Lighting device for a free and a restricted viewing mode

Abstract

Lighting device (1a) for a screen (1) which can be operated in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode in which light is emitted from the lighting device in an angular range that is restricted compared to the free viewing mode, comprising - an area-like extended backlight (2) that emits light into the restricted angular range, - a plate-shaped light guide (3) located in the viewing direction in front of the backlight (2) with two large surfaces and narrow sides connecting the large surfaces at their edges, wherein the light guide (3) has coupling elements (6) on at least one of the large surfaces and / or within its volume, wherein the light guide (3) is at least 50% transparent to the light emanating from the backlight (2), wherein each coupling element (6) has at least one functional surface for the defined coupling of light, at which light is coupled out of the light guide (3), - light sources (4) arranged laterally on the narrow sides of the light guide (3), - wherein in operating mode B2 the backlight (2) is switched on and the light sources (4) are switched off, and wherein in operating mode B1 at least the light sources (4) are switched on, characterized in that - that for at least a part of the output coupling elements (6) an orientation vector parallel to the large surface from which the light exits of each function surface with a preferred direction encloses an angle with a magnitude of up to 45°, wherein the orientation vector is a vector which maximizes the integral of the scalar product of this vector with a position-dependent normal vector of the function surface over the function surface, and wherein each normal vector encloses an angle between 5° and 85° with the large surface in question, whereby the optical fiber (3) exhibits a scattering behavior in the preferred direction that is at least 1.2 times stronger than in a direction perpendicular to the preferred direction, and thus exhibits anisotropic scattering behavior overall for light which passes through the optical fiber (3) through both large surfaces.

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.

[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. State of the art

[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 specific 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 lighting device which, in conjunction with a screen, enables the safe display of information 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. The invention should be implementable as cost-effectively as possible using simple means. In both operating modes, the highest possible resolution, preferably the native resolution of the screen used, should be visible. Furthermore, the solution should introduce only the lowest possible light loss, and the restricted viewing angle should achieve the most comprehensive possible visual screening effect.

[0014] This problem is solved according to the invention by a lighting device for 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 in which light is emitted by the lighting device within a narrower angular range compared to the free viewing mode. The lighting device comprises an area-like backlight that emits light within the restricted angular range and a plate-shaped light guide located in front of the backlight in the viewing direction. The light guide has two large surfaces and narrow sides connecting the large surfaces at their edges. The light guide has coupling elements on at least one of the large surfaces and / or within its volume and is at least 50% transparent, but preferably at least 70% transparent, to the light emitted by the backlight.Light sources are arranged laterally on the narrow sides of the light guide, including the possibility of light sources being arranged on only one side of the light guide. In operating mode B2, the backlight is on and the light sources are off, whereas in operating mode B1 at least the light sources are on. The shape, number per area, orientation, and / or extent of the coupling elements are selected such that the light guide—mediated via the coupling elements or at least a part thereof—exhibits anisotropic scattering behavior for light that penetrates the light guide through its large areas.

[0015] Specifically, this means that each output element has at least one functional surface for the defined output of light, at which light is coupled out of the optical fiber. In the simplest case, these functional surfaces are planar or at least have planar sections; however, they can also be curved in one or two linearly independent directions. An orientation vector is then defined for the functional surfaces, which lies parallel to the large surface at which the light emerges, i.e., in a plane parallel to said large surface. This orientation vector is a vector that maximizes the integral of the dot product of this vector with a position-dependent normal vector of the functional surface over the functional surface.For planar surfaces, the normal vector is of course constant at every point on the surface; however, for curved surfaces, it varies, as it is then the normal vector of a tangent plane at the respective point. Specifically, the orientation vector maximizes v→ the integral ∫An→⋅v→ dA, where n→ The normal vector of the functional surface A, which is position-dependent in coordinates x and y, forms an angle of up to 45° with a given preferred direction. The normal vector forms an angle between a minimum of 5° and a maximum of 85° with the large surface from which the light emerges; preferably, however, the lower limit is 30° and / or the upper limit is 60°.

[0016] If the coupling elements are designed in this way, this results in the optical fiber exhibiting a scattering behavior in the preferred direction that is at least 1.2 times stronger than in a direction perpendicular to the preferred direction, and thus overall exhibiting anisotropic scattering behavior for light that passes through the optical fiber through both large areas.

[0017] In principle, any area smaller than the hemisphere in front of the backlight can be considered a restricted angular range; however, a preferred angular range is, for example, + / -20° or 30° horizontally and / or vertically, or a cone around the surface normal or a selectable direction vector on the backlight; small amounts of light of less than 1% to 5% of maximum brightness can be disregarded when defining the restricted angular range.

[0018] 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.

[0019] Advantageously, the relevant part of the coupling elements comprises at least 30% of all coupling elements, preferably at least 50%, 70%, or 90% of all coupling elements. Additionally or alternatively, the orientation vectors of all coupling elements, on average, enclose an angle with the preferred direction of up to 45°, i.e., angles between -45° and +45°.

[0020] Preferably, the optical fiber exhibits stronger scattering behavior in the preferred direction than in the opposite direction. This is achieved by using appropriately asymmetrically shaped output coupling elements. More precisely, the cross-section of the output coupling elements should be asymmetric in a plane parallel to the preferred direction, provided that the scattering behavior without output coupling elements is the same in the preferred direction and perpendicular to it; if stronger scattering behavior in the preferred direction is achieved by other means, output coupling elements with a symmetrical cross-section can also be used. An asymmetrical cross-section in the preferred direction is also a prerequisite to achieve different scattering behavior in the preferred direction and in the opposite direction.

[0021] The anisotropic scattering behavior of the output coupling elements is characterized by measuring the scattering behavior with respect to at least two mutually perpendicular directions, along which the scattering behavior is measured: a preferred direction and a direction perpendicular to it. The scattering behavior to be considered is that which is caused by the output coupling elements when light passes approximately perpendicularly through an optical fiber.

[0022] Advantageously, the preferred viewing direction when looking at the lighting device is vertical, so that the light guide's scattering behavior is greater vertically than horizontally. The terms "vertical" and "horizontal" generally refer to two perpendicular directions on the surface of the backlight or a large area of ​​a light guide. In operation, depending on the orientation of the screen used with the lighting device (which is usually fixed), these directions correspond to a horizontal or vertical direction relative to the viewer's position and thus to the Earth's surface. The horizontal direction generally runs parallel to the line connecting the viewer's eyes; that is, their spatial orientation is ultimately what matters.

[0023] Preferably, the ratio of the area of ​​the functional surfaces of the aforementioned portion of the output coupling elements to the area of ​​a larger surface is defined such that the scattering behavior of the output coupling elements in the preferred direction is at least twice or three times greater than in the direction perpendicular to the preferred direction. However, this anisotropy can vary across the surface of the plate-shaped optical fiber. At areas of high density of output coupling elements, the anisotropy is typically higher than at areas of low density. For this purpose, the larger surface from which the light emerges is divided into sub-regions of a predetermined size, whereby the ratio of the area of ​​the functional surfaces in a sub-region to the area of ​​the respective sub-region differs for different sub-regions, so that the scattering behavior of the optical fiber varies across the larger surface from which the light emerges.

[0024] In a preferred embodiment of the lighting device, the light emitted by the backlight, at least in operating mode B2, is emitted horizontally within a limited angular range, so that the light experiences less scattering in the horizontal direction than in the vertical direction when passing through the light guide. As a result, light emitted within the limited angular range is typically scattered only minimally outside of this range, which enhances the privacy effect. This is a significant advantage of the invention.

[0025] "Slight" means, for example, that—due to the low scattering behavior—at an angle of, for example, 40° horizontally from the surface normal or another predetermined direction, measured along the horizontal direction, a maximum of 3% of the luminance is added by scattering due to the light guide emitted by the lighting device at an angle of 0°. In another embodiment, which can be combined with the first embodiment, "slight" means that in a solid angle range of ±20° in the preferred direction and ±10° in the direction perpendicular to the preferred direction, less than 10% of the light is scattered. Preferably, the haze value should also be below 15%.

[0026] However, the exact opposite can also be true: If the focusing of the light originating from the backlight into a limited horizontal angular range is too strong, a stronger scattering behavior in the horizontal direction (compared to the vertical direction) can be helpful, achieved by selectively fanning out the light. Furthermore, the anisotropic scattering behavior of at least some (or all) of the output coupling elements can be helpful in reducing visible interference patterns (e.g., moiré effects) that can occur in the interaction of the lighting system components with each other and / or with a screen.

[0027] The bidirectional transmittance distribution function (BTDF) is used to quantify the scattering behavior along two preferred axes. The BTDF quantifies how light with a specific angle of incidence (H) is scattered. i , V i) is transmitted. Scattered light is defined as any light deflected by more than 5°. To determine the measure of horizontal scattering S H To determine the horizontal scattering behavior, the measured BTDF is integrated accordingly. Similarly, the measure of vertical scatter S is determined. V (i.e., the vertical scattering behavior). The lower integration limit, i.e., the angle above which light is considered scattered, should be chosen larger than the usual 1.8° of the haze measurement, since the BTDF measurement can be performed with a laser beam that typically has a divergence of 4°.

[0028] The integrals for determining the measures S are given below. H as well as S V specified: SH=∫−90°−5BTDF(H,V=0°;Hi=0°,Vi=0°)dH+∫+5°+90°BTDF(H,V=0°;Hi=0°,Vi=0°)dH SV=∫−90°−5°BTDF(H=0°;V;Hi=0°,Vi=0°)dV+∫+5°+90°BTDF(H=0°;V;Hi=0°,Vi=0°)dV

[0029] In this, H is the angle in the horizontal direction, V is the angle in the vertical direction at which the transmission is measured, and H i and V i The angles at which a light beam strikes the object to be measured (here, 0° in each case) are defined. The anisotropy of the scattering behavior S required by the invention. V / S H This approach can therefore be formulated as follows: S V / S H ≠ 1 or for frequent use cases S V / S H > 1.

[0030] The following Table 1 gives exemplary values ​​for the normalized variance S. H as well as S V (i.e., for the scattering behavior) for different measuring points P1 to P5 on the plate-shaped optical fiber: Table 1: Example normalized values ​​for the dispersion SH and SV. Dispersion S H Dispersion S V Anisotropy S V / S H P1 0,037 0,139 3,757 P2 0,030 0,210 7,000 P3 0,054 0,372 6,889 P5 0,066 0,490 7,424 P4 0,083 0,598 7,205

[0031] The anisotropy S V / S HThis indicates how much stronger the scattering behavior is along the vertical direction. As described above, scattering here is understood to mean a deflection greater than 5°. The anisotropic scattering behavior in this example is obvious.

[0032] The extraction elements can be distributed in or on the optical fiber in various ways during its manufacture, depending on the adaptable and predefined conditions for light extraction. These extraction elements are locally confined structural modifications within the volume and / or on the surfaces of the optical fiber. Specifically excluded from the term "extraction element" are additional optical layers applied to the surfaces of the optical fiber, such as diffusion layers, reflection layers, (dual) brightness-enhancing collimating layers (brightness enhancement film - BEF), or polarization-recycling layers, such as polarization-selective Bragg mirrors (dual brightness enhancement film - (D)BEF) or wire-grid 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.

[0033] The structure of the coupling elements is specified according to the criteria described above, whereby the effect of each coupling element is known at least approximately and properties of the optical fiber or of the light emerging from the optical fiber can be specifically determined by a predefinable structure and distribution of the coupling elements, whereby the ratio of the sum of the areas of the functional surfaces to the area of ​​the total surface of the large area from which light is coupled out is particularly important.

[0034] 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.

[0035] 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 VThe maximum luminance can be defined as the ratio of the smallest luminance value to the largest value for a given area. 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".

[0036] The two operating modes, B1 and B2, differ in that in operating mode B2 the backlight is switched on and the light sources (on the narrow sides of the light guide) are switched off, while in operating mode B1 at least the light sources (on the narrow sides of the light guide) are switched on. Only light that was originally emitted into the light guide by the light sources and subsequently emitted again via the output elements is considered, with the emission occurring almost exclusively via the output elements.

[0037] It is possible that decoupling elements are attached to both large surfaces and / or additionally, optionally, within the volume.

[0038] 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).

[0039] Furthermore, for some applications it is advantageous that the aforementioned restricted angular range is designed asymmetrically around the surface normal of the backlight. The asymmetrical design is preferably implemented in one of the preferred directions. This is particularly helpful in vehicle applications, for example, when a screen to be combined with the lighting device 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 angular range for viewing, which in operating mode B2 is exclusively available to the front passenger, must be designed asymmetrically, i.e., directed towards the front passenger. The preferred direction in which the asymmetry is formed corresponds here to the horizontal.

[0040] 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.

[0041] 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.

[0042] Alternatively, and more technically simply, 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.

[0043] 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.

[0044] 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.

[0045] 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). Alternatively, a so-called focused backlight unit can be used, in which light from a (different) light guide is already coupled into a restricted angular range and, if necessary, further directed, deflected, or shaped.

[0046] Accordingly, the backlight can basically be constructed like an LED backlight, for example as a so-called direct-lit LED backlight, edge LED backlight, OLED or as another surface light source, on which, for example, at least one permanent privacy filter (with microlouvers) is applied.

[0047] For all the aforementioned variants of the lighting device, it is particularly advantageous if they further include a transmissive screen arranged in front of the lighting device in the direction of viewing, preferably in the form of an LCD panel, which can be operated in at least two operating modes due to the lighting device: B1 for a free viewing mode and B2 for a restricted viewing mode.

[0048] In some cases, it can also be helpful if the screen exhibits anisotropic scattering behavior for light passing through its large surface area. In such cases, the preferred direction in which the screen's scattering behavior is stronger should correspond to the preferred direction in which the optical fiber exhibits the strongest scattering behavior. This will often be the vertical direction. Furthermore, it is possible to arrange anisotropically scattering layers between the screen and the optical fiber, for example, to mask optical artifacts on the optical fiber, while again minimizing or completely unaffected the visual privacy effect. Anisotropically scattering layers are known in the art, such as holographic diffusers or binary (computer-generated) holograms.

[0049] 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.

[0050] A further embodiment of the lighting device extended by a screen consists of an additional light guide (e.g., made of glass or plastic) arranged in the viewing direction in front of the screen, containing means for extracting light, which can be supplied with light laterally by light sources. The means used for extraction here are, for example, those described above, or those known in the prior art, such as nanoparticles like titanium dioxide, barium sulfate, etc., in suitable sizes and quantities – as described, for example, in WO 2015 / 121398 A1 and WO 2017 / 089482 A1 – which are homogeneously distributed within the volume of the light guide. With this embodiment, any residual light that may still be unintentionally present in operating mode B2 can be superimposed or...The light source is so overexposed that no contrast is perceptible, and thus the corresponding light sources for the further light guide are designed to emit colored or white light. The light sources can emit light in a color that may or may not be present in the image displayed by the transmissive screen. No image perception is possible from the unapproved angles.

[0051] The lighting device according to the invention, with a screen, is particularly advantageous when used 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.

[0052] A lighting device according to the invention with a screen can be used for entering or displaying confidential data, for example PINs, emails, SMS or passwords, at ATMs, payment terminals or mobile devices.

[0053] 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.

[0054] 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.

[0055] In principle, the performance of the invention is maintained if the parameters described above are varied within certain limits.

[0056] 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

[0057] 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 the lighting device in a first embodiment in conjunction with a screen in mode B1 for a free viewing mode, Fig. 4. A schematic diagram of the lighting device in a first embodiment in conjunction with a screen in mode B2 for a restricted viewing mode. Fig. 5A A schematic diagram by top view of an optical fiber which is penetrated by a light beam through its large surfaces, to illustrate the anisotropic scattering behavior, Fig. 5B-5C Cross-sectional views through the light guide Fig. 5A along two mutually orthogonal directions, Fig. 6A-6C Schematic diagrams of various designs of a coupling element, Fig. 7A a top view of an output coupling element with sketched beam path, Fig. 7B a sectional view through the coupling element from Fig. 7A with indicated beam paths for light penetrating the light guide and the coupling elements, and Fig. 7C a cross-sectional view through another coupling element with indicated beam paths for light passing through the light guide and the coupling elements. Detailed description of the drawings

[0058] In Fig. Figure 1 is a schematic diagram illustrating the extraction of light coupled laterally from light sources 4 into a light guide 3. The diagram shows the lower surface of the light guide 3, where the extraction elements 6 are located. The extracted light exits the light guide 3 predominantly (more than 50%) at the upper surface. In the horizontal direction—which lies in the plane of the leaf and runs from right to left, while the vertical direction points into the leaf—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 are 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 (bold rays) are reflected back into the optical fiber 3 at the outer wall until they finally (possibly repeatedly) reach an output coupling element 6 for the desired output. The output coupling 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.

[0059] 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 large surface of the light guide 3, on which the extraction elements 6 are located. The light also exits the light guide 3 predominantly through the upper large 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.

[0060] Fig. 3 and Fig. Figure 4 shows a lighting device 1a which can be operated in at least two operating modes: B1 for a free viewing mode and B2 for a restricted viewing mode in which light is emitted from the lighting device within a narrower angular range compared to the free viewing mode. The lighting device 1a comprises an area-like backlight 2 that emits light within the restricted angular range and a plate-shaped light guide 3 located in front of the backlight 2 in the viewing direction. The light guide 3 has two large surfaces and narrow sides connecting the large surfaces at their edges. The light guide 3 has coupling elements 6 on at least one of the large surfaces and / or within its volume and is at least 50% transparent, but preferably at least 70% transparent, to the light emitted from the backlight 2.Light sources are arranged laterally on the narrow sides of the light guide, including the possibility that light sources are arranged on only one side of the light guide. In operating mode B2, the backlight is on and the light sources are off, whereas in operating mode B1 at least the light sources are on.

[0061] The shape, number per area, orientation and / or extent of the coupling elements 6 is chosen such that the optical fiber 3 - mediated via the coupling elements 6 or at least a part thereof - exhibits anisotropic scattering behavior for light which penetrates the optical fiber 3 through its large areas.

[0062] Specifically, this means that each output element 6 has at least one functional surface 5 for the defined output of light, at which light is accordingly coupled out of the optical fiber. In the simplest case, these functional surfaces 5 are planar or at least have planar surface sections; however, they can also be surfaces curved in one or two linearly independent directions. An orientation vector is now defined for the functional surfaces 5, which lies parallel to the large surface at which the light emerges, i.e., in a plane parallel to said large surface. This orientation vector is a vector that maximizes the integral of the scalar product of this vector with a position-dependent normal vector of the functional surface 5 over the functional surface 5.For planar surfaces, the normal vector is of course constant at every point on the function surface 5; however, for curved surfaces, it varies, as it is then the normal vector of a tangent plane at the respective point. Specifically, the orientation vector maximizes v→ the integral ∫A n→⋅v→ dA, where n→ The normal vector of the functional surface 5, denoted here by "A", is position-dependent in coordinates x and y. This alignment vector forms an angle of up to 45° with a given preferred direction. The normal vector forms an angle between a minimum of 5° and a maximum of 85° with the large surface from which the light emerges, preferably with a lower limit of 30° and / or an upper limit of 60°. The calculated alignment vector is a measure of the rotation of the functional surface 5 of the output coupling element 6 relative to the preferred direction, but does not necessarily correspond to the "average" of all surface normals that may be present on the functional surface 5 or their projection onto the large surfaces of the optical fiber 3.

[0063] If the coupling elements 6 are designed in this way, this results in the optical fiber 3 exhibiting a scattering behavior in the preferred direction that is at least 1.2 times stronger, preferably at least 2 times stronger or 3 times stronger, than in a direction perpendicular to the preferred direction, and thus exhibiting anisotropic scattering behavior overall for light that passes through the optical fiber 3 through both large surfaces.

[0064] The large area from which light emerges can also be divided into sub-areas of a given size, whereby the ratio of the area of ​​the functional surfaces in a sub-area to the area of ​​the respective sub-area is different for different sub-areas, so that the scattering behavior of the light guide 3 varies over the large area from which the light emerges.

[0065] In Fig. Figure 3 shows a schematic diagram of such a lighting device 1a in a first embodiment in conjunction with a screen 1 in mode B1 for a free viewing mode. In principle, any area smaller than the hemisphere in front of the backlight can be considered as a restricted angular range; however, preferably, an angular range of ±20° or 30° horizontally and / or vertically, or as a cone around the surface normal or a selectable direction vector on the backlight 2, is meant; small amounts of light of less than 1% to 5% of the maximum brightness can be disregarded when defining the restricted angular range.

[0066] The schematic diagrams in the drawings Fig. 3 and Fig. 4 are sectional views.

[0067] In contrast, Fig. Figure 4 shows a schematic diagram of the lighting device in a first embodiment in conjunction with a screen in mode B2 for a restricted viewing mode. The thick arrows indicate the angularly restricted light, while the dashed thin arrows symbolize that very little light is scattered horizontally compared to the light from the backlight 2. The resulting anisotropic scattering behavior of the output coupling elements 6 on the light guide 3, which is stronger in the vertical direction than in the horizontal direction, is discussed further below in connection with Fig. 5A - 5C explained in more detail.

[0068] In a preferred embodiment of the lighting device 1a, the light emitted by the backlight 2, at least in operating mode B2, is emitted in the horizontal direction within a restricted angular range, so that the light experiences less scattering in the horizontal direction than in the vertical direction when passing through the light guide 3, as shown in Fig. 4 indicated. This means that light emitted into the restricted angular range is only slightly scattered outside of said restricted angular range.

[0069] The two operating modes B1 and B2 differ in that in operating mode B2 the backlight 2 is switched on and the light sources 4 (on the narrow sides or on one narrow side of the light guide 3) are switched off, whereas in operating mode B1 at least the light sources (on the narrow sides of the light guide) are switched on. The light sources 4 emit light into the light guide 3. Subsequently, the output coupling elements 6 couple the light out of the light guide 3, with the emission occurring almost exclusively via the output coupling elements 6.

[0070] The backlight 2 consists, for example, of a flat spotlight, preferably a further light guide with additional light sources arranged laterally or on the back, and at least one light collimator integrated into and / or arranged in front of the flat spotlight, such as at least one prism film and / or at least one privacy filter (e.g. a lamellar filter).

[0071] Accordingly, the backlight 2 can basically be constructed like an LED backlight, for example as a so-called direct-lit LED backlight, edge-lit LED backlight, OLED or as another surface light source, on which, for example, at least one permanent privacy filter (e.g. with microlouvers) and / or another light collimator is applied or arranged.

[0072] The light guide 3 preferably consists of a transparent, thermoplastic or thermoelastic polymer, e.g., plastic, or of glass. For example, the light guide 3 can be made of polycarbonate.

[0073] Advantageously, said portion of the coupling elements 6 comprises at least 30%, preferably at least 50%, and particularly preferably more than 90% of the coupling elements 6, which are then selected in their shape, number per area, orientation, and / or extent such that they exhibit anisotropic scattering behavior for light penetrating the optical fiber 3 through its large areas. Alternatively or additionally, the orientation vectors of all coupling elements, on average, form an angle with the preferred direction of up to 45°. In particular, the optical fiber 3 can exhibit stronger scattering behavior in the preferred direction than in a direction perpendicular to it.

[0074] The anisotropic scattering behavior of the output coupling elements 6 is characterized by measuring the scattering behavior with respect to at least two mutually perpendicular directions along which the scattering behavior is measured: a preferred direction and a direction perpendicular to it. Particular attention is paid to the scattering behavior that results from the output coupling elements 6 when light passes approximately perpendicularly through an optical fiber 3. However, reference directions other than the perpendicular to the optical fiber 3 can also be considered.

[0075] The terms "vertical" and "horizontal" initially refer generally to a preferred direction and a perpendicular direction on the surface of the backlight or a large area of ​​an optical fiber. Advantageously, when a viewer looks at the illumination device 1a, the preferred direction corresponds to the vertical direction, and the perpendicular direction corresponds to the vertical direction, whereby the scattering behavior of the output coupling elements 6 is greater in the vertical direction than in the horizontal direction. As a rule, the horizontal direction also corresponds to the horizontal on the Earth's surface, at least for screens with optical fibers that do not change their orientation in this respect. In general, however, the horizontal direction should be understood as the direction that runs parallel to a line connecting a viewer's eyes, assuming that when the viewer moves, the direction of the horizontal direction changes.This line also changes the position of the screen being viewed, as is the case with mobile devices. With regard to the coordinate system of a mobile screen, it is ultimately an arbitrary definition which direction is horizontal and which is vertical; both directions simply need to be orthogonal to each other.

[0076] In this regard, it shows Fig. Figure 5A is a schematic diagram showing a top view of an optical fiber 3, through which a light beam is penetrated by its large surfaces, to illustrate the anisotropic scattering behavior. The dot in the circle represents a stylized light beam incident perpendicularly from below onto the optical fiber 3, penetrating the optical fiber 3 from large surface to large surface and also striking coupling elements 6 (not shown in the diagram). The short dashed arrow in the horizontal direction, compared to the longer dashed arrow in the vertical direction, indicates that, due to the anisotropic scattering behavior of the corresponding coupling elements 6, the scattering behavior in the horizontal direction is smaller than in the vertical direction.

[0077] Fig. Figure 5B shows a cross-sectional view through the optical fiber 3 in the direction perpendicular to the preferred direction, i.e., in this case in the horizontal direction. Fig. Figure 5C, on the other hand, shows a cross-sectional view through the optical fiber 3 in the preferred direction, i.e., in this case, in the vertical direction. The output coupling elements are not shown. Thick arrows symbolize the light penetrating the optical fiber 3 through both large surfaces—here, the top and bottom—which is emitted by the backlight 2 (not shown here). The dashed arrows indicate the maximum scattering angle range in the preferred direction. Fig. 5C noticeably larger than in the perpendicular direction in Fig. 5B is.

[0078] 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 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.

[0079] This includes Fig. Figure 6A 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 and are described in detail below. Fig. 6B and Fig. 6C is shown. The functional surface is always the surface pointing diagonally upwards. The one in Fig. The coupling element 6 shown in Figure 6A has a simplified form; as a rule, the functional surface shown here in plan form is rather rounded at its upper and lower edges and may also exhibit a curvature in one or two dimensions along its entire length, as shown by the Fig. 6B and Fig. Figure 6C shows. Typical dimensions are between 1 µm and 100 µm in each spatial dimension, preferably between 2 µm and 40 µm, wherein the height - in the plane of the drawing the vertical direction - is preferably not greater than 20 µm.

[0080] Fig. Figure 7A shows a top view of a coupling element 6, as it is in Fig. Figure 6A shows an example and can be designed, for instance, as a recess at the light entry surface, i.e., the large area of ​​the light guide where the light emitted from the backlight enters it. Light rays – not shown here – strike the light entry surface from below, i.e., from below the plane of the leaf, perpendicular to it. Due to the deflection at the functional surface 5, the light is deflected by up to 45° in the direction of the preferred direction – here the upward-pointing vertical direction in the plane of the leaf – which is better illustrated in Figure 6A. Fig. 7B can be seen. The functional surface 5 does not act perpendicular to the preferred direction, which is why the scattering effect is significantly lower in this direction.

[0081] Fig. 7B shows a sectional view of the coupling element from Fig. 7A, which is formed as a material recess in the optical fiber, the material of which is indicated by corresponding hatching. Due to the functional surface 5, the light is deflected in the preferred direction – here the horizontal direction in the plane of the sheet – by refraction and also scattering, as indicated by the two arrows. Perpendicular to this, i.e., also perpendicular to the plane of the sheet, the functional surface 5 has no effect; however, undesirable scattering components arise perpendicular to the preferred direction due to residual effects of the three-dimensional extent of the output coupling element.

[0082] Fig. 7C finally shows the sectional view of another output element, which is opposite the output element in Fig. 7B has two functional surfaces 5. This decoupling element 6 is also designed analogously as a recess in the material. The effect of the functional surfaces 5 corresponds to that in Fig. 7B.

[0083] For all the aforementioned variants of the lighting device 1a, it is particularly advantageous if they further include a transmissive image transmitter arranged in the viewing direction in front of the lighting device 1a as a screen 1, preferably in the form of an LCD panel, which can be operated in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode due to the lighting device 1a.

[0084] In some cases, it can also be helpful if screen 1 exhibits anisotropic scattering behavior for light passing through its large surface area. In such cases, the preferred direction in which the scattering behavior of screen 1 is lower should correspond to the preferred direction in which the optical fiber also exhibits the lower scattering behavior. This will often be the horizontal direction.

[0085] Means for reducing or controlling reflections, for example an anti-glare and / or an anti-reflective coating, may be arranged on the top surface of the screen 1 and / or on at least one of the large surfaces of the light guide 3 as well as on at least one of the privacy filters, if present.

[0086] 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.

[0087] The lighting device and the screen that can be implemented with it, as described above, solve the stated problem: They enable practically feasible solutions for ensuring the safe display of information through a selectively restricted viewing angle, while in another operating mode, an unobstructed view with no limitations on the viewing angle is possible. The invention can be implemented cost-effectively using simple means. In both operating modes, the native resolution of the screen can be utilized. Furthermore, the solution introduces only minimal light loss, and the restricted viewing angle achieves the most comprehensive possible visual privacy effect.

[0088] The invention described above can be advantageously applied wherever confidential data is displayed and / or entered, such as during PIN entry or data display at ATMs or payment terminals, or for password entry or reading emails on mobile devices. As described above, the invention can also be used in passenger cars. Reference symbol list 1 screen 1a Lighting equipment 2 Backlight 3 fiber optic cables 4 light bulbs 5 Functional area 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, 0050] US 2020 / 012129 A1

[0011] WO 2017 / 089482 A1

[0050]

Claims

[1] Lighting device (1a) for a screen (1) which can be operated in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode in which light is emitted from the lighting device in an angular range that is more restricted than in the free viewing mode, comprising - an area-like extended backlight (2) that emits light into the restricted angular range, - a plate-shaped light guide (3) located in the viewing direction in front of the backlight (2) with two large surfaces and narrow sides connecting the large surfaces at their edges, wherein the light guide (3) has coupling elements (6) on at least one of the large surfaces and / or within its volume, wherein the light guide (3) is at least 50% transparent to the light emanating from the backlight (2), wherein each coupling element (6) has at least one functional surface for the defined coupling of light, at which light is coupled out of the light guide (3), - light sources (4) arranged laterally on the narrow sides of the light guide (3), - wherein in operating mode B2 the backlight (2) is switched on and the light sources (4) are switched off, and wherein in operating mode B1 at least the light sources (4) are switched on, characterized by , - that for at least a part of the output coupling elements (6) an orientation vector parallel to the large surface from which the light exits of each function surface with a preferred direction encloses an angle with a magnitude of up to 45°, wherein the orientation vector is a vector which maximizes the integral of the scalar product of this vector with a position-dependent normal vector of the function surface over the function surface, and wherein each normal vector encloses an angle between 5° and 85° with the large surface in question, whereby the optical fiber (3) exhibits a scattering behavior in the preferred direction that is at least 1.2 times stronger than in a direction perpendicular to the preferred direction, and thus exhibits anisotropic scattering behavior overall for light which passes through the optical fiber (3) through both large surfaces. [2] Lighting device (1a) according to claim 1, characterized by, that the part of the coupling elements (6) comprises at least 30% of all coupling elements and / or that, on average, the orientation vectors of all coupling elements enclose an angle with the preferred direction of up to 45°. [3] Lighting device (1a) according to claim 1 or 2, characterized by , that the optical fiber (3) exhibits a stronger scattering behavior in the preferred direction than in the opposite direction. [4] Lighting device (1a) according to claim 3, characterized by , that the preferred direction when a viewer looks at the lighting device (1a) corresponds to the vertical direction, so that the scattering behavior of the light guide (3) is greater in the vertical direction than in the horizontal direction, the horizontal direction being parallel to a line between the eyes of the viewer. [5] Lighting device (1a) according to any one of claims 1 to 4, characterized by, that the ratio of the area of ​​the functional areas of the said part of the coupling elements to the area of ​​a large area is determined such that the scattering behavior of the coupling elements (6) in the preferred direction is at least by a factor of 2 or a factor of 3 greater than in the direction perpendicular to the preferred direction. [6] Lighting device (1a) according to any one of claims 1 to 5, characterized by , that the large area from which the light emerges is divided into sub-areas of a given size and the ratio of the area of ​​the functional surfaces in one sub-area to the area of ​​the respective sub-area is different for different sub-areas, so that the scattering behavior of the optical fiber (3) varies over the large area from which the light emerges.

Images