Patent ID: 12235540

DETAILED DESCRIPTION

Detailed description of the present invention is provided below along with figures and embodiments, which further clarifies the objectives, technical solutions, and advantages of the present invention. It is noted that schematic embodiments discussed herein are merely for illustrating the invention. The present disclosure is not limited to the embodiments disclosed.

FIG.1shows a prior art display device100in a perspective view. The display device100has a LCD panel110, a section111that contains a filter unit and a diffuser, a spacer layer112, and a section113that contains a mini-LED array. The filter unit contains color filter elements that convert an incident light into light of different wavelengths, respectively. The diffuser may include a layer of a diffusion material, diffuse light passing through it, and improve luminance uniformity by reducing the luminance of bright portions of the light. The layer112may be made of an adhesive material such as resin that is transparent to the light.

During operation of the display device100, light emitted from the mini-LED array in the section113spreads in and passes through the layer112, before irradiating the section111or the diffuser. Because the layer112is arranged thin for a thin display device100, the lower surface of the section111may have uneven luminance or uneven brightness. For example, regions immediately over the mini-LEDs may appear bright, while regions between the mini-LEDs may appear dim. In order to improve luminance uniformity, more mini-LEDs are added to the array, which increases the assembly and material cost. Further, even when more mini-LEDs are added to the mini-LED array, the diffuser is still needed for providing uniform luminance to the LCD panel.

FIG.2Aschematically shows a cross-sectional view of a display device200, according to embodiments of the present disclosure. The cross-sectional view is depicted in an X-Z plane. The display device200may include a display panel210, a wavelength conversion unit211, a backlight module212, and a diffuser213. The wavelength conversion unit211is adjacent to the display panel210and disposed between the display panel210and the diffuser213. The backlight module212is disposed proximate to the display module210and separated from the display module210by the wavelength conversion unit211, the diffuser213, and a region214. The region214may be configured between the diffuser213and backlight module212. Optionally, the region214may be arranged inside the backlight module212. In some other cases, the wavelength conversion unit211, diffuser213, and a part of the region214may be configured inside the display panel210. As used herein, the terms “unit”, “module”, or “component” have the same meaning or similar meanings and can be used interchangeably.

The display panel210contains a matrix of pixels that form an image by controlling transmission of light through the pixels. Light, as used herein, may also be referred to as light rays. As the display panel210does not generate light itself, it needs a backlight such as the backlight module212. The backlight module212emits light to illuminate the pixels of the display panel210to create an image. In some embodiments, the display panel210may be a LCD panel. In such cases, the display panel210may include a liquid crystal layer disposed between an upper substrate and a lower substrate, a first polarization layer, and a second polarization layer. The term “layer”, as used herein, may also indicate a member. The liquid crystal layer is formed of liquid crystal molecules. Transparent electrodes are disposed on the upper and lower substrates. Each pixel of the LCD panel consists of a portion of liquid crystal molecules aligned between an upper and lower transparent electrode. By applying a voltage to a pixel through the electrodes, the arrangement of the liquid crystal molecules of the pixel is changed, and a certain amount of light passes through the pixel and makes the pixel appear a specific level of gray.

In some cases, the wavelength conversion unit211may contain a matrix of color filters deposited on a plate or substrate aligned to the pixels of the LCD panel. As each pixel may have three subpixels corresponding to red, green, and blue color, respectively, three color filters are arranged for a pixel. Color filters may consist of coloring materials such as pigments or dyes for which only light of a certain range of wavelength is transmissive.

In some other cases, the wavelength conversion unit211may contain a matrix of wavelength conversion elements deposited on a plate or substrate. The wavelength conversion elements may absorb light of a shorter wavelength (e.g., light of near ultraviolet), and then emit light of a longer wavelength (e.g., light of red, green, or blue color). Hence, a matrix of wavelength conversion elements may work in a similar way to a matrix of color filters described above.

The diffuser213may contain a diffusion layer made of a diffusion material, and is used to improve luminance uniformity. The display panel210, wavelength conversion unit211, and diffuser213may be fabricated separately and then bonded together at a later time. Optionally, the diffuser213and wavelength conversion unit211may be deposited on a plate or substrate sequentially, and the display panel210may be subsequently made using the wavelength conversion unit211as a base or substrate. Optionally, the display panel210may be made first, and the wavelength conversion unit211and diffuser213may be sequentially deposited on the bottom or lower surface of the display panel210. In such cases, the diffuser213may become the bottom part of the display panel210. Alternatively, the display panel210and wavelength conversion unit211may be integrated and made together. For example, a layer containing a matrix of color filters or a matrix of wavelength conversion elements may be configured between two layers of the display panel210, such as between the liquid crystal layer and the first polarization layer (or the second polarization layer). Then, the wavelength conversion unit211may be fabricated between steps of depositing the liquid crystal and first polarization layers.

The backlight module212contains multiple light emitting elements disposed on a substrate. The light emitting elements form a matrix or array with a predetermined grid pattern to illuminate the display panel210. The light emitting elements may be referred to as light sources, and include lasers, LEDs, micro-LEDs, mini-LEDs, and other small light emitting devices. An LED may also be referred to as an LED chip. A micro-LED chip may have a size smaller than 100 microns. A mini-LED chip may have a size of 100 to 200 microns or 100 to 300 microns. In descriptions below, as an example, a backlight (e.g., the backlight module212) contains mini-LEDs. Alternatively, a light source may include a light emitting element and a lens that is configured for the light emitting element. That is, a light emitting element and a corresponding lens together may be referred to as a light source.

The region214may include a space between the backlight module212and the diffuser213or between the mini-LEDs and the diffuser213. The diffuser213and the space (or the region214) are configured between the wavelength conversion unit212(or the display panel210) and the backlight module212. When the wavelength conversion unit is a part of the display panel210, the wavelength conversion unit211may be disposed above the mini-LEDs and between a member of the display panel210and the substrate of the mini-LEDs. The space in the region214may be vacuum or filled with air or an inert gas. In some cases, the space may also be filled with a transparent adhesive material (e.g., transparent resin). As mini-LEDs are small, they may be disposed closer to the diffuser213than regular LEDs, and make the region214thinner, which may make the display device200thinner.

When mini-LEDs are disposed proximate to the diffuser213and display panel210, the mini-LEDs may irradiate the diffuser213with uneven luminance, causing uneven illumination on the display panel210. While more mini-LEDs may be added to the backlight module212to reduce the uneven luminance as used in prior art systems or devices, manufacturing cost would increase. As explained below, the present invention achieves even luminance while not increasing the number of mini-LEDs.

FIGS.2B and2Cschematically illustrate a cross-sectional view212A and a top view212B of the backlight module212shown inFIG.2A, according to embodiments of the present disclosure. The cross-sectional view212A is in an X-Z plane, and the top view212B is in an X-Y plane. As shown inFIGS.2B-2C, the backlight module212contains mini-LEDs221, lenses222, and a substrate215on which the mini-LEDs221are disposed. The lenses222are positioned over the mini-LEDs221, and aligned with the mini-LEDs221in the Z direction, respectively. Please note that the drawings or illustrations of the components/items in the figures (including the lenses) of this application are used for explanation purposes and they do not necessarily represent the actual shapes or dimensions of the components/items. In some embodiments, the mini-LEDs221form a matrix or array of light sources with a predetermined grid pattern, and the lenses222form a matrix or array of lenses (e.g., as shown inFIG.2C) with the same grid pattern. The quantity, dimension, shape, and arrangement of mini-LEDs and lenses shown inFIGS.2B and2Cand in other figures in the present disclosure are exemplary and for description purposes, although any suitable quantity, dimension, shape, and arrangement may be used for the disclosed backlight modules and display devices according to various embodiments of the present disclosure.

In the backlight module212, each lens222is aligned with a mini-LED221along the Z direction or a direction proximately perpendicular to the substrate215. In some cases, the lenses222may be fabricated individually, and then bonded with the mini-LEDs221respectively in an assembly process. In some other embodiments, an array of lenses222may be formed together by molding. For example, an optical unit or optical component may be molded that contains an array of the lenses222with a predetermined pattern. The optical unit may be held over the substrate215to make the lenses222align with the mini-LEDs221, respectively. Further, the optical unit may be bonded with the substrate215after the alignment is performed.

The mini-LEDs221and lenses222are configured such that when light is emitted from the mini-LEDs, the lenses direct light rays or change the propagation direction of the light of each mini-LED differently at different angles. When the intensity of light generated from each mini-LED is changed differently at different angles by the lens222, the light from the mini-LED array may merge and irradiate the diffuser213with relatively uniform luminance. In one aspect, fewer mini-LEDs221may be needed for the backlight module212and as a result, the manufacturing cost may be reduced. As the backlight module212may produce relatively uniform luminance, the diffuser213may have higher transmittance than those used in conventional display devices. The efficiency of the display device200may be increased. In addition, when the backlight module212provides luminance with uniformity beyond a certain level, the diffuser213may not be needed. That is, the display device200may not contain a diffuser (e.g., the diffuser213) in some cases, which may lower the manufacturing cost further.

In descriptions below, lenses (e.g., lenses222) are designed to create uniform luminance based on a light source array such as a mini-LED array. In some aspect, the mini-LED may be considered as a Lambertian light source that emits light in a Lambertian pattern. Optionally, the mini-LED may be an approximate Lambertian light source. The mini-LEDs are exemplarily used as a Lambertian light source in the following descriptions. As such, when there is no lens, the light from a mini-LED is dispersed according to Lambert's emission law. When a lens is incorporated with a mini-LED, the light emitted from the mini-LED is dispersed according to functions of the lens. The lens, as used herein, may indicate a lens system that contains one or more lenses. A lens may direct light differently at different angles. Since an array of lenses and array of mini-LEDs are used to create uniform luminance, the lens may be designed based on an array of Lambertian light sources and certain values of luminance uniformity on a surface or an interface. The term “interface”, as used herein, indicates a boundary between two regions of space occupied by different materials. A surface may indicate an interface between the air (or vacuum or a gaseous environment) and a solid matter.

In certain embodiments, when a Lambertian light source irradiates an interface via a lens and values of luminance at each spot on the interface are known, the distribution of light intensity in angular coordinates may be calculated. Based on the distribution of light intensity in the angular coordinates and the radiation pattern of the Lambertian light source, data of the lens may be calculated using, for example, certain methods or lens design software. More details about designing a lens are illustrated below. The term “spot”, as used herein, indicate a substantially small region or substantially small area that surrounds a point on an interface.

FIG.3Aschematically shows a top view300A of a backlight module300of a display device (not shown), according to embodiments of the present disclosure. The backlight module300contains an array of mini-LEDs311with a certain pattern disposed on a substrate310, while corresponding lenses (or a corresponding array of lenses with the same pattern) are omitted inFIG.3A. The array may exemplarily contain mini-LEDs A to I. The distance between centers of adjacent mini-LEDs311along the X direction has a value of a, and the distance between centers of adjacent mini-LEDs311along the Y direction has a value of b. In some cases, for example, the value of a and b may be in a range of 3 to 9 millimeters, respectively. Let X2−X1=a, X3−X2=a, Y2−Y1=b, and Y3−Y2=b. The values of a and b may be different in some cases. Optionally, the values of a and b may be the same in some other cases.

FIGS.3B and3Cschematically illustrate cross-sectional views300B and300C of a structure containing the backlight module300shown inFIG.3A, according to embodiments of the present disclosure. The structure may include the backlight module300and a diffuser321positioned over lenses312, mini-LEDs311, and the backlight module300. The structure may be a part of the display device and disposed below a display panel (not shown) of the display device. The diffuser321has a lower surface or lower interface322that faces the lenses312, the mini-LEDs311, and the substrate310. In some cases, provided that the space between the diffuser321and the backlight module300is filled with air. Then, the lower interface322is an interface between the air and a bottom layer or bottom part of the diffuser321.

FIG.3Dis a diagram300D that depicts spots1to9on the lower interface322. The diagram300D shows a view taken against the Z direction, i.e., a direction facing the backlight module300. Spots1-9are immediately over the mini-LEDs A-I, respectively. For example, spot5, the mini-LED E, and the lens of the mini-LED E are aligned along the Z direction or a direction approximately perpendicular to the substrate310. As such, spots1-9form an array that has the same pattern as that of the array formed by the mini-LEDs311. Hence, the centers of spots1-9are spaced apart by a in the X direction and by b in the Y direction.

As shown inFIGS.3A-3D, the mini-LEDs311emit light toward to the diffuser321through the lenses312. If there is no lens and the mini-LEDs irradiate the interface directly, spots1-9may be brightly irradiated, while it may be dimly irradiated in regions away from spots1-9. Thus, the luminance on the lower interface322is not uniform. If regular concave lenses are used to further spread light from the mini-LEDs, spots1-9may become less brightly irradiated, but the interface may still have uneven luminance with bright areas and dim areas. Consequently, additional mini-LEDs and a diffuser are needed to make the luminance more uniform.

In the present disclosure, light emitted from a mini-LED311is processed by a lens312. The configuration of the mini-LED array and the function of the lens312are arranged such that when all of the mini-LEDs311emit light during operation, the luminance uniformity in the area encircled by the mini-LEDs A-D and F-I is above a certain value. Thus, compared to conventional methods, fewer mini-LEDs may be employed.

FIGS.3E and3Fschematically show changes of luminance along the X direction and Y direction when a lens312is incorporated with the mini-LED E. InFIG.3E, the curve reflects the change of luminance along a line L1that passes through spots4,5, and6along the X direction with respect toFIG.3D. Line1also passes spots M′, M, N, and N′. The distances between spots4and M′,5and M,5and N, and6and N′ each have a value of e. The value of e is smaller than a/2. In some cases, e may be zero. When e equals zero, spots M′, M and N, and N′ merge with spots4,5, and6, respectively. In this case, spots4and M′, spots5, M, and N, and spots6and N′ are at the same location on the lower interface322, respectively. InFIG.3F, the curve reflects the change of luminance along a line L2that passes through spots8,5, and2along the Y direction with respect toFIG.3D. Line2also passes spots T′, T, S, and S′. The distances between spots2and S′,5and S,5and T, and8and T′ each have a value of f. The value of f is smaller than b/2. In some cases, f may be zero. When f equals zero, spots S′, S and T, and T′ merge with spots2,5, and8, respectively. In this case, spots2and S′, spots5, S, and T, and spots8and T′ are at the same location on the lower interface322, respectively.

As shown inFIGS.3E-3F, when the mini-LED E is powered on, the luminance along line L1is maximum (e.g., an arbitrary value 1) between spots M and N (including spots M and N), and minimum (e.g., zero, substantially close to zero, or below a predetermined darkness level) between spots4and M′ and spots N′ and6(including spots4,6, M′, and N′). Optionally, the luminance along line L1is substantially close to a maximum value between spots M and N (including spots M and N), and substantially close to a minimum value between spots4and M′ and spots N′ and6(including spots4,6, M′, and N′). In the meantime, the luminance along line L2is maximum (e.g., an arbitrary value 1) between spots T and S (including spots T and S), and minimum (e.g., zero, substantially close to zero, or below a predetermined darkness level) between spots8and T′ and spots S′ and2(including spots2,8, T′, and S′). Optionally, the luminance along line L2is substantially close to a maximum value between spots T and S (including spots T and S), and substantially close to a minimum value between spots8and T′ and spots S′ and2(including spots2,8, T′, and S′). The luminance along line L1changes linearly from the minimum value to the maximum value between spots M′ and M, and spots N′ and N. The luminance along line L2also changes linearly from the minimum value to the maximum value between spots T′ and T, and spots S′ and S. The curve shown inFIG.3Efollows equations 1A to 1D.

E⁢(x)=0(1⁢A)E⁢(x)=1(1⁢B)E⁢(x)=1-X⁢2-e-xa-2⁢e(1⁢C)E⁢(x)=1-x-X⁢2-ea-2⁢e(1⁢D)

Equation 1A applies when x is in ranges of X1 to X1+e and X3−e to X3, equation 1B applies when x is in a range of X2−e to X2+e, equation 1C applies when x is in a range of X1+e to X2−e, and equation 1D applies when x is in a range of X2+e to X3−c.

Similarly, the curve shown inFIG.3Ffollows equations 2A to 2D.

E⁢(y)=0(2⁢A)E⁢(y)=1(2⁢B)E⁢(y)=1-Y⁢2-f-yb-2⁢f(2⁢C)E⁢(y)=1-y-Y⁢2-fb-2⁢f(2⁢D)

Equation 2A applies when y is in ranges of Y1 to Y1+f and Y3−f to Y3, equation 2B applies when y is in a range of Y2−f to Y2+f, equation 2C applies when y is in a range of Y1+f to Y2−f, and equation 2D applies when y is in a range of Y2+f to Y3−f.

As equations 1C-1D and 2C-2D respectively describe the linear change and the minimum luminance is zero (or substantially close to zero), the luminance is half of the maximum value (or substantially close to half of the maximum value) at the midpoint between two corresponding spots (e.g., between spots4and5, spots M′ and M, spots2and5, or spots S and S′). The midpoint indicates a spot that has an equal distance to two corresponding spots (e.g., spots M′ and M).

Although equations 1A-1D and 2A-2D are arranged for spot5with regard to the mini-LED E, these equations may be adjusted to express the luminance on the lower interface322created by irradiation from other mini-LEDs, provided that the mini-LEDs A-I each have the same or substantially similar characteristics. For example, the mini-LEDs may generate values of maximum luminance on the lower interface322that are substantially close. For irradiation from the mini-LED D and a range of X1 to X2, for example, the luminance along line L1follows equations 3A-3C.

E⁢(x)=0(3⁢A)E⁢(x)=1(3⁢B)E⁢(x)=1-x-X⁢1-ea-2⁢e(3⁢C)

Equation 3A applies when x is in a range of X2−e to X2, equation 3B applies when x is in a range of X1 to X1+e, and equation 3C applies when x is in a range of X1+e to X2-e.

Provided that both mini-LEDs D and E are powered on. When equations 1A and 3B, 1B and 3A, and 1C and 3C are respectively combined, the total luminance is always 1, a constant. That is, the luminance along line L1from spot4to spot5(or X1 to X2) is always 1, a constant. In similar manners, when the mini-LEDs G and H are powered on, the luminance on a line connecting spots7and8is also always 1. When the mini-LEDs C and F are powered on, the luminance on a line connecting spots3and6is always 1, as well. The constant luminance applies to other lines connecting adjacent spots among spots1-9along the X or Y direction on the lower interface322.

FIG.3Gis schematic diagram300E that illustrates certain regions on the interface322according to embodiments of the present disclosure. As shown inFIG.3G, lines L3, L5, and L7are parallel to line L1or the X axis, and lines L4, L6, and L8are parallel to line L2or the Y axis, respectively. Line L7connects spots1and2, while line8connects spots1and4. Lines L3and L5pass through spots S and S′, and lines L4and L6pass through spots M and M′, respectively. Lines L1, L2, L7, and L8form a rectangle (or square) with spots1-2and4-5located at the corners of the rectangle (or square). The spots1-2and4-5correspond to the mini-LEDs A-B and D-E that may form a lighting unit in some embodiments. Lines L3-L6divide the rectangle (or square) into 9 regions R1-R9.

Provided that the mini-LEDs A-B and D-E are powered on. Let the luminance at any spot be E(x)*E(y) for each of the mini-LED. In the region R9, the luminance is determined by the mini-LED E. At any spot in the region R9, E(x) and E(y) are determined by equations 1B and 2B, respectively. Thus, the luminance at any spot in the region R9is always 1 according to equations 1B and 2B. The luminance in the region R8is controlled by the mini-LEDs D and E. For the mini-LED E, equations 1C and 2B express the luminance at any spot in the region R8. For the mini-LED D, equation 2B and an adjusted equation 1D may be used to express the luminance at any spot in the region R8. The addition of luminance of the mini-LEDs D and E at any spot is always 1 in the region R8. Similarly, the luminance in the region R6is controlled by the mini-LEDs B and E, and the addition of luminance of the mini-LEDs B and E at any spot is always 1 in the region R6.

The luminance in the region R5is controlled by the mini-LEDs A-B and D-E. For the mini-LED E, let the luminance at any spot in the region R5follow equation 4, which is based on equations 1C and 2D.

E⁢1⁢(x,y)=(1-X⁢2-e-xa-2⁢e)*(1-y-Y⁢2-fb-2⁢f)(4)

Similarly, for the mini-LEDs A, B, and D, we have the following equations to express the luminance created at any spot in the region R5, respectively.

E⁢2⁢(x,y)=(1-x-X⁢1-ea-2⁢e)*(1-Y⁢3-f-yb-2⁢f)(5)E⁢3⁢(x,y)=(1-X⁢2-e-xa-2⁢e)*(1-Y⁢3-f-yb-2⁢f)(6)E⁢4⁢(x,y)=(1-x-X⁢1-ea-2⁢e)*(1-y-Y⁢2-fb-2⁢f)(7)

When E1(x, y), E2(x, y), E3(x, y), and E4(x, y) are added up, the total value of luminance is 1. Thus, the luminance at any spot in the region R5is 1 when the mini-LEDs A-B and D-E are turned on.

In similar manners, the luminance at any spot in the regions R1-R4and R7may be determined. The luminance at any spot in the regions R1-R4and R7is 1 when the mini-LEDs A-B and D-E are turned on. Thus, the luminance at any spot in the regions R1-R9is 1 in such a case.

The method illustrated above may be used to express the expected luminance in the regions R1-R9and other regions on the lower interface322for a mini-LED. For example, based on equations 1A-1D, 2A-2D, and 4, the expected luminance on the lower interface322generated by the mini-LED E may be calculated, when x is from X1 to X3 and y is from Y1 to Y3. Let the luminance on the lower interface322be zero for the mini-LED E when x or y is outside above range.

In some embodiments, the array of mini-LEDs311, as shown inFIG.3A, may be considered as an array of a predetermined grid pattern that contains rectangle-shaped lighting units. Each lighting unit includes four light sources disposed at the lighting unit's four corners. The light source contains a mini-LED311. Optionally, the light source may contain a mini-LED311and a lens312. There are multiple lighting units as shown inFIG.3A. For example, one lighting unit may include the mini-LEDs A, B, D, and E at the four corners, and another lighting unit may include the mini-LEDs B, C, E, and F at the four corners. The lighting unit has a length a along the X direction, and width b along the Y direction.

The lighting unit irradiates a corresponding rectangular area with the same grid pattern (e.g., the same length a and width b) on the lower interface322. As shown inFIG.3D, for example, a corresponding rectangular area contains spots1,2,4, and5at its four corners. When e equals zero in some cases, spots M′ and M merge with spots4and5, respectively. That is, spots M′ and M become located at the corners, respectively. A line connecting two spots at the corners of a corresponding rectangular area along the X or Y direction may be referred to as a border line. Luminance in a corresponding rectangular area may be arranged using equations depicted above with some adjustment. When a lighting unit (i.e., four mini-LEDs) is powered on, it irradiates the corresponding rectangular area with luminance uniformity above a certain value. For example, luminance of a corresponding rectangular area including the four border lines may have the same luminance value or substantially similar luminance values. Additionally, when one mini-LED is turned on, it irradiates the corresponding rectangular area in the same manner as described above. For example, when the mini-LED E is on, it irradiates a border line connecting spots2and5with luminance that is illustrated inFIG.3F. The luminance may remain at a minimum value, change linearly from the minimum value to a maximum value, and remain at the maximum value at different segments of the border line.

FIG.3His a schematic diagram showing a light path for the mini-LED E corresponding to the configuration shown inFIG.3B. Provided that the min-LED E emits light rays that propagate along the light path and impinge on a spot Q on the lower interface322. The distance between the mini-LED E and the lower interface322is h. In some cases, for example, the value of h may be in a range of 3 to 6 millimeters. θ is the angle between the light path and the interface normal (i.e., against the Z direction). The distance between the mini-LED E and spot Q is s. Let E be the luminance and I the intensity of light (or light intensity) at spot Q. The luminance and light intensity follow equation 8.

E=(I/s2)*cos⁢θ(8)

Since values of luminance E on the lower interface322are known as illustrated above, the light intensity at various spots on the interface322may be calculated using equation 8.

FIGS.3I and3Jare schematic diagrams showing the intensity of light emitted from the mini-LED E with regard toFIGS.3A-3D. Arbitrary units are used in these figures. Based on equation 8, the light intensity may be calculated for points from X2 to X3 along line L1. For each point on line L1, angle θ may also be calculated. The curve of intensity versus angle along line L1is shown inFIG.3Ischematically. The curve of intensity versus angle from Y2 to Y3 along line L2is shown inFIG.3Jschematically.

After values of light intensity are obtained via calculation, data of a target lens may be obtained by using, for example, certain software including certain lens design software. Data of a lens includes, for example, the shape and dimensions of the incident and exit surfaces, the distance between the incident and exit surfaces, the lens material, the refractive index of the lens material, etc.

FIG.4shows a diagram of light passing through an exemplary concave lens410. The lens410has two surfaces412and413on opposite sides. The surface412faces a light source414and may be referred to as the light incident surface. The surface413faces away from the light source414and may be referred to as the light exit surface. Light rays impinge on the incident surface412and change the direction of propagation after passing through the incident surface412due to refraction. The light rays change the direction of propagation again after passing through the exit surface when exiting the lens411due to refraction.

Designing a lens involves determining the incident surface and the exit surface of the lens. In some cases, the incident surface may be determined first at the beginning of a lens design process to reduce the calculation load. The predetermined incident surface may include, for example, a flat surface or a curved surface (e.g., a convex surface, a concave surface, an aspheric surface, or a freeform surface). The term “free form surface”, as used herein, indicates a surface that has no rotational symmetry or translation around the optical axis. As both the incident and exit surfaces are used to change the propagation direction of light rays, it may be arranged that one of them makes a bigger change of propagation direction than the other one. For example, in some cases, about 50-70% of the change of propagation direction may be made by the exit surface.

FIG.5is a diagram illustrating light rays irradiating a surface after passing through a lens, and used to describe a lens design process schematically. Assuming that a light source511is disposed at a location under a lens. The lens has an incident surface512and exit surface513. The light source511generates light rays that pass through the lens and then illuminate a flat surface514(e.g., the bottom surface of a diffuser). Assuming that the surface514receives all light emitted from the light source511. Based on energy conservation, equation 9 is obtained.

∫∫I⁡(u,v)⁢dudv=∫∫E⁡(x,y)⁢dxdy(9)

I(u,v) represents the light intensity emitted by the light source511in an angular coordinate system (u,v). E(x,y) represents the luminance received on the surface514in a Cartesian coordinate system (or orthogonal coordinate system) (x,y). From equation 9, equations 10 and 11 are obtained.

∫∫I0⁢cos⁢u*cos2⁢v⁢dudv=∫∫E⁡(x,y)⁢dxdy(10)I0⁢cos⁢u*cos2⁢v⁢dudv=E⁡(x,y)⁢dxdy(11)

I0is a fixed value determined by prearranged conditions. Equation 11 illustrates energy conservation in a differential form, i.e., the luminance received in a small area at (x,y) on the surface514corresponds to the light intensity of a small portion of light rays at (u,v).

When light passes through the incident surface512and exit surface513sequentially, it is refracted twice. The refracted angle follows Snell's law of refraction. As such, the optical path of each light ray, from the light source511to the surface514via the lens, may be calculated using Snell's law.

When the radiation pattern (e.g., light intensity at different angles) of the light source511and desired values of luminance on the surface514are known, the shape of the incident and exit surfaces512and513and other data of the lens may be obtained by calculation. As illustrated above, the desired values of luminance on the surface514may be obtained using equations 1A-1D, 2A-2D, and 4 with some adjustment. The desired values of luminance may also be referred to as the expected values of luminance. In some cases, the incident surface512may be predetermined and thus has a known surface with fixed data. The exit surface513is a free form surface and may have certain predetermined initial data. For example, the exit surface513may have an initial shape that will be adjusted or modified multiple times during the lens design process.

As radiation patterns of the light source511and data of the incident surface512are known, after light rays pass through the incident surface512, a calculation process may be performed to determine optical paths or trajectories of the light rays inside the lens as a result of diffraction. The light rays may be divided into small portions and the trajectory of each small portion inside the lens is calculated. The exit surface513may be divided into small regions. Each small portion of the light rays may impinge onto one or more small regions of the exit surface513. The surface514may be divided into small areas. As the trajectory of each small portion of the light rays may be calculated after the light rays exit the lens, and each trajectory leads to one or more of the small areas of the surface514, the location of a corresponding small area or small areas of the surface514may be obtained. Subsequently, luminance in the corresponding small area or small areas may be calculated using equation 11 when the light rays impinge onto the surface514.

The calculated values of luminance on the surface514are compared with the expected values of luminance, and the difference between them is used to adjust the data of the exit surface513. For example, if the luminance value is too big in a small area of the surface514, one or more corresponding small regions of the exit surface513may be identified. Thereafter, the one or more corresponding small regions of the exit surface513may be adjusted to steer some part of the one or more corresponding small portions of light rays away from the one or more corresponding small areas of the surface514. The method may be performed to adjust every small regions of the exit surface513, and above steps may repeat multiple times until the difference between the calculated values of luminance and expected values of luminance on the surface514is below a certain level. Then, the finalized small regions of the exit surface513are stitched together to form the exit surface513.

FIGS.6and7schematically show configurations600and700of the light sources, according to embodiments of the present disclosure. As described above, light sources (e.g., mini-LEDs) may be arranged on a substrate based on the lighting units. The lighting units may have a rectangular or square shape. In descriptions below, a rectangular shape is used exemplarily. Referring to the configuration600ofFIG.6, in some embodiments, the lighting unit, depicted in dashed lines, may include four light sources disposed at the lighting unit's four corners. The lighting unit may have a length c along the X direction, and width d along the Y direction. Optionally, a rectangular area (not shown) may be arranged on an interface and aligned with the lighting unit along a direction perpendicular to the substrate of the light sources. The rectangular area may have the same dimensions as that of the lighting unit (e.g., the same length c and width d) on the interface, and the lighting unit is configured to irradiate a corresponding rectangular area with even luminance. In this case, the total area of the rectangular areas equals the total area of the lighting units of the configuration600.

Referring to the configuration700ofFIG.7, in some other embodiments, the lighting unit of configuration600, depicted in dashed lines, may each have a light source disposed at the center. As such, the configuration700has four lighting units as compared to nine in configuration600, therefore significantly reducing the number light sources needed to illuminate a panel (in exchange for sacrificing a small area along the edge of the panel). It should be noted that the configurations of600and700are for illustration purposes only. In actual devices, the number of lighting units and the number of light sources (e.g., LEDs) are significantly higher.

FIG.8shows a flow chart800for designing a lens for a backlight module, according to embodiments of the present disclosure. At step811, data of a light source array is obtained. The data of the array may include pitches of the array along the X and Y directions that determine the distance between adjacent light sources along the X and Y directions. The light sources are disposed at the grid points of the array.

At step812, a distance between a substrate and an illumination interface is obtained. The distance and data of the light source array are initial conditions for designing the lens. The light sources are disposed on a substrate, and the illumination interface may be a bottom surface of a diffuser that is away from the substrate with a predetermined distance. In some cases when the diffuser is inside or integrated with a display panel, the illumination interface may be disposed inside the display panel. That is, the illumination interface may be configured between the substrate and a layer (or member) of the display panel.

At step813, values of luminance on the illumination interface, as part of the initial conditions, are obtained by calculation and used as the expected values of luminance. The distance between adjacent light sources along the X and Y directions, and the distance between the substrate and illumination interface are used in the calculation. In some cases, equations such as equations 1A-1D, 2A-2D, and 4 may be used to acquire the expected values of luminance.

At step814, values of luminance on the illumination interface are calculated based on the above-described method. For example, equation 11, Snell's law, predetermined data of the lens including data of the incident surface, and temporary data of the exit surface of the lens may be used in the calculation.

At step815, the calculated values of luminance on the illumination interface are compared with the expected values of luminance. The exit surface may be divided into small regions. Based on the comparison results, each small region of the exit surface is adjusted individually. Thereafter, steps814and815may be repeated to calculate values of luminance on the illumination interface based on the adjusted data of the exit surface, and compare the calculated values of luminance with the expected values of luminance. When the difference between the calculated values of luminance with the expected values of luminance is below a certain level, data of the exit surface or data of the lens is finalized at step816.

Data of the lens may include data of the incident and exit surfaces, lens dimensions, refractive index of the lens material, and other characteristics. Without the lens, the light source emits light according to its original radiation pattern. For example, a mini-LED may emit light in a nearly Lambertian pattern. When the lens is coupled to the light source, the lens directs the light from the light source to irradiate the illumination interface. Light intensity is changed from an original radiation pattern to a modified pattern. Besides methods illustrated above, certain lens design software, which has been available in the field for some time, may be used to design the lens with the initial conditions. In some cases, the original radiation pattern of a light source may be measured and analyzed first. In some cases, as illustrated above, the incident surface of a lens may be predetermined as an initial condition to simplify the calculation process. Alternatively, both the incident and exit surfaces of a lens may be calculated, adjusted, and finalized at the same time.

Steps811-816describe methods to design a lens that may be used to improve luminance uniformity for a display device. The display device may contain a mini-LED array, a lens array, and a display panel. The mini-LED array and lens array are incorporated to illuminate the display panel with uniform luminance. Further, the mini-LED array and lens array may be scaled with the same grid pattern. For example, more mini-LEDs311and lenses312may be added to the arrays shown inFIGS.3A-3Cto expand the arrays. As such, the mini-LED array and lens array may be used for display devices of small sizes and large sizes conveniently. In addition, the mini-LED array and lens array may also be used for other devices or in other applications that need uniform luminance.

After the lens design process, data of the lens is recorded and transferred to a manufacturing facility. A number of the lenses may be made for constructing a lens array. Optionally, the lenses may be fabricated in the form of lens array. That is, a lens array arranged for a backlight module or display device may be prefabricated by, for example, a molding method before an assembly process.

FIG.9shows a flow chart900for fabricating a backlight module and a display device, according to embodiments of the present disclosure. A substrate is provided at step911for assembling a backlight module. The substrate may be a semiconductor substrate including a semiconductor material, or an insulating substrate including an electrically non-conductive material such as glass, a plastic material, or a ceramic material. Optionally, the substrate may also be a printed circuit board (PCB).

At step912, light sources (e.g., mini-LEDs) are mounted on the substrate to form a light source array with a predetermined pattern (e.g., with predetermined pitch values along the X and Y directions). In some embodiments, the light sources are bonded on the substrate with an adhesive material after an alignment step is performed.

At step913, lenses designed for the backlight module are provided. Each lens is disposed over and aligned with a light source on the substrate, and then fixed by, for example, a bonding method using an adhesive material and optionally, a lens fixture. In some embodiments, a lens array is prefabricated. The lens array may be placed over and aligned with the light source array in a direction approximately perpendicular to the substrate, and then get bonded using an adhesive material and optionally, a lens array fixture. In some embodiments, a housing unit may be provided for the backlight module. The housing unit may accommodate the substrate, light source array, and lens array. Optionally, the substrate may be disposed in the housing unit before the light sources are mounted.

At step914, a diffuser and a wavelength conversion unit are disposed over the lens array or the backlight module sequentially. The diffuser may be placed at a predetermined distance from the light source array or the substrate, aligned to the lens array or the light source array in a direction approximately perpendicular to the substrate, and then bonded using an adhesive material. In some cases, the diffuser may be bonded with the housing unit. Further, the wavelength conversion unit may be placed above the diffuser, aligned to the lens array or the light source array in a direction approximately perpendicular to the substrate, and then bonded using an adhesive material. In some cases, the wavelength conversion unit may be bonded with the housing unit.

At step915, a display panel is disposed over the wavelength conversion unit, aligned with the wavelength conversion unit in a direction approximately perpendicular to the substrate, and bonded with it. Optionally, the display panel may also be aligned with the substrate during the assembly process. For example, certain marks may be made on the substrate for alignment purpose. In some cases, the display panel may be bonded with the housing unit. In some embodiments, the housing unit may be designed to accommodate and protect all components of the display device including the backlight module and display panel.

Steps911-913describe methods and processes to fabricate a backlight module. In some cases, backlight modules may be made separately at a facility, and then sent to another facility for assembly of display devices. Alternatively, a display device may be fabricated through consecutive steps starting from mounting light sources on a substrate (e.g., steps911-912). The steps further include disposing a lens array over the light source array, a diffuser over the lens array, a wavelength conversion unit over the diffuser, and a display panel over the wavelength conversion unit.

Optionally, a display panel may contain a diffuser and a wavelength conversion unit. In such cases, the steps of disposing a diffuser and a wavelength conversion unit over a backlight module as described above may be omitted. The backlight module and display panel may be aligned and bonded to form a display device directly.

In some other embodiments, a display device may not contain a diffuser. Consequently, above-described methods may omit the step of mounting a diffuser (e.g., aligning and bonding a diffuser). A wavelength conversion unit may be configured over a lens array directly. That is, a wavelength conversion unit may be positioned over and aligned with a lens array directly in an assembly process of display devices.

FIG.10is an exemplary structural diagram1000of a display device. The display device may include a display panel1011, a wavelength conversion unit (not shown), a backlight module1012, and a controller1013. The display panel1011may be a LCD panel. The backlight module1012may include a mini-LED array and provide uniform luminance for the wavelength conversion unit via a lens array. The controller1013may include a first control circuit that sends control signals to a gate driving circuit (not shown) and a data driving circuit (not shown). The gate driving circuit and data driving circuit are arranged to drive the display panel1011during operation of the display device. For example, the gate driving circuit may output scan signals, and the data driving circuit may output data voltage. The controller1013may further include a second control circuit that controls the backlight module1012. The controller1013may be mounted on a PCB that is attached to a housing unit of the display device. The display device may also contain a power supply circuit (not shown) that supplies and controls various voltages or currents to the display panel1011, the first and second control circuits, the gate driving circuit, the data driving circuit, and the backlight module (i.e., the mini-LEDs).

Although specific embodiments of the invention have been disclosed, those having ordinary skill in the art will understand that changes can be made to the specific embodiments without departing from the spirit and scope of the invention. The scope of the invention is not to be restricted, therefore, to the specific embodiments. Furthermore, it is intended that the appended claims cover any and all such applications, modifications, and embodiments within the scope of the present invention.