Screen for a free and a restricted viewing mode

Abstract

Screen (1a) which can be operated in at least two modes B1 for a free viewing mode and B2 for a restricted viewing mode, comprising - a transmissive image display device (1) which modulates incident light to display an image content and which can be operated in the first operating mode B1 for the free viewing mode and in the second operating mode B2 for the restricted viewing mode, wherein the image display device (1) is an LCD panel, - a lighting device (2a) located behind the transmissive image reproduction device (1) in the viewing direction of a viewer, which can be operated in at least two operating modes B1 for the free viewing mode and B2 for the restricted viewing mode, wherein the lighting device (2a) emits light in the first operating mode B1 into an unrestricted viewing angle range and in the second operating mode B2 into a correspondingly restricted viewing angle range, - where the image display device • in a first alternative, either an LCD panel with two liquid crystal layers is included, one of which serves to modulate the light to enable the display of the image content, and the other of which serves to increase the viewing angle range in the first operating mode B1 for the free viewing mode and to restrict it in the second operating mode B2 for the restricted viewing mode, • or, in a second alternative, comprises a dual-view LCD panel which simultaneously displays two selectable image contents in different viewing angle ranges, wherein in the first operating mode B1 for the free viewing mode the two image contents are identical or different, and wherein in the second operating mode B2 for the restricted viewing mode at least one of the image contents is permanently black or monochrome, so that from the corresponding viewing angle range only a black or information-free, monochrome image is visible, - as well as a control for the transmissive image reproduction device (1) and the illumination device (2a) for switching between the at least two operating modes B1 and B2, - where the lighting device • a surface-like backlight (2) • a plate-shaped light guide (3) arranged in a viewing direction in front of the backlight (2) with two opposing large surfaces which are connected via narrow sides, wherein the light guide (3) has coupling elements (6) on at least one of the large surfaces and / or within its volume, and • includes light sources (4) arranged laterally on the narrow sides of the light guide (3), - wherein the coupling elements (6) are chosen in their shape, number per area and extent such that • each coupling element (6) is smaller in its horizontal and vertical dimensions than the minimum of the width and height of the smallest pixels of the image display device (1), - where in a first alternative • the backlight (2) emits light into a limited angular range, • the light guide (3) for the light emanating from the backlight (2) is at least 50% transparent, and • in the second operating mode B2 the backlight (2) is switched on and the light sources (4) are switched off, and in the first operating mode B1 at least the light sources (4) are switched on, - and in a second alternative • the light guide (3) for the light emanating from the backlight (2) is at least 30% transparent, • the light guide (3) emits light coupled laterally into at least one of its narrow sides into a restricted angular range, and • in the first operating mode B1 at least the backlight (2) is switched on and in the second operating mode B2 the light sources (4) are switched on and the backlight (2) is switched off, - where in both alternatives the viewing angle range and the restricted angle range overlap by at least 50%.

Description

Technical field of the invention

[0001] Significant progress has been made in recent years in widening the viewing angle of LCDs. However, there are often situations where this very wide viewing area of ​​a screen can be a disadvantage. Information such as banking details, personal information, and sensitive data is increasingly accessible on mobile devices like laptops and tablets. Accordingly, people need control over who can see this sensitive data; they must be able to choose between a wide viewing angle to share information on their display with others, for example, when viewing vacation photos or for advertising purposes. Conversely, they need a narrow viewing angle if they want to keep the image information confidential.

[0002] A similar problem arises in vehicle manufacturing: The driver must not be distracted by visual content, such as digital entertainment programs, when the engine is running, while the passenger wants to consume the same content while the vehicle is in motion. Therefore, a screen is needed that can switch between the corresponding display modes. State of the art

[0003] Additional films based on microlouvers have already been used for mobile displays to achieve optical privacy. However, these films were not switchable; they always had to be manually applied and then removed. They also had to be transported separately from the display when not in use. Furthermore, a significant disadvantage of using such lamellar films is the associated loss of light transmission.

[0004] The patent US 5,956,107 A discloses a switchable light source that allows a screen to be operated in multiple modes. A disadvantage of this method is that all light extraction relies on scattering, resulting in low efficiency and suboptimal light direction effects. In particular, the achievement of a focused light beam is not disclosed in detail.

[0005] CN 107734118 A describes a screen that uses two backlights to control the viewing angle. The upper of the two backlights is intended to emit focused light. A grid with opaque and transparent sections is specifically mentioned as a possible design element. However, this likely results in the light from the second backlight, which must pass through the first to reach the LCD panel, also being focused, thus significantly narrowing the viewing angle intended for a wide public viewing mode.

[0006] US 2007 / 030240 A1 describes an optical element for controlling the direction of light propagation from a backlight. This optical element requires, for example, liquid crystals in the form of PDLCs, which is not only expensive but also safety-critical, especially for end-user applications, since PDLC liquid crystals typically require voltages higher than 60V for their circuitry.

[0007] CN 1987606 A describes a screen that uses two backlights to control the viewing angle. Specifically, it employs a "first light plate," which must be wedge-shaped to achieve the intended focused light emission. Precise details regarding how to achieve this focused light emission with the corresponding angular conditions are not disclosed.

[0008] Furthermore, US 2018 / 0267344 A1 describes a design with two flat lighting modules. In this design, the light from the rear lighting module (in the direction of view) is focused by a separate structure. After focusing, the light must still pass through the front lighting module, which has diffusing elements. Therefore, achieving strong light focusing for privacy purposes is not optimally feasible.

[0009] Finally, US 2007 / 0008456 A1 discloses the division of a light beam angle into at least three areas, with two of these areas typically illuminated. This implies that a privacy screen using such an illuminated display cannot be viewed from only one direction.

[0010] WO 2015 / 121398 A1, filed by the applicant, describes a screen of the type described above. Scatter particles are essential for switching between operating modes and are present within the volume of the corresponding optical fiber. However, the scatter particles chosen, made of a polymer, generally have the disadvantage that light is coupled out from both large areas, causing approximately half of the useful light to be emitted in the wrong direction, namely towards the backlight, where it cannot be sufficiently recycled due to the design. Furthermore, the polymer scatter particles distributed within the volume of the optical fiber can, under certain circumstances, especially at higher concentrations, lead to scattering effects that reduce the visual privacy effect in the protected operating mode.

[0011] US2020 / 012129 A1 discloses a lighting device and a screen that describe two lights for switching between a narrow and a wide viewing mode. In this design, one of the light guides is configured with fibers. Furthermore, the diffusing output coupling structure of one light guide is limited to specific strips in the projection direction. This is detrimental to homogeneous image illumination and generally also causes unwanted moiré effects in the setup, for example, in conjunction with the pixel columns or rows of an overlying LCD panel.

[0012] The aforementioned methods and arrangements generally share the disadvantage that they significantly reduce the brightness of the main screen and / or require an active, or at least a special, optical element for switching modes and / or require complex and expensive manufacturing and / or reduce the resolution in the freely viewable mode. Description of the invention

[0013] It is therefore an object of the invention to describe a screen with which a safe display of information can be achieved by means of a selectively restricted viewing angle, while in a further operating mode a free view, preferably unrestricted in the viewing angle, should be possible. In both operating modes, the highest possible resolution, preferably the native resolution of the screen used, should be visible. Furthermore, the restricted viewing angle should achieve the most comprehensive possible visual privacy effect without placing increased demands on the lighting device to be used.

[0014] This problem is solved according to the invention by a screen that can be operated in at least two operating modes, B1 for a free viewing mode and B2 for a restricted viewing mode. Such a screen comprises a transmissive image display device that modulates incident light to display an image content and that can be operated in the first operating mode B1 for the free viewing mode and in the second operating mode B2 for the restricted viewing mode, wherein the image display device is an LCD panel.

[0015] In the viewing direction of a viewer looking at the screen, a lighting device is arranged behind the transmissive image reproduction device, which can be operated in at least two operating modes B1 for the free viewing mode and B2 for the restricted viewing mode, wherein in the first operating mode B1 the lighting device emits light into an unrestricted viewing angle range and in the second operating mode B2 light into a correspondingly restricted viewing angle range.

[0016] The image display device can be designed in two ways. In a first alternative, the image display device comprises either an LCD panel with two liquid crystal layers, one of which serves to modulate the light to enable the display of the image content, and the other of which serves to widen the viewing angle range in the first operating mode B1 for unobstructed viewing and to narrow it in the second operating mode B2 for restricted viewing. The corresponding arrangement is preferably designed as a single module and further comprises a polarization filter behind the rear liquid crystal layer, between the two, and in front of the front liquid crystal layer.

[0017] It is conceivable that the liquid crystal layer used to widen the viewing angle range in the first operating mode B1 for a free viewing mode and to narrow it in the second operating mode B2 for a restricted viewing mode is located in front of the other liquid crystal layer in the viewer's direction of view and switches the viewing angle range by means of different polarization for the two operating modes B1 and B2. Thus, even color- and image-modulated light is polarization-encoded for determining the viewing angle range, so that in operating mode B2, at least 90%, preferably over 97%, of the light is extinguished from oblique viewing directions at the front polarization filter, which acts as an analyzer, but not when viewed perpendicularly.For operating mode B1, correspondingly different polarization properties are modulated so that it can pass through the analyzer from essentially all directions of incidence.

[0018] In a second alternative, the image display device comprises a dual-view LCD panel that simultaneously displays two selectable image contents in different viewing angle ranges. In the first operating mode, B1, for a free viewing mode, the two image contents are identical or different. In the 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. White images are also considered monochrome in this context. As is known in the prior art, a dual-view LCD panel can, for example, comprise a barrier screen, a lens array, or a prism array, which displays selected groups of pixels in different viewing angle ranges.By applying pressure to these pixel groups, it is then possible to determine which pixels, and thus which respective image content, are perceptible from which viewing angle.

[0019] Furthermore, the screen includes a control unit for the transmissive image display unit and the illumination unit for switching between the at least two operating modes B1 and B2. The control unit for the transmissive image display unit and the illumination unit for switching between the at least two operating modes B1 and B2 preferably comprises an electronic device which preferably, but not necessarily, switches the two operating modes B1 and B2 synchronously for both the image display unit and the illumination unit 2a.

[0020] The lighting device comprises a planar backlight and a plate-shaped light guide arranged in front of the backlight in one viewing direction. The light guide has two opposing large surfaces connected via their narrow sides, and the light guide has coupling elements on at least one of the large surfaces and / or within its volume. Light sources are arranged laterally on the narrow sides of the light guide.

[0021] The coupling elements are selected in their shape, number per area, and extent such that each coupling element is smaller in its horizontal and vertical dimensions than the minimum width and height of the smallest pixels of the image display device. The pixels are typically color subpixels, but monochromatic pixels are also possible. Preferably, the coupling elements are further selected in their shape, number per area, and extent such that, in projection directions parallel to the surface normal of the optical fiber, parts or the entire surface of at least two coupling elements are arranged below each smallest pixel of at least one subset of the smallest pixels of the image display device. This subset can, in particular, include all the smallest pixels.

[0022] In the first alternative, the backlight emits light within a limited angular range. In this case, the light guide is at least 50% transparent to the light emitted by the backlight. In the second operating mode, B2, the backlight is on and the lamps are off; in the first operating mode, B1, at least the lamps are on.

[0023] In a second alternative, the light guide emits light, coupled laterally into at least one of its narrow sides, within a limited angular range. In this case, the light guide for the light emanating from the backlight is at least 30% transparent. Unlike the first alternative, in the second operating mode B2, the light sources are switched on and the backlight is switched off; in the first operating mode B1, at least the backlight is switched on.

[0024] In both alternatives, 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 visual protection, whereby the brightness curve in reality typically does not exhibit step-like behavior, but rather a continuous curve similar to a bell curve.

[0025] The particular advantage of combining these measures to implement the two operating modes B1 and B2 in both the image display unit and the lighting unit is that the effects that restrict the viewing angle complement each other for the second operating mode B2, so that the visual protection is particularly effective in this restricted viewing mode. For this to work, it is advantageous if the respective viewing angle ranges of the image display unit and the lighting unit for the second operating mode B2 overlap significantly or are identical.

[0026] Preferably, in the second operating mode B2, the lighting device emits light into a definable, limited viewing angle range such that outside this limited viewing angle range, measured in a selectable plane intersecting the screen, the maximum luminance value is at most 50%, preferably at most 20%, and particularly preferably at most 10% of the highest luminance present within the limited viewing angle range. Such a plane for defining the measurement can advantageously include, for example, the perpendicular to the center of the screen and be parallel to the lower edge of the screen to a tolerance of 7 degrees.

[0027] A "large" viewing angle range could be, for example, an angle measured in the aforementioned plane extending from approximately -60° to +60° or from approximately -60° to +30°, where, without loss of generality, the angle of 0° should coincide with the perpendicular bisector. A "restricted" viewing angle range would be, for example, from approximately -30° to +30°, or from approximately -20° to +30° (asymmetry is possible), or from approximately -10° to +50°. In principle, any area smaller than the hemisphere in front of the screen can qualify as a restricted viewing angle range.

[0028] Furthermore, for some applications it is advantageous that the aforementioned restricted viewing angle range is asymmetrically designed around the surface normal of the backlight. The asymmetrical design is preferably implemented in a selectable preferred direction. This is particularly helpful in vehicle applications, for example, when a screen according to the invention is arranged as a so-called center information display in the dashboard approximately midway between the driver and front passenger. In this case, the restricted viewing angle range, which in operating mode B2 is exclusively available to the front passenger, must be asymmetrically designed, i.e., directed towards the front passenger. The preferred direction in which the asymmetry is implemented here corresponds to the horizontal.

[0029] Furthermore, it can be advantageous if at least one optical component is arranged between the image display device and the light guide, preferably a diffuser (this can be isotropic or anisotropic) and / or a prism foil (this can also have an isotropic or anisotropic effect).

[0030] Furthermore, it is conceivable that the distribution of the output elements on at least one of the large surfaces and / or within the volume of the light guide is specified such that the light emitted into the light guide by the light sources and the light coupled out of the light guide by the output elements fulfills the following conditions: 1) At least 50% of the amount of light coupled out on one of the large surfaces between an angular range of -50° and +50° to the surface normal of the large surface is emitted between an angular range of -20° and +20° with respect to one or two specified preferred directions perpendicular to each other and to the surface normal, and / or at least 70% of the amount of light coupled out on one of the large surfaces between an angular range of -50° and +50° to the surface normal of the large surface is emitted between an angular range of -30° and +30° with respect to the one or two preferred directions.and 2) at least 50% of the amount of light coupled out of the optical fiber is coupled out in the direction away from or towards the backlight.

[0031] The lighting device may additionally include a collimating film at a suitable location in the setup, for example a lens or prism grid above or below the plate-shaped light guide.

[0032] The optical fiber is preferably made of a transparent, thermoplastic or thermoelastic polymer, e.g., plastic, or glass. For example, the optical fiber or its substrate can comprise at least 40% by weight of polymethyl methacrylate, preferably at least 60% by weight of polymethyl methacrylate. Alternatively, it can be, for example, polycarbonate (PC).

[0033] During the manufacturing process of the optical fiber, the coupling elements can be distributed within or on the fiber in various ways, depending on adaptable and predefined conditions for light extraction. These coupling elements are locally confined structural modifications within the volume and / or on the surfaces of the optical fiber. Specifically excluded from the term "coupling element" are additional optical layers applied to the surfaces of the optical fiber, such as diffusion layers, reflection layers, (dual) brightness-enhancing, collimating, or polarization-recycling layers (dual brightness enhancement film - (D)BEF), or reflective polarizers.These additional layers, which do not fall under the definition of the "coupling element," are connected to the optical fiber only at their edges, if at all. In the large areas, they usually just lie loosely on top and do not form a physical unit with the optical fiber. In contrast, varnishes applied to the large areas, which bond with the optical fiber through chemical reactions or other forces (e.g., van der Waals forces), form a physical unit and are inseparable; such varnishes are therefore not considered additional layers in the sense described above.

[0034] The structure of the coupling elements can be specified so that the effect of each coupling element is at least approximately known and properties of the optical fiber or the light emerging from the optical fiber can be specifically determined by a predefinable distribution of the coupling elements.

[0035] The required properties essential for the invention for the coupling elements with regard to their number per unit area, their shape, their orientation and extent in three dimensions as well as their distribution on at least one of the large areas and / or within the volume of the optical fiber can be determined, for example, with an optical simulation software such as “LightTools” from Synopsis or other providers and then physically implemented accordingly.

[0036] Advantageously, the distribution of the output elements on at least one of the large surfaces and / or within the volume of the optical fiber is specified such that the output light achieves a luminance homogeneity of 70% over at least 70% of the optical fiber's surface. The luminance homogeneity can be expressed as L V min / L V maxLuminance homogeneity can be defined as the ratio of the smallest luminance value to the largest value of a surface. Another applicable standard for measuring luminance homogeneity is defined in the "Uniformity Measurement Standard for Displays V1.3" by the "German Automotive OEM Work Group Displays". It is possible for decoupling elements to be located on both large surfaces and / or optionally within the volume.

[0037] The coupling elements for coupling light from at least one of the large surfaces of the optical fiber preferably consist of microlenses and / or microprisms and / or diffractive structures and / or three-dimensional structural elements and / or scattering elements with a maximum extent in their largest dimension that is less than 100 micrometers, preferably less than 50 micrometers. In the case of diffractive structures, these can be, for example, a hologram or a grating / diffraction grating.

[0038] The extraction elements themselves can also have the external form of microlenses, microprisms, scattering elements, and / or diffractive structures. They can then be designed, in particular, as cavities formed within the volume of the optical fiber. The cavities can be evacuated, but are preferably filled with a gaseous, liquid, or solid material. The material has a refractive index that differs from that of the material used for the optical fiber; preferably, it is lower. The filling material and the choice of material allow for influence over the light transmission and extraction. Alternatively or additionally, the haze value of the material also preferably differs from that of the material used for the optical fiber and is preferably higher. Advantages of these configurations include higher efficiency in light extraction.

[0039] Alternatively, and in a technically simpler way, the cavities can also be formed by constructing the optical fiber from two bonded substrate layers, preferably of the same type. The bond can be chemical, physical, or adhesive. The cavities are then formed as material recesses at at least one of the interfaces between the substrate layers.

[0040] If the coupling elements are attached to at least one of the large surfaces of the optical fiber, they are advantageously formed from a tool-structured plastic or glass, the structure of which was imprinted by means of a tool. This is possible, for example, in mass production by applying a UV-curing material—e.g., a lacquer, a monomer, etc.—to an optical fiber substrate, which is then structured by means of a tool and cured, e.g., polymerized, by UV radiation. Other radiation-curing materials can also be used. The formation of the recesses for the coupling elements can be achieved, for example, mechanically, lithographically, or using printing techniques, or by material deposition, conversion, ablation, or dissolution.

[0041] This allows, for example, the cost-effective and mass-producible implementation of lattice structures, microprisms – either convex with a plastic component on the surface pointing outwards, and / or concave as an indentation or recess within the surface layer of the structured plastic – other three-dimensional structural elements with different shapes, or even microlenses. Both concave and convex structures can be used.

[0042] The backlight consists, for example, of a flat light source, preferably a further light guide with additional light sources arranged laterally or on the rear, as well as at least one light collimator integrated into and / or arranged in front of the flat light source, such as at least one prism film and / or at least one privacy filter (lamellar filter). Accordingly, the backlight can therefore be fundamentally constructed like an LED backlight, for example as a so-called direct-lit LED backlight, edge LED backlight, OLED, or as another flat light source on which, for example, at least one permanent privacy filter (with microlamellae) is applied.

[0043] One advantage of the invention is that the requirements for the backlight are generally reduced compared to the prior art: By combining the view-restricting effects of the image display device and the lighting device (in which the backlight is integrated), it is not necessary to achieve privacy contrasts of 100:1 or better, as in the prior art. Rather, values ​​of 10:1 in the backlight are already extremely helpful in significantly improving the privacy effect of the image display device in operating mode B2. A residual light from the image display device in operating mode B2 of, for example, 0.5% of the maximum brightness at an angle of -40 degrees would already decrease to 0.05% if the lighting device emitted only 10% (but not the more difficult-to-achieve value of 1%) of the maximum brightness at -40 degrees.

[0044] Means for reducing or controlling reflections, for example an anti-reflective coating, may be arranged on the top of the screen and / or on at least one of the large surfaces of the light guide as well as on at least one of the privacy filters, if present.

[0045] The screen according to the invention is particularly advantageous for use in a vehicle for the selective display of image content solely for the passenger in operating mode B2, or simultaneously for the driver and passenger in operating mode B1. The former is helpful, for example, if the passenger is watching entertainment content that could distract the driver.

[0046] A screen according to the invention can be used for entering or displaying confidential data, for example PINs, emails, SMS messages or passwords, at ATMs, payment terminals or mobile devices.

[0047] In all the aforementioned embodiments, the light sources in question can be LEDs or LED arrays, or laser diodes. Other variants are conceivable and fall within the scope of the invention.

[0048] Furthermore, the desired restricted viewing angles for mode B2 can be defined and implemented independently for both the horizontal and vertical directions. For example, a larger angle (or even no restriction at all) might be useful in the vertical direction than in the horizontal direction, such as when ATMs are used to allow people of different heights to see the screen while the side view is to be severely or completely restricted. For POS payment terminals, however, security regulations often necessitate viewing restrictions in mode B2 in both the horizontal and vertical directions.

[0049] In principle, the performance of the invention is maintained if the parameters described above are varied within certain limits.

[0050] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations given, but also in other combinations or on their own, without leaving the scope of the present invention. Brief description of the drawings

[0051] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying drawings, which also disclose essential features of the invention. These exemplary embodiments serve only for illustration and are not to be interpreted as limiting. For example, a description of an exemplary embodiment with a plurality of elements or components is not to be interpreted as meaning that all of these elements or components are necessary for implementation. Rather, other exemplary embodiments may also contain alternative elements and components, fewer elements or components, or additional elements or components. Elements or components from different exemplary embodiments may be combined with one another unless otherwise specified. Modifications and variations described for one of the exemplary embodiments may also be applicable to other exemplary embodiments.To avoid repetition, identical or corresponding elements in different figures are designated with the same reference symbols and are not explained multiple times. They show: Fig. 1. A schematic diagram of the extraction of light, which is coupled laterally into an optical fiber, from the lower large surface of the optical fiber on which the extraction elements are located, wherein the light leaves the optical fiber at the upper large surface. Fig. 2. A schematic diagram of the extraction of light, which is coupled laterally into an optical fiber, from the upper large surface of the optical fiber on which the extraction elements are located, wherein the light leaves the optical fiber at the upper large surface. Fig. 3 a schematic diagram of a screen in a first embodiment in a first operating mode B1 for a free viewing mode, Fig. 4 a schematic diagram of a screen in a first embodiment in a second operating mode B2 for a restricted viewing mode, Fig. 5 a schematic diagram of an exemplary form of a coupling element, Fig. 6 a schematic diagram of a screen in a second embodiment in the first operating mode B1 for a free viewing mode, as well as Fig. 7 A schematic diagram of a screen in a second embodiment in the second operating mode B2 for a restricted viewing mode. Detailed description of the drawings

[0052] In Fig. Figure 1 is a schematic diagram of the extraction of light coupled laterally from light sources 4 into a light guide 3. The light is extracted onto the lower surface of the light guide 3, where the extraction elements 6 are located. The extracted light exits the light guide 3 at the upper surface. In the horizontal direction, the light is extracted from the upper surface of the light guide 3 at a wide angle (greater than 60°). The location of the extraction elements 6 is indicated by the number 6; however, the actual extraction elements 6 are not shown because they must be microscopically small. Thus, light from the light sources 4, e.g., LEDs, is coupled laterally into the light guide 3. Due to total internal reflection, rays of the coupled light (shown in bold) are reflected back into the light guide 3 at the outer wall until they finally (possibly...(for the second time) meet an output element 6 for the desired output. The output is stylized by the thin rays. The representation in . Fig. Figure 1 is highly stylized for better visibility; in reality, a very large number of light paths are implemented in the optical fiber 3. Furthermore, refractions at refractive index transition surfaces are not taken into account.

[0053] Fig. Figure 2 shows a schematic diagram of the extraction of light, which is coupled laterally from light sources 4 into a light guide 3, from the upper surface of the light guide 3, on which the extraction elements 6 are located. The light also exits the light guide 3 through this upper surface. The explanations regarding [reference to relevant section] apply accordingly. Fig. 1. The only technical difference here is the position and, if applicable, the design of the coupling elements 6, which are now located on the top side of the light guide 3 and thus couple the light directly upwards. In contrast to the situation described above, the coupled light does not need to pass through the light guide 3 a second time. Fig. 1.

[0054] The schematic diagrams in the following drawings Fig. 3, Fig. 4, Fig. 6 and Fig. 7 are sectional views.

[0055] The Fig. Figure 3 shows a schematic diagram of a screen 1a in a first embodiment in a first operating mode B1 for a free viewing mode, and Fig. 4 in a second operating mode B2 for a restricted viewing mode. A screen 1a, which can be operated in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode, initially comprises a transmissive image display device 1, which modulates incident light to display an image content, and which can be operated in at least a first operating mode B1 for a free viewing mode and in a second operating mode B2 for a restricted viewing mode. The image display device 1 is an LCD panel.In the viewing direction of a viewer behind the transmissive image display device 1 is a lighting device 2a, which can be operated in at least two modes: B1 for a free viewing mode and B2 for a restricted viewing mode. In the first mode, B1, the lighting device 2a emits light into an unrestricted viewing angle range, and in the second mode, B2, it emits light into a correspondingly restricted viewing angle range. The screen 1a also includes a control circuit for the transmissive image display device 1 and the lighting device 2a for switching between the at least two modes, B1, as exemplified in [reference]. Fig. 3 is shown, and B2, as exemplified in Fig. 4 is shown.

[0056] In the first embodiment shown here, the lighting device 2a comprises at least a surface-extended backlight 2, which emits light in a restricted angular range, a plate-shaped light guide 3 located in front of the backlight 2 in the viewing direction, which has coupling elements 6 on at least one of its large surfaces and / or within its volume, wherein the light guide 3 is at least 50% transparent to the light emitted from the backlight 2, and light sources 4 arranged laterally on the narrow sides of the light guide 3. In operating mode B2, the backlight 2 is switched on and the light sources 4 are switched off, whereas in operating mode B1 at least the light sources 4 are switched on.

[0057] In Fig. 3. The transmission of light originating from the lighting device 2a (thin arrows) through the image reproduction device 1 in all directions is indicated by the bold arrows. Conversely, in Fig. 4. The bold arrows indicate that the image display device 1 only allows light to pass through within a limited viewing angle range (dashed bold arrows mean that the light is not transmitted there or is only transmitted at a maximum of ten percent). At the same time, only limited light from the lighting device 2a reaches the image display device 1 within this viewing angle range.

[0058] The particular advantage of combining these measures to implement operating modes B1 and B2 in both the image display unit 1 and the lighting unit 2a is that the effects that restrict the viewing angle for operating mode B2 complement each other, resulting in a particularly strong visual shield in this restricted viewing mode. It is advantageous if the respective viewing angle ranges of the image display unit 1 and the lighting unit 2a for operating mode B2 overlap significantly or are identical.

[0059] The control system for the transmissive image display device 1 and the lighting device 2a for switching between the at least two operating modes B1 and B2, which is not shown in the drawing, preferably comprises an electronic device which preferably, but not necessarily, switches the two operating modes B1 and B2 synchronously for both the image display device 1 and the lighting device 2a.

[0060] In a first alternative, the image display device 1 comprises an LCD panel with two liquid crystal layers, one of which serves to modulate the light to enable the display of said image content, and the other of which serves to widen the viewing angle range in the first operating mode B1 for an unobstructed viewing mode and to narrow it in the second operating mode B2 for a restricted viewing mode. The corresponding arrangement is preferably designed as a single module and further comprises a polarizing filter located behind the rear liquid crystal layer, between the two liquid crystal layers, and in front of the front liquid crystal layer.

[0061] In a second alternative, the image display device 1 comprises a dual-view LCD panel which simultaneously displays two selectable image contents in different viewing angle ranges, wherein in the first operating mode B1 for the free viewing mode the two image contents are identical or different, and wherein in the second operating mode B2 for the restricted viewing mode at least one of the image contents is permanently black or monochrome - which also includes white - so that only a black or information-free, monochrome image is visible from the corresponding viewing angle range.

[0062] It is conceivable that the liquid crystal layer used to widen the viewing angle range in the first operating mode B1 for a free viewing mode and to narrow it in the second operating mode B2 for a restricted viewing mode is located in front of the other liquid crystal layer in the viewer's direction of view and switches the viewing angle range by means of different polarization for the two operating modes B1 and B2. Thus, even color- and image-modulated light is polarization-encoded for determining the viewing angle range, so that in operating mode B2, at least 90%, preferably over 97%, of the light is extinguished from oblique viewing directions at the front polarization filter (which acts as an analyzer), but not when viewed perpendicularly.For operating mode B1, correspondingly different polarization properties are modulated so that it can pass through the analyzer from essentially all directions of incidence.

[0063] Preferably, in the second operating mode B2, the lighting device 2a emits light into a definable, limited viewing angle range such that outside this limited viewing angle range, which is measured in a selectable plane intersecting the screen 1a, the maximum luminance value is at most 50%, preferably at most 20%, and particularly preferably at most 10% of the highest luminance present within the limited viewing angle range. Such a plane for defining the measurement can advantageously include, for example, the perpendicular to the center of the screen and be parallel to the lower edge of the screen 1a to a tolerance of 7 degrees.

[0064] A "large" viewing angle range could be, for example, an angle range measured in the aforementioned plane extending from approximately -60° to +60° or from approximately -60° to +30°, where, without loss of generality, the angle of 0° should coincide with the perpendicular bisector. A "restricted" viewing angle range would be, for example, from approximately -30° to +30°, or from approximately -20° to +30° (asymmetry is possible), or from approximately -10° to +50°.

[0065] The coupling elements 6 for coupling light from at least one of the large surfaces of the optical fiber 3 preferably consist of microlenses and / or microprisms and / or diffractive structures and / or three-dimensional structural elements and / or scattering elements with a maximum dimension of 100 micrometers, preferably 50 micrometers. In the case of diffractive structures, these can be, for example, a hologram or a grating / diffraction grating.

[0066] This includes Fig. Figure 5 shows a schematic diagram of an exemplary form of a coupling element 6, here in the form of a microprism. This type of coupling element can be distributed homogeneously, or preferably inhomogeneously (i.e., for example, with increasing distance from the light sources 4, in greater numbers per area) on one or both large surfaces and / or in the volume of the light guide 3, e.g., as an air-filled recess. Other forms of coupling elements 6 are, of course, possible.

[0067] The coupling elements are selected in their shape, number per area, and extent such that each coupling element is smaller in its horizontal and vertical dimensions than the minimum width and height of the smallest pixels of the image display device. The pixels are typically color subpixels, but monochromatic pixels are also possible. Preferably, the coupling elements are further selected in their shape, number per area, and extent such that, in projection directions parallel to the surface normal of the optical fiber, parts or the entire surface of at least two coupling elements are arranged below each smallest pixel of at least one subset of the smallest pixels of the image display device 1. This subset can, in particular, include all the smallest pixels.

[0068] Furthermore, they show Fig. 6 a schematic diagram of a screen 1a in a second embodiment in the first operating mode B1 for a free viewing mode as well as Fig. 7 in the second operating mode B2 for a restricted viewing mode. This configuration is an alternative to the one described in the Fig. 3 and Fig. 4 shown design. The one in the Fig. 6 and Fig. The lighting device 2a of the screen 1 shown in Figure 7 comprises at least one area-like backlight 2, a plate-shaped light guide 3 located in front of the backlight 2 in the viewing direction, which has coupling elements 6 on at least one of its large surfaces and / or within its volume, wherein the light guide 3 is at least 30% transparent to the light emitted from the backlight 2, and wherein the light guide 3 emits light coupled laterally into at least one of its narrow sides within a limited angular range, as well as light sources 4 arranged laterally on narrow sides of the light guide 3. In the first operating mode B1 for the limited viewing mode according to Fig. 6 at least the backlight 2 is switched on, whereas in the second operating mode B2 for the free viewing mode according to Fig. 7 the light source 4 is switched on and the backlight 2 is switched off.

[0069] In Fig. Figure 6 shows the transmission of light (thin arrows) from the lighting device 2a through the image display device 1 in all directions, indicated by the bold arrows. Conversely, in Fig. 7. The bold arrows indicate that the image display device 1 only allows light to pass through within a limited viewing angle range (dashed bold arrows mean that the light is not transmitted there or is only transmitted at a maximum of ten percent). At the same time, only limited light from the lighting device 2a reaches the image display device 1 within this viewing angle range.

[0070] The lighting device 2a can additionally include a collimation film at a suitable location in the setup, for example a lens or prism grid above or below the plate-shaped light guide 3.

[0071] The optical fiber 3 preferably consists of a transparent, thermoplastic or thermoelastic polymer, e.g., plastic, or of glass. For example, the optical fiber or its substrate can comprise at least 40% by weight of polymethyl methacrylate, preferably at least 60% by weight of polymethyl methacrylate. Alternatively, it can be, for example, polycarbonate (PC).

[0072] The extraction elements 6 can be distributed in or on the optical fiber 3 in various ways during its manufacture, according to adaptable and predefined conditions for light extraction. These extraction elements 6 are locally confined structural modifications within the volume and / or on the surfaces of the optical fiber. Specifically excluded from the term extraction element 6 are additional optical layers applied to the surfaces of the optical fiber 3, such as diffusion layers, reflection layers, (dual) brightness-enhancing, collimating, or polarization-recycling layers (dual brightness enhancement film - (D)BEF), or reflective polarizers.These additional layers, which do not fall under the definition of the "coupling element" 6, are connected to the optical fiber 3 only at their edges, if at all. In the large areas, they usually only lie loosely on top and do not form a physical unit with the optical fiber 3. In contrast, varnishes applied to the large areas, which bond with the optical fiber 3 through chemical reactions or other forces (e.g., van der Waals forces), form a physical unit and can no longer be separated; such varnishes therefore do not count as an additional layer in the sense described above.

[0073] The structure of the coupling elements 6 can be predetermined so that the effect of each coupling element 6 is at least approximately known, and the properties of the optical fiber 3 or the light emerging from the optical fiber 3 can be specifically determined by a predefinable distribution of the coupling elements 6. The required properties of the coupling elements 6, essential to the invention, with regard to their number per unit area, their shape, their orientation and extent in three dimensions, as well as their distribution on at least one of the large surfaces and / or within the volume of the optical fiber 3, can be determined, for example, using optical simulation software such as "LightTools" from Synopsis or other providers, and then physically implemented accordingly. It is possible for coupling elements 6 to be located on both large surfaces and / or optionally also within the volume of the optical fiber 3.

[0074] The backlight 2 consists, for example, of a flat light source, preferably a further light guide with additional light sources arranged laterally or on the rear, as well as at least one light collimator integrated into and / or arranged in front of the flat light source, such as at least one prism film and / or at least one privacy filter (lamellar filter). Accordingly, the backlight 2 can therefore be fundamentally constructed like an LED backlight, for example as a so-called direct-lit LED backlight, edge LED backlight, OLED, or as another flat light source on which, for example, at least one permanent privacy filter (with microlamellae) is applied.

[0075] One advantage of the screen described above is that the requirements for the backlight 2 are generally reduced compared to the prior art: By combining the view-restricting effects of the image display unit 1 and the illumination unit 2a (in which the backlight 2 is integrated), it is not necessary to achieve privacy contrasts of 100:1 or better, as is required in the prior art. Instead, values ​​of 10:1 in the backlight 2 are already extremely helpful in significantly improving the privacy effect of the image display unit 1 in operating mode B2. A residual light from the image display unit 1 in operating mode B2 of, for example, 0.5% of the maximum brightness at an angle of -40 degrees would already decrease to 0.05% if the illumination unit emitted only 10% (but not the more difficult-to-achieve value of 1%) of the maximum brightness at -40 degrees.

[0076] The screen is particularly advantageous in a vehicle for optionally displaying images only to the passenger in operating mode B2, or simultaneously to both the driver and passenger in operating mode B1. The former is helpful, for example, if the passenger is watching entertainment content that might distract the driver. A screen like the one described above can also be used to enter or display confidential data, such as PINs, emails, SMS messages, or passwords, at ATMs, payment terminals, or mobile devices.

[0077] In all the aforementioned embodiments, the light sources in question can be 4 LEDs or LED arrays, or laser diodes. Other variants are conceivable and fall within the scope of the invention.

[0078] The lighting system described above and the screen that can be implemented with it solve the stated problem: A screen has been described that enables the safe display of information by means of a selectable restricted viewing angle, while in another operating mode a clear view with as little restriction as possible in terms of the viewing angle is possible. In both operating modes, the highest possible resolution, i.e., the native resolution of the screen used, is visible. Furthermore, the restricted viewing angle achieves a comprehensive visual privacy effect without placing increased demands on the lighting system.

[0079] The screen described above can be advantageously used wherever confidential data is displayed and / or entered, such as for PIN entry or data display at ATMs or payment terminals, for password entry, or when reading emails on mobile devices. As described above, it can also be used in cars. Reference symbol list 1 Image display unit 1a screen 2 Backlight 2a Lighting equipment 3 optical fibers 4 light bulbs 6 decoupling element QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 5,956,107 A

[0004] CN 107734118 A

[0005] US 2007 / 030240 A1

[0006] CN 1987606 A

[0007] US 2018 / 0267344 A1

[0008] US 2007 / 0008456 A1

[0009] WO 2015 / 121398 A1

[0010] US 2020 / 012129 A1

[0011]

Claims

[1] Screen (1a) which can be operated in at least two modes B1 for a free viewing mode and B2 for a restricted viewing mode, comprising - a transmissive image display device (1) which modulates incident light to display an image content and which can be operated in the first operating mode B1 for the free viewing mode and in the second operating mode B2 for the restricted viewing mode, wherein the image display device (1) is an LCD panel, - a lighting device (2a) located behind the transmissive image reproduction device (1) in the viewing direction of a viewer, which can be operated in at least two operating modes B1 for the free viewing mode and B2 for the restricted viewing mode, wherein the lighting device (2a) emits light in the first operating mode B1 into an unrestricted viewing angle range and in the second operating mode B2 into a correspondingly restricted viewing angle range, - where the image display device • in a first alternative, either an LCD panel with two liquid crystal layers is included, one of which serves to modulate the light to enable the display of the image content, and the other of which serves to increase the viewing angle range in the first operating mode B1 for the free viewing mode and to restrict it in the second operating mode B2 for the restricted viewing mode, • or, in a second alternative, comprises a dual-view LCD panel which simultaneously displays two selectable image contents in different viewing angle ranges, wherein in the first operating mode B1 for the free viewing mode the two image contents are identical or different, and wherein in the second operating mode B2 for the restricted viewing mode at least one of the image contents is permanently black or monochrome, so that from the corresponding viewing angle range only a black or information-free, monochrome image is visible, - as well as a control for the transmissive image reproduction device (1) and the illumination device (2a) for switching between the at least two operating modes B1 and B2, - where the lighting device • a surface-like backlight (2) • a plate-shaped light guide (3) arranged in a viewing direction in front of the backlight (2) with two opposing large surfaces which are connected via narrow sides, wherein the light guide (3) has coupling elements (6) on at least one of the large surfaces and / or within its volume, and • includes light sources (4) arranged laterally on the narrow sides of the light guide (3), - wherein the coupling elements (6) are chosen in their shape, number per area and extent such that • each coupling element (6) is smaller in its horizontal and vertical dimensions than the minimum of the width and height of the smallest pixels of the image display device (1), - where in a first alternative • the backlight (2) emits light into a limited angular range, • the light guide (3) for the light emanating from the backlight (2) is at least 50% transparent, and • in the second operating mode B2 the backlight (2) is switched on and the light sources (4) are switched off, and in the first operating mode B1 at least the light sources (4) are switched on, - and in a second alternative • the light guide (3) for the light emanating from the backlight (2) is at least 30% transparent, • the light guide (3) emits light coupled laterally into at least one of its narrow sides into a restricted angular range, and • in the first operating mode B1 at least the backlight (2) is switched on and in the second operating mode B2 the light sources (4) are switched on and the backlight (2) is switched off, - where in both alternatives the viewing angle range and the restricted angle range overlap by at least 50%. [2] Screen (1a) according to claim 1 with an image display device (1) according to the first alternative, characterized by, that the liquid crystal layer which serves to increase the viewing angle range in the first operating mode B1 for the free viewing mode and to restrict it in the second operating mode B2 for the restricted viewing mode, lies in front of the other liquid crystal layer in the viewing direction of a viewer and switches the viewing angle range by means of different polarization for the two operating modes B1 and B2. [3] Screen (1a) according to any of the preceding claims, characterized by, that the lighting device (2a) in the second operating mode B2 emits light into a definable restricted viewing angle range such that outside this restricted viewing angle range, which is measured in a selectable plane that intersects the screen (1a), at most 50%, preferably at most 20%, particularly preferably at most 10% of the highest luminance present within the restricted viewing angle range is present as the maximum luminance value. [4] Screen (1a) according to any of the preceding claims, characterized by , that at least one optical component is arranged between the image display device (1) and the light guide (3), preferably a diffuser and / or a prism foil. [5] Screen (1a) according to any of the preceding claims, characterized by, that the distribution of the coupling elements (6) on at least one of the large areas and / or within the volume of the light guide (3) is specified such that the light emitted by the light sources (4) into the light guide (3) and coupled out of the light guide (3) by the coupling elements (6) meets the following conditions: - at least 50% of the amount of light coupled out on one of the large surfaces between an angular range of -50° and +50° to the surface normal of the large surface is emitted between an angular range of -20° and +20° with respect to one or two predetermined preferred directions perpendicular to each other and to the surface normal, and / or at least 70% of the amount of light coupled out on one of the large surfaces between an angular range of -50° and +50° to the surface normal of the large surface is emitted between an angular range of -30° and +30° with respect to the one or two preferred directions, and - at least 50% of the amount of light coupled out of the light guide (3) is coupled out in the direction away from or towards the backlight (2). [6] Screen (1a) according to any of the preceding claims, characterized by , that the output coupling elements (6) consist of microlenses and / or microprisms and / or diffractive structures and / or three-dimensional structural elements and / or scattering elements. [7] Screen (1a) according to any of the aforementioned claims, characterized by , that the coupling elements (6) are chosen in their form, number per surface and extent such that in projection directions parallel to the surface normal of the light guide (3) parts or the entire surface of at least two coupling elements (6) are arranged below each smallest pixel of at least one subset of the smallest pixels of the image display device (1).

Images