Backlight module and viewing angle adjustment method therefor, and display device comprising backlight module

Abstract

A backlight module, comprising an upper backlight unit and a lower backlight unit disposed below the upper backlight unit. The upper backlight unit comprises an upper light source, an upper light guide plate receiving light emitted by the upper light source, and a first prism sheet located on a light exit side of the upper light guide plate. The first prism sheet comprises a plurality of first prism columns arranged in a first direction, each first prism column extends in a second direction and has a tip facing the upper light guide plate, and the upper light source is provided with a plurality of light emitting members arranged in the second direction. When both the upper backlight unit and the lower backlight unit are turned on, the backlight module is in a wide viewing angle mode, and when the upper backlight unit is turned on and the lower backlight unit is turned off, the backlight module is in a narrow viewing angle mode, so that the backlight module has a function of switching between the wide viewing angle mode and the narrow viewing angle mode. The present invention further provides a display device comprising the backlight module.

Description

Backlight module, viewing angle adjustment method thereof, and display device including the backlight module

[0001] This application claims priority to Chinese patent application No. 202311286718.7 filed on October 7, 2023, entitled “Backlight module, viewing angle adjustment method thereof, and display device comprising the backlight module”, the entire contents of which are hereby incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of optical equipment, and in particular to a backlight module and a method for adjusting a viewing angle thereof, and a display device comprising the backlight module. Background Art

[0003] With technological advancements, electronic devices equipped with LCDs have become indispensable in modern life. However, users have varying viewing angle requirements for display devices in different situations. For example, if a user wants to share on-screen information with others, they require a display with a wide viewing angle, allowing multiple people to see the content from different angles. This is known as a sharing mode. However, if a user is handling personal matters and wants to protect their privacy, they prefer a display with a narrow viewing angle, meaning a privacy mode.

[0004] As the number of in-car displays increases, it's becoming increasingly important for displays beyond the instrument panel to switch viewing angles to prevent driver distraction and potentially compromise driving safety. Traditional display devices typically require privacy protection by simply adding a privacy filter to the outermost layer, which often results in a significant reduction in brightness. Controlling viewing angles through the display panel requires an active, dedicated display panel for different viewing modes, which can be expensive to manufacture.

[0005] Summary of the Invention

[0006] Therefore, an object of the present invention is to provide a backlight module and a display device that can be applied to different usage environments and can actively switch viewing angles without increasing manufacturing costs or reducing brightness.

[0007] The backlight module of the present invention comprises an upper backlight unit and a lower backlight unit disposed below the upper backlight unit. The upper backlight unit includes an upper light source, an upper light guide plate for receiving light emitted by the upper light source, and a first prism sheet located on the light-emitting side of the upper light guide plate. The first prism sheet includes a plurality of first prism columns arranged along a first direction, each first prism column extending along a second direction with its tip facing the upper light guide plate. The upper light source includes a plurality of light-emitting elements arranged along the second direction.

[0008] Another technical means of the present invention is that the upper light guide plate has a light incident surface facing the upper light source, a bottom surface connected to the light incident surface and facing the lower backlight unit, and multiple dimming structures arranged on the bottom surface, each dimming structure has a light-facing surface facing the light incident surface and a non-light-facing surface connected to the light-facing surface and away from the light incident surface, a first angle is formed between the light-facing surface and the bottom surface, and a second angle is formed between the non-light-facing surface and the bottom surface, and the first angle is greater than the second angle.

[0009] Another technical means of the present invention is that the area ratio of the dimming structure relative to the bottom surface of the upper light guide plate at a position adjacent to the upper light source is smaller than the area ratio of the dimming structure relative to the bottom surface of the upper light guide plate at a position far from the upper light source.

[0010] Another technical means of the present invention is that the size of the dimming structure at a position adjacent to the upper light source is smaller than the size of the dimming structure at a position away from the upper light source.

[0011] Another technical solution of the present invention is that the spacing between adjacent dimming structures at positions close to the upper light source is greater than the spacing between adjacent dimming structures at positions far from the upper light source.

[0012] Another technical means of the present invention is that the upper light guide plate also has a light emitting surface connected to the light incident surface and opposite to the bottom surface, and a plurality of strip-shaped microstructures arranged on the light emitting surface, each strip-shaped microstructure faces the first prism sheet, and each strip-shaped microstructure extends along the first direction.

[0013] Another technical means of the present invention is that the lower backlight unit includes two diffusion sheets, and the upper one of the two diffusion sheets directly faces the upper light guide plate of the upper backlight unit without any other components blocking the two.

[0014] Another technical means of the present invention is that the lower backlight unit includes a lower light source, a lower light guide plate for receiving the light emitted by the lower light source, and at least one optical film located on the light output side of the lower light guide plate. The lower light guide plate has a light input side, which is connected to the light output side, and the light input side receives the light emitted by the lower light source.

[0015] Another technical means of the present invention is that the lower backlight unit includes a lower light source, a diffusion plate for receiving light from the lower light source, and at least one optical film located on the light-emitting side of the diffusion plate. The diffusion plate has a light-incident side, which is opposite to the light-emitting side, and the light-incident side receives light emitted by the lower light source.

[0016] Another technical means of the present invention is that the number of optical films in the lower backlight unit is multiple, and they include two diffusers and two second prism sheets located between the two diffusers. Each second prism sheet includes a plurality of second prism columns. The tips of the second prism columns of each second prism sheet are all directed toward the upper backlight unit, and the second prism columns of the two second prism sheets extend in different directions.

[0017] Another object of the present invention is to provide a viewing angle adjustment method for adjusting the viewing angle of the aforementioned backlight module. The viewing angle adjustment method includes a narrow viewing angle mode and a wide viewing angle mode. When the upper backlight unit is turned on and the lower backlight unit is turned off, the backlight module is in the narrow viewing angle mode. When both the upper backlight unit and the lower backlight unit are turned on, the backlight module is in the wide viewing angle mode.

[0018] Another object of the present invention is to provide a display device comprising the backlight module as described above and a display panel disposed on the backlight module.

[0019] The effect of the present invention is that when the upper backlight unit is turned on and the lower backlight unit is turned off, the backlight module is in a narrow viewing angle mode. The design of the tip of the first prism column of the first prism sheet of the upper backlight unit is directed toward the upper light guide plate, and the arrangement direction of the multiple light-emitting elements of the upper backlight unit is the same as the extension direction of each first prism column. Therefore, a positive viewing angle can be generated, the side light output energy is reduced, and the narrow viewing angle effect is achieved. When both the upper backlight unit and the lower backlight unit are turned on, the backlight module is in a wide viewing angle mode, so that the energy required for the side viewing angle is supplemented by the lower backlight unit. In this way, the backlight module has the active switching function between the wide viewing angle mode and the narrow viewing angle mode, and there is no need to specially manufacture a display panel with a switching function or an external anti-peeping film, which can reduce manufacturing costs and maintain brightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is an exploded perspective view of a preferred embodiment of a backlight module of the present invention, wherein the lower backlight unit is an edge-type backlight structure;

[0021] FIG2 is a side view for assisting in explaining FIG1;

[0022] FIG3 is a partial enlarged schematic diagram of the frame shown in FIG2;

[0023] FIG4 is a graph showing light distribution in a narrow viewing angle mode;

[0024] FIG5 is a graph showing light distribution in a wide viewing angle mode;

[0025] FIG6 is a graph showing the light distribution when the lower backlight unit is turned on alone;

[0026] FIG7 is a side view of another embodiment of the preferred embodiment, wherein the lower backlight unit is a direct-type backlight structure;

[0027] FIG. 8 is a side view of a preferred embodiment of a display device of the present invention. DETAILED DESCRIPTION

[0028] The features and technical content of the related patent applications of this invention will be clearly presented in the detailed description of the preferred embodiments below with reference to the accompanying drawings. Before proceeding with the detailed description, it should be noted that similar elements are represented by the same reference numerals. The directional terms mentioned in the following embodiments, such as "up," "down," "left," "right," "front," "back," "bottom," and "top," are only used with reference to the directions in the accompanying drawings. Therefore, the directional terms used are for illustrative purposes only and are not intended to limit the present invention.

[0029] Referring to Figure 1 , a preferred embodiment of a backlight module according to the present invention is shown, comprising an upper backlight unit 2 and a lower backlight unit 3 disposed below the upper backlight unit 2. The upper backlight unit 2 includes an upper light source 21, an upper light guide plate 22 for receiving light emitted by the upper light source 21, and a first prism sheet 23 located on the light-emitting side of the upper light guide plate 22. The first prism sheet 23 includes a plurality of first prism columns 231 arranged along a first direction E1. The first prism columns 231 extend along a second direction E2 with their tips facing the upper light guide plate 22. The upper light source 21 includes a plurality of light-emitting elements 211 arranged along the second direction E2.

[0030] Through the above design, when the upper backlight unit 2 is turned on and the lower backlight unit 3 is turned off, the backlight module is in narrow viewing angle mode. By utilizing the design in which the tip of the first prism column 231 of the first prism sheet 23 of the upper backlight unit 2 is directed toward the upper light guide plate 22, and the design in which the arrangement direction of the multiple light-emitting elements 211 of the upper backlight unit 2 is the same as the extension direction of each first prism column 231, a positive viewing angle can be generated, reducing the side light output energy, thereby achieving the effect of a narrow viewing angle. When both the upper backlight unit 2 and the lower backlight unit 3 are turned on, the backlight module is in wide viewing angle mode, so that the energy required for the side viewing angle is supplemented by the lower backlight unit 3. In this way, the backlight module has the ability to actively switch between wide viewing angle mode and narrow viewing angle mode, eliminating the need for a specially manufactured display panel with switching function or an external privacy film, which can reduce manufacturing costs and maintain brightness.

[0031] 2 , the upper light guide plate 22 includes a light incident surface 221 facing the upper light source 21, a bottom surface 222 connected to the light incident surface 221 and facing the lower backlight unit 3, a light emitting surface 223 connected to the light incident surface 221 and opposite the bottom surface 222, a plurality of dimming structures 224 disposed on the bottom surface 222, and a plurality of strip-shaped microstructures 225 disposed on the light emitting surface 223. The strip-shaped microstructures 225 face the first prism sheet 23, and each strip-shaped microstructure 225 extends along a first direction E1, that is, perpendicular to the extension direction of the first prism column 231, thereby further improving the uniformity of the light emitting side of the upper light guide plate 22.

[0032] In more detail, the first prism sheet 23 of the upper backlight unit 2 is an inverse prism sheet. The extension direction of each first prism column 231 of the first prism sheet 23 is the same as the arrangement direction of the multiple light-emitting elements 211 of the upper light source 21, and they are all arranged along the second direction E2. As a result, the light output angle can present forward collimated light, which has anti-peeping properties.

[0033] Referring to FIG. 3 , this type of inverse prism sheet requires a very specific range of incident light angles to convert light into a light output form with a normal viewing angle. Therefore, in this embodiment, each dimming structure 224 is designed to have a light-facing surface 226 facing the light-incident surface 221 and a non-light-facing surface 227 connected to the light-facing surface 226 and facing away from the light-incident surface 221. A first angle θ1 is formed between the light-facing surface 226 and the bottom surface 222, while a second angle θ2 is formed between the non-light-facing surface 227 and the bottom surface 222. The first angle θ1 is greater than the second angle θ2. Therefore, the slope of the light-facing surface 226 facing the light-incident surface 221 is gentler, resulting in a larger area than the steeper slope of the non-light-facing surface 227 facing away from the light-incident surface 221. This maximizes the guidance of light toward the first prism sheet 14, further improving light utilization efficiency and uniformity.

[0034] Referring to FIG. 2 , for more details, the area ratio of the dimming structure 224 relative to the bottom surface 222 of the upper light guide plate 22 at a position adjacent to the upper light source 21 is smaller than the area ratio of the dimming structure 224 relative to the bottom surface 222 of the upper light guide plate 22 at a position further away from the upper light source 21. In one embodiment, the size of the dimming structure 224 at a position adjacent to the upper light source 21 is smaller than the size of the dimming structure 224 at a position further away from the upper light source 21. In another embodiment, the spacing between adjacent dimming structures 224 at a position adjacent to the upper light source 21 is greater than the spacing between adjacent dimming structures 224 at a position further away from the upper light source 21. In other words, the size of the dimming structure 224 increases as the distance from the upper light source 21 increases, while the spacing between adjacent dimming structures 224 decreases as the distance from the upper light source 21 increases. With the above design, the dimming structure 224 adopts a looser layout in the area close to the upper light source 21, and a tighter layout in the area far from the upper light source 21, so that the light source energy can be effectively utilized to ensure high uniformity and energy saving.

[0035] As for the lower backlight unit 3, there is no restriction on its style and light source placement. In the disclosure of this embodiment, the lower backlight unit 3 includes a lower light source 31a, a lower light guide plate 32 that receives the light emitted by the lower light source 31a, and at least one optical film 33 located on the light-emitting side 321 of the lower light guide plate 32. The lower light guide plate 32 has a light-incident side 322 connected to the light-emitting side 321. The light-incident side 322 receives the light emitted by the lower light source 31a. In this embodiment, the number of optical films 33 of the lower backlight unit 3 is multiple, and includes two diffusers 331a, 331b and two second prism sheets 34 located between the two diffusers 331a, 331b. Each second prism sheet 34 includes a plurality of second prism columns 341. The tips of the second prism columns 341 of the second prism sheet 34 are all facing the upper backlight unit 2, and the second prism columns 341 of the two second prism sheets 34 extend in different directions respectively. The diffuser 331a located above directly faces the upper light guide plate 22 of the upper backlight unit 2, with no other components blocking the way. Therefore, light emitted by the lower backlight unit 3 can directly enter the upper backlight unit 2 without being blocked by other components and reducing light transmittance, nor will a large proportion of light be reflected back to the lower backlight unit 3, which helps improve the brightness of light output in wide-viewing angle mode.

[0036] The viewing angle adjustment method of the backlight module of the present invention is used to adjust the viewing angle of the backlight module as shown in Figure 1. The viewing angle adjustment method includes a narrow viewing angle mode and a wide viewing angle mode. When the upper backlight unit 2 is turned on and the lower backlight unit 3 is turned off, the backlight module is in the narrow viewing angle mode. When both the upper backlight unit 2 and the lower backlight unit 3 are turned on, the backlight module is in the wide viewing angle mode.

[0037] Referring to Figures 2 and 3 , when the upper backlight unit 2 is turned on, light from the upper light source 21 enters the upper light guide plate 22 via the light-incident surface 221. A portion of this light passes through the stripe-shaped microstructures 225 before entering the first prism sheet 23. The dimming structure 224, located on the bottom surface 222 of the upper light guide plate 22, reflects the light traveling from the bottom surface 222 back into the upper light guide plate 22 via the angled design of its light-facing surface 226, thereby increasing the amount of light entering the stripe-shaped microstructures 225 from the upper light guide plate 22. After passing through the stripe-shaped microstructures 225, the light then exits through the first prism sheet 23. Because the first prism sheet 23 is in the form of an inverted prism, its light collection angle is relatively limited. The asymmetric design of the dimming structure 224 increases the proportion and reflection efficiency of the light-facing surface 226. Furthermore, the strip-shaped microstructure 225 is provided on the light-emitting surface 223 of the upper light guide plate 22 to spread the light and improve its uniformity. This improves the light utilization efficiency of the first prism sheet 23, thereby improving the light extraction efficiency of the upper light guide plate 22 at a specific angle. Therefore, when the upper backlight unit 2 is turned on and the lower backlight unit 3 is turned off, the above configuration allows light to be emitted at a nearly 90-degree angle. As shown in FIG4 , at a viewing angle of 0 degrees, sufficient intensity of collimated forward light is provided. At viewing angles of ±45 degrees, the light intensity is less than 5% (0.05) of that at a viewing angle of 0 degrees, indicating a narrow viewing angle mode. In narrow viewing angle mode, the screen display is prevented from being seen by people on either side, providing an anti-peeping effect. Therefore, when used in vehicle-mounted devices other than dashboards (e.g., screens located in front of the passenger seat), switching to narrow viewing angle mode can also prevent the driver from being distracted by viewing the screen, thereby improving driving safety.

[0038] Referring again to Figure 2, when both the upper backlight unit 2 and the lower backlight unit 3 are turned on, light from the lower light source 31a enters the lower light guide plate 32 via the light entrance side 322. After exiting the light exit side 321, it passes sequentially through the lower diffuser 331b, two second prism sheets 34, and the upper diffuser 331a before entering the upper backlight unit 2. The second prism columns 341 of the two second prism sheets 34 extend in different directions, allowing the light from the lower light source 31a to spread in different directions, improving uniform brightness. It is also important to note that the upper diffuser 331a directly faces the upper light guide plate 22 of the upper backlight unit 2, with no other components blocking the way. Therefore, light from the lower backlight unit 3 can directly enter the upper backlight unit 2 without being reflected back to the lower backlight unit 3, helping to improve overall brightness. When both the upper backlight unit 2 and the lower backlight unit 3 are turned on, as shown in Figure 5 , in addition to providing sufficient intensity of collimated forward light at a viewing angle of 0 degrees, the light intensity at viewing angles of ±45 degrees is also 45% (0.45) higher than the light intensity at a viewing angle of 0 degrees, indicating a wide viewing angle mode. Referring to Figure 6 , in contrast, when only the lower backlight unit 3 is turned on, the light is split into two beams with wide viewing angles, resulting in significantly insufficient light intensity at a viewing angle of 0 degrees.

[0039] As shown in FIG2 , in this embodiment, the lower backlight unit 3 is an edge-lit backlight structure. As shown in FIG7 , in certain embodiments, the lower backlight unit 3 may also be a direct-lit backlight structure, and includes a lower light source 31b, a diffuser plate 35 for receiving light from the lower light source 31b, and at least one optical film 33 located on a light-emitting side 352 of the diffuser plate 35. The diffuser plate 35 further has a light-entry side 351 opposite the light-emitting side 352, which receives light emitted by the lower light source 31b.

[0040] As shown in FIG8 , a display panel 4 is provided on the backlight module to form the display device of the present invention. It should be noted that the display panel 8 can also be provided on the backlight module shown in FIG7 .

[0041] In summary, in the backlight module and the viewing angle adjustment method thereof of the present invention, a wide viewing angle mode can be provided by simultaneously turning on the upper backlight unit 2 and the lower backlight unit 3, and a narrow viewing angle mode is provided by turning on the upper backlight unit 2 and turning off the lower backlight unit 3. Therefore, the backlight module and the display device of the present invention have the function of switching between a wide viewing angle mode and a narrow viewing angle mode. At the same time, the structural design of the upper light guide plate 22 can improve the light utilization rate of the first prism sheet 23, and there are no other components blocking the upper light guide plate 22 of the upper backlight unit 2 and the diffuser 331 located above the lower backlight unit 3, which helps to improve the overall brightness in the wide viewing angle mode. Therefore, the backlight module of the present invention can actively switch between a narrow viewing angle mode and a wide viewing angle mode, and does not require a specially made display panel with a switching function or an external anti-peeping film, which can reduce manufacturing costs and maintain brightness, and can indeed achieve the purpose of the present invention.

[0042] In addition, with the increasing use of in-car displays, there is also a need for anti-peeping. To avoid affecting the driver's driving vision and improve driving safety, the present invention switches the light source to meet the needs of narrow viewing angle mode (anti-peeping mode) and wide viewing angle mode (sharing mode), achieving multi-tasking in different scenarios. It is particularly suitable for in-car displays. In sharing mode, the driver and passengers can view the screen content simultaneously. In anti-peeping mode, the driver is prevented from seeing the content on the display screen, thereby avoiding driver distraction and protecting the privacy of passengers.

[0043] The above description is only a preferred embodiment of the present invention and should not be used to limit the scope of implementation of the present invention. That is, any simple equivalent changes and modifications made according to the scope of the claims and the content of the specification of the present invention are still within the scope of the patent of the present invention.

[0044] [List of reference numerals] 2 Upper backlight unit 21 Upper light source 211 Light-emitting element 22 Upper light guide plate 221 Light incident surface 222 Bottom surface 223 Light emitting surface 224 Dimming structure 225 Strip microstructure 226 Light-facing surface 227 Non-light-facing surface 23 First prism sheet 231 First prism column 3 Lower backlight unit 31a Lower light source 31b Lower light source 32 Lower light guide plate 321 Light-emitting side 322 Light incident side 33 Optical film 331a Diffuser sheet 331b Diffuser sheet 34 Second prism sheet 341 Second prism column 35 Diffuser plate 351 Light incident side 352 Light emitting side 4 Display panel E1 First direction E2 Second direction θ1 First angle θ2 Second angle

Claims

1. A backlight module, comprising: An upper backlight unit includes an upper light source, an upper light guide plate receiving light emitted by the upper light source, and a first prism sheet located on the light emitting side of the upper light guide plate, wherein: The first prism sheet comprises a plurality of first prism columns arranged along a first direction, each of the first prism columns extends along a second direction with a tip thereof facing the upper light guide plate, and the upper light source comprises a plurality of light emitting elements arranged along the second direction; and The lower backlight unit is arranged below the upper backlight unit.

2. The backlight module according to claim 1, wherein: The upper light guide plate has a light incident surface facing the upper light source, a bottom surface connected to the light incident surface and facing the lower backlight unit, and a plurality of dimming structures arranged on the bottom surface, each of the dimming structures has a light facing surface facing the light incident surface and a non-light facing surface connected to the light facing surface and away from the light incident surface, a first angle is formed between the light facing surface and the bottom surface, a second angle is formed between the non-light facing surface and the bottom surface, and the first angle is greater than the second angle.

3. The backlight module according to claim 2, wherein: The area ratio of the dimming structure relative to the bottom surface of the upper light guide plate at a position adjacent to the upper light source is smaller than the area ratio of the dimming structure relative to the bottom surface of the upper light guide plate at a position away from the upper light source.

4. The backlight module according to claim 3, wherein: The size of the dimming structure at a position adjacent to the upper light source is smaller than the size of the dimming structure at a position away from the upper light source.

5. The backlight module according to claim 3, wherein: The spacing between adjacent dimming structures at positions adjacent to the upper light source is greater than the spacing between adjacent dimming structures at positions away from the upper light source.

6. The backlight module according to claim 1, wherein: The upper light guide plate also has a light emitting surface connected to the light incident surface and opposite to the bottom surface, and a plurality of strip-shaped microstructures arranged on the light emitting surface, each of the strip-shaped microstructures faces the first prism sheet, and each of the strip-shaped microstructures extends along the first direction.

7. The backlight module according to claim 1, wherein: The lower backlight unit includes two diffusion sheets, and the upper one of the two diffusion sheets directly faces the upper light guide plate of the upper backlight unit, and there is no other component blocking the two.

8. The backlight module according to claim 1, wherein: The lower backlight unit includes a lower light source, a lower light guide plate for receiving light emitted by the lower light source, and at least one optical film located on the light output side of the lower light guide plate. The lower light guide plate has a light input side, which is connected to the light output side and receives light emitted by the lower light source.

9. The backlight module according to claim 1, wherein: The lower backlight unit includes a lower light source, a diffusion plate for receiving light from the lower light source, and at least one optical film located on the light-emitting side of the diffusion plate. The diffusion plate has a light-entering side, which is opposite to the light-emitting side and receives light emitted by the lower light source.

10. The backlight module according to claim 8 or 9, wherein: The number of the optical films of the lower backlight unit is multiple, and includes two diffusion sheets and two second prism sheets located between the two diffusion sheets, each of the second prism sheets includes a plurality of second prism columns, the tip of the second prism column of each second prism sheet is facing the upper backlight unit, and the second prism columns of the two second prism sheets extend in different directions respectively.

11. A method for adjusting the viewing angle of a backlight module, for adjusting the viewing angle of the backlight module according to any one of claims 1 to 10, the viewing angle adjustment method comprising a narrow viewing angle mode and a wide viewing angle mode, when the upper backlight unit is turned on and the lower backlight unit is turned off, the backlight module is in the narrow viewing angle mode, and when the upper backlight unit and the lower backlight unit are both turned on, the backlight module is in the wide viewing angle mode.

12. A display device, comprising the backlight module according to any one of claims 1 to 10 and a display panel arranged on the backlight module.

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