Backlight module, viewing angle switching method thereof, and display device including that backlight module

Abstract

To provide a backlight module capable of switching between a side viewing mode and a narrow viewing mode.SOLUTION: A backlight module has a first side viewing angle luminance LAS1 and a first normal viewing angle luminance LAN1 in a side viewing mode, where LAS1 / LAN1>50%. The backlight module has a second side viewing angle luminance LAS2 and a second normal viewing angle luminance LAN2 in a narrow viewing mode, where LAS2 / LAN2<0.5%. The first side viewing angle and the second side viewing angle occur in a slanting direction. The first normal viewing angle and the second normal viewing angle occur in a normal direction. When executing a side viewing execution step, an upper backlight unit and a lower backlight unit are both turned on as the side viewing mode. When executing a narrow viewing execution step, the upper backlight unit is turned off and the lower backlight unit is turned on as the narrow viewing mode.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical device, and particularly to a backlight module and a display device capable of generating different viewing angle modes.

Background Art

[0002] With the progress of science and technology, electronic devices equipped with liquid crystal displays have become indispensable in modern people's lives. However, users have different requirements for the viewing angle of the display device depending on the situation. For example, when a user wants to share information on the screen, it is necessary to give the display device a wide viewing angle so that multiple people can view the content on the screen at different angles, that is, to set the display device to the sharing mode. When an individual wants to handle personal affairs and maintain privacy, it is desirable that only the user himself / herself can see the display screen, and it is necessary for the display product to have a narrow viewing angle function, that is, a peeping prevention mode.

[0003] With the increasing number of applications of in-vehicle displays, in-vehicle displays other than the dashboard can also switch the viewing angle, and it is preferable to avoid the impact on driving safety caused by side glances. In conventional display devices, if there is a need to prevent peeping, the simplest method is to add a peeping prevention sheet to the outermost layer. However, such a drawback is that the normal brightness is significantly reduced. When controlling different viewing angles by a display panel, an active-type display panel dedicated to different viewing angle modes is required, resulting in a high manufacturing cost.

[0004] In particular, for a display applied in front of the passenger seat of a vehicle, in order to prevent the light from the screen from affecting the driver or reflecting on the window, a narrow viewing angle function is required. However, since there may be a need to share a message with the driver so that the light does not reflect on the window, a biased viewing angle function that biases to one side is required.

Summary of the Invention

[0005] Therefore, an object of the present invention is to provide a backlight module that can be switched between a narrow viewing angle and an off-axis viewing angle.

[0006] The backlight module of the present invention is a backlight module that can be switched between an off-axis viewing angle mode and a narrow viewing angle mode. In the off-axis viewing angle mode, the backlight module has a first off-axis viewing angle luminance LAS1 and a first on-axis viewing angle luminance LAN1, where LAS1 / LAN1 > 50%. In the narrow viewing angle mode, the backlight module has a second off-axis viewing angle luminance LAS2 and a second on-axis viewing angle luminance LAN2, where LAS2 / LAN2 < 0.5%. The first off-axis viewing angle and the second off-axis viewing angle occur in an inclined direction, and the first on-axis viewing angle and the second on-axis viewing angle occur in a positive direction.

[0007] Another technical means of the present invention is that the backlight module includes an upper backlight unit and a lower backlight unit located below the upper backlight unit. The upper backlight unit includes an upper light source and an upper light guide plate that receives light rays emitted by the upper light source. The upper light guide plate has at least one first side and at least one second side. The first side is substantially parallel to a first axial direction, and the second side is substantially parallel to a second axial direction. The second axial direction and the first axial direction are not parallel to each other. The first axial direction is between +90° and -90°, and the upper light source is provided on a side closer to +90° in the first axial direction and extends along the second axial direction.

[0008] Another technical means of the present invention is that the upper light guide plate is substantially rectangular, the first side is one long side of the rectangle, the second side is one short side of the rectangle, and the upper light source is close to the short side.

[0009] Another technical means of the present invention is that the upper light guide plate has a light emitting surface, a reflecting surface, and a plurality of dot structures formed on the reflecting surface. The light emitting surface is located in a plane defined by both the first axial direction and the second axial direction. The light emitting surface and the reflecting surface are located on opposite sides of the upper light guide plate respectively. Each of the dot structures has a central region and an outer annular region surrounding the central region. The height h of the central region is greater than 1 μm, and the diameter φ of the outer annular region is greater than 2h.

[0010] Another technical means of the present invention is that the height h of the central region of each of the dot structures is 3 to 7 μm, including the end values, and the diameter φ of the outer annular region is 15 to 35 μm, including the end values.

[0011] Another technical means of the present invention is that the central region of each of the dot structures is concave with respect to the reflecting surface, and the outer annular region is in the shape of an annular flange with respect to the reflecting surface.

[0012] Another technical means of the present invention is that the central region of each of the dot structures is convex with respect to the reflecting surface, and the outer annular region is in the shape of a concave annular groove with respect to the reflecting surface.

[0013] Another technical means of the present invention is that the backlight module is provided on the light emitting side of the upper backlight unit, and further includes an upper light control film for condensing the emitted light along the second axial direction of the backlight module into a positive viewing angle.

[0014] Another technical means of the present invention is that the backlight module is provided between the upper backlight unit and the lower backlight unit, and further includes at least one lower light control film for condensing the emitted light along the first axial direction of the backlight module into a positive viewing angle. The upper light control film and the lower light control film control light rays in different directions.

[0015] Another technical means of the present invention is that the backlight module further includes two prism sheets provided between the upper backlight unit and the lower backlight unit, and each prism sheet has a plurality of strip-shaped fine structures arranged in parallel and facing the upper backlight unit, and the extending directions of the strip-shaped fine structures of the two prism sheets are perpendicular to each other.

[0016] Another technical means of the present invention is that the lower backlight unit includes a lower light source, a lower light guide plate that receives the light rays of the lower light source, and at least one optical film located on the light-emitting side of the lower light guide plate. The lower light guide plate has a light-incident side that is connected to the light-emitting side and receives the light rays emitted by the lower light source, and the lower light source extends along the first axial direction.

[0017] Another technical means of the present invention is that the lower backlight unit includes a lower light source, a diffusion plate that receives the light rays of the lower light source, and at least one optical film located on the light-emitting side of the diffusion plate, and the diffusion plate has a light-incident side that is opposite to the light-emitting side and receives the light rays emitted by the lower light source.

[0018] Another technical means of the present invention is that the positive direction is the viewing angle position located substantially at 0° in the first axial direction, and the inclination direction is the viewing angle position located substantially at -45° in the first axial direction.

[0019] Another object of the present invention is to provide a method for switching the viewing angle of the backlight module for switching the viewing angle of the backlight module. The method for switching the viewing angle includes a step of executing a partial viewing angle and a step of executing a narrow viewing angle. When the step of executing the partial viewing angle is executed, both the upper backlight unit and the lower backlight unit are turned on as the partial viewing angle mode. When the step of executing the narrow viewing angle is executed, the upper backlight unit is turned off, and the lower backlight unit is turned on as the narrow viewing angle mode.

[0020] Another technical means of the present invention is that the backlight module is applied to an in-vehicle display, and the viewing angle switching method further includes a sensing step of determining whether to execute the partial viewing angle execution step or the narrow viewing angle execution step based on the vehicle speed or the driver's eye gaze tracking.

[0021] Another object of the present invention is to provide a display device including the above-mentioned backlight module and a display panel provided on the backlight module.

[0022] When applied to an in-vehicle display provided on the passenger seat, the effect of the present invention is that in the narrow viewing angle mode, LAS2 / LAN2 < 0.5%, the lateral emission luminance is reduced to 0.5% or less of the second frontal viewing angle luminance LAN2, and the luminance is concentrated in the frontal viewing angle direction. Therefore, only the passenger can see it, avoiding the influence on the driver by the lateral emission light and achieving the effect of the narrow viewing angle. When LAS1 / LAN1 > 50% in the partial viewing angle mode, the luminance required for the lateral viewing angle has at least 50% of the first frontal viewing angle luminance LAN1, allowing both the driver and the passenger to see it simultaneously, and having sufficient luminance for the driver to see, thus achieving the effect of the partial viewing angle.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0024] The features and technical contents of the patent applications related to the present invention are clearly shown in the detailed description of the preferred embodiments with reference to the following drawings. Before the detailed description, it should be noted that similar elements are denoted by the same numbers. The directional terms mentioned in the following embodiments, such as up, down, left, right, front, back, bottom, top, etc., are only in the directions referring to the attached drawings. Therefore, the directional terms used are for the purpose of explanation and do not limit the present invention.

[0025] In the following description, the terms "about", "substantially", "nearly" or "the same" usually indicate being within 10%, 5%, 3%, 2%, 1%, or 0.5% of a predetermined value. Here, the predetermined number is an approximate number, that is, in the case where there is no specific explanation of "about", "substantially", "nearly" or "the same", it may include the meaning of "about", "substantially", "nearly" or "the same".

[0026] The backlight module of the present invention can be switched between a wide viewing angle mode and a narrow viewing angle mode. In the wide viewing angle mode, the backlight module has a first wide viewing angle luminance LAS1 and a first normal viewing angle luminance LAN1, provided that LAS1 / LAN1 > 50%. In the narrow viewing angle mode, the backlight module has a second wide viewing angle luminance LAS2 and a second normal viewing angle luminance LAN2, provided that LAS2 / LAN2 < 0.5%. The first wide viewing angle and the second wide viewing angle occur in an inclined direction, and the first normal viewing angle and the second normal viewing angle occur in a positive direction. Thus, when the present invention is applied to an in-vehicle display provided on the passenger seat, in the narrow viewing angle mode, LAS2 / LAN2 < 0.5%, the lateral emission light luminance is reduced to 0.5% or less of the second normal viewing angle luminance LAN2, and the luminance is concentrated in the normal viewing angle direction, so that only the passenger on the passenger seat can see it, the influence on the driver by the lateral emission light is avoided, and the effect of the narrow viewing angle can be achieved. When LAS1 / LAN1 > 50% in the wide viewing angle mode, the luminance required for the lateral viewing angle has at least 50% with respect to the first normal viewing angle luminance LAN1, and can be seen simultaneously by the driver and the passenger on the passenger seat, and has sufficient luminance for the driver to see, and the effect of the wide viewing angle can be achieved.

[0027] FIG. 1 is a preferred embodiment of the backlight module of the present invention. The backlight module includes an upper backlight unit 2 and a lower backlight unit 3 located below the upper backlight unit 2. The upper backlight unit 2 includes an upper light source 21 and an upper light guide plate 22 that receives light rays from the upper light source 21.

[0028] As shown in FIG. 2, the upper light guide plate 22 has at least one first side 221 and at least one second side 222. The first side 221 is substantially parallel to the first axial direction X, the second side 222 is substantially parallel to the second axial direction Y, and the second axial direction Y is not parallel to the first axial direction X. The first axial direction X is between +90° and -90°, the upper light source 21 is provided on the side closer to +90° in the first axial direction X, and extends along the second axial direction Y.

[0029] As shown in FIG. 1, the upper light guide plate 22 has a light emitting surface 223, a reflection surface 224, and a plurality of dot structures 23 formed on the reflection surface 224. The dot structure 23 can destroy total internal reflection of light and uniformly transmit light rays from the light emitting surface 223 of the upper light guide plate 22. The light emitting surface 223 and the reflection surface 224 are respectively located on opposite sides of the upper light guide plate 22. The light emitting surface 223 is located in a plane defined by the first axial direction X and the second axial direction Y. In this embodiment, in the case of a display that is rectangular and has a long side in the horizontal direction, the upper light guide plate 22 is substantially rectangular, the first side 221 is one long side of the rectangle, the second side 222 is one short side of the rectangle, the upper light source 21 is adjacent to the second side 222, the first axial direction X is the horizontal direction of the long side, and the second axial direction Y is the vertical direction of the short side. Also, the upper light source 21 is provided on the side close to +90° in the first axial direction X, or provided on the right side in the horizontal direction of the long side, and extends along the second axial direction Y, that is, the vertical direction of the short side. Therefore, it can be said that the light rays emitted by the upper light source 21 travel to the left side in the horizontal direction of the long side and emit light through the light emitting surface 223 of the upper light guide plate 22.

[0030] In this embodiment, since there is no other prism sheet for changing the traveling direction of light rays above the light emitting surface 223 of the upper light guide plate 22, when the light rays travel toward the left side in the horizontal direction of the long side, they do not reverse, and still emit from the light emitting surface 223 of the upper light guide plate 22 in a negative inclination direction between 0° and -90°. Thereby, in the off-axis viewing angle mode, at least 50% of the maximum luminance in the on-axis viewing angle is retained for the luminance required for the side viewing angle, and the effect of the off-axis viewing angle can be achieved.

[0031] Compared with the case where the upper light source in the prior art is installed on one side in the second axial direction and along the horizontal direction of the long side, its light field distribution spreads and diffuses without being located in the first axial direction, and the light rays cannot be concentrated on the side viewing angle, and the luminance of the side viewing angle does not reach the required level of at least 50% of the maximum luminance in the on-axis viewing angle.

[0032] Referring to FIG. 3, each of the dot structures 23 on the upper light guide plate 22 has a central region 231 and an outer annular region 232 surrounding the central region 231. The height h of the central region 231 is greater than 1 μm, and the diameter φ of the outer annular region 232 is greater than 2h. In this embodiment, as shown in FIG. 3, each of the dot structures 23 can have the central region 231 presenting a convex shape with respect to the reflecting surface 224 and the outer annular region 232 presenting a concave annular groove shape with respect to the reflecting surface 224. Thereby, each of the dot structures 23 does not present a hemispherical protrusion with a high height (or a hemispherical concave hole with a deep depth), but presents an arc-shaped protrusion with a low height as shown in FIG. 3 (or an arc-shaped concave hole with a shallow depth as shown in FIG. 4), which can not only achieve the basic effects in the narrow viewing angle mode and the off-axis viewing angle mode, but also be advantageous for the efficiency and difficulty of laser processing in the mold. In order to improve the luminance required for the lateral viewing angle, reduce the energy loss, and improve the display quality (front-of-screen, FOS), in this embodiment, as shown in FIG. 3, the protrusion height of each dot structure 23 can be further increased (or as shown in FIG. 4, the depth of the concave hole of each dot structure 23 can be further increased). Here, the height h of the central region 231 of each of the dot structures 23 is 3 to 7 μm, including the end point values. The diameter φ of the outer annular region 232 is 15 μm to 35 μm, including the end point values. In addition, in other embodiments, as shown in FIG. 4, each of the dot structures 23 has the central region 231 presenting a concave shape with respect to the reflecting surface 224 and the outer annular region 232 presenting an annular flange shape with respect to the reflecting surface 224.

[0033] Referring to FIG. 1, the backlight module further includes an upper light control film 4 provided on the light emitting side of the upper backlight unit 2, two lower light control films 5 provided between the upper backlight unit 2 and the lower backlight unit 3, and two prism sheets 6 provided between the upper backlight unit 2 and the lower backlight unit 3. The upper light control film 4 and the lower light control films 5 control light rays in different directions. The upper light control film 4 is for condensing the emitted light along the second axial direction Y of the backlight module at a normal viewing angle, so that when applied to an in-vehicle product, such as a center console (Center Information Display, CID) or a display in front of the passenger seat (Passenger Information Display, PID), the light rays in the vertical direction may be converged to the center so as not to be reflected by the windshield. The lower light control film 5 is for condensing the emitted light along the first axial direction X of the backlight module at a normal viewing angle, thereby converging the light field distribution generated by the lower backlight unit 3 and converging from the left and right horizontal directions to the center, so as to enhance the narrow viewing angle effect and avoid the light rays that are spread and diffused too much from passing through the upper backlight unit 2 and affecting the narrow viewing angle mode and the off-axis viewing angle mode.

[0034] Furthermore, here, each prism sheet 6 has a plurality of strip-shaped fine structures 61 that are parallel and face the upper backlight unit 2, and the extending directions of the strip-shaped fine structures 61 of the two prism sheets 6 are orthogonal to each other. Here, the prism sheet 6 directly faces the upper light guide plate 22 of the upper backlight unit 2, and the light path is not blocked by a member that does not transmit other light between them. Therefore, the light rays emitted from the lower backlight unit 3 pass through the lower light control film 5 and the prism sheet 6 and are directly incident on the upper backlight unit 2, and the light path is not blocked by a member that does not transmit other light, so that the light transmittance is not reduced, and an excessive proportion of light rays are not reflected back to the lower backlight unit 3, contributing to the improvement of the emission luminance in the narrow viewing angle mode and the off-axis viewing angle mode.

[0035] Regarding this lower backlight unit 3, its specifications and the arrangement position of the light source are not limited. In this embodiment, as shown in FIG. 1, the lower backlight unit 3 is an edge-type light source, and includes a lower light source 31, a lower light guide plate 32 that receives the light rays of the lower light source 31, at least one optical film 33 located on the light-emitting side 322 of the lower light guide plate 32, and a reflective sheet 34. The lower light guide plate 32 has a light-incident side 321, which is connected to the light-emitting side 322. The light-incident side 321 receives the light rays emitted by the lower light source 31, and the lower light source 31 extends along the first axial direction X. In some embodiments, as shown in FIG. 5, the lower backlight unit 3 is a direct-type light source, and may include a lower light source 31, a diffusion plate 35 that receives the light rays of the lower light source 31, at least one optical film 33 located on the light-emitting side 352 of the diffusion plate 35, and a reflective sheet 34. The diffusion plate 35 has a light-incident side 351 on the opposite side of the light-emitting side 352, and the light-incident side 351 receives the light rays emitted by the lower light source 31. Referring to FIG. 6, a display panel 7, which is a display device of the present invention, is provided on the backlight module. FIG. 6 shows the backlight module shown in FIG. 1 as an example, and in some embodiments, the display panel 7 is provided on the backlight module shown in FIG. 5.

[0036] The present invention further provides a method for switching the viewing angle of the backlight module for switching the viewing angle of the backlight module. The viewing angle switching method includes an off-axis viewing angle execution step and a narrow viewing angle execution step. When the off-axis viewing angle execution step is executed, both the upper backlight unit 2 and the lower backlight unit 3 are turned on in the off-axis viewing angle mode. When the narrow viewing angle execution step is executed, the upper backlight unit 2 is turned off, and the lower backlight unit 3 is turned on in the narrow viewing angle mode.

[0037] As described above, the backlight module has a first off-axis viewing angle luminance LAS1 and a first on-axis viewing angle luminance LAN1 in the off-axis viewing angle mode, provided that LAS1 / LAN1 > 50%. The backlight module has a second off-axis viewing angle luminance LAS2 and a second on-axis viewing angle luminance LAN2 in the narrow viewing angle mode, provided that LAS2 / LAN2 < 0.5%. In particular, the first off-axis viewing angle and the second off-axis viewing angle occur in the inclined direction, and the first on-axis viewing angle and the second on-axis viewing angle occur in the positive direction. Referring to FIG. 2, the positive direction is the viewing angle position located substantially at 0° in the first axial direction X, and the inclined direction is the viewing angle position located substantially at -45° in the first axial direction X. For example, when the backlight module is applied to an in-vehicle display and provided directly in front of the passenger seat, the positive direction (0° viewing angle) is the position corresponding to the passenger seat, and the inclined direction (-45° viewing angle) is the position corresponding to the driver's seat. Further, as shown in FIG. 1, the upper light source 21 must be provided at the short side position away from the driver's seat of the upper light guide plate 22 so that the light rays of the upper light source 21 are projected toward the driver's seat.

[0038] As described above, in the narrow viewing angle mode, the upper backlight unit 2 is turned off and the lower backlight unit 3 is turned on. At this time, the relationship between the second oblique viewing angle luminance LAS2 and the second normal viewing angle luminance LAN2 is LAS2 / LAN2 < 0.5%. That is, the luminance (LAS2) in the tilt direction at this time is quite low so as not to cause any trouble to the driver. More specifically, when the lower backlight unit 3 is turned on, the light incident side 321 of the lower light guide plate 32 receives the light rays emitted by the lower light source 31 and emits light through the light exit side 322. The lower light control film 5 is for condensing the light emitted along the first axial direction X into the normal viewing angle (that is, concentrating the light rays on both the left and right sides to the central position). As shown by the arrow A in FIG. 1, the light rays are emitted close to the positive direction, and collimated positive direction light with sufficient intensity is provided at the position of the viewing angle of 0 degrees. Therefore, in the narrow viewing angle mode, people on both the left and right sides can be prevented from seeing the content displayed on the screen, and the effect of preventing peeping can be achieved. When applied to in-vehicle devices other than the dashboard (for example, a screen provided in front of the passenger seat), by switching to the narrow viewing angle mode, the driver can be prevented from looking sideways at the screen, and driving safety can be improved.

[0039] In the partial viewing angle mode, both the upper backlight unit 2 and the lower backlight unit 3 are turned on. At this time, the relationship between the first partial viewing angle luminance LAS1 and the first frontal viewing angle luminance LAN1 is LAS1 / LAN1 > 50%. Therefore, the luminance (LAS1) in the tilt direction of this partial viewing angle mode is sufficient for the driver to view. More specifically, when both the upper backlight unit 2 and the lower backlight unit 3 are turned on, the light rays of the lower backlight unit 3 converge through the prism sheet 6 and the lower light control film 5 and are directly incident on the upper backlight unit 2. Since the upper light source 21 of the upper backlight unit 2 is provided at the short side position away from the driver's seat of the upper light guide plate 22, the light rays of the upper light source 21 are projected in the direction of the driver's seat. When both the upper backlight unit 2 and the lower backlight unit 3 are turned on, as shown in FIG. 1, in addition to providing collimated forward light (arrow A) with sufficient intensity at the position of the viewing angle of 0 degrees, at the same time, light rays (arrow B) with sufficient intensity are also provided at the position of the viewing angle of -45 degrees so that the passenger on the passenger seat and the driver can view simultaneously. The upper light control film 4 provided in the light emission direction of the upper backlight unit 2 is for condensing the light emitted along the second axial direction Y of the backlight module to the frontal viewing angle to avoid the light rays being reflected through the front glass.

[0040] Referring to FIG. 7, it is a horizontal luminance distribution diagram in the off-axis angle mode, and is compared with dot structures 23 of different sizes. The dashed line indicates that the height h of the central region 231 of each of the dot structures 23 is 1 μm and the diameter φ of the outer annular region 232 is 25 μm. The solid line indicates that the height h of the central region 231 of each of the dot structures 23 is 5 μm and the diameter φ of the outer annular region 232 is 25 μm. As can be seen from FIG. 7, when the height h of the central region 231 of each of the dot structures 23 is 5 μm, compared with the case where the height h of the central region 231 of each of the dot structures 23 is 1 μm, both the first on-axis angle luminance LAN1 in the positive direction (viewing angle 0°) and the first off-axis angle luminance LAS1 in the inclined direction (viewing angle -45°) can be improved. That is, it enables the passenger on the passenger seat and the driver to view simultaneously. Also, the luminance distribution between -10° and -45° can be improved, and the difference in visual sensitivity can be reduced. Further, at viewing angles of -45° or less and +45° or more, the luminance can be reduced, unnecessary emitted light can be reduced, and energy saving can be achieved. Referring to FIG. 8, it is a spatial luminance distribution diagram in the off-axis angle mode. Note that the spatial luminance distribution diagram is a computer simulation diagram and is originally a color diagram, and in the present application, it is represented as a grayscale diagram. As can be seen from the spatial luminance distribution diagram of FIG. 8, in the off-axis angle mode, an energy concentration phenomenon was observed both in the center and on the left side. In addition to this, when the height h of the central region 231 of each of the dot structures 23 is 5 μm, the electrical energy consumed for performing viewing angle adjustment control is about 50% of that when the height h of the central region 231 of each of the dot structures 23 is 1 μm, which has the effect of saving electrical energy and is also advantageous for application to the usage environment of electric vehicles.

[0041] In addition, the viewing angle switching method further includes a sensing step of determining whether to execute the partial viewing angle execution step or the narrow viewing angle execution step based on the vehicle speed or the driver's eye gaze tracking. For example, when the vehicle speed detected by the sensing step is 0 or when it is not necessary for the driver to maintain a state of looking straight ahead, the partial viewing angle execution step is executed. At this time, both the upper backlight unit 2 and the lower backlight unit 3 are turned on in the partial viewing angle mode, enabling the driver to view the screen. When the vehicle speed is not 0 or when the driver is looking straight ahead, the narrow viewing angle execution step is executed. At this time, the upper backlight unit 2 is turned off, and the lower backlight unit 3 is turned on in the narrow viewing angle mode, making it impossible for the driver to clearly view the screen.

[0042] As described above, in the backlight module and its viewing angle switching method of the present invention, by turning on the upper backlight unit 2 and the lower backlight unit 3 simultaneously, a partial viewing angle mode is provided. By turning on the lower backlight unit 3 and turning off the upper backlight unit 2, a narrow viewing angle mode is provided. Therefore, the backlight module and the display device of the present invention have the function of switching between the partial viewing angle mode and the narrow viewing angle mode. At the same time, due to the installation position of the upper light source 21, light rays can be emitted in the direction towards the driver's seat without being reflected through the window of the passenger seat. In addition, with the increase in the number of in-vehicle displays applied, there is also a need for anti-peeping. To avoid the influence on the driver's driving line of sight and improve driving safety, the present invention satisfies the narrow viewing angle mode (anti-peeping) and the partial viewing angle mode (sharing) by switching the light source, achieves multi-task use applicable to different scene conditions. Especially when applied to a vehicle display, especially when applied to a display (Passenger Information Display, PID) in front of the passenger seat of the vehicle, in the case of the partial viewing angle mode (sharing), the driver and the passenger can view the screen content simultaneously. In the case of the narrow viewing angle mode (anti-peeping), it is advantageous to prevent the driver from viewing the content of the display screen, avoid the driver from looking sideways, and protect the privacy of the passenger. Furthermore, it is possible to avoid the influence on driving caused by side window reflected light and ensure the advantage of driving safety, meet the active switching needs for the privacy mode and the sharing mode of the PID screen, and the light field in the sharing mode can be concentrated in a specific area, improving the utilization rate of light.

[0043] What has been described above is only a preferred embodiment of the present invention, and thus the scope of implementation of the present invention cannot be limited thereby. That is, simple equivalent changes and modifications made based on the scope of the patent claims of the present invention and the description content of the invention are all within the scope of the patent claims of the present invention.

Explanation of Reference Numerals

[0044] 2 Upper backlight unit 21 Upper light source 22 Upper light guide plate 221 First side 222 Second side 223 Light emitting surface 224 Reflective surface 23 Dot structure 231 Central region 232 Outer annular region 3 Lower backlight unit 31 Lower light source 32 Lower light guide plate 321 Light incident side 322 Light emitting side 33 Optical film 34 Reflective sheet 35 Diffuser plate 351 Light incident side 352 Light emitting side 4 Upper light control film 5 Lower light control film 6 Prism sheet 61 Strip-shaped fine structure 7 Display panel A Arrow B Arrow X First axial direction Y Second axial direction φ Diameter h Height

Claims

1. A backlight module switchable between a biased viewing angle mode and a narrow viewing angle mode, comprising: the backlight module has, in the biased viewing angle mode, a first biased viewing angle luminance LAS1 and a first normal viewing angle luminance LAN1, where LAS1 / LAN1>50%, and the backlight module has, in the narrow viewing angle mode, a second biased viewing angle luminance LAS2 and a second normal viewing angle luminance LAN2, where LAS2 / LAN2<0.5%, the first biased viewing angle and the second biased viewing angle occur in an inclined direction, and the first normal viewing angle and the second normal viewing angle occur in a normal direction.

2. 2. The backlight module according to claim 1, comprising: an upper backlight unit; and a lower backlight unit located below the upper backlight unit, the upper backlight unit comprising: an upper light source; and an upper light guide plate that receives light emitted from the upper light source, the upper light guide plate having at least one first side edge and at least one second side edge, the first side edge being substantially parallel to a first axial direction, the second side edge being substantially parallel to a second axial direction, the second axial direction and the first axial direction being not parallel to each other, the first axial direction being between +90° and -90°, and the upper light source being provided on a side closer to +90° in the first axial direction and extending along the second axial direction.

3. 3. The backlight module of claim 2, wherein the upper light guide plate has a light exit surface, a reflective surface, and a plurality of dot structures formed on the reflective surface, the light exit surface being located on a plane defined by both the first axial direction and the second axial direction, the light exit surface and the reflective surface being located on opposite sides of the upper light guide plate, each dot structure having a central region and an outer annular region surrounding the central region, a height h of the central region being greater than 1 μm, and a diameter φ of the outer annular region being greater than 2h.

4. The backlight module of claim 3, characterized in that the height h of the central region of each of the halftone dot structures is 3 to 7 μm, including end point values, and the diameter φ of the outer annular region is 15 to 35 μm, including end point values.

5. 3. The backlight module according to claim 2, further comprising an upper light control film provided on the light emission side of the upper backlight unit for concentrating light emitted along the second axis of the backlight module to a regular viewing angle.

6. The backlight module according to claim 5, further comprising at least one lower light control film arranged between the upper backlight unit and the lower backlight unit for concentrating the emitted light along the first axial direction of the backlight module to a regular viewing angle, wherein the upper light control film and the lower light control film control light rays in different directions.

7. 7. The backlight module according to claim 2, wherein the positive direction is a viewing angle position located substantially at 0° in the first axial direction, and the tilt direction is a viewing angle position located substantially at -45° in the first axial direction.

8. A method for switching the viewing angle of the backlight module according to any one of claims 2 to 7, comprising the steps of: A viewing angle switching method comprising: a biased viewing angle execution step and a narrow viewing angle execution step, wherein when the biased viewing angle execution step is executed, the upper backlight unit and the lower backlight unit are both turned on in the biased viewing angle mode, and when the narrow viewing angle execution step is executed, the upper backlight unit is turned off and the lower backlight unit is turned on in the narrow viewing angle mode.

9. The method for switching a viewing angle of a backlight module according to claim 8, characterized in that the backlight module is applied to an in-vehicle display, and the viewing angle switching method further includes a sensing step of determining whether to execute the biased viewing angle execution step or the narrow viewing angle execution step based on a vehicle speed or a driver's eye tracking gaze.

10. A display device comprising: a backlight module according to any one of claims 1 to 7; and a display panel provided in the backlight module.

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