Patent Publication Number: US-10323819-B2

Title: LED display screen covers and LED displays

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application of U.S. patent application Ser. No. 15/217,492 filed on Jul. 22, 2016, which is a continuation application of U.S. patent application Ser. No. 15,043,069 filed on Feb. 12, 2016, which claims priority under 35 U.S.C. § 120 to PCT Application No. PCT/CN2015/084447 filed on Jul. 20, 2015 and Chinese Patent Application No. CN 201510080390.2 filed on Feb. 15, 2015. The contents of these applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to optical structures, particularly to LED display screen covers and LED displays. 
     BACKGROUND 
     Compared to a conventional picture tube display and a liquid crystal display, a light emitting diode (abbreviated as “LED”) display possesses relatively outstanding advantages, and one can carry out connection with any resolution ratio and can realize a wireless connection with it, and thereby satisfy the requirements for display dimensions and resolving rate in different scenes. 
     A plurality of LED lamps that are provided in the LED display are arranged to form an array, and one LED lamp forms one LED pixel unit. Since light-emission area of the LED lamp is smaller than the physical surface area occupied by the LED pixel unit, its filling coefficient is relatively small, and this results in clear black areas present in spaces between adjacent LED pixel units, which is manifested as a periodic black area grid structures on the entire display. Since the majority of image acquisition devices of current photographic equipment are charge-coupled devices (abbreviated as “CCD”), they similarly are provided with a periodic structure, and therefore when the photographic equipment captures the LED display, and the spatial frequency whose image is formed by the LED display on the CCD is close to the spatial frequency of the CCD, clear moire fringes appears, which affects the definition of the image. Moreover, when the filling coefficient of the LED pixel unit is relatively small, this will cause graininess and lower the degree of viewing comfort. At the same time, in order to guarantee the overall brightness, the brightness of the light issued by the LED lamp is universally rather great, but owing to the fact that the light-emitting region is small it easily causes glare, and it is not possible for viewers to watch it for a long time. 
     SUMMARY 
     One aspect of the invention features a screen cover including a screen cover body including a plurality of cover units disposed in an array of multiple rows and multiple columns, each cover unit configured to be positioned over a respective LED lamp of an array of LED pixel units of an LED screen. A top of each cover unit forms an arched structure extending away from the LED lamp, and the arched structures of adjacent cover units are configured and joined along the columns and rows so as to provide the screen cover with a filling coefficient of more than 93%. 
     In some implementations, each cover unit includes a light blocking part configured to block off light from adjacent LED pixel units and a scattering part installed on top of the light blocking part and forming the top of the cover unit. An outer surface of the scattering part can be spherical. In a particular example, a spherical radius of the outer surface of the scattering part is within a range of √{square root over (2)}a/2˜0.9a, where a is a period of the LED pixel units. 
     In some implementations, an inner surface of each cover unit is positioned so as to form a gap between the inner surface and an upper surface of the LED lamp. The inner surface can be arched away from the LED lamp. The inner surface can be spherical. In a particular example, an outer surface of the scattering part is spherical, and the inner surface has a radius r determined by: 
             r   ≥         R   2     -   ab   +       1   2     ⁢     b   2                 
where R is a radius of the outer surface, a is a period of the LED pixel units, and b is an edge length of the LED lamp.
 
     In some examples, a transitional circular arc is formed between the spherical inner surface and an adjacent inner wall of the screen cover. A radius of the transitional circular arc can be within a range of 0.08a-0.2a, where a is a period of the LED pixel units. 
     The screen cover body can have a haze of no less than 50%. The screen cover can include a material having an RGB color ratio of about (1±0.2):(1±0.2):(1±0.2). 
     Another aspect of the invention features a screen cover has a screen cover body including a plurality of cover units disposed in an array of multiple rows and multiple columns, each cover unit configured to be positioned on top of a respective LED lamp of an array of LED pixel units of an LED screen. A top of each cover unit forms an arched structure extending away from the LED pixel lamp, the arched structures of adjacent cover units being configured and joined along the columns and rows such that, when placed over an illuminated LED screen, no perceptible light gaps are visible between adjacent screen pixels, as viewed through the screen cover body. The screen cover is configured to have a filling coefficient of more than 93%. 
     In some implementations, each cover unit includes a light blocking part configured to block off light from adjacent LED pixel units and a scattering part installed on top of the light blocking part and forming the top of the cover unit. An inner surface of the scattering part can be a spherical surface, and a transitional circular arc can be provided between the inner surface and an inner wall of the light blocking part. 
     A further aspect of the invention features an LED display screen cover including a screen cover body including a plurality of cover units disposed in an array of multiple rows and multiple columns, each cover unit configured to be positioned on top of a respective LED pixel lamp and including a blocking part and a scattering part on top of the blocking part. An outer surface of the scattering art has an arched structure towards a direction away from the LED pixel lamp, and the arched structures of scattering parts of adjacent cover units are configured joined along the columns and rows, and a material of the blocking part is selected such that the blocking part is configured to block off light from adjacent LED pixel lamps. The arched structures of the adjacent cover units can be configured so as to provide the LED display screen cover with a filling coefficient of more than 93%. 
     In some implementations, the LED display screen cover is arranged over an array of LED pixel lamps such that each cover unit is disposed over a respective one of the LED pixel lamps, the cover units of the screen cover together configured such that, with the LED pixel lamps illuminated, there is no perceptible light gap between adjacent pixel units, as viewed through the screen cover. 
     A fourth aspect of the invention features an LED display including an LED display screen body of an array of LED pixel units each having a respective LED lamp and an LED display screen cover coupled to the LED display screen body and including a plurality of cover units disposed in an array of multiple rows and multiple columns, each cover unit configured to be positioned on top of a respective LED lamp. A number of the cover units in the LED display screen cover is the same as a number of the LED lamps in the LED display screen body, and a top of each cover unit has an arched structure towards a direction away from the respective LED lamp, and the arched structures of adjacent cover units are configured and joined along the columns and rows so as to provide the screen cover with a filling coefficient of more than 93%. 
     A fifth aspect of the invention features a covered LED screen including an array of LED pixel units arranged in multiple rows and multiple columns and a screen cover body with an array of LED cover units disposed in multiple rows and multiple columns, each cover unit configured to be positioned over an LED lamp of a respective one of the LED pixel units. An outer surface of each cover unit is convex, the outer surfaces of adjacent cover units being configured and joined along the columns and rows, and each cover unit has an inner surface spaced from an outer surface of an underlying LED lamp to form a gap. 
     The inner surface of each cover unit can be concave. Each concave inner surface can transition to adjacent side walls of a cavity of the cover unit containing the respective LED lamp by a transitional radius. 
     A sixth aspect of the invention features a device for eliminating moire fringes from an LED screen and improving the filling coefficient. The device includes a scattering cover and an LED screen body. The above-described scattering cover covers the front end of the LED screen body, and the scattering cover is fixedly connected with the LED screen body; and the size of the above-described scattering cover mutually corresponds to the size of the LED screen body; the front side of the above-described scattering cover is formed by an array of ball top structures, and the back side of the above-described scattering cover defines an array of cavities corresponding to the ball top structures. The device also includes a plurality of LED pixel lamps provided on the above-described LED screen body, each LED pixel lamp extending into a corresponding one of the cavities. The scattering cover can be configured to provide the LED screen with a filling coefficient of more than 93%, when viewed through the scattering cover. 
     A seventh aspect of the invention features a device for eliminating moire fringes from an LED screen and improving the filling coefficient. The device is primarily composed of a scattering cover and an LED screen body. The above-described scattering cover covers a front end of the LED screen body, and the scattering cover is fixedly connected with the LED screen body; and a size of the above-described scattering cover mutually corresponds to a size of the LED screen body; the front side of the above-described scattering cover is provided with a plurality of ball top structures, and a back side of the above-described scattering cover is an independent groove provided with partition structures or does not have any structures. The device also includes a plurality of LED pixel lamps provided on the above-described LED screen body. The above-described LED pixel lamps mutually correspond to the ball top structures, and the above-described scattering cover is provided with a haze that is not lower than 70%. 
     The above-described scattering cover can include a variety of spherical structures: positive ball top solid bodies or shells, oval ball top solid bodies or shells, and structures where several flat surfaces are joined to form quasi-ball top structures or structures whose surfaces are uneven. The above-described positive ball top structures can be determined based on pixel dimensions of the LED pixel lamp and a haze of the scattering cover: if the pixel side length of an LED pixel lamp is a, then a ball top radius r of the ball top structures is (√{square root over (2)}/2)a˜0.9a; the ball center of the ball top structures is located at a position that has the same length difference as the radius from the pixel apex angle of the upper surface of the LED pixel lamp to the center normal line of the LED pixel lamp. The above-described ball top radius r can be selected based on a light emission position and light emission scattering angle distribution of the LED pixel lamps and a haze of the scattering cover. 
     In some implementations, the above-described partition structures are independent grooves that are produced according to a cycle of the LED pixel lamps. The above-described grooves can be rectangular structures, and the length, width and depth of those rectangular structures can be similar to the length, width and depth of the sealed structures of the LED pixel lamp. The bottom part of the above-described grooves can be spherical arc-shaped depression structures, and a radius of the arc-shaped depression structures can be determined by a haze of a selected material of the LED screen cover. The radius of the arc-shaped depression structures is at a maximum not smaller than the radius r of the ball top structures, and the depression depth is in a range of 0 to 0.5 mm. 
     There can be two implementation methods for connecting the above-described scattering cover and the LED screen body: a fixed connection with a fixing pin on the scattering body or a fixed connection by direct bonding on the surface of the LED screen by glue on the back side. 
     An eighth aspect of the invention features a method using a device for eliminating moire fringes from an LED screen and improving a filling coefficient described in the seventh aspect. The device for eliminating moire fringes from an LED screen and improving the filling coefficient described in any one of the above features is used. The method includes the following steps: 
     1) production of the scattering cover: a light-permeable material that is provided with a haze of no less than 70% is employed to produce the scattering cover; 
     2) LED screen production; 
     3) installation: fixed installation employing a fixing pin: the scattering cover whose injection molding is completed in step 1) covers the front end of the LED screen body, the fixing pins pass through the through holes on the printed circuit board (PCB); the fixing pins that are passed through the back side of the PCB are heated to make them melt, and after they cool they are remolded, that is, the scattering cover is fixedly installed on the LED screen body; or installation employing bonding with glue: glue is directly applied to the back side of the scattering body or on the partition structures, and directly bonded on the surface of the LED screen body. 
     A ninth aspect of the invention features an LED display screen cover including a screen cover main body. There is provided a plurality of lamp cover units forming an array on the above-described screen cover main body, and each lamp cover unit is used for covering above a respective LED lamp. A top of the described lamp cover unit is an arch structure that faces in a direction away from the LED lamp. 
     In some implementations, the above-described lamp cover unit includes a light partitioning part that partitions off a space between neighboring LED lamps, and a scattering part that is installed on a top of the above-described light partitioning part. The above-described scattering part is the top of the above-described lamp cover unit. The outer surface of the above-described scattering part can be a positive spherical surface. A haze of the above-described scattering part can be greater than or equal to 50%. 
     In some implementations, a gap used for light diffusion is provided in a space between an inner surface of the above-described scattering part and an upper surface of the LED lamp. The inner surface of the above-described scattering part has an arched structure facing towards a direction away from the LED lamp. The inner surface of the above-described scattering part can be an arc surface. 
     In some examples, a transitional circular arc is provided between the inner surface of the scattering part corresponding to an apex angle of the above-described LED lamp and the inner wall of the light partitioning part. The radius of the above-described transitional circular arc can be 0.08a-0.2a, where a is the period of the LED pixel unit. 
     The spherical radius of the outer surface of the above-described scattering part can be √{square root over (2)}a/2˜0.9a, where a is a period of the LED pixel unit. The arc surface radius r of the inner surface of the above-described scattering part can be obtained by calculating with the following equation: 
             r   ≥         R   2     -   ab   +       1   2     ⁢     b   2                 
where R is the spherical radius of the outer surface of the scattering part, a is the period of the LED pixel unit, and b is the edge length of the LED lamp.
 
     A tenth aspect of the invention features an LED display including a screen body of an LED lamp array and the LED display screen cover described in any one of the ninth aspect that is connected with the above-described screen body. The quantity of the lamp cover units in the above-described LED display screen cover is the same quantity as the LED lamps. 
     An eleventh aspect of the invention features a screen cover including a screen cover body including an array of cover units arranged in multiple rows and multiple columns, each cover unit configured to be positioned over a respective LED lamp of an array of LED pixel units. Each cover unit has a shaped outer surface with edges, including an edge in common with an adjacent cover unit in a same row and an edge in common with an adjacent cover unit in a same column, such that the outer surfaces of the cover units along the columns and rows together form a continuous outer cover surface. 
     Each cover unit can include a light blocking part configured to block off light from adjacent LED pixel units. Each cover unit can have an inner surface facing away from the shaped outer surface and defining a recess sized based on an upper extent of an LED housing of an underlying LED lamp. A depth of the recess can be within a range of 0.05a ˜0.25a, where a is a period of the LED pixel units. The inner surface can be an immense extent of the cover unit. The recess can have a transitional circular arc between adjacent sides of the recess. The shaped outer surface can be configured such that the recess is enclosed by the shaped outer surface. 
     A distance between a top of the shaped outer surface and a top of the recess can be determined based on a shape of the shaped outer surface. A distance between a top of the shaped outer surface and a top of the recess can be within a range of 0.3˜0.9a, where ‘a’ is a period of the LED pixel units. 
     In some cases, the shaped outer surface of the cover unit is spherical. In some cases, the shaped outer surface of the cover unit comprises a non-spherical surface including one of ellipsoid, paraboloid, and Bessel surface. 
     In some implementations, the shaped outer surface of the cover unit comprises a square pyramid surface. A height defined by the square pyramid surface can be within a range of 0.3a˜0.9a, where a is a period of the LED pixel units. In some implementations, the shaped outer surface of the cover unit comprises a square frustum surface. A height defined by the square frustum surface can be within a range of 0.3a˜0.9a. An edge length of a top of the square frustum surface can be within a range of 0.4a˜0.7a, where ‘a’ is a period of the LED pixel units. 
     A twelfth aspect of the invention features a covered LED screen including an array of LED pixel units arranged in multiple rows and multiple columns and a screen cover body with an array of LED cover units disposed in multiple rows and multiple columns, each cover unit configured to be positioned over an LED lamp of a respective one of the LED pixel units. Each cover unit has a shaped outer surface with edges, including an edge in common with an adjacent cover unit in a same row and an edge in common with an adjacent cover unit in a same column, such that the outer surfaces of the cover units along the columns and rows together form a continuous outer cover surface. 
     The shaped outer surface of the cover unit can have a lowest extent no higher than a lighting element of an underlying LED lamp. Each LED pixel unit can be enclosed in an LED housing, and sides of the LED housing can directly face to adjacent sides of LED housings of adjacent LED pixel units. 
     In some implementations, the covered LED screen further includes a plurality of columns each protruded from an intersection of bottoms of adjacent cover units and arranged between the respective LED pixel units under the adjacent cover units. Each column can extend from the bottoms of the adjacent cover units to a printed circuit board (PCB) coupled to bottoms of the LED pixel units. 
     A thirteenth aspect of the invention features a screen cover including a screen cover body including an array of cover units arranged in multiple rows and multiple columns, each cover unit configured to be positioned over a respective LED lamp of an array of LED pixel units. Each cover unit has a non-spherical shaped outer surface including one of ellipsoid, paraboloid, and Bessel surface. 
     A fourteenth aspect of the invention features a screen cover including a screen cover body including an array of cover units arranged in multiple rows and multiple columns, each cover unit configured to be positioned over a respective LED lamp of an array of LED pixel units. Each cover unit has a square pyramid outer surface. 
     A fifteenth aspect of the invention features a screen cover including a screen cover body including an array of cover units arranged in multiple rows and multiple columns, each cover unit configured to be positioned over a respective LED lamp of an array of LED pixel units. Each cover unit has a square frustum outer surface. 
     A sixteenth aspect of the invention features a covered LED screen, including: an array of LED pixel units arranged in multiple rows and multiple columns and a screen cover body with an array of LED cover units disposed in multiple rows and multiple columns, each cover unit configured to be positioned over an LED lamp of a respective one of the LED pixel units. Each LED pixel unit is enclosed in an LED housing, and sides of the LED housing directly face to adjacent sides of LED housings of adjacent LED pixel units. 
     A seventeenth aspect of the invention features a covered LED screen, including: an array of LED pixel units arranged in multiple rows and multiple columns; a screen cover body with an array of LED cover units disposed in multiple rows and multiple columns, each cover unit configured to be positioned over an LED lamp of a respective one of the LED pixel units; and a plurality of columns each protruded from an intersection of bottoms of adjacent cover units and arranged between the respective LED pixel units under the adjacent cover units. Each column can extend from the bottoms of the adjacent cover units to a printed circuit board (PCB) coupled to bottoms of the LED pixel units. 
     Particular embodiments of the subject matter described in this specification can be implemented so as to realize one or more of the following advantages. Owing to the facts that a plurality of lamp cover units forming an array are installed on a screen cover main body, that each lamp cover unit is provided above one LED pixel unit, and that a top part of each lamp cover unit is installed as an arched structure that faces in a direction away from the LED pixel unit, the light rays emitted by an LED pixel unit can propagate from its own lamp cover unit, and the screen cover will not cause interference for adjacent pixel units, and this guarantees a definition of an image displayed by the LED screen. In addition, there are no black areas present in a space between two adjacent LED pixel units, and thus the screen cover will not generate periodic black area grid structures for the entire LED display screen, and makes the space between pixel units “zero distance”, which effectively eliminates moire fringes during screen capture; at the same time, the screen cover improves the pixel filling coefficient, e.g., higher than 93%, and eliminates incoherence and “graininess” of the screen under conditions where sharpness and definition of the image are ensured. The arched structures of the screen cover make light scattering uniform. When a viewer views the LED display screen from a large inclined angle, the brightness decay is not significant. Three primary colors (e.g., red, green, and blue) in a single pixel can be mixed evenly in the scattering cover, which causes a softer viewing effect than a conventional separated three primary colors on an LED lamp. At the same time, the scattering cover reduces the overall brightness of the LED screen, reduces the light contamination that might be produced, and prevents damage caused to the viewer&#39;s eyes due to excessive brightness. 
     Further advantages and advantageous embodiments of the subject of the invention can be seen from the description, the claims and the drawing. The above-mentioned features, as well as the further features listed below, can likewise be used independently or multiple features combined as desired. The embodiments shown and described are not to be understood as a conclusive list, but should rather be treated as examples to illustrate the invention. The figures in the drawing show the subject in accordance with the invention in a highly schematic way, and are not to be understood as being drawn to scale. 
    
    
     
       BRIEF DESCRIPTIONS OF DRAWINGS 
         FIG. 1  is a schematic diagram of an example assembly of an LED display screen cover and an LED display screen body. 
         FIG. 2  is a schematic diagram of a locally enlarged structure of the assembly of the LED display screen cover with the LED screen body. 
         FIG. 3  is a schematic diagram of a frontal view of the LED display screen cover. 
         FIG. 4  is a schematic diagram of an example structure of a front side of the LED display screen cover. 
         FIG. 5  is a schematic diagram of an example structure of a back side of the LED display screen cover. 
         FIG. 6  is a schematic diagram of an example structure of a lamp cover unit in the LED display screen cover. 
         FIG. 7  is a schematic diagram of another view of the lamp cover unit in the LED display screen cover. 
         FIG. 8  is an example light path schematic diagram in which a scattering glass is fitted to an LED lamp. 
         FIG. 9  is an example light path schematic diagram in which the LED display screen cover is fitted to an LED lamp. 
         FIG. 10  is a schematic diagram of a spherical center position in which an outer surface of a scattering part of the lamp cover unit in the LED display screen cover is a positive spherical surface. 
         FIG. 11  is a planar view of the spherical-shaped lamp cover unit of  FIG. 10 . 
         FIG. 12  is a cross-sectional view of two adjacent lamp cover units in another example LED display screen cover. 
         FIG. 13  is a cross-sectional view of two adjacent lamp cover units in another example LED display screen cover. 
         FIG. 14  is a light path schematic comparative diagram in which two lamp cover units in two example LED display screen covers each is fitted with an LED lamp. 
         FIG. 15  is a schematic diagram of a spherical center position in which an inner surface of a scattering part of the lamp cover unit in the LED display screen cover is a positive spherical surface. 
         FIG. 16  is a structural schematic diagram of the lamp cover unit in the LED display screen cover is fitted with an LED lamp. 
         FIG. 17  is a light path schematic diagram in which the LED display screen cover is fitted to an LED lamp. 
         FIG. 18  is a structural schematic diagram of an example LED display screen cover without light blocking parts installed with fixing pins. 
         FIG. 19  is a schematic diagram of glue over a back surface of an example LED display screen lamp without light blocking parts. 
         FIG. 20  is a schematic diagram of positions of glue on light blocking parts of an example LED display screen lamp. 
         FIG. 21  is a structural schematic diagram of an example LED display screen cover with light blocking parts installed with fixing pins. 
         FIG. 22  is a structural diagram of an example LED lamp scattering angle. 
         FIG. 23  is a schematic diagram showing a filling coefficient of an LED display. 
         FIG. 24  is a schematic diagram of an example light path in which light from an LED lamp propagates into an adjacent cover unit. 
         FIG. 25  is a cross-sectional view of two adjacent lamp cover units in an example LED display screen cover, where light from an LED lamp is restricted from propagating into an adjacent cover unit. 
         FIG. 26A  is a cross-sectional view of two adjacent lamp cover units without light blocking parts in another example LED display screen cover. 
         FIG. 26B  is a cross-sectional view of two adjacent lamp cover units without light blocking parts installed with fixing columns in another example LED display screen cover. 
         FIG. 26C  is a bottom view of the LED display screen cover of  FIG. 26B . 
         FIG. 27A  is a cross-sectional view of an example lamp cover unit having a square pyramid structure in another example LED display screen cover. 
         FIG. 27B  is a schematic diagram of a front side of the LED display screen cover of  FIG. 27A . 
         FIG. 28A  is a cross-sectional view of an example lamp cover unit having a square frustum structure in another example LED display screen cover. 
         FIG. 28B  is a schematic diagram of a front side of the LED display screen cover of  FIG. 28A . 
     
    
    
     DETAILED DESCRIPTION 
     Implementations of the present disclosure are generally directed to an LED display screen cover. The LED display screen cover is installed on a surface of a screen body of an LED display screen, and can provide no perceptible light gap between adjacent LED pixels, which can effectively eliminate periodic black area grid structures of the LED display. In some implementations, the LED display screen cover enables that eliminating moire fringes from the LED display screen and improving the filling coefficient to be higher than 93% are simultaneously achieved. In addition, independence of LED pixels is ensured, mutual interference between the LED pixels can be avoided, and sharpness and definition of images displayed by the LED display is ensured. 
     The filling coefficient is defined as a ratio between a light-emitting area in a single pixel and a pixel physical surface area. For example,  FIG. 22  shows an example distribution of an LED lamp light scattering angle.  FIG. 23  shows an LED display screen including nine pixel units. A small square with dotted lines is a single pixel physical surface, whose dimensions are 3 mm×3 mm. A square with solid lines is an LED lamp package edge, and a circle is an LED light-emitting region, whose radius is 0.7 mm. Thus, the filling coefficient of the LED screen is (π×0.7 2 /(3×3))×100%=17.1%. A relatively smaller filling coefficient results in the screen being incoherent and incomplete when viewed from a relatively close distance, and the unevenness of the brightness causes graininess and relatively serious glare, while the screen with a larger filling coefficient can eliminate “graininess” and make the screen softer, and does not possess clear brightness decay when viewing with a large inclined angle. 
       FIG. 1  is a schematic diagram of an assembled structure of an LED display screen body  1  of an LED display and an LED display screen cover  2  according to an example embodiment. The screen body  1  of the LED display is provided with a PCB circuit board, and there is a plurality of LED lamps  11  welded on the PCB circuit board, and each LED lamp  11  forms one LED pixel unit. A plurality of LED lamps  11  form an array structure. The screen body  1  is connected with the LED display screen cover  2 , and the LED display screen cover  2  includes a screen cover main body and a plurality of lamp cover units  21  forming an array of multiple rows and multiple columns provided on the screen cover main body. Each lamp cover unit  21  is positioned on top of about a respective LED pixel lamp  11  and used for covering the LED pixel lamp  11 . The screen cover main body can be bonded together with the screen body  1  (e.g., by glue bonding), connected by employing a bolt, connected by clamping with a fastener, or connected with pins. 
       FIG. 2  is a schematic diagram of the locally enlarged structure of the assembly of the LED display screen cover  2  with the LED screen body  1 . The screen cover  2  includes a plurality of cover units  21  and is positioned on top of the LED screen body  1 .  FIG. 3  is a schematic diagram of a frontal view of the LED display screen cover  2 .  FIG. 4  is a schematic diagram of an example structure of a front side of the LED display screen cover  2 . The cover units  21  are joined together along the rows and columns to form a two-dimensional screen cover  2 .  FIG. 5  is a schematic diagram of an example structure of a back side of the LED display screen cover  2 . As discussed below, the screen cover  2  includes a light blocking part  211 . One or more fixing pins  215  can be set up on the surface of the back side for fixing the screen cover  2  and the screen body  1  with the PCB circuit board. 
     Each lamp cover unit  21  can have a same structure.  FIG. 6  is a schematic diagram of an example structure of the lamp cover unit  21  in the LED display screen cover  2 , and  FIG. 7  is a schematic diagram of another angle of the lamp cover unit  21  in the LED display screen cover  2 . As shown in  FIGS. 6 and 7 , a top part of the lamp cover unit  21  has an arched structure facing away from the LED lamp  11 . 
     The structure of the lamp cover unit  21  can be implemented in different ways. In some implementations, as  FIGS. 6 and 7  show, the lamp cover unit  21  includes a light blocking part  211  that blocks off light from adjacent LED lamps  11  and a scattering part  212  installed on the top part of the light blocking part  211 . The outer surface of the scattering part  212  is an arch facing towards a direction away from the LED lamp  11 . The light blocking part  211  and the scattering part  212  can be formed integrally or be bonded together. 
     In some examples, a sealed (e.g., packaged or assembled) structure of the LED lamp  11  is cuboid, and an inner wall of the light blocking part  211  surrounds the cuboid structure and accommodates the LED lamp  11 . In order to adapt to the structure of the adjacent LED lamps  11 , outer walls on the four side surfaces of the light blocking part  211  can be planes. Two adjacent lamp cover units  21  can be joined by putting the outer walls of the light blocking parts  211  together. Alternatively, the light blocking parts  211  of two adjacent lamp cover units  21  can be an integral structure. 
     As for the arched structure in which the scattering part  212  faces in a direction away from the LED lamp  11 , an intersection line of two adjacent scattering parts  212  is coplanar with the outer wall of the light blocking part  211 , and said plane is perpendicular to the surface of the LED lamp  11  provided in the screen body  1 . In a situation where the light blocking part  211  in two adjacent lamp cover units  21  is an integral structure, the intersection line of the two adjacent scattering parts  212  is located between the light blocking part  211 . 
       FIG. 8  is a light path schematic diagram in which a scattering glass is fitted to an LED lamp. A piece of scattering glass is provided as a cover on two LED lamps  11 . The scattering glass has a back plane that faces towards an inner surface of the LED lamps  11  and a front plane that faces away from an outer surface of the LED lamps. Light-emitting points of the two LED lamps  11  are O 1  and O 2 , respectively. In light rays emitted from the light-emitting point O 1 , the light rays O 1 E, O 1 F and O 1 G that are emitted towards the center of the two LED lamps  11  on the left and right respectively coincide on the projection points E, F and G on the scattering glass with the light rays O 2 E, O 2 F and O 2 G that are emitted from light-emitting point O 2 . Therefore, the two light rays that are respectively located at each projection point position interfere with each other, and this results in an image at the projection point being relatively indistinct, which in turn results in the edges of the LED pixel units being relatively indistinct. The scattering glass includes a scattering film (or layer) on its surface to cause light scattering, however, due to restrictions of scattering film technology, the scattering angle of the scattering glass is not large, and the screen brightness rapidly decays along with an increase of the viewing angle. 
       FIG. 9  is a light path schematic diagram in which the LED display screen cover  2  is fitted to an LED lamp  11 . The lamp cover unit  21  is provided above the LED lamp  11 , and the light rays emitted by the LED lamp  11  exhibit a dispersed state and are emitted towards the lamp cover unit  21 .  FIG. 9  shows two left and right adjacent LED lamps  11 , and one lamp cover unit  21  is provided as a cover above each LED lamp  11 . The light-emitting points of the two left and right LED lamps are O 1  and O 2 , respectively. Taking light-emitting point O 1  as an example, among light rays emitted by O 1 , light ray O 1 A is irradiated on an intersection line of the scattering part  212  of the two lamp cover units  21 , the projection point on the intersection line is A, and it is only when the light O 1 A further passes through the AB segment that reaches point B on the scattering part  212  of the right lamp cover unit  21 . The light brightness (or intensity) is largely consumed in the AB segment light path, and consequently becomes extremely weak even if the light ray O 1 A can enter the right lamp cover unit  21 . Using O 1 A as the boundary line, if the dispersion angle in the light rays emitted by the light-emitting point O 1  is relatively large and even if the light rays beneath O 1 A can enter the right lamp cover unit  21 , their brightness is also extremely weak. On the other hand, if the dispersion angle is relatively small and the light rays above O 1 A (e.g., O 1 C and O 1 D) are all incident on the scattering part  212  of their own lamp cover unit  21  and propagate out, they will not enter the right lamp cover unit  21 . Therefore, the light rays emitted by the right LED lamp  21  will propagate from their own lamp cover unit  21 , and will not cause interference towards the adjacent LED pixel units. Moreover, no black areas are present in the space between two adjacent LED pixel units, which improves the pixel filling coefficient and makes the space between LED pixels a “zero distance” and in turn makes the LED screen softer and clearer. 
     Referring back to  FIG. 9 , for the above-described scattering part  212 , its inner surface is a surface facing towards the LED lamp  11 , and the outer surface is a surface facing away from the LED lamp  11 . The outer surface of the above-described scattering part  212  has an arched structure facing towards in a direction away from the LED lamp  11 . 
     The arched structure of the scattering part  212  can be implemented in different ways. In some implementations, the outer surface of the scattering part  212  is a spherical surface, e.g., a positive spherical surface or an ellipsoid. In some implementations, the outer surface is an arc surface, e.g., a hyperboloid or a paraboloid, or several planes are joined to form the arched structure. The scattering part  212  can be a solid body structure or a shell-shaped structure. In some implementations, the scattering part  212  includes a positive ball top solid body or shell, oval ball top solid body or shell, or a structure where several flat surfaces are joined to form a quasi-ball top structure or an uneven structure. 
     For purpose of illustration, the present embodiment uses a scattering part  212  whose outer surface is a positive spherical surface as shown in  FIGS. 1-7 and 9 . To provide a more detailed explanation of the structure of the lamp cover unit  21 , a person skilled in this field can apply the technical scheme provided in the present embodiment to a lamp cover unit with another shape, or make modifications and apply them to a lamp cover unit with another shape. 
     In some implementations, the scattering part  212  has a positive spherical surface, and its spherical surface radius R can be determined based on dimensions of the LED pixel unit. If an LED lamp  11  is a square structure when viewed from above and a period of the LED pixel unit is a, the spherical surface radius R can be √{square root over (2)}a/2 to 0.9a. The period of the LED pixel unit is defined as a distance between light-emitting points of two adjacent LED lamps  11 , e.g., a distance between O 1  and O 2  in  FIG. 9 . When a scattering part  212  with a positive spherical surface is employed, its outer surface can be continuous, round, and smooth, which can not only avoid light ray interference between adjacent pixel units but also improve the filling coefficient. For the structure shown in  FIG. 9 , since the top surface of the lamp cover unit  21  is a positive spherical surface, the light rays are dispersed in all directions after they propagate from the light cover unit  21 , and consequently the brightness decay under conditions of a relatively large viewing angle is not significant. 
       FIG. 10  is a schematic diagram of a spherical center position in which the outer surface of the lamp cover unit scattering part in the LED display screen cover is a positive spherical surface.  FIG. 11  is a planar view of the spherical-shaped lamp cover unit of  FIG. 10 . Point N and point P are intersection points of the intersection line of two adjacent lamp cover units  21  and two relative edges in the light blocking part  211 . A line segment MP is parallel to the PCB circuit board and also parallel to the bottom surface of the light blocking part  211 . A line segment NY is a distance from point N to the bottom surface of the light blocking part  211 , and it is also the height of the light blocking part  211 . The length L NY  of line segment NY can be 0.45a-0.7a, and a is the period of the LED pixel unit. The spherical center M of the outer surface of the scattering part  212  is within the plane of the NP line segment and the location of the projection of the NP segment on the PCB circuit board, and is located on the central perpendicular line segment TX of the NP segment (i.e., the central normal line of the LED pixel unit). On the central perpendicular line segment TX, the length of line segment TX is equal to the length L NY  of the line segment NY, that is, 0.45a-0.7a, and the length L MT  of line segment MT is: 
               L   MT     =         R   2     -       1   2     ⁢     a   2                 
where R is the spherical surface radius of the outer surface of the scattering part  212 , and a is the period of the LED pixel unit. A distance between the spherical center M of the outer surface of the scattering part  212  and the bottom surface of the light blocking part  211  is equal to the length L MX  of the line segment MX, which is the difference between the length of the above-described line segment TX and the length of line segment MT.
 
     In addition to possessing the above-described functions and advantages, the scattering part  212  also possesses the function of carrying out scattering for the light rays emitting from the LED lamp  11  to make the light rays that emit from the scattering point no longer irritating to the eye, and the extent of its scattering is called the haze. In some implementations, a scattering film is pasted on the outer surface of the scattering part  212 . The scattering film can cause the scattering part  212  to have a haze larger than 50%, preferably larger than 70%. In some implementations, a material possessing a fixed haze is used to make the scattering part  212 . The material can cause the scattering part  212  to have a haze larger than 50%, preferably larger than 70%. 
     The above-described light blocking part  211  can also have a fixed haze, and if the light blocking part  211  and scattering part  2212  integrally constitute the lamp cover unit  21 , it is possible to use a material with a fixed haze to make the entire lamp cover unit  21 . The light rays propagate from the lamp cover unit  21  and will be dispersed in every direction, and the light source seen by the naked eye is the entire lamp cover unit  21  with light emerging, and in this way the point light source is expanded to the surface of the entire lamp cover unit  21 . When viewed from the outside of the LED display screen cover, the entire LED display screen cover is lit up, and one cannot see the shape of the LED lamps  11 , and this can eliminate the graininess of the LED display screen cover. 
     Further, if the lamp cover unit  21  is made by employing materials with a fixed haze, it is specifically possible to make it by using materials whose haze is larger than 50%, and preferably larger than 70%, which possesses relatively good visual effects. 
     In some implementations, the above-described spherical surface radius of the outer surface of the scattering part of the lamp cover unit  21  is set based on the light emission position of the LED lamp  11 , the distribution of the light scattering angle of the LED lamp  11 , and the haze of the lamp cover unit  21 . 
     Further improvements of the structure of the lamp cover unit  21  can be carried out. In some implementations, when the scattering part  212  in the lamp cover unit  21  is a real solid structure, it is possible to provide a groove that faces in the direction away from the LED lamp  11  from the inner surface of the scattering part  212 , and thereby provide a gap used for light dispersion between the inner surface of the scattering part  212  and the upper surface of the LED lamp  11 . The cross section of the groove can be rectangular, round, oval, etc., and said cross section is the surface on which the LED lamp  11  is provided parallel to the screen body  1 . 
       FIG. 12  is a cross-sectional view of two adjacent lamp cover units in the LED display screen cover. A gap that is used for light dispersion is provided in the space between the inner surface of the scattering part  212  and the upper surface of the LED lamp  11 . Specifically, a groove  22  that is rectangular in cross section is provided in the space between the upper surface of the LED lamp  11  and the inner surface of the scattering part  212 , and the groove  22  forms a gap in the space between the inner surface of the scattering part  212  and the upper surface of the LED lamp  11 . The length and breadth of the groove  22  matches the dimensions of the LED lamp  11 , and the depth HI of the groove  22  can be determined based on the sealing dimensions of the LED lamp  11 , the circumstances of the welding spots and light angle distribution characteristics, and the optical characteristics of the materials used to make the scattering part  212 . The depth HI of the groove  22  can be 0.35b to 0.8b, wherein b is the side length of the LED lamp  11 . In a particular example, the depth HI is within a range of 0 to 0.5 mm. 
     The groove  22  provides a space for placing the LED lamp  11 , and the groove  22  can also be used to carry out dispersion and mixing three primary color light rays (e.g., red, green, blue) emitted by the LED lamp  11  before they enter the lamp cover unit  21 . For example, the LED lamp  11  includes three LED emitters for emitting red, green, blue color light, respectively. 
     In  FIG. 12 , the scattering part  212  and light blocking part  211  are an integral structure, and the light blocking part  211  serves as the side wall of the groove  22  and can be used for fixing on the above-described screen body  1  or stuck in the space between adjacent LED lamps  11 . The light blocking part  211  plays a role of supporting the scattering part  212 , and it can also play the role of position fixing and thereby make one lamp cover unit correspond to one LED lamp  11  for which it is provided as a cover and make the entire screen cover have no movement in relative to the LED lamps  11 . 
       FIG. 13  is a cross-sectional view of two adjacent lamp cover units in the LED display screen cover provided in another embodiment. As shown in  FIG. 13 , a first column  23  is provided in the space between the side wall of the groove  22  (or otherwise the light blocking part  211 ) and the surface of the PCB circuit board  12 . The first column  23  is located in the space between two adjacent LED lamps  11 , and is used to support the light blocking part  211 . The first column  23  can be bonded, bolted or connected with pins on the PCB circuit board  12  to realize the fixing, or through hole created inside the PCB board  12 . A second column  24  can be provided inside the through hole, and can be bonded or welded inside the through hole of the PCB board. The second column  24  can be used to support the first column  23 . Alternatively, the first column  23  and second column  24  can be an integral structure. In  FIG. 13 , the first column  23  can be a cylinder or cube, and the second column  24  can be a cylinder or cube. Taking a cylinder as an example, the diameter of the first column  23  is relatively rough, whereas the diameter of the second column  24  is relatively fine and the length is relatively long, and the contact surface with the PCB circuit board  12  is relatively large, and it is used for fixing on the PCB circuit board  12 . 
     On the basis of the above-described technical scheme, another embodiment can be carried out for improvements of the structure of the lamp cover unit  21 : the inner surface of the scattering part  212  faces towards the arch in a direction facing away from the LED lamp  11 . That is, the inner surface of the scattering part  212  is an arch-like structure or arched structure, and said structure can be a spherical surface, e.g., a positive spherical surface or an ellipsoid; alternatively it is an arc surface, e.g., a hyperboloid, a paraboloid, etc.; or several planes are joined to form the structure of an arch. 
       FIG. 14  is a light path schematic comparative diagram in which two lamp cover units in the LED display screen cover provided in another embodiment each are fitted with an LED lamp. The inner surface of the scattering part  212  in the right lamp cover unit  21  is an arched or arc surface, while the inner surface of the scattering part  212  in the left lamp cover unit  21  is not an arched structure but rather a plane. For the left structure, the light rays emitted by the LED lamp enter the inside of the scattering part  212  and refraction occurs, and the angle of the refraction is relatively small; the light rays converge towards the center of the scattering part  212 , and this may be unfavorable for dispersion of the light rays in all directions, and furthermore this may result in a black side formed on the boundary of the LED pixel unit. 
     On the other hand, the light rays emitted by the right LED lamp  11  enter the inside of the scattering part  212  and refraction occurs, but owing to the act that the incidence surface is an arched or arc surface, the angle of the refraction is relatively large, the light rays are dispersed in all directions and the occurrence of a black side on the boundary of the LED pixel unit can be avoided. In the lamp cover unit  21  displayed in  FIG. 7 , the inner surface of the scattering part  212  is a positive spherical surface, and the spherical surface radius r of the inner surface of said scattering part  212  can be obtained by calculating with the following equation: 
             r   ≥         R   2     -   ab   +       1   2     ⁢     b   2                 
where R is a spherical surface radius of the outer surface of the scattering part  212 , a is the period of the LED pixel unit, and b is the side length of the LED lamp  11 .
 
     In some implementations, the spherical surface radius r of the inner surface of the scattering part is determined by a haze of a material of the scattering part, and a maximum of the radius r is not smaller than the spherical surface radius R of the outer surface of the scattering part. 
     In addition, for the spherical center position of the inner surface of the scattering part  212 , one can refer to  FIG. 15 .  FIG. 15  is a schematic diagram of the spherical center position in which the inner surface of the lamp cover unit scattering part  212  in the LED display screen cover is a positive spherical surface.  FIG. 15  shows a perspective view of the lamp cover unit  21 , where the boundary of the inside of the lamp cover unit is indicated by the dot-dash line. Point V and point W are respectively the intersection points between the intersection line between the inner surface of the scattering part  212  and the inner surface of the light blocking part  211  and the two relative edges in the light blocking part  211 . The line segment VW is parallel to the PCB circuit board  12 , and is also parallel to the bottom surface light blocking part  211 . The distance between point W and the bottom surface of the light blocking part  211  (that is, the distance LZ Q  between the midpoint of the line segment VW and the bottom surface of the light blocking part  211 ) can be determined based on the height of the LED lamp  11  and the depth HI of the groove  22 . The spherical center U of the inner surface of the scattering part  212  is located within the plane of line segment VW and the projection location of line VW on the PCB circuit board  12 , and is also located on the central perpendicular line segment ZQ of the VA segment (that is, the central normal line of the LED pixel unit). On the central perpendicular line segment ZQ, the length L UZ  of line segment UZ is: 
               L   UZ     =         R   2     -       1   4     ⁢     c   2                 
where R is spherical surface radius of the outer surface of the scattering part  212  and c is the side length of the groove  22 . The side length of the groove  22  can be a little bit larger than the side length of the LED lamp  11 . The distance L UQ  between the spherical center U of the inner surface of the scattering part  212  and the bottom surface of the light blocking part  211  is the difference between the distance L ZQ  between the midpoint A and the bottom surface of the light blocking part  211  and the length L UZ  of the line segment UZ, that is, L UQ =L ZQ −L UZ .
 
     On the basis of the above-described technical scheme, further improvements can be made for the lamp cover unit  21 . In some implementations, a transition circular arc is provided in the space between a corner of the inner surface of the scattering part  212  and the inner wall of the light blocking part  211 . The cover unit  21  can have the transition circular arcs on all four connection corners between the inner surface of the scattering part  212  and the inner wall of the light blocking part  211 . 
       FIG. 16  is a structural schematic diagram of the lamp cover unit in the LED display screen cover provided in another embodiment is fitted with an LED lamp, and  FIG. 17  is a light path schematic diagram in which the LED display screen cover is fitted to an LED lamp. In order to undertake a more detailed description of the above-described technical scheme, the view angle of  FIG. 17  is a cross-sectional view that is opened along the diagonal of the LED lamp, and what is displayed on the right side of  FIG. 17  is that a transitional arc  214  is provided in the space between the corner of the inner surface of the scattering part  212  and the inner wall of the light blocking part  211 , and what is displayed on the left side thereof is that no such transitional arc  214  has been provided in the space between the corner of the inner surface of the scattering part  212  facing the LED lamp and the inner wall of the light blocking part  211 , and this is just for the sake of comparison. 
     As  FIG. 17  shows, no transitional circular arc is set up between the inner surface of the scattering part  212  on the left side and the inner wall of the light blocking part  211 . J is the conjunction point of the inner surface of the scattering part  212  and the inner wall of the light blocking part  211 . Some of the light from the LED lamp  11  is projected to the point J where it is reflected toward JK and JL. So a black area appears at the conjunction point of the outer surface of the scattering part  212  and the outer wall of the light blocking part  211 . That is, a black area appears, e.g., between K and L, around the top part of the LED lamp. 
     A transitional circular arc is set up between the inner surface of the scattering part  212  on the right side and the inner wall of the light blocking part  211 . The light from the LED lamp  11  is refracted by the transitional circular arc to evenly reach the conjunction point of the outer surface of the scattering part  212  and the outer wall of the light blocking part  211 . No black area appears at the conjunction point. That is, no black area appears around the top corner of the LED lamp. In the same way, the light from LED lamp  11  evenly reaches the whole surface of the scattering part  212  and completely gets rid of the black area on the top corner of the LED pixel unit. A radius of the transitional circular arc can be determined in accordance with the sizes of the scattering part  212 , the light blocking part  211 , and the LED lamp. In some examples, the radius of the transitional circular arc is from 0.08a to 0.2a, where a is the period of LED pixel unit. 
     The color of the LED display screen cover itself is an important specification because it can shift the overall color of images displayed by the LED display screen toward the color of the LED display screen cover. For example, if the color of the LED display screen cover is red, then the overall color of images is shifted toward red. In some implementations, to avoid the impact of the color of the LED display screen cover itself on the overall color of images, dark-colored materials are selected for manufacturing the LED display screen cover. In some examples, materials of a grayscale value from 0 to 125 are selected, and the RGB (red:green:blue) ratio is about (1±0.2):(1±0.2):(1±0.2). In a particular example, the ratio is 1:1:1. 
     The RGB ratio can be determined based on color cards that are commonly used in this industry. For example, Ral Plastics color card provides the following colors: RAl 1000-P, RAl 1011-P, RAl 1020-P, RAl 4007-P, RAl 5003-P, RAl 5011-P, RAl 6003-P, RAl 6009-P, RAl 7001-P, RAl 7004-P, RAl 7011-P, RAl 7012-P, RAl 7015-P, RAl 7016-P, RAl 7021-P, RAl 7024-P, RAl 7031-P, RAl 7037-P, RAl 8014-P, RAl 8017-P, RAl 8025-P, and RAl 9011-P. The above-referenced colors are not fixed. Other colors can be also selected. 
     The LED display screen cover used for the LED display screen includes an array of lamp cover units over the LED display screen. Each lamp cover unit is placed above a respective LED lamp, and the top of the lamp cover unit is an arched structure facing away from the LED lamp. In such a way, light from each LED lamp can only go out through the respective lamp cover unit above, and won&#39;t affect adjacent LED pixel units. Also the arched structures of the lamp cover units can uniformly diffuse or scatter the light emitted by the LED lamps to a size of the physical area occupied by the LED pixel units, and the filling coefficient can be greater than 93%. This mechanism makes the images displayed by the LED display clearer. No perceptible black area appears between two adjacent LED pixel units. Therefore, periodic black area grid structures will be eliminated from the entire LED display screen, which makes “no gap” between two adjacent LED pixel units or very small gaps such that it is impossible to form interference fringes. Images become softer and are free from a grainy look. 
       FIG. 18  is a structural illustration of another implementation of the LED screen cover. The lamp cover unit  21  has the above referenced scattering part  212 , but no light blocking part  211 . The top of the lamp cover unit  21  is a structure that arches away from the LED lamp. The details of how to design the arched structure are described above. As  FIG. 18  shows, the lamp cover unit  21  does not have a light blocking part  211 , so the lamp cover units  21  and the PCB circuit board can be screwed or pinned together, e.g., by at least one fixing pin  215 . The lamp cover units  21  and the PCB circuit board can be also glued together. As shown in  FIG. 19 , a fixed connection between them is achieved by direct bonding on the surface of the LED screen by glue on the back side of the lamp cover units  21 . 
       FIG. 1  shows another implementation of an LED display screen. This implementation includes the LED display screen body  1  that has an array of LED pixel lamps and the LED display screen cover  2  that includes a plurality of lamp cover units  21  and is connected to the screen body  1 . The number of the lamp cover units  21  and the number of the LED lamps  11  can be the same. The size of the LED display screen cover  2  corresponds to the size of the LED screen body  1 . The plurality of lamp cover units  21  of the LED display screen cover can be integrally formed into a whole piece. In some examples, if an LED display screen has 192×192 LED lamps and if an LED display screen cover has 32×16 cover units, then 6×12 pieces of LED display screen covers are needed to cover the LED display screen. 
     There are multiple methods to connect the LED display screen cover  2  and screen body  1 . 
     One of the methods is to glue them together.  FIG. 20  shows a schematic diagram of places for applying glue for the implementations method. Glue is applied to an end of the light blocking part  211  in the LED display screen cover so that it can be connected to the PCB circuit board of the LED screen body  1  between two adjacent LED lamps. Each lamp cover unit is placed above a respective LED lamp. 
     Another implementations method is to pin them together.  FIG. 21  shows places for applying pins. At least one fixing pin  215  is set up on the surface of the screen cover that faces the LED lamps. Correspondingly, the PCB circuit board of the screen body  1  has a pin hole. The LED display screen cover  2  and screen body  1  are connected when the fixing pin  215  is inserted into the pin hole of the PCB circuit board. 
     Implementations of the present disclosure also provides methods of manufacturing LED displays or LED display screens with the following steps: 
     1) a light-permeable material having a haze greater than 50% (or greater than 70%) is selected to manufacture the LED display screen cover. Plastic injection technology can be applied. 
     2) the LED display screen body is manufactured. An array of LED pixel lamps is arranged on a substrate (e.g., PCB circuit board) to form the LED display screen body. In some examples, each LED pixel lamp is a packaged lamp including three emitters emitting three primary colors (red, green and blue). In some examples, the LED display screen body is formed by directly placing three emitters on the center of each LED pixel on the substrate without packaging (or assembling). The LED display screen cover can be configured to cover the three emitters for each LED pixel. 
     3) the LED display screen cover and the LED display screen body are installed together by at least one of the methods: 
     I) pinning them together. The LED display screen cover manufactured in step 1) is placed in front of the LED display screen body manufactured in step 2). Fixing pin  215  is inserted into the pin hole on the PCB circuit board. Heat is used to melt the pin end sticking out on the back side of the PCB circuit board. After the pin end cools off, the screen cover and the screen body are fixed together, or 
     II) gluing them together. Glue can be directly to the back side or the light blocking part of the LED display screen cover. Then the LED display screen cover is pressed on the surface of the LED display screen body. 
     In a particular example, for P2.5 LED display screen body, its pixel period is 2.5 mm. The package size of the LED display screen body is 2 mm×2 mm×0.7 mm. The thickness of the PCB circuit board is 2 mm. The resolution of the LED display screen body is 80×32. That is, there are 80×32 LED lamps on a PCB circuit board. The manufacturing of the LED display screen can include the following steps: 
     Step 1: production of the LED display screen cover. Polycarbonate (PC) injection molding is used, and one LED display screen cover is made into 16×16, that is, it can cover 16×16 LED pixel lamps. The polycarbonate material haze is 95%. When a black master batch with a thickness smaller than 1 mm is added, the light permeability of the material becomes 50%. The LED display screen cover period is 2.5 mm; the spherical surface radius of the spherical surface scattering part in the lamp cover unit is designed to be 2.06 mm; the groove  22  has a length and a breadth that are both 2 mm+0.1 mm (positive allowance), and a depth that is 0.7 mm+0.05 mm (positive allowance); for the groove bottom, based on the circumstances, it is possible to make a spherical arc-shaped depression structure (that is, a structure in which the inner surface inside the above-described scattering part  212  is an arc surface). In the present embodiment the arc surface radius is 3 mm and the arc surface depth is 0.2 mm; the fixing pin is a cylinder with dimensions of Φ 0.7 mm-0.5 mm (negative allowance)×2.3 mm. One LED screen body requires 5×2 LED screen covers. 
     Step 2: production of the LED screen body. It can be produced according to general LED screen production methods. To install 5×2 scattering covers on the LED screen body, through holes Φ 0.7 mm+0.5 mm (positive allowance) are created respectively in the corresponding positions. 
     Step 3: installation. The injection molded LED display screen covers are covered on the front end of the LED screen body according to a mode of 5×2, and the fixing pins pass through the through holes on the printed circuit board (PCB). The fixing pins that are passed through the back side of the PCB are heated to make them melt, and after they cool they are remolded such that the scattering cover is fixedly installed on the LED screen body. 
     In such a way, the production of one LED screen body with LED display screen covers is completed. After that, several LED screen bodies installed with LED display screen covers may be connected according to installation and production process of ordinary LED large screens to achieve a larger LED display screen. 
     Alternatively, in the above-described step 3, the LED display screen covers can be fixed to the LED screen body by applying glue to the back side of the LED display screen covers. After the glue has been applied to the entire flat surface of the back side of the LED display screen covers, the LED display screen covers may be directly covered on the surface of the LED screen body and bonding may be done. 
       FIG. 24  is a schematic diagram of an example light path in which light from an LED lamp  244  in an LED pixel unit propagates into an adjacent cover unit. The LED lamp  244  includes LED lighting elements  245 , e.g., red LED, green LED, and blue LED, positioned on an LED base  247 , which can be further arranged on a PCB board. The lighting elements  245  can be electrically coupled to drive circuits on the PCB board and emit light when driven by the drive circuits. In some implementations, the lighting elements  245  are packaged in an LED housing  246 , e.g., a transparent cover. 
     The cover unit  240  is configured to be positioned over the respective underlying LED lamp  244 . The cover unit  240  can be similar to the cover unit  21  of  FIGS. 1, 2, and 4 . The cover unit  240  includes a scattering part  241 . The scattering part  241  can be similar to the scattering part  212  of  FIG. 7 , and can have a spherical outer surface. The spherical outer surface of the scattering part  241  has edges including an edge in common with an adjacent cover unit in a same row and an edge in common with an adjacent cover unit in a same column. Outer surfaces of cover units arranged in the columns and the rows can together form a continuous outer cover surface. 
     The scattering part  241  has an inner surface facing away from the spherical outer surface and defining a recess  243  sized based on the LED housing  246  of the underlying LED lamp  244 . The recess  243  can have a transitional circular arc between adjacent sides of the recess  243 . The transitional circular arc can be similar to the transitional circular arc  214  of  FIG. 17 . 
     The cover unit  240  includes a light blocking part  242  configured to block off light from an adjacent LED lamp and/or light from the LED lamp  244  to the adjacent cover unit. The light blocking part  242  can be similar to the light blocking part  211  of  FIG. 7 . 
     In some cases, due to the packaging of the LED light elements  245 , the LED light elements  245  can emit light from sides, as illustrated in  FIG. 24 . In some cases, the light blocking part  242  can scatter light. For example, the light blocking part  242  can be made of a material same as that of the scattering part  214 . When the cover unit  240  is positioned above the LED lamp  244 , the light emitted from the sides of the LED light elements  245  can be scattered by the light blocking part  242  to the adjacent cover unit, e.g., to a top of the scattering part of the adjacent cover unit, as illustrated in  FIG. 24 , which can cause light interference between adjacent LED pixel units. 
       FIG. 25  is a cross-sectional view of two adjacent lamp cover units  250  in an example LED display screen cover. By changing a shape of an outer surface of the lamp cover unit  250 , light from an LED lamp  254  in an LED pixel unit can be restricted or prevented from propagating into an adjacent cover unit. The LED lamp  254  can be similar to the LED lamp  244  of  FIG. 24 , and includes 
     LED light elements  255  positioned on an LED base  257  and packaged by an LED housing  256 . The cover unit  250  is configured to be positioned over the LED lamp  254 . The cover unit  250  also includes a scattering part  251  and a blocking part  252 . An inner surface of the scattering part  251  defines a recess  253  sized based on an upper extent of the LED housing  256  of the underlying LED lamp  254 . 
     Different from the cover unit  240  of  FIG. 24 , the cover unit  250  has a shaped outer surface that is non-spherical. That is, the scattering part  251  is different from the scattering part  241  of  FIG. 24  and has a non-spherical shaped outer surface. The non-spherical shaped outer surface can include one of ellipsoid, paraboloid, and Bessel surface. 
     A top (or a highest extent) of the scattering part  251  can be higher than that of the scattering part  241 , and a bottom (or a lowest extent) of the scattering part  251  can be lower than that of the scattering part  241 , such that the recess  253  is enclosed, at least partially, by the non-spherical shaped outer surface of the scattering part  251 . The non-spherical shaped outer surface of the scattering part  251  has a lowest extent no higher than a lighting element  255  of the underlying LED lamp  254 . In some cases, a distance between the top of the non-spherical shaped outer surface of the scattering part  251  and a top of the recess  253  is within a range of 0.3˜0.9a, where a is a period of the LED pixel units. An optimal value of the distance can be determined based on a shape of the outer surface of the scattering part  251  and/or a type of the LED lamp  254 . 
     As noted above in  FIG. 24 , the light blocking part  242  of the cover unit  240  can scatter light emitted from sides of the LED lamp  244  to the adjacent cover unit, which can cause light interference between the adjacent LED pixel units. However, if a cover unit has no light blocking part, the light interference between the adjacent LED pixel units can be reduced or eliminated. 
     As an example,  FIG. 26A  shows a cross-sectional view of two adjacent lamp cover units  260  without light blocking parts in another example LED display screen cover. The cover unit  260  only includes a light scattering part  261 . An LED lamp  264  in an LED pixel unit includes LED lighting elements  265  positioned on an LED base  267  and packaged by an LED housing  266 . The LED base  267  can be fixed on top of a PCB board. Without light blocking parts of the cover units  260 , sides of the LED housing  266  of the LED lamp  264  directly face to adjacent side of an LED housing of an adjacent LED lamp. 
     As illustrated in  FIG. 26A , without a light blocking part, a majority portion of light emitted from a side of the LED lamp  264  (e.g., the LED lighting elements  265 ) is incident on a top of an LED housing of an adjacent LED lamp and is obstructed or prevented to propagate further. Only a small portion of the light can propagate to enter at an angle into a top of a scattering part of an adjacent cover unit for the adjacent LED lamp. Moreover, the angle into the top of the scattering part of the adjacent cover unit is increased compared to that with the light blocking part (as shown in  FIG. 24 ). Thus, the light from the LED lamp  264  entering into the top of the scattering part of the adjacent cover unit can be greatly reduced. 
     Similar to the scattering part  241  of  FIG. 24 , the scattering part  261  can have a spherical outer surface. An inner surface of the scattering part  261  can be an immense extent of the cover unit  260 . The inner surface of the scattering part  261  faces away from the spherical outer surface and defines a recess  263  sized based on an upper extent of the LED housing  266  of the underlying LED lamp  264 . A depth of the recess  263  can be smaller than that of the recess  243  of  FIG. 24 . The depth can be within a range of 0.05a˜0.25a, where a is a period of the LED pixel units. A width of the recess  263  can be slightly larger than a width of the LED lamp  264 , such that, during installation, the LED housing  266  can be positioned within the recess  263  to locate a relative position between the cover unit  260  and the LED lamp  264 . 
     In some implementations, at a cross section of every four adjacent LED pixel units, a fixing column  268  is installed, as illustrated in  FIGS. 26B and 26C .  FIG. 26B  is a cross-sectional view of two adjacent lamp cover units  260  without light blocking parts installed with fixing columns  268  in another example LED display screen cover, and  FIG. 26C  is a bottom view of the LED display screen cover of  FIG. 26B . Each column  268  can be protruded from an intersection of adjacent cover units  260  and arranged between four adjacent LED lamps  264 . A height of the column can be a distance from a bottom of the scattering part  261  of the cover unit  260  to the top of the PCB board coupled to the bottom of the LED base  264 . When installing the LED display screen cover to an array of underlying LED pixel units, the columns  268  can be fixed to the PCB board under the LED bases  267 , for example, bottoms of the columns  268  can be glued to the top of the PCB board, to fix the LED display screen cover. 
     Compared to the LED display screen cover having cover units with light blocking parts (as shown in  FIG. 24 ), the LED display screen cover having cover units without light blocking parts (as shown in  FIGS. 26A-26C ) is easier to fabricate. As a density of LED pixel units is increasing, a distance between adjacent LED lamps is decreasing accordingly, which requires a thinner light blocking part between the adjacent LED lamps. However, due to restrictions in manufacturing or fabricating technologies, it may be difficult to fabricate the thinner light blocking part. In comparison, the LED display screen cover having cover units without light blocking parts does not suffer from the restrictions and can have a higher fabrication accuracy and a better performance. 
       FIG. 27A  is a cross-sectional view of an example lamp cover unit  270  having a square pyramid structure in another example LED display screen cover.  FIG. 27B  is a schematic diagram of a front side of the LED display screen cover of  FIG. 27A . The cover unit  270  can have a performance similar to the cover unit  240  or realize functions similar to the cover unit  240 . 
     Similar to the cover unit  240  of  FIG. 24 , the cover unit  270  includes the scattering part  271 , a light blocking part  272  and a recess  273 . Different from the cover unit  240 , where the scattering part  241  has a spherical structure with a spherical outer surface, the cover unit  270  includes a square pyramid structure as the scattering part  271  and has a square pyramid outer surface. Corners of an LED lamp  274  under the cover unit  270  in an LED pixel unit are connected to an apex of the square pyramid structure along sides of the square pyramid structure. In some implementations, a height H defined by the square pyramid structure (or the square pyramid outer surface) is within a range of 0.3a˜0.9a, where a is a period of the LED pixel units. 
       FIG. 28A  is a cross-sectional view of an example lamp cover unit  280  having a square frustum structure in another example LED display screen cover.  FIG. 28B  is a schematic diagram of a front side of the LED display screen cover of  FIG. 28A . The cover unit  270  can have a performance similar to the cover unit  240  or realize functions similar to the cover unit  240 . 
     Similar to the cover unit  240  of  FIG. 24 , the cover unit  280  includes the scattering part  281 , a light blocking part  282  and a recess  283 . The cover unit  280  is configured to be positioned over an LED lamp  284  in an LED pixel unit. Different from the cover unit  240 , where the scattering part  241  has a spherical structure with a spherical outer surface, the cover unit  280  includes a square frustum structure as the scattering part  281  and has a square frustum outer surface. The square frustum structure has a flat top surface. An edge length of the top surface of the square frustum structure can be within a range of 0.4a˜0.7a, where a is a period of the LED pixel units. A height H defined by the square frustum structure (or the square frustum outer surface) is within a range of 0.3a˜0.9a. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, screen covers described here can be also used in liquid crystal displays (LCDs) or other image or video display systems. Light sources of the display systems can be LED lamps, lasers, semiconductor diodes, or any suitable light sources. Accordingly, other embodiments are within the scope of the following claims.