of the first functional layer  46  to the light rays. After the reflected light rays are subjected to a circulating reflecting effect of the first functional layer  46  and the reflective layer  45 , transmitting of the small-angle light rays will be decreased, transmitting of the large-angle light rays will be increased, and finally uniform light intensity is achieved. 
       FIG. 26  is a graph of the reflectivity of the first functional layer according to an embodiment of the present application. 
     Referring to  FIG. 26 , when the light sources adopt blue light emitting diodes, a wavelength of light emitted from the blue light emitting diodes is 440 nm to 450 nm. According to the first functional layer, for blue light waves, the smaller the incident angle of the light rays, the larger the reflectivity of the first functional layer; and the larger the incident angle of the light rays, the smaller the reflectivity of the first functional layer. It can be seen from  FIG. 26  that the reflectivity of the first functional layer  46  to blue light is decreased with increasing of the incident angle of the incident light rays, when the incident angle of the blue light is 0° to 30°, the reflectivity is large, when the incident angle is increased to 40°, the reflectivity is lowered slightly, and when the incident angle is increased to 50° to 70°, the reflectivity is greatly lowered. 
     Therefore, disposing the first functional layer  46  on the light emitting side of the blue light emitting diodes may uniformize the light emitted from the blue light emitting diodes. 
     The second functional layer  47  is located between the first functional layer  46  and the wavelength conversion layer  44 . The second functional layer  47  is disposed as a whole layer with a shape substantially same as the shape of the wavelength conversion layer  44 , which may be square or rectangular usually. 
     The second functional layer  47  is configured to transmit light emitted from the light sources  43  and reflect exciting light emitted from the wavelength conversion layer  44 . The second functional layer  47  may transmit small-angle light, and meanwhile, reflect small-angle exciting light emitted from the wavelength conversion layer  44  to the light emitting side of the backlight module. 
     The second functional layer  47  in the present application may be the above transmittance-enhancement film layer. 
       FIG. 27  is a schematic diagram of emitting light rays of the wavelength conversion layer according to an embodiment of the present application. 
     Referring to  FIG. 27 , the light rays emitted from the wavelength conversion layer  44  by excitation are not only emitted to the light emitting side of the backlight module, but also emitted to a side of the circuit board wherein the light sources are located. In local dimming scenario, it is desired that small-angle light rays a emitted from the light sources  43  have a coverage range X1 after passing the wavelength conversion layer  44 , so that the light rays emitted from the adjacent light sources cannot have crosstalk with each other. However, the light emitted by the wavelength conversion layer  44  by excitation is also emitted to one side of the light sources  43 , so that the small-angle light rays a emitted from the light sources  43  excite a part of light rays a′ in the light rays emitted from the wavelength conversion layer  44  to enter the reflective layer  45 , and after reflection by the reflective layer  45 , finally emitting light rays b have a coverage range X2. It can be seen from  FIG. 26  that the coverage range of the light rays emitted from the light sources at present will cover a region wherein the adjacent light sources are located, which finally causes crosstalk of the light rays, negatively affecting local dimming. 
       FIG. 28  is a diagram of a work principle of the second functional layer according to an embodiment of the present application. 
     Referring to  FIG. 28 , the second functional layer  47  is disposed on a side of the wavelength conversion layer  44  facing the light sources  43  in the embodiment of the present application, and the second functional layer  47  is configured to transmit the small-angle light rays emitted from the light sources  43  and reflect the small-angle light rays excited by the wavelength conversion layer  44 . In this way, the small-angle light rays a emitted from the light sources  43  may be transmitted by the second functional layer  47 , after the small-angle light rays enter the wavelength conversion layer  44 , small-angle light rays a′ in the light rays excited by the wavelength conversion layer  44  are emitted to one side of the light sources, in this case, this part of light rays a′ will enter the second functional layer  47  to be reflected by the second functional layer  47  towards the light emitting side of the backlight module (e.g., reflected light rays b), and thus the small-angle light rays emitted from the light sources  43  and the small-angle light rays excited by the wavelength conversion layer  44  both have good convergence, light cross-talk between partitions is avoided, and the display contrast is increased. 
     In the embodiments of the present application, the light sources  43  may use the blue light emitting diodes, the blue light emitting diodes emit blue light, while the wavelength conversion layer  44  emits red light and green light under excitation of the blue light. 
       FIG. 29  is a graph of the transmittance of the second functional layer according to an embodiment of the present application. 
     It can be seen from  FIG. 29  that the second functional layer  47  in the embodiments of the present application has a high transmittance for small-angle incident blue light (440 nm to 450 nm), and the transmittance is lowered for large-angle incident blue light. As shown in  FIG. 28 , when the incident angle of the blue light is 0° or 40°, the transmittance of the second functional layer  47  to the incident blue light is high, and when the incident angle of the blue light is 70°, the transmittance of the second functional layer  47  to the incident blue light is lowered. The second functional layer  47  has a low transmittance for incident red light and green light. 
       FIG. 30  is a graph of the reflectivity of the second functional layer according to an embodiment of the present application. 
     It can be seen from  FIG. 30  that, in the embodiments of the present application, the second functional layer  47  has a low reflectivity to the blue light (440 nm to 450 nm) and has a high reflectivity to the red light (620 nm to 660 nm) and the green light (525 nm to 545 nm). 
       FIG. 31  is a graph of the transmittance of the second functional layer to the blue light according to an embodiment of the present application. 
     It can be seen from  FIG. 31  that the second functional layer  47  in the embodiments of the present application has a high transmittance for the small-angle incident blue light, and the transmittance of the second functional layer  47  to the blue light is lowered with increasing of the incident angle of the blue light. As shown in  FIG. 31 , when the incident angle of the blue light is 0° to 30°, the transmittance of the second functional layer  47  is high, and when the incident angle of the blue light is increased to 50° or more, the transmittance of the second functional layer  47  is nearly 0. 
     It can be seen that the second functional layer  47  in the embodiments of the present application may transmit the blue light and reflect the red light and the green light, the second functional layer  47  may transmit the small-angle blue light and reflect the small-angle red light and green light, and meanwhile, the transmittance of the second functional layer  47  to the blue light is decreased with increasing of the incident angle. 
     In the embodiments of the present application, the first functional layer  46  is configured to reflect the small-angle light rays emitted from the light sources, and the second functional layer  47  is configured to transmit the small-angle light rays transmitted from the light sources. Therefore, when the two functional layers are disposed adjacently, the effect of the functional layers cannot be achieved, and the technical effects required by the present application cannot be achieved. 
     Therefore, as shown in  FIG. 25 , the diffusion layer  48  is disposed between the first functional layer  46  and the second functional layer  47  in the embodiments of the present application. 
     The diffusion layer  48  is disposed as a whole layer with a shape being substantially same as that of the first functional layer  46  and the second functional layer  47 . Usually, the shape may be a rectangle or a square. 
     The diffusion layer  48  is configured to scatter the incident light rays, scattering particle materials are disposed in the diffusion layer  48 , and the light rays will be refracted and reflected continuously after entering the scattering particle materials, so that the effect of dispersing the light rays is realized to achieve light uniformizing. 
     Disposing the diffusion layer  48  between the first functional layer  46  and the second functional layer  47  may make the two functional layers be collectively used in the backlight module, and the light rays emitted from the light sources pass the first functional layer  46 , thereby having high uniformity; and after the light rays emitted from the first functional layer  46  pass the diffusion layer  48 , the angle of the light rays entering the second functional layer  47  is random, so that emitting light with good convergence may be obtained after the light rays pass the second functional layer  47 . Therefore, an ultra-thin direct backlight module structure may be achieved, which solves the problem of non-uniform light emitting caused by a large distance between the light sources and improves the convergence of the emitting light rays at the same time. 
     The optical film  49  is located on a side of the wavelength conversion layer  44  away from the second functional layer  47 . The optical film  49  is disposed as a whole layer, and a shape of the optical film  49  is substantially same as that of the wavelength conversion layer  44  and usually may be a rectangle or a square. 
     Disposing the optical film  49  may make the backlight module adaptive to various practical applications. 
     The optical film  49  may include a prism sheet, and the prism sheet may change an emitting angle of light rays to change a viewing angle of the display apparatus. The prism sheet usually has the effect of converging light rays to a front view angle direction, thereby increasing front view angle brightness. 
     The optical film  49  may further include a reflective polarizer. As a brightness enhancement sheet, the reflective polarizer may increase the brightness of the backlight module, improve use efficiency of light rays, and make emitting light rays have a polarizing property, so a polarizer may be omitted in the liquid crystal panel. 
       FIG. 32  is a second schematic cross-sectional view of the backlight module according to an embodiment of the present application. 
     Referring to  FIG. 32 , the backlight module in the embodiments of the present application further includes: a diffusion plate K located between the light sources  43  and the first functional layer  46 . 
     A shape of the diffusion plate K is substantially same as that of the first functional layer  46  and usually may be a rectangle or a square. A thickness of the diffusion plate K is 1.5 mm to 3 mm. The diffusion plate K and the light sources  43  have a certain distance, and thus the light rays emitted from all the light sources  43  may be mixed to make the emitting light rays more uniform. 
     The diffusion plate K has large haze, and usually may be processed through an extrusion process. A material of the diffusion plate K is generally selected from at least one of polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS) or polypropylene (PP). 
     When the diffusion plate K is adopted in the backlight module, the thickness of the diffusion layer  48  between the first functional layer  46  and the second functional layer  47  is relatively small. The diffusion layer  48  is usually formed by coating a base material with diffusion particles, the base material may use polyethylene terephthalate (PET) or glass, and the diffusion particles may adopt titanium dioxide, zinc oxide, calcium oxide and the like. 
     In other embodiments of the present application, as shown in  FIG. 25 , the diffusion layer  48  between the first functional layer  46  and the second functional layer  47  may adopt the diffusion plate, so that the first functional layer  46  may be attached to a surface of a side of the diffusion plate facing the light sources, and the second functional layer  47  may be attached to a surface of a side of the diffusion plate away from the light sources. 
     By adopting the structure of the backlight module as shown in  FIG. 25 , one diffusion layer may be omitted, so that the structure of the backlight module is more compact, and mounting complexity is lowered. 
       FIG. 33  is a third schematic cross-sectional view of the backlight module according to an embodiment of the present application. 
     Referring to  FIG. 33 , the backlight module in other embodiments of the present application further includes: a transparent substrate L. 
     The transparent substrate L is located between the light sources  43  and the first functional layer  46 . A shape of the transparent substrate L is substantially same as that of the first functional layer  46  and usually may be a rectangle or a square. The transparent substrate L may be made of PMMA or glass. 
     The first functional layer  46  is disposed on a surface of a side of the transparent substrate L away from the back plate  41 , so that the transparent substrate L supports the first functional layer  46 . The diffusion layer  48  may use diffusion plate, and by adopting the above structure, the first functional layer may be prevented from being attached to the diffusion layer  48 , thereby lowering processing complexity. 
     In the embodiments of the present application, the first functional layer  46  and the second functional layer  47  are both disposed by utilizing the principle of film interference. During specific implementation, the first functional layer  46  and the second functional layer  47  each include a plurality of film layers disposed in a laminated mode, and every two adjacent film layers have different refraction indexes. The refraction indexes and thicknesses of the film layers meet a condition of film interference. 
       FIG. 34  is a schematic diagram of film interference according to an embodiment of the present application. 
     Referring to  FIG. 33 , when light rays enter a surface of a thin film with a refraction index being n 2  from a medium with a refraction index being n 1  with an incident angle of i, light reflection and refraction occur at an interface of two media with refraction index n 1  and refraction index n 2 , a reflection angle and the incident angle are equal and are still i, and a refraction angle is γ; and when refracted light rays enter a lower surface of the thin film, light reflection and refraction also occur on the lower surface, wherein reflected light rays will pass an upper surface of the thin film to be refracted in the medium n 1 , and thus two beams of reflected light rays (1) and (2) are formed on the upper surface and the lower surface of the thin film. An optical path difference δ′ between the reflected light ray (1) and the reflected light ray (2) is: 
       δ′= n   2 (   AB + BC   )− n   1     AD .  
 
     If a thickness of the thin film with the refraction index being n 2  is d and the thickness of the thin film is uniform, due to  AB = BC =d/cos γ and  AD = AC  sin i=2d tan γ×sin i, the following may be obtained: 
     
       
         
           
             
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                       ( 
                       
                         
                           n 
                           2 
                         
                         - 
                         
                           
                             n 
                             1 
                           
                           ⁢ 
                           sin 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           i 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           sin 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           γ 
                         
                       
                       ) 
                     
                     . 
                   
                 
               
             
           
         
       
     
     It can be known from the refraction law that: 
     
       
         
           
             
                 
             
             ⁢ 
             
               
                 
                   
                     n 
                     1 
                   
                   ⁢ 
                   sin 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   i 
                 
                 = 
                 
                   
                     n 
                     2 
                   
                   ⁢ 
                   sin 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   γ 
                 
               
               ; 
             
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               
                 so 
                 : 
                 
                   
 
                 
                 ⁢ 
                 
                   δ 
                   ′ 
                 
               
               = 
               
                 
                   
                     
                       2 
                       ⁢ 
                       d 
                       ⁢ 
                       
                         n 
                         2 
                       
                     
                     
                       cos 
                       ⁢ 
                       r 
                     
                   
                   ⁢ 
                   
                     ( 
                     
                       1 
                       - 
                       
                         
                           sin 
                           2 
                         
                         ⁢ 
                         γ 
                       
                     
                     ) 
                   
                 
                 = 
                 
                   
                     
                       
                         2 
                         ⁢ 
                         
                           n 
                           2 
                         
                         ⁢ 
                         d 
                       
                       
                         cos 
                         ⁢ 
                         γ 
                       
                     
                     ⁢ 
                     
                       cos 
                       2 
                     
                     ⁢ 
                     γ 
                   
                   = 
                   
                     
                       2 
                       ⁢ 
                       
                         n 
                         2 
                       
                       ⁢ 
                       d 
                       ⁢ 
                       cos 
                       ⁢ 
                       γ 
                     
                     = 
                     
                       
                         2 
                         ⁢ 
                         
                           n 
                           2 
                         
                         ⁢ 
                         d 
                         ⁢ 
                         
                           
                             1 
                             - 
                             
                               
                                 sin 
                                 2 
                               
                               ⁢ 
                               γ 
                             
                           
                         
                       
                       = 
                       
                         2 
                         ⁢ 
                         d 
                         ⁢ 
                         
                           
                             
                               
                                 n 
                                 2 
                                 2 
                               
                               - 
                               
                                 
                                   n 
                                   1 
                                   2 
                                 
                                 ⁢ 
                                 
                                   sin 
                                   2 
                                 
                                 ⁢ 
                                 i 
                               
                             
                           
                           . 
                         
                       
                     
                   
                 
               
             
           
         
       
     
     It can be seen from the above formula that, if a multi-layer film structure is disposed, an optical path difference between reflected light of the light rays on the upper and lower surfaces of each layer of medium is only related to a refraction index and a thickness of this layer and an incident angle. In practical applications, light rays usually enter a thin film from an air medium, light reflection occurs on an upper surface and a lower surface of the thin film, that is, the refraction index in the above formula is n 1 =1, and thus the above formula may be simplified as: 
       δ′=2 d √{square root over ( n   2   2   −n   1   2  sin 2    i )}=2 d √{square root over ( n   2   2 −sin 2    i )}.
 
     It can be known from the thin-film interference principle that, when the optical path difference between the reflected light rays on the upper surface and the lower surface of the thin film is integer times of a wavelength, the two beams of light rays are coherently added; and when the optical path difference between the reflected light rays on the upper surface and the lower surface is odd times of a half-wavelength, the two beams of light rays are coherently subtracted. According to the principle of energy conservation, if the reflected light is coherently added, energy of the reflected light is enhanced, and energy of transmittance light is weakened; and if the reflected light is coherently subtracted, the energy of the reflected light is weakened, and the energy of the transmittance light is enhanced. 
     When the above principle is applied to the embodiments of the present application, for any film layer in the first functional layer  46  and the second functional layer  47 , an incident angle of reflection enhancement is set as θ 1  and an incident angle of anti-reflection is set as θ 2 , and by utilizing the above principle, a proper film layer material may be selected, so that the refraction index and the thickness of the film layer meet reflection enhancement for light rays with the incident angle θ 1  and transmittance enhancement for light rays with the incident angle ↓ 2 . 
     Those skilled in the art may make various modifications and variations to the present application without departing from the spirit and scope of the present application. Those modifications shall fall within the protection scope of the disclosure.