Switchable light filter, lighting device and screen

Abstract

The invention relates to a switchable light filter (5) comprising at least means for selectively influencing the angularly dependent transmittance of the switchable light filter (5) for the light incident thereon, in which at least at one point in time, at a plurality of different positions on the switchable light filter (5), the angle dependent transmittance of the switchable light filter (5) is dependent on the angle dependent transmittance of the light incident on the switchable light filter (5). The device for influencing the angle-dependent transmittance produces, for at least one direction of the hemisphere, at least three mutually different values of the transmittance, i.e., the minimum value, the intermediate value and the maximum value of the transmittance, for a selectable angle which is the same at a plurality of different positions on the switchable light filter (5). The invention further discloses a switchable lighting device and a switchable screen.

Description

Technical Field

[0001] In recent years, liquid crystal displays (LCDs) have made great progress in terms of viewing angle expansion. However, in some cases, a large viewing angle range of the screen is often a disadvantage. There is more and more information on mobile devices such as laptops and tablets, for example, bank data or other personal information, as well as sensitive data. Therefore, people need to control who can see this sensitive data and must be able to choose between a wide viewing angle (public mode) for displaying information such as travel photos or advertising content to share with others and a narrow viewing angle (private mode) for privately processing the display information.

[0002] A similar problem also exists in the automotive industry: when the vehicle is moving, the driver cannot be distracted by the screen content such as digital entertainment programs, while the passengers want to watch the screen content. Therefore, a screen that can switch between corresponding display modes is needed.

[0003] Additional films based on the micro-louver technology have been used in mobile displays to achieve visual data protection. However, this additional film is not switchable or controllable, and must be manually attached and then removed. And when people do not need this additional film, they must also carry it separately from the display device. In addition, a major disadvantage of such louver films is the light loss that occurs with their use. Background Art

[0004] US 6,765,550 B2 describes this anti-peeping achieved through micro-louvers. The biggest disadvantage of this solution is the mechanical removal or mechanical attachment of the light filter, as well as the light loss in the protected mode.

[0005] US 5,993,940 A describes the use of a thin film on the surface of which small strip-shaped prisms are evenly arranged to achieve a visually restricted mode with a small viewing angle range. The technical difficulty of its research and development and manufacturing is quite high.

[0006] In WO 2012 / 033583 A1, switching between the free mode and the restricted mode is achieved through the liquid crystal control between the so-called "color" layers. This results in light loss, and its technical difficulty is also quite high.

[0007] US2012 / 0235891A1 describes a rather complex screen backlight. According to FIGS. 1 and 15 thereof, not only are multiple light guide plates used, but also other complex optical elements, such as the microlens element 40 and the prism structure 50, which can convert the light illuminated from the rear into the light illuminated from the front. This is both expensive and complex and causes light loss. According to the variant described in FIG. 17 of US2012 / 0235891A1, both light sources 4R and 18 generate light with a narrow emission viewing angle, and the light from the rear light source 18 has to be complexly converted into light with a large emission viewing angle. As described above, such complex conversion greatly reduces the brightness.

[0008] US2013 / 0308185A1 describes a special stepped light guide plate that emits light from different directions to a large surface according to which narrow side of the light guide plate is illuminated. When combined with a transmissive image display device (e.g., a liquid crystal display screen), it can produce a screen that can be switched between a free viewing mode and a restricted viewing mode. Its disadvantages include that the restricted viewing effect can only be used for the left / right side or for the upper / lower side, but not simultaneously for the left / right / upper / lower sides, which is necessary in some payment processes. In addition, even in the restricted viewing mode, residual light can still be seen from the occluded viewing angles.

[0009] The applicant's WO2015 / 121398A1 describes a screen with two operating modes, in which the scattering particles present in the volume of the corresponding light guide plate are substantially used to achieve the switching of the operating modes. However, the scattering particles made of polymers generally have the disadvantage of emitting light from two large surfaces, so about half of the useful light is emitted in the wrong direction, that is, towards the backlight, and this light cannot be recycled within a sufficient range due to structural reasons. In addition, in some cases, especially at high concentrations, the scattering particles made of polymers in the volume of the light guide plate will cause a scattering effect, thus reducing the anti-peeping effect in the protected mode.

[0010] The core idea of the "electrical birefringence (EDB)" technology is to use the switchable liquid crystals added to the liquid crystal panel to "filter" the light emitted from the imaging layer at a specific angle. However, this technology has some disadvantages, including higher additional energy consumption and cost, and a difficult-to-adjust optimal viewing angle (i.e., the best viewing position), which is usually fixed at about ±40°. In addition, the light absorption ability of the liquid crystal structure is also insufficient, because for viewing angles greater than the optimal viewing angle, the light intensity attenuation is insufficient, and as a result, the light intensity can still reach 3% of the maximum light intensity at viewing angles greater than ±40°.

[0011] The above methods and devices generally have the following disadvantages: they significantly reduce the brightness of the base screen, and / or, require complex and expensive optical elements for mode switching, and / or, reduce the resolution in the freely viewable and public mode, and / or, visual artifacts appear on very high-resolution displays. In particular, with respect to partial switching between modes, visible edges may occur in the areas between different modes. Summary of the Invention

[0012] The object of the present invention is to describe an optical filter, in which light incident on the optical filter is selectively transmitted or partially or (almost) completely absorbed at different positions on the optical filter or on a screen having the optical filter. Among them, at least three working modes are feasible to prevent visible edges from appearing during partial switching, and in particular, the transmittance can be converted for a specific angle or direction. In addition, a corresponding screen or lighting device is also described, and its angle-dependent brightness distribution can be partially and regionally changed. Among them, visible edges between areas in different modes can also be prevented.

[0013] This object is achieved by a switchable optical filter according to an embodiment of the present invention, which includes:

[0014] means for selectively influencing the angle-dependent transmittance of the switchable optical filter for light incident thereon, wherein,

[0015] at least at one point in time, at a plurality of different positions on the switchable optical filter, for a selectable angle that is the same for a plurality of different positions on the switchable optical filter, the means for influencing the angle-dependent transmittance generates at least three mutually different values of the transmittance for at least one direction of the hemisphere, that is, the minimum value, the intermediate value, and the maximum value of the transmittance. This does not necessarily apply to multiple or all possible angles, but at least to one selectable and equal angle. The term "intermediate value" is only a name, and it may or may not precisely refer to the average of the minimum value and the maximum value. Preferably, in one embodiment, at least five, eight, or more mutually different values of the transmittance are generated at the corresponding five, eight, or more positions.

[0016] For using the optical filter according to the present invention, it is beneficial to further have a device for generating linearly polarized light. For example, an LC panel with a polarizer, or in the presence of another image source or light source, a polarization filter. In the first embodiment, the device for influencing the angle-dependent transmittance of the switchable optical filter includes at least one guest-host liquid crystal arrangement or polymer-dispersed liquid crystal respectively having a plurality of liquid crystal molecules, wherein the orientations of the plurality of liquid crystal molecules respectively determine the angle-dependent transmittance of the switchable optical filter, and the orientations of the plurality of liquid crystal molecules at a plurality of different positions on the switchable optical filter are different from each other.

[0017] In contrast, in the second embodiment, the device for influencing the angle-dependent transmittance of the switchable optical filter is integrated in a dual-cell structure or a multi-cell structure, wherein, in the dual-cell structure or the multi-cell structure, the orientations of the plurality of liquid crystal molecules respectively responsible for the variable angle-dependent transmittance are different at a plurality of different positions on the switchable optical filter.

[0018] Furthermore, in the third embodiment, the switchable optical filter includes:

[0019] A first optical element, which includes:

[0020] A plurality of light-absorbing transition dipoles, which are arranged in a layer with a thickness of at least 0.2 micrometers,

[0021] wherein, the plurality of transition dipoles are arranged parallel to a selectable first preferred direction of the first optical element or fluctuate around the first preferred direction with a tolerance of at most 20° at least in the first state, the first preferred direction is set at a predetermined angle α with respect to the perpendicular bisector of the first optical element, and the angle α is measured in a selectable first plane containing the perpendicular bisector,

[0022] so that light rays incident on the first optical element with an incident direction and a polarization state are transmitted or at least partially absorbed according to the incident direction and the polarization state of the light rays with respect to the first optical element;

[0023] A device for selectively applying at least a first electric field EF1, a second electric field EF2, and a third electric field EF3, wherein the first electric field EF1, the second electric field EF2, and the third electric field EF3 can all be applied differently at a plurality of different positions on the switchable optical filter;

[0024] A liquid crystal layer, which is arranged in front of or behind the first optical element along the viewing direction, the first electric field EF1, the second electric field EF2, and the third electric field EF3 are all applied to the liquid crystal layer, and the polarization state of the light rays passing through the liquid crystal layer is affected depending on the electric field;

[0025] When the liquid crystal layer is disposed in front of the first optical element along the viewing direction, a first linear polarization filter disposed in front of the liquid crystal layer along the viewing direction

[0026] so that the transmission characteristics of the switchable optical filter 5 are different at each position among at least a third operating mode B3 of a first operating mode B1 in which a first electric field EF1 is applied, a second operating mode B2 in which a second electric field EF2 is applied, and a third electric field EF3 is applied, wherein the respective relative transmittances in the first operating mode B1, the second operating mode B2, and the third operating mode B3 are respectively expressed as a first transmittance T corresponding to the first operating mode B1 B1 (β), a second transmittance T corresponding to the second operating mode B2 B2 (β), and a third transmittance T corresponding to the third operating mode B3 B3 (β), the first transmittance, the second transmittance, and the third transmittance are all related to the angle β and are normalized so that the transmittance values satisfy T B1 (α)=1, T B2 (α)=1, and T B3 (α)=1

[0027] wherein

[0028] when light is incident on the first optical element at an angle β satisfying β = α - 40° or β = α + 40°, at a plurality of positions in the first operating mode B1 in which the first electric field EF1 is applied, the s-polarized component of the light is transmitted at least at a normalized first transmittance value T B1 (β)≥0.25

[0029] when light is incident on the first optical element at an angle β satisfying β = α - 40° or β = α + 40°, at a plurality of positions in the second operating mode B2 in which the second electric field EF2 is applied, the p-polarized component of the light is transmitted at most at a normalized second transmittance value T B2 (β)≤0.2, and

[0030] when light is incident on the first optical element at an angle β satisfying β = α - 40° or β = α + 40°, at a plurality of positions in the third operating mode B3 in which the third electric field EF3 is applied, the light has a normalized third transmittance value T B2 (β)<

[0031] T B3 (β)<T B1(β) is transmitted. S-polarized light represents a ray having an electric field perpendicular to the plane of incidence and oriented towards the medium, and P-polarized light represents a ray oriented parallel to the plane of incidence. The plane of incidence is spanned by the normal to the interface of the medium and the direction of incidence.

[0032] Furthermore, in a fourth embodiment, the switchable optical filter comprises:

[0033] a first optical element, which comprises:

[0034] a plurality of absorptive transition dipoles, which are arranged in a layer having a thickness of at least 0.2 micrometers,

[0035] wherein the plurality of transition dipoles are arranged parallel to a selectable first preferred direction of the first optical element or fluctuate around the first preferred direction with a tolerance of at most 20° at least in a first state, the first preferred direction being set at a predetermined angle α with respect to the perpendicular bisector of the first optical element, the angle α being measured in a selectable first plane containing the perpendicular bisector,

[0036] such that light incident on the first optical element is transmitted or at least partially absorbed depending on the direction of incidence and polarization state of the light with respect to the first optical element;

[0037] a liquid crystal layer having a plurality of liquid crystal molecules, which is arranged in front of or behind the first optical element in the viewing direction, and the orientation of the plurality of liquid crystal molecules can be affected pixel by pixel by a locally controllable electric field, such that the liquid crystal layer affects the polarization state of the light passing through the liquid crystal layer according to the individually pixel-selectable orientation of the plurality of liquid crystal molecules,

[0038] wherein the locally controllable electric field is controlled by a control circuit, and the control circuit can be controlled by a plurality of digital signals, wherein the plurality of digital signals exist pixel by pixel, and at least at one time point, at least one maximum digital signal, one minimum digital signal, and one digital signal between the maximum digital signal and the minimum digital signal are selected;

[0039] a first linear polarization filter located in front of the liquid crystal layer in the viewing direction in the case where the liquid crystal layer is arranged in front of the first optical element in the viewing direction,

[0040] such that at a time point, in the case where the control circuit is controlled by at least three digital signals, at least three different values of the transmittance are generated at a plurality of different positions on the switchable optical filter for a selectable angle that is the same for the plurality of different positions on the switchable optical filter, that is, the minimum value, the intermediate value, and the maximum value of the transmittance.

[0041] For example, the corresponding digital signal can correspond to one of 256 gray levels stored in a bitmap file.

[0042] Optionally, these digital signals can be adjusted dynamically.

[0043] Particularly preferably, in all embodiments, for the same angle, at least three mutually different values of the transmittance are respectively generated at a plurality of positions of the switchable optical filter, preferably, the plurality of positions are directly adjacent. That is, for a fixed angle, the transmittance values decrease from the maximum value to the minimum value along a selectable straight line on the surface of the switchable optical filter, or conversely increase. Since at least the intermediate value of the transmittance is still spatially located therebetween, a smoother transition of the transmittance values from the minimum value to the maximum value (or vice versa) can be achieved.

[0044] As described above, it is necessary to set more than three transmittance values (for example, five, eight or more) to make the above transition more continuous and visually more comfortable.

[0045] For all the foregoing embodiments, the same technical effect applies: at a selectable angle that generally corresponds to the angle α, but can also be set to other values (for example, at a 45° angle in the horizontal direction of the observer, that is, when the position on the switchable optical filter is in the privacy mode), the local position of the minimum transmittance is not immediately adjacent to the position of the maximum transmittance, but at least one position that reflects the intermediate value of the transmittance at the given angle, or at least one position of the plurality of values of the transmittance located therebetween as described above. In the third and fourth embodiments, it can be rewritten for some specific applications as:

[0046] Preferably, polarized light is incident on the liquid crystal layer and the first optical element, wherein the dichroic dye is arranged parallel or perpendicular to the surface of the substrate. Local different first electric fields EF1 and second electric fields EF2 can be applied to the electrodes E1 and E2 for selecting the transmission characteristics. By static and / or dynamic superposition of the first electric field EF1 and the second electric field EF2, a specific intermediate value of the transmittance can be generated, thereby minimizing the perceptibility of the edge between the positions having the first electric field and the second electric field respectively.

[0047] Generally speaking, the term "position" refers to a two-dimensional coordinate position, which (if any) respectively indicates the same X coordinate and Y coordinate on the surface of the first optical element 1 and the switchable optical filter 5. Therefore, "position" can be used synonymously for both (i.e., the optical element and the optical filter).

[0048] If any, the first optical element and / or the liquid crystal layer can be divided into a plurality of independently switchable partitions, so as to achieve local switching between various possible working states.

[0049] In a specific embodiment, the switchable optical filter can include at least two first optical elements, and optionally, a retardation plate is arranged between at least two such first optical elements.

[0050] The present invention further includes an illumination device for a screen, which can be operated in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode. In the restricted viewing mode, light is emitted within a viewing angle range restricted for the viewer relative to the free viewing mode. The illumination device includes:

[0051] A backlight extending in a plane for emitting light, and optionally, it is arranged to emit light directly;

[0052] A switchable light filter arranged in front of the backlight along the viewing direction as described above.

[0053] In addition, the present invention further includes a screen, which can be operated in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode. In the restricted viewing mode, light is emitted within a viewing angle range restricted for the viewer relative to the free viewing mode. The screen includes:

[0054] The illumination device as described above;

[0055] In the case where a first linear polarization filter is not provided in the switchable light filter of the illumination device, a second linear polarization filter arranged in front of the backlight along the viewing direction, whereby the light emitted from the backlight and transmitted through the second linear polarizer has its propagation direction restricted; and

[0056] A transmissive image display device arranged in front of the switchable light filter along the viewing direction,

[0057] wherein a second electric field EF2 is applied in the second operating mode B2, and a first electric field EF1 is applied in the first operating mode B1.

[0058] Wherein, the first linear polarization filter or the second linear polarization filter can be arranged in the transmissive image display device or a part thereof.

[0059] In addition, the object of the present invention can be achieved by a screen, which includes:

[0060] An image display device;

[0061] A switchable light filter arranged in front of or behind the image display device along the viewing direction as described above.

[0062] Wherein, the switchable light filter 5 can be installed by the user later and / or installed on the image display device beforehand.

[0063] In addition, the present invention further includes a screen which can be operated in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode. In the restricted viewing mode, light is emitted within a viewing angle range restricted for the viewer relative to the free viewing mode. The screen includes:

[0064] A transmissive image display device, preferably an LC panel;

[0065] A backlight disposed behind the transmissive image display device along the viewing direction, wherein the backlight has an asymmetric light density distribution, and preferably, the asymmetry exists with respect to the horizontal direction of the viewer (i.e., the direction parallel to the imaginary line connecting the viewer's two eyes);

[0066] A switchable light filter disposed in front of or behind the image display device along the viewing direction as described above.

[0067] In addition, the present invention can also be implemented by an illumination device for a screen which can be operated in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode. In the restricted viewing mode, light is emitted within a viewing angle range restricted for the viewer relative to the free viewing mode. The illumination device includes:

[0068] A planar-extended backlight for emitting light within a restricted angle range, and optionally, it is arranged to emit light directly;

[0069] A light guide plate disposed in front of the backlight along the viewing direction, which has a plurality of light-emitting elements on at least one large surface and / or within its volume;

[0070] A light source laterally disposed beside at least one narrow edge of the light guide plate;

[0071] Optionally, a linear polarization filter; and

[0072] A switchable light filter disposed in front of the backlight along the viewing direction as described above,

[0073] wherein the backlight is turned on and the light source is turned off in the second operating mode B2, and at least the light source is turned on in the first operating mode B1.

[0074] Alternatively, the illumination device for the screen can be operated in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode. In the restricted viewing mode, light is emitted within a viewing angle range restricted for the viewer relative to the free viewing mode, and includes:

[0075] A planar-extended backlight that emits light within an unrestricted angular range and, optionally, is configured to emit light directly;

[0076] A light guide plate disposed in front of the backlight along the viewing direction, having a plurality of light-emitting elements on at least one major surface and / or within its volume, wherein the light-emitting elements couple out most of the light coupled into the light guide plate from at least one narrow side in a restricted angular range;

[0077] A light source that is laterally disposed beside at least one narrow side of the light guide plate,

[0078] Optionally, a linear polarization filter; and

[0079] A switchable light filter disposed in front of the backlight along the viewing direction as described above,

[0080] wherein, in the second operating mode B2, the backlight is turned off and the light source is turned on, and in the first operating mode B1, at least the light source is turned on.

[0081] A switchable lighting device that can be operated in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode, in which the light is emitted within a viewing angle range restricted for the viewer relative to the free viewing mode. The switchable lighting device is also used to achieve the same technical effect and includes:

[0082] A planar-extended backlight that emits light within a restricted angular range in a first alternative and within an unrestricted angular range in a second alternative, and optionally, is configured to emit light directly;

[0083] A light guide plate disposed in front of the backlight along the viewing direction, having a plurality of light-emitting elements on at least one major surface and / or within its volume; and

[0084] A light source that is laterally disposed beside at least one narrow side of the light guide plate,

[0085] wherein, in the first alternative, in the second operating mode B2, the backlight is turned on and the light source is turned off, and in the first operating mode B1, at least the light source is turned on, and in the second alternative, in the second operating mode B2, the backlight is turned off and the light source is turned on, and in the first operating mode B1, at least the backlight is turned on, wherein the backlight and / or the light guide plate, i.e., when one or both of the backlight and the light guide plate emit light, at least at one point in time, at multiple different positions on the backlight and / or the light guide plate, for selectable but the same angles at multiple different positions, produce at least three mutually different brightness values, namely, the minimum value, the medium value, and the maximum value of the brightness.

[0086] Similarly, the description of the foregoing embodiments also applies here. Particularly preferably, for the same angles, at least three mutually different values of the transmittance are respectively generated at a plurality of positions where the backlight and / or the light guide are adjacent (preferably, directly adjacent).

[0087] Finally, the present invention also includes a switchable screen having the same technical effects in application, which at least includes:

[0088] An image display device;

[0089] A device for influencing the angle-dependent brightness of the switchable screen, wherein,

[0090] The device for influencing the angle-dependent brightness generates at least three mutually different brightness values, namely, the minimum value, the medium value, and the maximum value of the brightness, at a plurality of different positions on the switchable screen at least at one time point for selectable but the same angles at the plurality of different positions.

[0091] To implement the device for influencing the angle-dependent brightness, controllable angle-dependent absorption, reflection, or contrast, and scattering techniques can be used.

[0092] The above light filter, lighting device, or such a screen can be advantageously applied to mobile devices, vehicles, aircraft, ships, payment terminals, or access control systems. By switching between the above working modes, sensitive data can be protected (i.e., the visual content is only displayed to a single observer), and at the same time, multiple observers can view the image content.

[0093] Basically, when the above parameters vary within a specific range, the performance of the present invention can still be maintained.

[0094] It can be understood that the features mentioned above and those to be explained below can be used not only in the corresponding combinations indicated, but also in other combinations or alone without departing from the scope of the present invention. Description of the Drawings

[0095] The present invention will be described in detail below with reference to the embodiments in conjunction with the accompanying drawings, which also disclose the essential technical features of the present invention. These embodiments are only for illustrative purposes, and their content should not be construed as a limitation on the scope of protection. For example, the description of an embodiment containing multiple elements or components should not be construed as all of these elements or components being necessary for the implementation. More precisely, other embodiments can be implemented by using alternative elements or components, reducing the number of elements, or adding additional elements. Unless otherwise specified, the elements or components in different embodiments can be combined with each other. The modifications and variations described for one embodiment can also be applied to other embodiments. To avoid repetition, the same or corresponding elements in different drawings are denoted by the same reference numerals and will not be described one by one. Among them:

[0096] Figure 1a Schematic diagram of the working principle of an exemplary switchable optical filter having locally different transmittances;

[0097] Figure 1b Schematic diagram of the working principle of an exemplary switchable optical filter in three different local operating modes B1, B2, and B3;

[0098] Figure 2 Schematic diagram of an exemplary structure of a switchable optical filter in the first embodiment;

[0099] Figure 3 Exemplary normalized transmittance curve of the switchable optical filter for the maximum transmittance T1 over the horizontal angle range in the first (local) operating mode B1 (schematic diagram based on measured data simulation);

[0100] Figure 4 Exemplary normalized transmittance curve of the switchable optical filter for the minimum transmittance T2 over the horizontal angle range in the second (local) operating mode B2 (schematic diagram based on measured data simulation);

[0101] Figure 5 Exemplary normalized transmittance curve of the switchable optical filter for the first intermediate transmittance T3 over the horizontal angle range in the third (local) operating mode B3 (schematic diagram based on measured data simulation);

[0102] Figure 6 Exemplary normalized transmittance curve of the switchable optical filter for the second intermediate transmittance T3 over the horizontal angle range in the third (local) operating mode B3 (schematic diagram based on measured data simulation);

[0103] Figure 7Exemplary normalized transmittance curve (schematic diagram simulated based on measured data) of the switchable optical filter in the third (local) operating mode B3 for the third intermediate transmittance T3 over a horizontal angular range;

[0104] Figure 8 Schematic diagram of a digital signal corresponding to one of the 256 gray levels in the prior art;

[0105] Figure 9a Another schematic diagram of a digital signal corresponding to one of the 256 gray levels, wherein the visibility of the vertical edge between regions of different operating modes is reduced;

[0106] Figure 9b Another schematic diagram of a digital signal corresponding to one of the 256 gray levels, wherein the visibility of the horizontal edge between regions of different operating modes is reduced; and

[0107] Figure 10 Another schematic diagram of a digital signal corresponding to one of the 256 gray levels, wherein the radial visibility of the transition between regions of different operating modes is reduced. Detailed Description

[0108] The drawings are only for illustrative purposes and are not drawn to scale.

[0109] Figure 1a Schematic diagram showing the operating principle of an exemplary switchable optical filter 5 having locally different transmittances T1, T2, and T3. The region of the minimum transmittance T2 is completely surrounded by the region of the intermediate transmittance T3, which in turn is completely surrounded by the region of the maximum transmittance T1. Other embodiments may also be employed.

[0110] Such an exemplary switchable optical filter 5 at least includes:

[0111] An apparatus for selectively influencing the angle-dependent transmittance of a switchable optical filter 5 for light incident thereon, wherein, at least at one point in time, at a plurality of different positions on the switchable optical filter 5, for a selectable angle that is the same for a plurality of different positions on the switchable optical filter 5, the apparatus for influencing the angle-dependent transmittance produces at least three mutually different values of transmittance for at least one direction of a hemisphere, namely, a minimum value T2 of transmittance, an intermediate value T3, and a maximum value T1. This does not necessarily apply to a plurality or all possible angles, but at least to one selectable and equal angle. The term "intermediate value" is merely a name and may or may not precisely refer to the average of the minimum and maximum values. In a preferred embodiment, at least five, eight, or more mutually different values of transmittance are produced at corresponding five, eight, or more positions.

[0112] For using an optical filter according to the present invention, it is beneficial to also have an apparatus for generating linearly polarized light. For example, an LC panel with a polarizer, or in the presence of another image source or light source, a polarization filter is used.

[0113] Figure 1b A schematic diagram showing the operating principle of an exemplary switchable optical filter 5 in three different local operating modes B1, B2, and B3 is shown. The exemplary optical filter 5 includes:

[0114] a. A first optical element 1, which includes:

[0115] i. A plurality of transition dipole moments, which are arranged in a layer with a thickness of at least 0.2 micrometers,

[0116] ii. wherein the plurality of transition dipole moments are arranged at least in a first state parallel to a selectable first preferred direction of the first optical element 1 with a tolerance of at most 20° or fluctuate around the first preferred direction, and the first preferred direction is set at a predetermined angle α with respect to the perpendicular bisector of the first optical element 1, and the angle α is measured in a selectable first plane containing the perpendicular bisector,

[0117] iii. such that light incident on the first optical element 1 is transmitted or at least partially absorbed according to the incident direction and polarization state of the light with respect to the first optical element 1;

[0118] b. An apparatus for selectively applying at least a first electric field EF1, a second electric field EF2, and a third electric field EF3, wherein the first electric field EF1, the second electric field EF2, and the third electric field EF3 can all be applied differently at a plurality of different positions on the switchable optical filter 5;

[0119] c. A liquid crystal layer 3, which is disposed in front of or behind the first optical element 1 along the viewing direction, and the first electric field EF1, the second electric field EF2, and the third electric field EF3 are all applied to the liquid crystal layer 3, and the polarization state of the light passing through the liquid crystal layer 3 is affected depending on the electric field;

[0120] d. When the liquid crystal layer 3 is disposed in front of the first optical element 1 along the viewing direction, a first linear polarization filter X located in front of the liquid crystal layer 3 along the viewing direction;

[0121] e. So that the transmission characteristics of the switchable optical filter 5 are different at each position between the first operating mode B1 in which the first electric field EF1 is applied, the second operating mode B2 in which the second electric field EF2 is applied, and at least one third operating mode B3 in which the third electric field EF3 is applied, wherein the respective relative transmittances in the first operating mode B1, the second operating mode B2, and the third operating mode B3 are respectively represented as the first transmittance Tb1(β)B1(β) corresponding to the first operating mode B1, the second transmittance Tb2(β)B2(β) corresponding to the second operating mode B2, and the third transmittance TB3(β) corresponding to the third operating mode B3 at any position within a selectable tolerance. The first transmittance, the second transmittance, and the third transmittance are all related to the angle β and are normalized so that the transmittance values satisfy TB1(α)=1, TB2(α)=1, and TB3(α)=1 with respect to a predetermined angle α.

[0122] f. Specifically,

[0123] i. When the light is incident on the first optical element 1 at an angle β that satisfies β = α - 40° or β = α + 40°, at multiple positions in the first operating mode B1 in which the first electric field EF1 is applied, the s-polarization component of the light is transmitted at least with a normalized first transmittance value TB1(β)≥0.25.

[0124] ii. At multiple positions in the second operating mode B2 in which the second electric field EF2 is applied, the P-polarization component of the light is transmitted at least with a normalized second transmittance value T B2 (β)

[0125] ≤0.2, and

[0126] iii. At multiple positions in the third operating mode B3 in which the third electric field EF3 is applied, the light is transmitted with a normalized third transmittance value T B2 (β)<T B3 (β)<T B1

[0127] (β).

[0128] The letters "S" and "P" respectively refer to S-polarized light or P-polarized light. In the local working mode B3 with an intermediate transmittance T3, if |β - a| > 30°, only part of the light (i.e., S-polarized light) is transmitted to the side, while most of the P-polarized light is absorbed by the first optical element 1. T B2 (β) or T B3 (β) or T B1 The value of (β) can be associated or equated with the transmittance T2 or the transmittance T3 or the transmittance T1 respectively for one (or more) selected but fixed angles β.

[0129] Regarding the transmittance T B1 (α) = 1 and T B2 For the normalization of (α) = 1, the following should be noted: Obviously, the angles β and α need to be measured in the same aforementioned plane. In principle, it is also possible that T B1 (α) > 1 and / or T B2 (α) > 1 applies to the angle β ≠ α, but in most cases, T B1 (α) < 1 and / or T B2 (α) < 1 applies to the angle β ≠ α.

[0130] For better illustration, the value of the angle α in Figure 1 is greater than 0°. For all subsequent studies, α = 0° is applicable in principle. A value of α ≠ 0° may cause the preferred transmission direction (i.e., the maximum transmission direction) of the switchable optical filter 5 to be tilted.

[0131] Advantageously, a plurality of transition dipole moments are composed of one or more dichroic dyes, and these dyes are mixed with the liquid crystal in a guest-host arrangement. For the permanent transition dipole moments, the liquid crystal can be fixed by a curing process. The dichroic dye molecules are usually oriented parallel to the liquid crystal molecules.

[0132] Exemplarily, the first preferred direction can form an angle of 0° to 45° with the surface normal of the first optical element 1. In addition, the first preferred direction can vary on the surface of the first optical element 1. For the present invention, the average weighted preferred direction is applicable.

[0133] In addition, Figure 2 A schematic diagram showing an exemplary structure of the switchable optical filter 5 in the first embodiment is shown. Among them, the liquid crystal layer 3 is arranged in front of the first optical element 1 along the viewing direction (from top to bottom). In addition, this first embodiment includes a first linear polarization filter X in front of the liquid crystal layer 3 along the viewing direction, and its preferred polarization transmission direction is preferably parallel to the edge of the first optical element 1 (preferably, the lower edge).

[0134] In addition, Figure 3Shows an exemplary normalized transmittance curve of the switchable optical filter 5 in the first (partial) operating mode B1 over a horizontal angle range for the maximum transmittance T1 (schematic diagram simulated based on measured data). For selectable angles, the maximum transmittance T1 (after normalization) can be selected here.

[0135] In addition, Figure 4 Shows an exemplary normalized transmittance curve of the switchable optical filter in the second (partial) operating mode B2 over a horizontal angle range for the minimum transmittance T2 (schematic diagram simulated based on measured data). For selectable angles, the minimum transmittance T2 (after normalization) can be selected here.

[0136] Figure 5 Shows an exemplary normalized transmittance curve of the switchable optical filter in the third (partial) operating mode B3 over a horizontal angle range for the first intermediate transmittance T3 (schematic diagram simulated based on measured data). For selectable angles, the first intermediate transmittance T3 (after normalization) can be selected here.

[0137] In addition, Figure 6 Shows an exemplary normalized transmittance curve of the switchable optical filter in the third (partial) operating mode B3 over a horizontal angle range for the second intermediate transmittance T3 (schematic diagram simulated based on measured data). For selectable angles, the second intermediate transmittance T3 (after normalization) can be selected here.

[0138] Figure 7 Shows an exemplary normalized transmittance curve of the switchable optical filter in the third (partial) operating mode B3 over a horizontal angle range for the third intermediate transmittance T3 (schematic diagram simulated based on measured data). For selectable angles, the third intermediate transmittance T3 (after normalization) can be selected here.

[0139] Exemplarily, according to Figures 3 to 7 the curve shown, it can be generated with reference to Figure 1b and Figure 2 based on the third embodiment explained above.

[0140] In addition, in the fourth embodiment, the switchable optical filter 5 further includes the first optical element 1 with reference to FIG. 1 and Figure 2 which includes:

[0141] a plurality of light-absorbing transition dipoles, which are arranged in a layer with a thickness of at least 0.2 microns,

[0142] Among them, multiple transition dipole moments are arranged parallel to an optional first preferred direction of the first optical element 1 with a tolerance of at most 20° in the first state or fluctuate around the first preferred direction. The first preferred direction is set at a predetermined angle α with respect to the perpendicular bisector of the first optical element 1. The angle α is measured in an optional first plane containing the perpendicular bisector.

[0143] So that the light incident on the first optical element 1 is transmitted or at least partially absorbed according to the incident direction and polarization state of the light with respect to the first optical element 1.

[0144] A liquid crystal layer having a plurality of liquid crystal molecules is disposed in front of or behind the first optical element 1 along the viewing direction. The orientation of the plurality of liquid crystal molecules can be affected pixel by pixel by a locally controllable electric field, so that the liquid crystal layer 3 affects the polarization state of the light passing through the liquid crystal layer according to the individually pixel-selectable orientation of the plurality of liquid crystal molecules. Among them, the locally controllable electric field is controlled by a control circuit, and the control circuit can be controlled by a plurality of digital signals. Among them, the plurality of digital signals exist pixel by pixel, and at least at one time point, at least one maximum digital signal, one minimum digital signal, and one digital signal between the maximum digital signal and the minimum digital signal are selected.

[0145] In the case where the liquid crystal layer 3 is disposed in front of the first optical element 1 along the viewing direction, a first linear polarization filter X in front of the liquid crystal layer 3 along the viewing direction.

[0146] So that at a time point, when the control circuit is controlled by at least three digital signals, at multiple different positions on the switchable optical filter 5, for an optional angle that is the same for multiple different positions on the switchable optical filter 5, at least three different values of the transmittance are generated, that is, the minimum value T2, the intermediate value T3, and the maximum value T1 of the transmittance.

[0147] Exemplarily, the corresponding digital signal can correspond to one of 256 gray levels, for example, which is stored in a bitmap file. Optionally, these digital signals can be dynamically adjusted. Such digital signals can also be used in the third embodiment to generate the electronic control of the first electric field EF1, the second electric field EF2, and the third electric field EF3, but are also used in the aforementioned first embodiment and second embodiment, the corresponding modifications of the dual-cell panel structure, or other embodiments. Figure 8 Schematic diagram of an exemplary digital signal corresponding to one of 256 gray levels in a bitmap in the prior art. When applied according to the Figure 8 bitmap in the fourth implementation variant, when the observer slightly moves the head (for example, a few centimeters), a clearly visible edge between the left region in the first working mode B1 and the right region in the second working mode B2 can be seen.

[0148] and Figure 9a is another schematic diagram of an exemplary digital signal corresponding to one of the 256 gray levels in the bitmap, wherein when such a bitmap is used in the fourth embodiment, the visibility of the vertical edges between regions of different operating modes is reduced.

[0149] and Figure 9b is another schematic diagram of an exemplary digital signal corresponding to one of the 256 gray levels in the bitmap, wherein when such a bitmap is used in the fourth embodiment, the visibility of the horizontal edges between regions of different operating modes is reduced.

[0150] and Figure 10 is another schematic diagram of an exemplary digital signal corresponding to one of the 256 gray levels in the bitmap, wherein when such a bitmap is used in the fourth embodiment, the radial visibility of the transition between regions of different operating modes is reduced.

[0151] There are also several other embodiments of such bitmaps and digital signals.

[0152] Particularly preferably, in all embodiments, for the same angle, at least three mutually different values of the transmittance are respectively generated at a plurality of positions of the switchable optical filter 5, preferably, the plurality of positions are directly adjacent. That is, for a fixed angle, the transmittance values decrease from the maximum value to the minimum value, or conversely increase, along a selectable straight line on the surface of the switchable optical filter 5. Because at least the intermediate value of the transmittance is still spatially located therebetween, a smoother transition of the transmittance values from the minimum value to the maximum value (or vice versa) can be achieved.

[0153] As described above, it is necessary to set more than three transmittance values (for example, five, eight or more) to make the above transition more continuous and visually more comfortable.

[0154] For all the foregoing embodiments, the same technical effect applies: at a selectable angle that is usually corresponding to the angle α but can also be set to other values (for example, at a 45° angle in the horizontal direction of the observer, that is, when the position on the switchable optical filter 5 is in the privacy mode), the local position of the minimum transmittance T2 is not immediately adjacent to the position of the maximum transmittance T1, but at least one position that reflects the intermediate transmittance value T3 at the given angle, or at least one of the plurality of values of the transmittance located therebetween as described above.

[0155] Generally speaking, the term "position" refers to a two-dimensional coordinate position, which (if any) respectively indicates the same X coordinate and Y coordinate on the surface of the first optical element 1 and the switchable optical filter 5. Therefore, "position" can be used synonymously for both the first optical element 1 and the switchable optical filter 5.

[0156] The present invention achieves the proposed object: it is intended to describe an optical filter in which light incident on the optical filter is selectively transmitted or partially or (almost) completely absorbed at different positions on the optical filter or on a screen having the optical filter. Herein, in order to prevent visible edges from occurring during partial switching of at least three operating modes B1, B2, and B3, and in particular, local conversion can be performed for a specific angle or direction. In addition, a corresponding screen and lighting device are also described, the angle-dependent brightness distribution of which can be partially and regionally changed. Herein, it is also possible to prevent visible edges from occurring between regions in different modes.

[0157] The above-mentioned present invention can be used in combination with an image display device and is applicable to scenarios where it is necessary to display and / or input private data. For example, entering a PIN or displaying data on an ATM or payment terminal, entering a password, or reading an email on a mobile device. As described above, the present invention can also be applied to a passenger vehicle to selectively avoid image content from interfering with the driver or co-driver.

[0158] Reference Signs

[0159] 1 First optical element

[0160] 3 Liquid crystal layer

[0161] 5 Switchable optical filter

[0162] P P-polarized light

[0163] S S-polarized light

[0164] T1 Maximum transmittance

[0165] T2 Minimum transmittance

[0166] T3 Intermediate transmittance

[0167] X Polarization filter

Claims

1. A switchable optical filter (5), comprising: A device for selectively influencing the angle-dependent transmittance of the incident light on the switchable optical filter (5), characterized in that, at least at one point in time, at a plurality of different positions on the switchable optical filter (5), for a selectable angle that is the same for a plurality of different positions on the switchable optical filter (5), the device for influencing the angle-dependent transmittance produces at least three mutually different values of the transmittance for at least one direction of the hemisphere, namely, the minimum value, the intermediate value, and the maximum value of the transmittance.

2. The switchable optical filter (5) according to claim 1, characterized in that, The device for influencing the angle-dependent transmittance of the switchable optical filter (5) includes at least one guest-host liquid crystal arrangement or polymer-dispersed liquid crystal each having a plurality of liquid crystal molecules, wherein the orientations of the plurality of liquid crystal molecules respectively determine the angle-dependent transmittance in the switchable optical filter (5), and the orientations of the plurality of liquid crystal molecules are different at the plurality of different positions on the switchable optical filter (5).

3. The switchable optical filter (5) according to claim 1, characterized in that, The device for influencing the angle-dependent transmittance in the switchable optical filter (5) is integrated in a dual-cell structure or a multi-cell structure, wherein, in the dual-cell structure or the multi-cell structure, the orientations of the plurality of liquid crystal molecules respectively responsible for the variable angle-dependent transmittance are different at the plurality of different positions on the switchable optical filter (5).

4. The switchable optical filter (5) according to claim 1, comprising: A first optical element (1), comprising: a plurality of light-absorbing transition dipoles, which are arranged in a layer with a thickness of at least 0.2 micrometers, wherein the plurality of transition dipoles are arranged parallel to a selectable first preferred direction of the first optical element (1) or fluctuate around the first preferred direction with a tolerance of at most 20° at least in a first state, the first preferred direction is set at a predetermined angle α with respect to the perpendicular bisector of the first optical element (1), and the angle α is measured in a selectable first plane containing the perpendicular bisector, so that light incident on the first optical element (1) with an incident direction and a polarization state is transmitted or at least partially absorbed according to the incident direction and the polarization state of the light with respect to the first optical element (1); a device for selectively applying at least a first electric field (EF1), a second electric field (EF2), and a third electric field (EF3), wherein the first electric field (EF1), the second electric field (EF2), and the third electric field (EF3) can all be applied differently at a plurality of different positions on the switchable optical filter (5); a liquid crystal layer (3), which is arranged in front of or behind the first optical element (1) along the viewing direction, the first electric field (EF1), the second electric field (EF2), and the third electric field (EF3) are all applied to the liquid crystal layer (3), and the polarization state of the light passing through the liquid crystal layer (3) is affected depending on the electric field; a first linear polarization filter (X), which is arranged in front of the liquid crystal layer (3) along the viewing direction when the liquid crystal layer (3) is arranged in front of the first optical element (1) along the viewing direction, such that the transmission characteristics of the switchable optical filter (5) are different at each position between a first operating mode B1 in which the first electric field (EF1) is applied, a second operating mode B2 in which a second electric field (EF2) is applied, and at least one third operating mode B3 in which a third electric field (EF3) is applied, wherein the respective transmissivities in the first operating mode B1, the second operating mode B2, and the third operating mode B3 are each represented as a first transmissivity T B1 (β) corresponding to the first operating mode B1, a second transmissivity T B2 (β) corresponding to the second operating mode B2, and a third transmissivity T B3 (β) corresponding to the third operating mode B3, the first transmissivity, the second transmissivity, and the third transmissivity are all related to the angle β and normalized such that the values of the transmissivities satisfy T B1 (α) = 1, T B2 (α) = 1, and T B3 (α) = 1 wherein, In the case where light is incident on the first optical element (1) at the angle β satisfying β = α - 40° or β = α + 40°, at a plurality of positions in the first operating mode B1 in which the first electric field (EF1) is applied, the s-polarization component of the light is transmitted with at least a first transmittance value T B1 (β) ≥ 0.25, In the case where light is incident on the first optical element (1) at the angle β satisfying β = α - 40° or β = α + 40°, at a plurality of positions in the second operating mode B2 where the second electric field (EF2) is applied, the p-polarization component of the light is transmitted at a normalized second transmittance value T B2 (β) ≤ 0.2, and When the light is incident on the first optical element (1) at the angle β satisfying β = α - 40° or β = α + 40°, at a plurality of positions in the third operating mode B3 where the third electric field (EF3) is applied, the light is transmitted with a normalized third transmittance value T B2 (β) < T B3 (β) < T B1 (β).

5. The switchable optical filter (5) according to claim 1, comprising: A first optical element (1), comprising: A plurality of light-absorbing transition dipoles, which are arranged in a layer with a thickness of at least 0.2 micrometers, wherein the plurality of transition dipoles are arranged parallel to an optional first preferred direction of the first optical element (1) or fluctuate around the first preferred direction with a tolerance of at most 20° at least in a first state, and the first preferred direction is set at a predetermined angle α with respect to the perpendicular bisector of the first optical element (1), and the angle α is measured in an optional first plane containing the perpendicular bisector. So that the light incident on the first optical element (1) is transmitted or at least partially absorbed according to the incident direction and the polarization state of the light with respect to the first optical element (1). A liquid crystal layer (3) having a plurality of liquid crystal molecules, which is arranged in front of or behind the first optical element (1) along the viewing direction, and the orientation of the plurality of liquid crystal molecules can be affected pixel by pixel by a locally controllable electric field, so that the liquid crystal layer (3) affects the polarization state of the light passing through the liquid crystal layer (3) according to the individually pixel-selectable orientation of the plurality of liquid crystal molecules. Wherein the locally controllable electric field is controlled by a control circuit, and the control circuit can be controlled by a plurality of digital signals, wherein the plurality of digital signals exist pixel by pixel, and at least at one time point, at least one maximum digital signal, one minimum digital signal, and one digital signal between the maximum digital signal and the minimum digital signal are selected. A first linear polarization filter (X), which is located in front of the liquid crystal layer (3) along the viewing direction when the liquid crystal layer (3) is arranged in front of the first optical element (1) along the viewing direction, so that at the time point, when the control circuit uses the at least three digital signals for control, at multiple different positions on the switchable optical filter (5), at least three different values of the transmittance are generated for an optional angle that is the same for multiple different positions on the switchable optical filter (5), that is, the minimum value, the intermediate value, and the maximum value of the transmittance.

6. The switchable optical filter (5) according to any one of claims 1 to 5, characterized in that, For the same angle, at least three different values of the transmittance are respectively generated at multiple positions on the switchable optical filter (5), preferably, the multiple positions are directly adjacent.

7. A lighting device for a screen, the lighting device being capable of operating in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode, in the restricted viewing mode, light being emitted at a viewing angle range restricted for a viewer relative to the free viewing mode, the lighting device comprising: A planar extended backlight for emitting light, and A switchable optical filter (5) according to any one of claims 1 to 6, which is arranged in front of the backlight along the viewing direction.

8. A screen, comprising: An image display device; A switchable optical filter (5) according to any one of claims 1 to 6, which is arranged in front of or behind the image display device along the viewing direction.

9. A screen that can be operated in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode, in which light is emitted at a viewing angle range restricted for the viewer relative to the free viewing mode, the screen comprising: A transmissive image display device; A backlight, which is arranged behind the transmissive image display device along the viewing direction, wherein the backlight has an asymmetric light density distribution. A switchable optical filter (5) according to any one of claims 1 to 6, which is arranged in front of or behind the transmissive image display device along the viewing direction. Wherein, the second electric field (EF2) is applied in the second operating mode B2, and the first electric field (EF1) is applied in the first operating mode B1.

10. A switchable lighting device that can be operated in at least a first operating mode B1 for a free viewing mode and a second operating mode B2 for a restricted viewing mode, in which light is emitted at a viewing angle range restricted for the viewer relative to the free viewing mode, the switchable lighting device comprising: A planar extending backlight lamp, which emits light within a limited angular range in a first alternative and within an unrestricted angular range in a second alternative, and A light guide plate arranged in front of the backlight lamp along the viewing direction, which has a plurality of light emitting elements on at least one large surface and / or within its volume; A light source, which is arranged laterally beside at least one narrow side of the light guide plate, Wherein, in the first alternative, the backlight lamp is turned on and the light source is turned off in the second operating mode B2, and at least the light source is turned on in the first operating mode B1, and, in the second alternative, the backlight lamp is turned off and the light source is turned on in the second operating mode B2, and at least the backlight lamp is turned on in the first operating mode B1, Characterized in that the backlight lamp and / or the light guide plate, that is, when one or both of the backlight lamp and the light guide plate emit light, at least at one time point, at a plurality of different positions on the backlight source and / or the light guide plate, for a selectable but identical angle at the plurality of different positions, at least three mutually different brightness values are generated, that is, the minimum value, the medium value, and the maximum value of the brightness.

11. The switchable lighting device according to claim 10, characterized in that, For the identical angle, the at least three mutually different values of the brightness are respectively generated at a plurality of positions on the backlight source and / or the light guide plate, preferably, the plurality of positions are directly adjacent.

12. A switchable screen, at least comprising: An image display device; A device for influencing the angle-dependent brightness of the switchable screen, characterized in that The device for influencing the angle-dependent brightness generates at least three mutually different brightness values, that is, the minimum value, the medium value, and the maximum value of the brightness, at least at one time point, at a plurality of different positions on the switchable screen, for a selectable but identical angle at the plurality of different positions.

Images