Screen for free vision mode and restricted vision mode

Abstract

To provide a screen that can operate in at least two operation modes, an operation mode for a free vision mode and an operation mode for a limited vision mode. [Solution] The present invention comprises a transmissive image display device 1 that modulates incident light to display image content and is capable of operating in at least one first operating mode for a free-viewing mode and a second operating mode B2 for a limited-viewing mode, and an illumination device 2a that is positioned behind the transmissive image display device 1 in the viewing direction of the viewer and is capable of operating in at least two operating modes, an operating mode for the free-viewing mode and an operating mode B2 for the limited-viewing mode, and further comprises a control unit for the transmissive image display device 1 and the illumination device 2a that emits light in an unrestricted viewing angle range in the first operating mode and emits light in a restricted viewing angle range in the second operating mode B2, and that switches between the at least two operating modes.

Description

[Technical Field]

[0001] In recent years, LCD displays have made great strides in offering wider viewing angles. However, there are often situations in which this very wide viewing range can be a drawback. Furthermore, mobile devices such as notebooks and tablet PCs increasingly carry information such as banking data and other personal and confidential information.

[0002] Therefore, it is necessary to limit who can see this sensitive data. For example, when viewing vacation photos or for promotional purposes, a wide viewing angle should be selected to share the information on the display with others. On the other hand, if you want to keep the image information secret, a narrow viewing angle should be selected.

[0003] A similar problem exists in automobile manufacturing: the driver must not be distracted by visual content such as digital entertainment programs while the engine is running, but passengers themselves want to be able to enjoy them while driving, so a screen that can switch between display modes is needed. [Background technology]

[0004] To achieve visual data protection, mobile displays already use additional films based on microlouvers. However, these films are non-switchable and always have to be manually applied first and then removed again. They also have to be carried separately from the display when not in use. Furthermore, the use of such louver films has the significant drawback of light loss.

[0005] US Patent Application No. US5956107A discloses a switchable light source that allows a screen to operate in multiple modes. The drawback is that all light emission is based on scattering, resulting in low efficiency and suboptimal light direction effects. In particular, achieving a focused light cone is not disclosed in detail.

[0006] Chinese patent application CN107734118A describes a screen designed to control the viewing angle using two backlights. The upper backlight emits concentrated light for this purpose. A grid with opaque and transparent areas is specifically cited as a configuration for this. However, this also concentrates the light of the second backlight, which must pass through the first backlight toward the LCD panel, resulting in a significantly narrower viewing angle in public viewing mode, which is intended to provide a wide viewing angle.

[0007] US Patent Application No. US2007 / 030240A1 describes an optical element for controlling the propagation direction of light coming from a backlight, which requires liquid crystals, for example in the form of PDLC, which on the one hand are expensive, but on the other hand PDLC liquid crystals usually require a voltage higher than 60V in their circuits, which raises safety concerns, especially in end-user applications.

[0008] Chinese Patent Application No. CN1987606A also describes a screen designed to use two backlights to control the viewing angle of the screen. It specifically mentions a "first light plate," which must be wedge-shaped to allow the intended focused light to be emitted. It does not disclose the exact details of how to achieve focused light emission under the appropriate angle conditions.

[0009] Furthermore, US Patent Application US2018 / 0267344A1 describes a structure with two flat lighting modules, where the light from the rear lighting module in the viewing direction is collected by a separate structure. After being collected, the light still has to pass through the front lighting module, which has a scattering element. Therefore, strong light collection for anti-peeping purposes cannot be optimally implemented.

[0010] Finally, US Patent Application No. US2007 / 0008456A1 discloses dividing the light emission angle into at least three regions, two of which are normally illuminated, so that a privacy screen using such an illuminated display can be viewed from more than one direction.

[0011] The applicant's international patent application WO 2015 / 121398 A1 describes a screen of the aforementioned type, in which scattering particles are essentially present within the volume of the corresponding light guide for switching modes. However, the polymeric scattering particles selected there have the disadvantage that light is generally emitted from both major surfaces, so that approximately half of the available light is emitted in the wrong direction, i.e., towards the backlight, where it cannot be fully recycled by the structure. Furthermore, the polymeric scattering particles distributed within the volume of the light guide can, in certain circumstances, especially at high concentrations, cause scattering effects that can reduce the anti-peeping effect in the protected mode.

[0012] US Patent Application No. US2020 / 012129A1 discloses an illumination device and a screen that describe two light guides for switching between narrow and wide viewing modes. On the one hand, one of the light guides is formed of a fiber. On the other hand, the scattering structure of the light guide is limited to a specific stripe in the projection direction. This is detrimental to homogeneous image illumination and usually causes undesirable moiré effects in the structure due to interactions with, for example, pixel columns or pixel rows of an overlying liquid crystal panel.

[0013] The drawbacks that are common to all of the above methods and arrangements in principle are that they significantly reduce the brightness of the basic screen, and / or they require active but at least one special optical element for mode switching, and / or they require complex and expensive manufacturing, and / or they reduce the resolution in free viewing mode. Summary of the Invention

[0014] The object of the invention is therefore to describe a screen that allows for the secure display of information by selectively restricting the viewing angle, while in another mode allowing free viewing with as little restriction as possible. In both modes, the highest possible resolution is visible, particularly preferably the native resolution of the screen used. Furthermore, the restricted viewing angle achieves the widest possible range of anti-spying effects without increasing the demands on the lighting device used.

[0015] According to the present invention, this problem is solved by a screen that can operate in at least two operating modes: an operating mode B1 for a free viewing mode and an operating mode B2 for a limited viewing mode. Such a screen includes a transmissive image display device that modulates light incident thereon to display image content and can operate in a first operating mode B1 for the free viewing mode and a second operating mode B2 for the limited viewing mode. In this case, the image display device is a liquid crystal panel.

[0016] An illumination device is arranged behind the transmissive image display device in the viewing direction in which the viewer views the screen. The illumination device is operable in at least two operating modes B1 for a free-viewing mode and at least two operating modes B2 for a limited-viewing mode. In the first operating mode B1, the illumination device emits light over an unrestricted viewing angle range, and in the second operating mode B2, the illumination device emits light over a comparatively restricted viewing angle range.

[0017] The image display device can be designed in two ways. In a first alternative, the image display device comprises a liquid crystal panel with two liquid crystal layers, one of which serves to modulate light to enable the display of image content, and the other of which serves to switch between a wide viewing angle range in a first operating mode B1 for a free-viewing mode and a limited viewing angle range in a second operating mode B2 for a limited-viewing mode. The corresponding arrangement is preferably formed as a module and further comprises a polarizing filter after the rear liquid crystal layer, between the two liquid crystal layers and in front of the front liquid crystal layer.

[0018] A liquid crystal layer that broadens the viewing angle range in a first operating mode B1 for the free-viewing mode and restricts it in a second operating mode B2 for the restricted-viewing mode is positioned in front of the other liquid crystal layer in the viewer's viewing direction, and the viewing angle range is switched by different polarizations for both operating modes B1 and B2. The color-modulated and image-modulated light is then polarization-encoded to determine the viewing angle range, and in operating mode B2, the light is extinguished by at least 90%, preferably 97% or more, from oblique viewing directions by a front polarizing filter that functions as an analyzer, but is not extinguished for perpendicular viewing. For operating mode B1, other polarization characteristics are appropriately modulated to allow light to pass through the analyzer from substantially all incident directions.

[0019] In a second alternative, the image display device includes a dual-view liquid crystal panel that simultaneously displays two selectable image contents at different viewing angles. In a first operating mode B1 for a free-viewing mode, the image contents are identical or different, and in a second operating mode B2 for a restricted-viewing mode, at least one of the image contents is permanently black or monochrome, so that only a black or information-free monochrome image is visible from the corresponding viewing angle range. In this context, a white image is also considered a monochrome image. Dual-view liquid crystal panels known in the prior art include, for example, barrier screens, lenticular, or prism louvers, and display selected pixel groups at different viewing angle ranges. By loading these pixel groups, it is possible to determine which pixels, and therefore which image content, can be perceived from which viewing angle range.

[0020] The screen further includes a control unit for the transmissive image display device and the illumination device for switching between at least two operating modes B1 and B2. The control unit for the transmissive image display device and the illumination device for switching between at least two operating modes B1 and B2 preferably includes an electronic device that preferably, but not necessarily, switches between both operating modes B1 and B2 for the image display device and the illumination device 2a, respectively, in a synchronized manner.

[0021] The lighting device comprises a planar backlight and a plate-like light guide arranged in front of the backlight in the viewing direction and having two opposing main faces joined via a narrow side, the light guide having an output element on and / or within the volume of at least one of the main faces, and a light source arranged laterally on the narrow side of the light guide.

[0022] The shape, number per unit area, and extension of the emitting elements are selected such that the horizontal and vertical dimensions of each emitting element are smaller than the minimum width and height of the smallest pixel of the image display device. The pixels will typically be color subpixels, but may also be monochrome pixels. Preferably, the shape, number per unit area, and extension of the emitting elements are further selected such that, in a projection direction parallel to the surface normal of the light guide, for at least one subset of the smallest pixels of the image display device, a portion or the entire surface of at least two emitting elements is respectively located below each smallest pixel of this subset of the image display device. The subset may in particular include all the smallest pixels.

[0023] In a first alternative, the backlight emits light over a limited angular range. In this case, the light guide is at least 50% transparent to the light emerging from the backlight. In a second operating mode B2, the backlight is on and the light source is off, while in a first operating mode B1, at least the light source is on.

[0024] In contrast to this, in the second alternative, the light guide emits light incident laterally on at least one of its narrow sides over a limited angular range, where the light guide is at least 30% transparent to the light emerging from the backlight. Unlike the first alternative, here in the second operating mode B2 the light source is on and the backlight is off, whereas in the first operating mode B1 at least the backlight is on.

[0025] In either alternative, the viewing angle range and the restricted angle range overlap by at least 50%, preferably by at least 75%, and particularly preferably by at least 85%. The greater the overlap, the better the protection against spying, and the brightness curve in reality usually does not exhibit a stepped behavior, but rather a continuous course resembling a bell curve.

[0026] A particular advantage of combining these measures for implementing the two operating modes B1 and B2 is that the effects of restricting the viewing angle range, particularly for the second operating mode B2, of both the image display device and the lighting device complement each other, resulting in a particularly strong anti-spy effect in this restricted viewing mode. For this purpose, it is advantageous if the viewing angle ranges of the image display device and the lighting device for the second operating mode B2 overlap strongly or are identical.

[0027] Preferably, the lighting device emits light in the second operating mode B2 into a definable limited viewing angle range, so that outside this limited viewing angle range, measured in a selectable plane intersecting the screen, there is a maximum luminance value that is at most 50%, preferably at most 20%, particularly preferably at most 10% of the maximum luminance present inside the limited viewing angle range. Such a plane for defining the measurement values ​​can advantageously, for example, contain the central normal of the screen and be located parallel to the bottom edge of the screen with a tolerance of up to 7 degrees.

[0028] A "wide" viewing angle range is considered to be, for example, an angular range of about -60° to +60° or about -60° to +30°, measured in the above-mentioned plane, and without limiting generality, the 0° angle preferably coincides with the central perpendicular. A "limited" viewing angle range would be, for example, about -30° to +30° or about -20° to +30° (asymmetrical options are possible), or about -10° to +50°. In principle, any range smaller than the half-space in front of the screen can be considered a limited viewing angle range.

[0029] Furthermore, it may be advantageous in some applications if the limited viewing angle range is asymmetrically configured around the surface normal of the backlight. The asymmetric configuration is preferably performed in a selectable preferred direction. This is particularly useful in vehicle applications, for example, when the screen according to the present invention is positioned as a so-called center information display on the dashboard, approximately centered between the driver and passenger. In this case, the limited viewing angle range that is exclusively available to the passenger in operating mode B2 must be designed asymmetrically, i.e., toward the passenger. The preferred direction in which the asymmetry is configured corresponds here to the horizontal direction.

[0030] Furthermore, it would be advantageous if at least one optical component, preferably a diffuser plate (which may have isotropic or anisotropic properties) and / or a prism film (which may also have an isotropic or anisotropic effect), is arranged between the image display device and the light guide.

[0031] Furthermore, it is conceivable that the distribution of the output elements on at least one major surface and / or within the volume of the light guide is configured so that light incident from a light source into the light guide and output from the light guide by the output elements satisfies the following conditions: 1) at least 50% of the amount of light emitted at one of the major surfaces within an angular range of −50° to +50° relative to a surface normal to the major surface is emitted within an angular range of −20° to +20° relative to one or two set preferred directions perpendicular to each other and to the surface normal, and / or at least 70% of the amount of light emitted at one of the major surfaces within an angular range of −50° to +50° relative to a surface normal to the major surface is emitted within an angular range of −30° to +30° relative to one or two set preferred directions, and 2) at least 50% of the amount of light output from the light guide is output in a direction away from or towards the backlight.

[0032] The lighting device may additionally include collimating films at appropriate locations within the structure, for example lenticular or prismatic louvers above or below the plate-like light guide.

[0033] The light guide preferably consists of a transparent thermoplastic or thermoelastic polymer, such as plastic or glass. For example, the light guide or its substrate may contain at least 40% by weight, preferably at least 60% by weight, of polymethyl methacrylate, based on its weight. Alternatively, it may be, for example, polycarbonate (PC).

[0034] During the manufacture of a light guide, output elements can be distributed within or on the light guide in various ways, depending on the adaptable and configurable requirements for light output. Output elements are locally limited structural changes within the volume and / or on the surface of the light guide. Therefore, the term "output elements" explicitly excludes additional optical layers attached to the surface of the light guide, such as diffusing layers, reflective layers, (dual) brightness enhancement layers, collimating layers, or polarization recycling films ((dual) brightness enhancement films - (D)BEF) or reflective polarizers. These additional layers, which do not fall under the term "output elements," are only bonded to the light guide at their edges, if at all, and often simply rest loosely on the light guide in the area of ​​the main surfaces, without forming a physical unit with the light guide. In contrast, lacquers applied to the main surfaces and bonded to the light guide by chemical reactions or other forces (e.g., van der Waals forces) form a physical unit that can no longer be separated from the light guide. Therefore, such lacquers are not counted as additional layers in the above sense.

[0035] Since the structure of the output elements can be predefined, the effect of each output element is at least approximately known, and the configurable distribution of the output elements allows the properties of the light guide or of the light leaving the light guide to be precisely determined.

[0036] The required characteristics of the output elements essential to the invention in terms of number per unit area, shape, three-dimensional orientation and extension, and distribution on at least one major surface and / or within the volume of the light guide can be determined using optical simulation software, e.g., Synopsys "LightTools" or other suppliers, and then physically implemented accordingly.

[0037] Advantageously, the distribution of the emitting elements on at least one major surface and / or within the volume of the light guide is set so that the emitted light achieves a luminance homogeneity of 70% over at least 70% of the surface of the light guide. For this purpose, the luminance homogeneity is defined as L V min / L V max It can be defined as the ratio of the minimum brightness to the maximum brightness of a surface. Another applicable standard for measuring brightness uniformity is defined in the "Uniformity Measurement Standard for Displays V1.3" by the "German Automotive OEM Working Group Displays". The output elements can be provided on both main surfaces and / or additionally optionally within the volume.

[0038] The exit elements for exiting light at at least one main surface of the light guide preferably consist of microlenses and / or microprisms and / or diffractive structures and / or three-dimensional structure elements and / or scattering elements having an extension of at most 50 micrometers. In the case of diffractive structures, this can be, for example, a hologram or a grating / diffraction grating.

[0039] However, the emitting elements themselves can also only have the external shapes of microlenses, microprisms, scattering elements, and / or diffractive structures. In that case, they can be specifically designed as cavities formed within the volume of the light guide. The cavities can be empty, but are preferably filled with a gas, liquid, or solid material. This material has a refractive index different from, and preferably lower than, that of the material used in the light guide. The filling material and the choice of material can influence the conduction and emission of light. Alternatively or complementary, the haze value of the material is preferably different from, and higher than, that of the material used in the light guide. The advantage of these designs is a high light emission efficiency.

[0040] Alternatively, and technically simpler, the cavity can be formed when the light guide is formed by bonding two substrate layers, preferably of the same type. The bonding can be chemical, physical or adhesive. The cavity is formed as a cutout in the material at the interface of at least one of the substrate layers.

[0041] If the exit elements are attached to at least one main surface of the light guide, they are preferably made of plastic or glass, in which a structure is imprinted by a tool. This is possible, for example, in mass production, by applying a UV-curable material, such as a lacquer or a monomer, to the substrate of the light guide, which is then structured by a tool and hardened by UV radiation, e.g., polymerized. Other materials that are hardened by radiation can also be used. The formation of the cutouts for the exit elements can be achieved, for example, mechanically, by lithography or printing, or by applying, converting, removing, or dissolving a material.

[0042] In this way, for example, grating structures, microprisms (convex outwardly facing plastic components at the surface and / or concave indentations or recesses in the surface layer of the structured plastic), three-dimensional structural elements of other shapes, or even microlenses can be realized in a cost-effective and mass-producible manner. Concavely and convexly shaped structures can be used equally well.

[0043] The backlight consists, for example, of a surface emitter, preferably another light guide with other light sources arranged laterally or at the rear, and at least one light collimator, such as at least one prismatic film and / or at least one privacy filter (lamella filter), integrated into and / or arranged in front of the surface emitter. The backlight can therefore essentially be configured as an LED backlight, for example as a so-called direct LED backlight, an edge LED backlight, an OLED or other surface emitter, onto which, for example, at least one permanent privacy filter (with microlamella) is applied.

[0044] An advantage of the present invention is that the requirements for backlighting are generally reduced compared to the prior art. That is, by combining the viewing-limiting effects of the image display device and the lighting device (with a built-in backlight), it is not necessary to achieve a privacy contrast ratio of 100:1 or more as in the prior art. In fact, even a backlight ratio of 10:1 is extremely useful for significantly improving the anti-peeping effect of the image display device in operation mode B2. For example, the residual light of 0.5% of the maximum brightness of the image display device at an angle of -40 degrees in operation mode B2 can be reduced to 0.05% by simply having the lighting device emit 10% of the maximum brightness at an angle of -40 degrees (rather than the more difficult-to-achieve value of 1%).

[0045] Above the screen and / or at least one major surface of the light guide, and also at least one privacy filter (if present), means for reducing or controlling reflections, such as an anti-reflective coating, may be disposed.

[0046] Particularly advantageously, the screen according to the invention can be used in a vehicle to selectively display image content to a passenger only in operating mode B2, and to both the driver and passenger simultaneously in operating mode B1, which is useful, for example, when the passenger is viewing entertainment content that may distract the driver.

[0047] The screens of the present invention can also be used in ATMs, payment terminals, mobile devices, etc. to enter or display sensitive data such as PINs, emails, SMS, passwords, etc.

[0048] In all the above embodiments, the light source can be an LED or an LED line or a laser diode. Other variations are possible and are within the scope of the present invention.

[0049] Furthermore, the desired restricted angle range for restricted viewing mode B2 can be defined and implemented independently for the horizontal and vertical directions. For example, in an ATM where people of different heights will be viewing the same image, it may make sense to have a larger vertical angle than the horizontal (or even no restriction at all), but with a strong or complete restriction on side viewing. In contrast, for point-of-sale payment terminals, security regulations often require restricted viewing in mode B2 in both the horizontal and vertical directions.

[0050] In principle, the performance of the present invention can be maintained even if the above parameters are varied within certain ranges.

[0051] It is clear that the features mentioned above and those described below can be used not only in the combinations described, but also in other combinations or alone without departing from the scope of the invention.

[0052] The present invention will now be described in detail by way of examples with reference to the accompanying drawings, which also disclose the essential features of the present invention. These examples are merely illustrative and should not be construed as limiting the invention. For example, a description of an embodiment having a large number of elements or components should not be construed as meaning that all of these elements or components are required for implementation. Rather, other embodiments may include alternative, fewer, or additional elements or components. Elements or components of different embodiments may be combined with one another unless otherwise specified. Modifications and variations described with respect to one embodiment may also be applied to other embodiments. To avoid redundancy, identical or corresponding elements in different figures will be given the same reference numerals and will not be described repeatedly. [Brief explanation of the drawings]

[0053] [Figure 1] FIG. 1 is a diagram showing the principle of emitting light laterally incident on a light guide from the lower main surface of the light guide where the emitting elements are located, and the light leaves the light guide at the upper main surface.

[0054] [Figure 2] FIG. 2 is a diagram showing the principle of emitting light laterally incident on a light guide from the upper main surface of the light guide where the emitting elements are located, and the light leaves the light guide at the upper main surface.

[0055] [Figure 3] FIG. 3 is a principle diagram of the screen of the first embodiment in the operating mode B1 relative to the free-viewing mode.

[0056] [Figure 4] FIG. 4 is a principle diagram of the screen of the first embodiment in the second operating mode B2 for the limited viewing mode;

[0057] [Figure 5] FIG. 5 is a principle diagram of an exemplary shape of the output element.

[0058] [Figure 6] FIG. 6 is a principle diagram of the screen of the second embodiment in the first operating mode B1 for free viewing mode.

[0059] [Figure 7] FIG. 7 is a principle diagram of the screen of the second embodiment in the second operating mode B2 for the limited viewing mode. DETAILED DESCRIPTION OF THE INVENTION

[0060] FIG. 1 shows a schematic diagram of the principle of light entering the light guide 3 laterally from a light source 4 and exiting through the lower major surface of the light guide 3, where an output element 6 is located. However, the emitted light leaves the light guide 3 at the upper major surface. Here, the light is horizontally emitted from the upper major surface of the light guide 3 at a wide angle (greater than 60°). The location of the output element 6 is indicated by the numeral 6, but the actual output element 6 is not shown here because it would be microscopically small. Thus, light enters the light guide 3 laterally from the light source 4, e.g., an LED. The incident light rays (shown in bold) bounce off the outer wall of the light guide 3 by total internal reflection and eventually (possibly repeatedly) strike the output element 6 to achieve the desired output. The output is shown schematically as a thin ray. The representation in FIG. 1 is significantly simplified for clarity; in reality, a large number of ray paths are realized within the light guide 3. Furthermore, refraction at refractive index transition surfaces is not taken into account.

[0061] Figure 2 shows a principle diagram for light entering the light guide 3 laterally from a light source 4 and exiting from the upper main surface of the light guide 3, on which the output elements 6 are arranged. Here too, the light leaves the light guide 3 through the upper main surface. The explanation given for Figure 1 applies accordingly. The only technical difference here is the position and, if applicable, the configuration of the output elements 6, which are now located above the light guide 3, so that the light exits directly upwards. The exiting light does not have to pass through the light guide 3 again, as in the situation in Figure 1.

[0062] The following Figures 3, 4, 6 and 7 are cross-sectional views.

[0063] FIG. 3 shows a principle diagram of the display screen 1a of the first embodiment in a first operating mode B1 for the free viewing mode, and FIG. 4 shows a principle diagram of the display screen of the first embodiment in a second operating mode B2 for the limited viewing mode. The display screen 1a, which can operate in at least two operating modes, the first operating mode B1 for the free viewing mode and the second operating mode B2 for the limited viewing mode, includes a transmissive image display device 1 that modulates incident light to display image content. The transmissive image display device 1 can operate in at least two operating modes, the first operating mode B1 for the free viewing mode and the second operating mode B2 for the limited viewing mode. The image display device 1 is a liquid crystal panel. An illumination device 2a is located behind the transmissive image display device 1 in the viewer's viewing direction, and can operate in at least two operating modes, the first operating mode B1 for the free viewing mode and the second operating mode B2 for the limited viewing mode. The illumination device 2a emits light over an unrestricted viewing angle range in the first operating mode B1, and emits light over a restricted viewing angle range in the second operating mode B2. Furthermore, the screen 1a also includes a control unit for the transmissive image display device 1 and the illumination device 2a for switching between at least two operating modes: an operating mode B1 as exemplarily shown in FIG. 3 and an operating mode B2 as exemplarily shown in FIG. 4.

[0064] In the first embodiment shown here, the lighting device 2a comprises a planar backlight 2 emitting light in a limited angular range, and a plate-like light guide 3 located in front of the backlight in the viewing direction and having output elements 6 on at least one major surface and / or within its volume. The light guide 3 is at least 50% transparent to the light emerging from the backlight 2. Furthermore, a light source is arranged laterally on the narrow side of the light guide. In operating mode B2, the backlight is on and the light source is off, whereas in operating mode B1 at least the light source is on.

[0065] In Fig. 3, the thick arrows indicate that light (thin arrows) from the illumination device 2a passes through the image display device 1 in all directions. Conversely, in Fig. 4, the thick arrows indicate that the image display device 1 transmits light only within a limited viewing angle range (thick dashed arrows indicate that no light is transmitted there, or that only 10% of the light is transmitted there). At the same time, only light within a limited viewing angle range reaches the image display device 1 from the illumination device 2a.

[0066] A particular advantage of combining these measures for implementing the operating modes B1 and B2 is that the effects of restricting the viewing angle range, particularly for the second operating mode B2, of both the image display device and the lighting device complement each other, resulting in a particularly strong anti-spy effect in this restricted viewing mode. For this purpose, it is advantageous if the viewing angle ranges of the image display device and the lighting device for the second operating mode B2 overlap strongly or are identical.

[0067] A control unit (not shown) for the transmissive image display device 1 and the illumination device 2a for switching between the at least two operating modes B1 and B2 preferably includes electronics that preferably, but not necessarily, switch between the two operating modes B1 and B2 for both the image display device 1 and the illumination device 2a, respectively, in a synchronized manner.

[0068] In a first alternative, the image display device 1 comprises a liquid crystal panel having two liquid crystal layers, one of which serves to modulate light to enable the display of image content, and the other of which serves to switch between a wide viewing angle range in a first operating mode B1 for a free-viewing mode and a limited viewing angle range in a second operating mode B2 for a limited-viewing mode. The corresponding arrangement, preferably formed as a module, further comprises a polarizing filter after the rear liquid crystal layer, between the two liquid crystal layers and in front of the front liquid crystal layer.

[0069] In a second alternative, the image display device 1 includes a dual-view liquid crystal panel that simultaneously displays two selectable image contents in different viewing angle ranges, and in a first operating mode B1 for a free viewing mode, both image contents are the same or different, and in a second operating mode B2 for a limited viewing mode, at least one of the image contents is permanently black or a monochrome (including white) image, so that only a black or monochrome image without information is visible from the corresponding viewing angle range.

[0070] A liquid crystal layer serving to switch the viewing angle range between a first operating mode B1 for the free-viewing mode and a second operating mode B2 for the restricted-viewing mode is positioned in front of the other liquid crystal layer in the viewer's viewing direction, and the viewing angle range is switched by different polarizations for both operating modes B1 and B2. The already color-modulated and image-modulated light is then polarization-encoded to determine the viewing angle range, and in operating mode B2, it is extinguished by at least 90%, preferably 97% or more, from oblique viewing directions by a front polarizing filter (which functions as an analyzer), but is not extinguished for perpendicular viewing. For operating mode B1, other polarization properties are appropriately modulated to allow light to pass through the analyzer from substantially all incident directions.

[0071] Preferably, the lighting device 2a emits light in the second operating mode B2 within a definable limited viewing angle range, so that outside this limited viewing angle range, measured in a selectable plane intersecting the screen 1a, there exists a maximum luminance value that is at most 50%, preferably at most 20%, particularly preferably at most 10% of the maximum luminance present within the limited viewing angle range. Such a plane for defining the measurement values ​​can advantageously be located, for example, containing the central normal of the screen and parallel to the lower edge of the screen 1a with a tolerance of up to 7 degrees.

[0072] What is considered a "wide" viewing angle range is, for example, an angular range of about -60° to +60° or about -60° to +30°, measured in the plane mentioned above, and without limiting generality, the 0° angle preferably coincides with the central normal. A "limited" viewing angle range would be, for example, about -30° to +30°, or about -20° to +30° (asymmetrical possible), or about -10° to +50°.

[0073] The exit elements 6 for exiting light at at least one main surface of the light guide 3 preferably consist of microlenses and / or microprisms and / or diffractive structures and / or three-dimensional structure elements and / or scattering elements having an extension of at most 100 micrometers in their largest dimension, preferably at most 50 micrometers. In the case of diffractive structures, this can be, for example, a hologram or a grating / diffraction grating.

[0074] 5 shows in this respect a principle diagram of an exemplary form of the exit elements 6, here in the form of microprisms. Exit elements of this type can be distributed uniformly or preferably non-uniformly (i.e., with exceptions, in greater number per area with increasing distance from the light source 4) on one or both main faces and / or within the volume of the light guide 3, for example as air-filled recesses. Other forms of exit elements 6 are of course also possible.

[0075] The shape, number per unit area and extension of the emitting elements are selected such that the horizontal and vertical dimensions of each emitting element are smaller than the minimum width and height of the smallest pixel of the image display device. The pixels will typically be color subpixels, but may also be monochrome pixels. Preferably, the shape, number per unit area and extension of the emitting elements are further selected such that, in the projection direction parallel to the surface normal of the light guide, for at least one subset of the smallest pixels of the image display device 1, a portion or the entire surface of at least two emitting elements is respectively located below each smallest pixel of this subset of the image display device. The subset may in particular include all the smallest pixels.

[0076] Furthermore, FIG. 6 shows a principle diagram of a screen 1a of a second embodiment in a first operating mode B for a free-viewing mode, and FIG. 7 shows a principle diagram of the screen 1a in a second operating mode B2 for a limited-viewing mode. This embodiment is an alternative to the embodiment shown in FIGS. 3 and 4. The illumination device 2a of the screen 1 shown in FIGS. 6 and 7 includes at least one planar backlight 2 and a plate-like light guide 3 located in front of the backlight 2 in the viewing direction. The light guide 3 has an emission element 6 on at least one major surface and / or within its volume. Here, the light guide 3 is at least 30% transparent to light emitted from the backlight 2, and the light guide 3 emits light incident laterally on at least one of its narrow sides within a limited angular range. Furthermore, a light source 4 is arranged laterally on the narrow side of the light guide 3. In a first operating mode B1 for a limited viewing mode according to FIG. 6, at least the backlight 2 is on, whereas in a second operating mode B2 for an unlimited viewing mode according to FIG. 7, the light source 4 is on and the backlight 2 is off.

[0077] In Fig. 6, the thick arrows indicate that light (thin arrows) from the illumination device 2a passes through the image display device 1 in all directions. Conversely, in Fig. 7, the thick arrows indicate that the image display device 1 transmits light only within a limited viewing angle range (thick dashed arrows indicate that no light is transmitted there, or that only 10% of the light is transmitted there). At the same time, only light within a limited viewing angle range reaches the image display device 1 from the illumination device 2a.

[0078] The lighting device 2 a may further include collimating films at suitable locations within the structure, for example lenticular or prismatic louvers above or below the plate-like light guide 3 .

[0079] The light guide 3 preferably consists of a transparent thermoplastic or thermoelastic polymer, such as plastic or glass. For example, the light guide or its substrate may contain at least 40% by weight, preferably at least 60% by weight, of polymethyl methacrylate, based on its weight. Alternatively, it may be, for example, polycarbonate (PC).

[0080] During the manufacture of the light guide 3, the output elements 6 can be distributed in or on the light guide in various ways, depending on the adaptable and configurable requirements for light output. The output elements 6 are locally limited structural changes within the volume and / or on the surface of the light guide. Therefore, additional optical layers attached to the surface of the light guide 3, such as diffusing, reflective, (dual) brightness enhancement, collimating, or polarization recycling layers ((dual) brightness enhancement films - (D)BEF), or reflective polarizers, are expressly excluded from the term "output elements 6." These additional layers, which do not fall under the term "output elements" 6, are only bonded to the light guide 3 at their edges, and in the area of ​​the main surfaces, they often simply rest loosely on the light guide and do not form a physical unit with the light guide 3. In contrast, lacquers applied to the main surfaces and bonded to the light guide 3 by chemical reactions or other forces (e.g., van der Waals forces), form a physical unit that can no longer be separated from each other. Such lacquers therefore do not count as additional layers in the above sense.

[0081] Since the structure of the output elements 6 can be predefined, the effect of each output element 6 is at least approximately known, and the configurable distribution of the output elements 6 allows for precise determination of the properties of the light guide 3 or of the light exiting the light guide 3. The required properties of the output elements 6 essential to the invention, in terms of number per unit area, shape, three-dimensional orientation and extension, and distribution on at least one major surface and / or within the volume of the light guide 3, can be determined using optical simulation software, for example from Synopsys "LightTool" or other suppliers, and then physically implemented accordingly. Output elements 6 can be provided on both major surfaces and / or optionally additionally within the volume of the light guide 3.

[0082] The backlight 2 consists, for example, of a surface emitter, preferably a further light guide with other light sources arranged laterally or at the rear, as well as at least one light collimator, such as at least one prismatic film and / or at least one privacy filter (lamella filter), integrated into and / or arranged in front of the surface emitter. The backlight 2 can therefore essentially be configured as an LED backlight, for example as a so-called direct LED backlight, an edge LED backlight, an OLED or as another surface emitter, onto which, for example, at least one permanent privacy filter (with microlamella) is applied.

[0083] One advantage of the above-described screen is that the requirements for the backlight 2 are generally reduced compared to the prior art. That is, by combining the viewing restriction effects of the image display device 1 and the illumination device 2a (in which the backlight 2 is incorporated), it is not necessary to achieve a privacy contrast ratio of 100:1 or more as in the prior art. In fact, even a 10:1 value for the backlight 2 is extremely useful for significantly improving the anti-peeping effect of the image display device 1 in operation mode B2. In operation mode B2, the residual light of, for example, 0.5% of the maximum brightness at an angle of −40 degrees of the image display device 1 will be reduced to 0.05% if the illumination device simply emits 10% of the maximum brightness at an angle of −40 degrees (rather than 1%, which is a more difficult value to achieve).

[0084] Particularly advantageously, the screen can be used in a vehicle to selectively display image content to passengers only in operating mode B2, or to both the driver and passengers simultaneously in operating mode B1. The former is useful, for example, when passengers want to view entertainment content that may distract the driver. Such screens can also be used to enter or display sensitive data such as PINs, emails, SMS, passwords, etc., at ATMs, payment terminals, mobile devices, etc.

[0085] In all the above embodiments, the light source 4 can be an LED or an LED line or a laser diode. Other variations are also possible and are within the scope of the present invention.

[0086] The lighting device described above and the screen that can be implemented therewith solve the set problem: a screen has been described that allows for the secure display of information with a selectively restricted viewing angle, while in another operating mode, free viewing is possible with as little restricted viewing angle as possible. In both operating modes, the highest possible resolution is visible, i.e., the native resolution of the screen used. Furthermore, the restricted viewing angle allows a wide range of anti-spying effects to be achieved without increasing the demands on the lighting device used.

[0087] The above-described screen can be advantageously used wherever sensitive data is displayed and / or entered, for example, for PIN entry and data display at an ATM or payment terminal, for password entry, or for viewing email on a mobile device, etc. The screen can also be applied in a passenger vehicle, as mentioned above. The above-described embodiment can also be described as follows, but is not limited to the following. [Configuration 1] A screen (1a) that can operate in at least two operation modes: an operation mode B1 for a free vision mode and an operation mode B2 for a limited vision mode; a transmissive image display device (1) that modulates incident light to display image content and is operable in a first operating mode B1 for a free-viewing mode and a second operating mode B2 for a limited-viewing mode, wherein the image display device (1) is a liquid crystal panel; the illumination device (2a) is located behind the transmissive image display device (1) in the viewing direction of a viewer and is operable in at least two operation modes, an operation mode B1 for a free-viewing mode and an operation mode B2 for a limited-viewing mode, wherein the illumination device (2a) emits light in an unrestricted viewing angle range in the first operation mode B1 and emits light in a restricted viewing angle range in the second operation mode B2; Here, the image display device In a first alternative, the display device includes a liquid crystal panel having two liquid crystal layers, one of which serves to modulate light to enable display of image content, and the other of which serves to switch between a wide viewing angle range in a first operating mode B1 for a free-viewing mode and a limited viewing angle range in a second operating mode B2 for a limited-viewing mode; Or, in a second alternative, the device includes a dual-view liquid crystal panel that displays two selectable image contents simultaneously in different viewing angle ranges, wherein in a first operating mode B1 for a free-viewing mode, both image contents are the same or different, and in a second operating mode B2 for a restricted-viewing mode, at least one of the image contents is permanently black or monochrome, so that only a black or monochrome image without information is visible from the corresponding viewing angle range; and a control unit for the transmission type image display device (1) and the illumination device (2a) for switching between at least two operation modes B1 and B2; Here, the lighting device - Surface backlight (2), a plate-like light guide (3) arranged in front of the backlight (2) in the viewing direction and having two opposing main faces joined via a narrow side, the light guide (3) having an output element (6) on and / or within the volume of at least one of the main faces; a light source (4) disposed laterally on the narrow side of the light guide (3), wherein the shape, number per unit area, and extension of the emitting elements (6) are selected such that the horizontal and vertical dimensions of each emitting element (6) are smaller than the minimum width and height of the smallest pixel of the image display device (1); Here, in the first alternative The backlight (2) emits light over a limited angular range, The light guide (3) is at least 50% transparent to the light emitted from the backlight (2); In the second operating mode B2, the backlight (2) is on and the light source (4) is off, and in the first operating mode B1, at least the light source (4) is on; Now, in the second alternative The light guide (3) is at least 30% transparent to the light emitted from the backlight (2); The light guide (3) emits light incident laterally on at least one narrow side thereof over a limited angular range; A screen (1a) in which in a first operating mode B1 at least the backlight (2) is on, and in a second operating mode B2 the light source (4) is on and the backlight (2) is off. [Configuration 2] In a screen (1a) equipped with an image display device (1) according to the first alternative, a liquid crystal layer that switches the viewing angle range to a wide range in a first operating mode B1 for a free-viewing mode and to a limited viewing angle range in a second operating mode B2 for a limited-viewing mode is located in front of the other liquid crystal layer in the viewing direction of the viewer, and the viewing angle range is switched by different polarizations for both operating modes B1 and B2, respectively, as described in configuration 1. [Configuration 3] Screen (1a) according to configurations 1 or 2, characterized in that in the second operating mode B2 the lighting device (2a) emits light into a definable limited viewing angle range, so that outside this limited viewing angle range, measured in a selectable plane intersecting the screen (1a), there exists a maximum luminance value that is at most 50%, preferably at most 20%, particularly preferably at most 10% of the maximum luminance present within the limited viewing angle range. [Configuration 4] 4. A screen (1a) according to any one of configurations 1 to 3, characterized in that at least one optical component, preferably a diffuser and / or a prism film, is arranged between the image display device (1) and the light guide (3). [Configuration 5] The distribution of the output elements (6) on at least one major surface and / or within the volume of the light guide (3) is such that light incident from the light source (4) into the light guide (3) and output by the output elements (6) from the light guide (3) satisfies the following conditions: At least 50% of the amount of light emitted at one of the major surfaces within an angular range of -50° to +50° relative to the surface normal of the major surface is emitted within an angular range of -20° to +20° relative to one or two set preferred directions perpendicular to each other and to the surface normal, and / or at least 70% of the amount of light emitted at one of the major surfaces within an angular range of -50° to +50° relative to the surface normal of the major surface is emitted within an angular range of -30° to +30° relative to one or two set preferred directions, and The screen (1a) according to any one of configurations 1 to 4, characterized in that it is set so as to satisfy the requirement that at least 50% of the amount of light emitted from the light guide (3) is emitted in a direction away from the backlight (2) or in a direction towards the backlight (2). [Configuration 6] Screen (1a) according to any one of configurations 1 to 5, characterized in that the exit elements (6) consist of microlenses and / or microprisms and / or diffractive structures and / or three-dimensional structure elements and / or scattering elements. [Configuration 7] 7. A screen (1a) according to any one of configurations 1 to 6, characterized in that the exit elements (6) are selected in terms of their shape, number per unit area and extension such that, in a projection direction parallel to the surface normal of the light guide (3), for at least one subset of the smallest pixels of the image display device (1), a portion or the entire surface of at least two exit elements (6) are respectively arranged under each smallest pixel of this subset. [Configuration 8] Use of a screen (1a) according to any one of configurations 1 to 7 in a vehicle to selectively display image content to a passenger only in operational mode B2 and to a driver and passenger simultaneously in operational mode B1. [Explanation of symbols]

[0088] 1 Image display device 1a screen 2 Backlight 2a Lighting device 3 Light guide 4 light source 6. Emission element

Claims

1. A screen (1a) that can operate in at least two operation modes: an operation mode B1 for a free vision mode and an operation mode B2 for a limited vision mode; a transmissive image display device (1) operable in at least one first operating mode (B1) for a free-viewing mode and a second operating mode (B2) for a limited-viewing mode by modulating incident light to display image content, wherein the image display device (1) includes a liquid crystal panel having two liquid crystal layers, one of which functions to modulate light to enable display of the image content, and the other of which functions to expand a viewing angle range in the first operating mode (B1) for the free-viewing mode and to limit the viewing angle range in the second operating mode (B2) for the limited-viewing mode, the viewing angle range being measured in a selectable plane intersecting the screen (1a); The display device further includes an illumination device (2a) located behind the transmission type image display device (1) in the viewing direction of the viewer, and operable in at least two operation modes B2, an operation mode B1 for a free vision mode and an operation mode B2 for a limited vision mode, wherein the illumination device (2a) emits light in an unrestricted viewing angle range in the first operation mode B1 and emits light in a restricted viewing angle range in the second operation mode B2; Here, the limited viewing angle range of the image display device (1) for the second operation mode B2 is the same as the limited viewing angle range of the illumination device (2 a) for the second operation mode B2, Here, the lighting device (2a) includes at least i. a planar backlight (2) that emits light over a limited angular range; ii. a plate-like light guide (3) positioned in front of the backlight (2) in the viewing direction and having output elements (6) on at least one major surface and / or within its body, wherein said light guide (3) is at least 50% transparent to light emerging from said backlight (2); iii. A light source (4) disposed laterally on the narrow side of the light guide (3), wherein in a second operating mode B2 the backlight (2) is switched on and the light source (4) is switched off, and in a further operating mode B1 at least the light source (4) is switched on, wherein the emitting elements (6) are arranged in their shape and number per unit area and extension such that: i. The horizontal and vertical dimensions of each of the emission elements (6) are smaller than the minimum width and height of the smallest pixel of the image display device (1); ii. at least two of the output elements (6) are selected such that a part or the entire surface of each of the output elements (6) is located below each smallest pixel of the image display device (1) in a projection direction parallel to the surface normal of the light guide (3); Furthermore, the screen (1a) has a control for the transmissive image display device (1) and the illumination device (2a) for switching between at least two operating modes B1 and B2.

2. 2. Screen (1a) according to claim 1, characterized in that the liquid crystal layer which functions to widen the viewing angle range in a first operating mode B1 for a free-viewing mode and to restrict the viewing angle range in a second operating mode B2 for a restricted-viewing mode is located in front of the other liquid crystal layer in the viewing direction of the viewer and switches the viewing angle range by different polarizations for both operating modes B1 and B2.

3. 3. Screen (1a) according to claim 2, characterized in that the already image-modulated light is polarization-coded to determine the viewing angle range and in operating mode B2 is extinguished by at least 90% from oblique viewing directions by a polarizing filter that is positioned in the viewing direction of the viewer in front of the liquid crystal layer and functions as an analyzer, which functions to expand the viewing angle range in a first operating mode B1 for a free viewing mode and to restrict the viewing angle range in a second operating mode B2 for a restricted viewing mode, and in operating mode B1 a corresponding different polarization characteristic is modulated so that light can pass through the analyzer from substantially all incident directions.

4. A screen (1a) that can operate in at least two operation modes: an operation mode B1 for a free vision mode and an operation mode B2 for a limited vision mode; a transmissive image display device (1) operable in at least one first operating mode (B1) for a free-viewing mode and a second operating mode (B2) for a limited-viewing mode, modulating incident light to display image contents, wherein the image display device (1) includes a dual-view liquid crystal panel for simultaneously displaying two selectable image contents in different viewing-angle ranges, the viewing-angle ranges being measured in a selectable plane intersecting the screen (1a), wherein in the first operating mode (B1) for the free-viewing mode, both image contents are the same or different, and in the second operating mode (B2) for the limited-viewing mode, at least one of the image contents is permanently black or monochrome, such that only a black or monochrome image without information is visible from the corresponding viewing-angle range; The display device further includes an illumination device (2a) located behind the transmission type image display device (1) in the viewing direction of the viewer, and operable in at least two operation modes B2, an operation mode B1 for a free vision mode and an operation mode B2 for a limited vision mode, wherein the illumination device (2a) emits light in an unrestricted viewing angle range in the first operation mode B1 and emits light in a restricted viewing angle range in the second operation mode B2; Here, the limited viewing angle range of the image display device (1) for the second operation mode B2 is the same as the limited viewing angle range of the illumination device (2 a) for the second operation mode B2, Here, the lighting device (2a) includes at least i. a planar backlight (2) that emits light over a limited angular range; ii. a plate-like light guide (3) positioned in front of the backlight (2) in the viewing direction and having output elements (6) on at least one major surface and / or within its body, wherein said light guide (3) is at least 50% transparent to light emerging from said backlight (2); iii. A light source (4) disposed laterally on the narrow side of the light guide (3), wherein in a second operating mode B2 the backlight (2) is switched on and the light source (4) is switched off, and in a further operating mode B1 at least the light source (4) is switched on, wherein the emitting elements (6) are arranged in their shape and number per unit area and extension such that: i. The horizontal and vertical dimensions of each of the emission elements (6) are smaller than the minimum width and height of the smallest pixel of the image display device (1); ii. at least two of the output elements (6) are selected such that a part or the entire surface of each of the output elements (6) is located below each smallest pixel of the image display device (1) in a projection direction parallel to the surface normal of the light guide (3); Furthermore, the screen (1a) has a control for the transmissive image display device (1) and the illumination device (2a) for switching between at least two operating modes B1 and B2.

5. 2. The screen (1a) according to claim 1, characterized in that in the second operating mode B2 the lighting device (2a) emits light into a definable limited viewing angle range, in such a way that outside this limited viewing angle range there is a maximum brightness value that is at most 50% of the highest brightness present within the limited viewing angle range.

6. 2. Screen (1a) according to claim 1, characterized in that at least one optical component is arranged between the image display device (1) and the light guide (3).

7. 7. Screen (1a) according to claim 6, wherein said at least one optical component is an anisotropic diffuser.

8. The distribution of the output elements (6) on at least one major surface of the light guide (3) and / or within the body thereof is such that light incident from a light source (4) into the light guide (3) and output by the output elements (6) from the light guide (3) satisfies the following conditions: At least 50% of the amount of light emitted on one major surface in an angular range between −50° and +50° relative to the surface normal of the major surface is emitted in an angular range between −20° and +20° relative to one or two set preferred directions perpendicular to each other and to the surface normal, and / or at least 70% of the amount of light emitted on one major surface in an angular range between −50° and +50° relative to the surface normal of the major surface is emitted in an angular range between −30° and +30° relative to one or two set preferred directions, and 2. The screen (1a) according to claim 1, characterized in that it is set so as to satisfy the following: at least 50% of the amount of light emitted from the light guide (3) is emitted in a direction away from the backlight (2) or in a direction towards the backlight (2).

9. 2. Screen (1a) according to claim 1, characterized in that the limited viewing angle range is formed asymmetrically with respect to the surface normal of the backlight (2) in a selectable preferred direction.

10. 2. Screen (1a) according to claim 1, characterized in that the exit elements (6) consist of microlenses and / or microprisms and / or diffractive structures and / or three-dimensional structure elements and / or scattering elements.

11. 10. Use of a screen (1a) according to claim 1 in a vehicle for selectively displaying image content to a passenger only in an operating mode B2 and to a driver and passenger simultaneously in an operating mode B1.

Images