Screen for a free and a restricted view mode

Abstract

Screen (1) which can be operated in at least two operating modes B1 and B2, comprising - a surface-like backlight (2) which emits light along a first preferred direction in a restricted angular range of not more than 60 degrees, - a plate-shaped first light guide (3) located in front of the background lighting (2) in the viewing direction, which has decoupling elements on at least one of the large surfaces and / or within its volume, and which decoups light that is laterally coupled into it along the first preferred direction in a wide angular range of at least 100 degrees, - illuminants (4) arranged laterally on the narrow sides of the first light guide (3), - a transmissive imager (5) which is located in front of the first light guide (3) in the viewing direction, - a light filter (6) which transmits light along a second preferred direction, which is perpendicular to said first preferred direction, only in a limited angular range of at most 60 degrees, and which is arranged in front of or behind the transmissive imager (5) in the viewing direction, - wherein in operating mode B2 the background lighting (2) is switched on and the lamps (4) are switched off, and wherein in operating mode B1 at least the lamps (4) are switched on, so that - the screen (1) in operating mode B1 is visible along the first preferred direction from a wide angular range of at least 100 degrees, and is visible along the second preferred direction only from a restricted angular range of at most 60 degrees, and so that - the screen (1) in operating mode B2 is visible along both the first and the second preferred direction only from a limited angular range of not more than 60 degrees, - whereby the screen is visible from the angular ranges defined above if and only if at least 4% of the maximum brightness emitted by the screen (1) in any direction is emitted into such an angular range.

Description

Field of the InventionIn recent years, great advances have been made in widening the visual angle of LCDs. However, there are often situations where this very wide range of vision of a screen may be disadvantageous. Increasingly, information is also becoming available on mobile devices such as notebooks and tablet PCs, such as bank data or other personal information, and sensitive data. Accordingly, people need control over who can see these sensitive data; they must be able to choose between a wide viewing angle in order to share information on their display with others, e.g. when viewing vacation photographs or also for advertising purposes. On the other hand, they require a small viewing angle if they want to handle the image information confidentially.A similar problem arises in vehicle construction: there, when the engine is switched on, the driver must not be distracted by image contents, such as digital entertainment programs, while the passenger would like to consume the same while driving. Thus, a screen is needed that can switch between the respective display modes.Prior ArtAdditional films based on micro-lamellae have already been used for mobile displays in order to achieve their optical data protection. However, these films were not (switchable), they had to be laid up first by hand and then removed again. It must also be transported separately to the display if it is not required. A substantial disadvantage of the use of such laminated films is also associated with the associated light losses.U.S. Pat. No. 6,765,550 B2 describes such a visual protection by micro-lamellae. The greatest disadvantage here is the mechanical removal or mechanical attachment of the filter and the loss of light in the protected mode.U.S. Pat. No. 5,993,940 A describes the use of a film which has small prism strips arranged uniformly on its surface in order to achieve a privacy mode. Development and production are very complicated.In WO 2012 / 033583 A1, the switching between free and restricted view is produced by means of the control of liquid crystals between so-called "chromonic" layers. This results in a loss of light and the outlay is very high.US 2012 / 0235891 A1 describes a very complex backlight in a screen. According to FIGS. 1 and 15, not only a plurality of light guides are used there, but also further complex optical elements such as microlens elements 40 and prism structures 50, which convert the light from the rear illumination on the way to the front illumination. This is expensive and complicated to implement and also associated with light loss. According to the variant according to FIG. 17 in US 2012 / 0235891, both light sources 4R and 18 produce light with a narrow illumination angle, wherein the light from the rear light source 18 is only converted in a complicated manner into light with a large illumination angle. This complex conversion is, as already mentioned above, greatly reducing brightness.According to JP 2007-155783 A, special optical surfaces 19 are used which are expensive to calculate and produce and which then deflect light into different narrow or wide ranges depending on the angle of incidence of light. These structures are similar to Fresnel lenses. Furthermore, interference flanks are present which deflect light in undesired directions. It thus remains unclear whether really useful light distributions can be achieved.US 2013 / 0308185 A1 describes a special light guide formed with steps, which emits light on a large surface in different directions, depending on the direction from which it is illuminated from a narrow side. In cooperation with a transmissive image display device, e.g. an LC display, a screen switchable between free and restricted viewing modes can thus be generated. One disadvantage here is that the restricted visual effect can be generated simultaneously either only for left / right or for top / bottom, but not for left / right / top / bottom, as is necessary for particular payment processes. In addition, a residual light is still visible from blocked viewing angles even in the restricted viewing mode.WO 2015 / 121398 A1 by the applicant describes a screen with two operating modes in which particles that are essential for switching the operating modes are present in the volume of the corresponding light guide. However, the scattering particles selected there from a polymer generally have the disadvantage that light is coupled out from both large surfaces, as a result of which approximately half of the useful light can be emitted in the wrong direction, namely toward the backlighting, and cannot be recycled to a sufficient extent there on account of the structure. Moreover, the scattering particles of polymer distributed in the volume of the light guide can under certain circumstances, in particular at a higher concentration, lead to scattering effects which reduce the visual protection effect in the protected operating mode.WO 2015 / 121 398 A1 by the applicant describes a switchable lighting device and its use. This does not make it readily possible to switch between two operating modes, of which a restricted viewing angle can be realized in the horizontal and simultaneously in the vertical direction, while in the other operating mode an unrestricted view in viewing angle is possible only in one direction, for example the horizontal direction. The same applies to WO 2019 / 034 557 A1 and WO 2017 / 089482 A1 of the applicant.WO 2017 / 097975 A1 discloses a screen for free and restricted viewing modes. In this case, the viewing angle restriction is generated by fading with, for example, white light into those angular ranges which are not intended to be perceptible. This document likewise does not suggest switching between two operating modes, of which a restricted viewing angle can be realized in the horizontal and simultaneously in the vertical direction, while in the other operating mode an unrestricted view in viewing angle is possible only in one direction, for example the horizontal direction.US 2019 / 0369319 A1 describes an illumination device with crossed prism grids. This document also does not suggest switching between two operating modes, of which a restricted viewing angle can be realized in the horizontal and simultaneously in the vertical direction, while in the other operating mode an unrestricted view in viewing angle is possible only in one direction, for example the horizontal direction. The latter also applies to DE 11 2010 004 660 T5, which discloses a liquid crystal display device.JP 002007212507 A describes an arrangement by which the light of a screen can be restricted in the horizontal and vertical directions. However, in this case, no changeover is possible, which for example optionally enables the restriction only along the horizontal.The aforementioned methods and arrangements are generally associated with the disadvantage that they significantly reduce the brightness of the base screen and / or require an active, but at least one special, optical element for mode switching and / or require complicated and expensive production and / or reduce the resolution in the freely viewable mode.Moreover, the vertical direction is disregarded in the prior art, although requirements for visual protection can also be additionally met there.DESCRIPTION OF THE INVENTIONIt is therefore the object of the invention to describe a screen which can realize a secure display of information by means of an optionally restricted viewing angle in the horizontal and vertical directions, wherein in a further operating mode a view which is restricted only in one direction, for example the horizontal view, as far as possible in the viewing angle, is to be possible. It should thus be possible to include the vertical direction in the visual protection.The invention is intended to be implementable as inexpensively as possible using simple means. In both operating modes, the highest possible resolution, particularly preferably the native resolution of the screen used, should be visible.This object is achieved according to the invention by a screen which can be operated in at least two operating modes B1 and B2, comprisinga surface-like extended background illumination which emits light along a first preferred direction into a restricted angular range of at most 60 degrees,a plate-shaped first light guide which is situated in front of the backlighting in the viewing direction and has output elements on at least one of the large surfaces and / or within its volume, and which outputs light which is coupled laterally into it along the first preferred direction into a wide angle range of at least 100 degrees,lighting means arranged laterally on narrow sides of the first light guide,a transmissive imager which is situated in front of the first light guide in the viewing direction,a light filter which transmits light along a second preferred direction which is perpendicular to said first preferred direction only in a restricted angular range of at most 60 degrees, and which is arranged in front of or behind the transmissive imager in the viewing direction,wherein in operating mode B 2 the backlighting is switched on and the lighting means are switched off, and wherein in operating mode B 1 at least the lighting means are switched on, so thatthe screen is visible in the operating mode B 1 from a wide angular range of at least 100 degrees along the first preferred direction, and is visible only from a restricted angular range of at most 60 degrees along the second preferred direction, and so thatthe screen in operating mode B 2 is visible only from a restricted angular range of at most 60 degrees, both along the first and along the second preferred direction,wherein the screen is visible from the above defined angular ranges exactly when at least 4%, preferably only at least 2%, of the maximum brightness emitted by the screen in any direction is emitted into such an angular range.In preferred embodiments, the lower edge of the screen forms the reference for the horizontal direction and the first preferred direction lies parallel to this horizontal direction. As a result, the vertical direction, i.e. the second preferred direction, is also inherently defined.In other words: The screen can be switched in the two operating modes between a 4-way visual protection, i.e. a visual protection which acts in simultaneously four directions, such as top, bottom, left and right, and a 2-way visual protection, i.e. a visual protection which is active in simultaneously only two directions, such as only top and bottom or only left and right.In principle, other operating modes would also be conceivable within the scope of the invention, for example an operating mode B 3 in which the visual protection is effective only in one direction, that is to say for example at the top or at the bottom, or even in three directions, for example at the top, left and right.Furthermore, it is possible that at least one such restricted angular range of at most 60 degrees is oriented symmetrically about the perpendicular bisector onto the image-reproducing surface of the screen.Alternatively, at least one such restricted angular range of at most 60 degrees may be oriented asymmetrically about the perpendicular bisector to the image-reproducing surface of the screen. This is helpful in particular in applications in the vehicle, for example if 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 in the middle between the driver and the passenger. Then, the restricted angular range released in operating mode B 2 exclusively for the passenger must be designed asymmetrically for vision, i.e. directed towards the passenger. The preferred direction in which the asymmetry is formed corresponds here to the horizontal.It is also possible, furthermore, for the operating mode B2 for even both said restricted angular ranges of at most 60 degrees to be oriented asymmetrically in each case about the mean perpendicular to the image-reproducing surface of the screen.Furthermore, for very particular applications, the asymmetry in question can even differ between the two modes of operation B 1 and B 2.The two operating modes B 1 and B 2 finally differ in that in operating mode B 2 the backlighting is switched on and the lighting means (on the narrow sides of the first light guide) are switched off, and wherein in operating mode B 1 at least the lighting means (on the narrow sides of the first light guide) are switched on. Only light is taken into account here, which was originally radiated into the first light guide by the lighting means and was subsequently radiated again by the latter via the decoupling elements, wherein the radiation takes place almost exclusively via the decoupling elements.In operating mode B 1, as described above, at least the lighting means on the narrow sides of the first light guide are switched on. It is possible here for the background illumination to be switched on or off.Reflector bands can be attached to those narrow sides of the first light guide, on which no lighting means are arranged, in order to increase the efficiency, or else to reduce uncontrolled light in the build-up absorber.It is possible for decoupling elements to be attached to both large surfaces of the first light guide and additionally optionally in its volume.Furthermore, a distribution of the decoupling elements on at least one of the large surfaces and / or within the volume of the first light guide is predefined such that light radiated into the first light guide by the lighting means and decoupled from the first light guide by the decoupling elements satisfies the following condition:at least 50% of the amount of light coupled out on one of the large surfaces between an angle range of -50° and +50° with respect to the surface normal of the large surface is radiated between an angle range of -20° and +20° with respect to the second preferred direction, and / or at least 70% of the amount of light coupled out on one of the large surfaces between an angle range of -50° and +50° with respect to the surface normal of the large surface is radiated between an angle range of -30° and +30° with respect to the second preferred direction.Furthermore, it is advantageous if at least 50% of the amount of light coupled out of the first light guide is coupled out in the direction away from the background illumination or towards it.In a development of this configuration, a distribution of the decoupling elements on at least one of the large areas and / or within the volume of the first light guide is predefined such that light radiated into the first light guide by the lighting means and decoupled from the first light guide by the decoupling elements is radiated along the second preferred direction into a restricted angular range of at most 60 degrees.The number of decoupling elements per area and the extent thereof are selected such that the first light guide has an average haze value of less than 7% over at least 50%, preferably 80% of its area, preferably less than 2%, particularly preferably less than 1%, measured according to ASTM D1003 - wherein the measurement according to the more common procedure A is used as a basis for a hazemeter as a reference-, whereby the light emitted by the backlight at least in the operating mode B2 into a restricted angular range is at most slightly scattered outside said angular range during passage through the first light guide. By "slight" is meant, for example, that, due to the small haze, a maximum of 1% of the luminance at an angle of, for example, horizontally 40° from the surface normal is added by scattering, which the backlighting emits at an angle of 0°.During the production of the first light guide, the decoupling elements can be distributed in principle in different ways in or on the first light guide according to adaptable and predeterminable conditions for decoupling the light. The decoupling elements are locally limited structural changes in the volume and / or on the surfaces of the light guide. The term decoupling element therefore expressly does not fall under the term additional optical layers which are applied to the surfaces of the light guide, i.e. for example diffusion layers, reflection layers or (dual) brightness-enhancing or else polarization-recycling layers ((dual) brightness enhancement film-(D)BEF). These additional layers, which do not fall under the term "decoupling element", are connected to the first light guide only at the edges, but lie only loosely on the areas of the large surfaces and do not form a physical unit with the first light guide. In contrast, lacquers applied to the large surfaces, which are connected to the light guide by chemical reactions, form a physical unit; such lacquers are therefore no longer to be separated from one another; such lacquers are therefore not included as an additional layer in the above-mentioned sense.The structure of the decoupling elements can be predefined, so that the effect of each decoupling element is at least approximately known and properties of the first light guide or of the light coming from the first light guide can be defined in a targeted manner by a predefinable distribution of the decoupling elements.The required properties for the decoupling elements that are helpful for the invention with regard to their number per unit area, their shape and extent in three dimensions and their distribution on at least one of the large areas and / or within the volume of the first light guide can be determined, for example, with an optical simulation software such as, for example, "LightTool" from Synopsis or other supplier and then correspondingly physically implemented.Examples of possible helpful three-dimensional shapes of the decoupling elements are described in U.S. Pat. No. 2018 / 0088270 A1, here in particular in the drawings FIGS. 3A, 4B, 5A, 9 or 10 in conjunction with the associated description text.In an exemplary embodiment, such decoupling elements can be distributed in a large number (e.g. several million pieces per square decimeter) according to the aforementioned FIG. 5A of US 2018 / 0088270 A1 uniformly or with varying density (in particular with increasing density with increasing distance from the lighting means) on the lower large surface of the corresponding light guide, wherein they have a tilt angle in the prism of approximately 50 degrees. Light is thus coupled out in a predeterminable angular range, as is helpful for the invention.Furthermore, the distribution of the decoupling elements on at least one of the large areas and / or within the volume of the light guide is predefined such that the decoupled light reaches a luminance homogeneity of 70% over at least 70% of the area of the first light guide. The luminance homogeneity can be defined for this purpose as L vmin / L vmax that is to say as the ratio of the smallest value of the luminance to the largest value per unit area. Another applicable specification for defining luminance homogeneity is defined in the "Uniformity Measurement Standard for Displays V1.2" from the Deutsche Flat Display Forum.Finally, the decoupling elements can have maximum dimensions of 100 μm, preferably between 1 μm and 30 μm.The decoupling elements for decoupling light at at least one of the large surfaces of the first light guide preferably consist of microlenses and / or micro-prisms and / or diffractive structures and / or three-dimensional structural elements and / or scattering elements with a maximum extent in their largest dimension which is smaller than 35 micrometers, preferably smaller than 15 micrometers. In the case of diffractive structures, it can be a hologram or a grating / diffraction grating, for example.However, the decoupling elements themselves can also have the external shape of microlenses, micro-prisms, scattering elements and / or diffractive structures alone. They can then be configured in particular as cavities which are then formed in the volume of the first light guide. The cavities can be empty of air, but they are preferably filled with a gaseous, liquid or solid material. The material has a refractive index which differs from that of the material used for the first light guide; it is preferably lower. By filling with material and by selecting material, one can influence the light conduction or decoupling. Alternatively or additionally, the haze value of the material also preferably deviates from that of the material used for the first light guide, is preferably higher. Advantages of these configurations are higher efficiency in the coupling out of light.Alternatively and in a technically simpler manner, the cavities can also be formed if the first light guide is formed from two substrate layers connected to one another, the substrate layers preferably being of the same type. The connection can be made chemically, for example by adhesive bonding. The cavities are then formed as material recesses on at least one of the boundary surfaces of the substrate layers.If the decoupling elements are attached to at least one of the large surfaces of the first light guide, these are advantageously formed from a plastic or glass structured with a tool, the structure of which has been embossed 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 a light guide substrate, which material is structured by means of a tool and cured, e.g. polymerized, by UV radiation. Other radiation curing materials may also be used. The recesses for realizing the decoupling elements can be formed mechanically, lithographically or by printing, for example, or else by applying, converting, removing or dissolving material.Thus, for example, grating structures, micro-prisms-either convexly with plastic content pointing outward on the surface, and / or concavely as an impression or recess within the surface layer of the structured plastic-other three-dimensional structure elements with other shapes, or else microlenses can be implemented cost-effectively and with mass-production capability. Concave and convex structures can likewise be used.It is furthermore favorable if the surface-like extended background illumination emits light along the second preferred direction in a restricted angular range of at most 60 degrees.The screen according to the invention is particularly useful in that its brightness in both operating modes B 1 and B 2 is controlled in a sensor-controlled manner as a function of the intensity of the ambient light. That is, in the case of a rather dark environment, such as at night, the screen is dimmed in its brightness, while in the case of a light environment, such as sunlight, it is set as light as possible.The light guide can consist of a transparent, thermoplastic or thermoelastic plastic or of glass. Thus, the first light guide or its substrate can comprise at least 40 percent by weight polymethyl methacrylate, preferably at least 60 percent by weight polymethyl methacrylate, based on its weight. Alternatively, it may be polycarbonate (PC) or another polymer, for example.Furthermore, it is conceivable for special application cases that the screen switches over the operating modes B 1 and B 2 only for a part of its imaging surface, while the other part operates permanently in the operating mode B 1 or B 2. A possible implementation of this partial changeover in this respect is described in WO 2019 / 034557 A1 by the applicant.In an exemplary embodiment of the screen according to the invention, the background illumination consists ofa planar radiator, preferably a second light guide with lighting means arranged laterally or on the rear side, wherein optionally (apart from a definable residual light, e.g. a maximum of 5% or 10% of the total coupled-out quantity of light) the second light guide operates in a directed manner, i.e. emits light along the first and optionally also the second preferred direction into a restricted angle range of a maximum of 60 degrees,optionally at least one light collimator integrated into the planar radiator and / or arranged in front thereof, which transmits light along the first and optionally also the second preferred direction in a restricted angle range of a maximum of 60 degrees, andoptionally at least one isotropic or anisotropic prism grid.A further advantageous embodiment of the invention provides that for operating mode B 1 depending on predefined limit angles σ, γ, the coupled-out light which exits from the first light guide at an angle β has at each point of the surface of the first light guide in angle ranges which satisfy the conditions 80°>β>γ and / or -80°<β<-σ, with 10°<γ<80° and 10°<σ<80°, preferably γ=σ=40°, measured perpendicularly to the surface of the first light guide and in at least one of the two preferred directions at most 80%, preferably 60%, particularly preferably at most 50%, of the light intensity which the light which exits from such a point of the surface of the first light guide along the normal of the surface. The preferred direction is often the vertical orientation. A negative angle is generally assigned (without any restriction of generality) to the side on which the light is coupled in, i.e., an angle of -90° corresponds to a direction from which the light is coupled in. The critical angles σ, γ are fixedly predefined here, specifically on the basis of the optical power desired for the respective application. In the case of the particularly preferred limit angles y=σ=40°, the light intensity condition then applies nu for angles between -40° and -80° and 40° and 80°. The smaller the critical angles σ, γ are in each case, the more the light is concentrated in the preferred direction or directions corresponding to the mean perpendicular. For example, in a car where the driver and the passenger look at a screen with the lighting device according to the invention at viewing angles that can be defined relatively well in operating mode B 1, the vertical limit angles σ, γ can be selected to be less than 40°. In contrast, values of about 40° or greater may be useful in a laptop on account of the foldability of the screen and the universal deployment scenario with regard to the viewing angles of different persons. The 80° limit may also be 70°.The radiation characteristic described above is not achieved in the prior art without additional layers such as reflectors, BEF, DBEF, prism foils or diffusers. The particular emission characteristic here serves in particular to achieve a sufficient efficiency of the light yield because a screen equipped with the illumination device according to the invention is typically only viewed in a narrow vertical angle range-usually only -20° to +20° or -30° to +30°. Care must be taken that at the same time the low haze values essential to the invention are also achieved in order not to impair the visual protection effect of the operating mode B2.It is also advantageous for the invention if an imager is used which is composed of pixels which in turn consist of subpixels, and each dimension of said decoupling elements in height, depth and width is smaller than the minimum of width and height of the subpixels of an imager used, i.e. smaller than the minimum of these two values. Preferably, each dimension of said decoupling elements in height, depth and width is even smaller by a factor of 1.3; 1.5 or 2.0 than the minimum of width and height of the subpixels of an image generator used. The image becomes more homogeneous in this way and superposition phenomena of structure pattern and subpixel pattern can possibly be avoided.A further expedient configuration of the screen according to the invention consists in that a further, third light guide (for example made of glass or plastic) with means for decoupling light is arranged in front of the imager in the viewing direction, which can be fed with light laterally by further lighting means. The means for decoupling used here are, for example, those described further above or else those as known in the prior art, for example nanoparticles such as titanium dioxide, barium sulfate, etc., in suitable sizes and amounts-as described, for example, in WO 2015 / 121398 A1 and WO 2017 / 089482 A1-which are homogeneously distributed in the volume of the third light guide. By means of this configuration, any remaining light still unintentionally present in operating mode B 2 can still be superimposed or illuminated into the angular ranges actually protected from viewing in such a way that no contrast can be perceived any longer and therefore no image perception from the non-released angles is possible any longer.The corresponding lighting means are designed for emitting colored or white light. In this case, the lighting means can emit light in a color which does not occur in the image represented by the transmissive imager.Alternatively, it is possible for the lighting means to emit light in a color which occurs in the image represented by the transmissive imager or lies close to such a color in the color spectrum. Finally, it is conceivable that the lighting means emit light in a color which corresponds approximately to the complementary color of a color which occurs in the image represented by the transmissive imager.By "colored light" is meant in particular visible light which is not white, i.e. for example light in the colors red, green, blue, turquoise, cyan, magenta or yellow. Furthermore, this light can be selectively emitted in different brightness levels. In addition, it is possible that the chromaticity of the light emitted by the lighting means is also modulated in time, for example in color and / or brightness. In addition, the lighting means can also be implemented with different individual lighting means, for example RGB LEDs in LED lines, which emit light of different colors and / or different brightness simultaneously or offset in time and / or offset in space in each case.The screen according to the invention is particularly advantageously used in a vehicle for the selective display of image contents only for the passenger in the operating mode B 2 or simultaneously for the driver and the passenger in the operating mode B 1. The former is helpful, for example, when the passenger is watching entertainment contents that could divert the driver. However, there may also be application cases in which only the driver can see the image contents in the operating mode B 2 and the passenger cannot.In addition, a screen according to the invention can be used in a mobile device for the selective display of image contents only for one viewer in operating mode B 2 and at the same time for a plurality of viewers in operating mode B 1.A screen according to the invention can be used as it were for the input or display of confidential data, for example of PIN secret numbers, e-mails, SMS or password, to automated teller machines or to payment terminals.On the upper side of the image generator and / or on at least one of the large surfaces of the first light guide, if present, of the second light guide, as well as on other components in the screen, means for reducing or controlling reflections, for example an anti-glare and / or an anti-reflection coating, can be arranged.In all of the aforementioned embodiments, the lighting means can be LEDs or LED lines or laser diodes. Other variants are conceivable and are within the scope of the invention.Further, the desired restricted angular ranges for the restricted view mode B 2 may be defined and implemented independently for the horizontal and vertical directions, respectively. For example, a larger angle (or possibly no restriction at all) in the vertical direction could be expedient than in the horizontal direction, for example if persons of different sizes are intended to see an image in automated teller machines, while the side view is intended to remain strongly or completely restricted. In contrast, for POS payment terminals, due to safety regulations, visual restrictions in mode B2 are often necessary both in the horizontal and in the vertical direction.In principle, the performance of the invention is maintained if the above-described parameters are varied within certain limits.It is understood that the features mentioned above and those still to be explained below can be used not only in the combinations indicated, but also in other combinations or alone, without departing from the scope of the present invention.Brief Description of the DrawingsThe invention is explained in more detail below with reference to drawings, which also show features essential to the invention. It shows FIG. 1 shows a schematic diagram of a first embodiment of an exemplary screen, shown here in operating mode B 1, FIG. 1 ashows an exemplary luminance distribution of the screen in the horizontal direction in operating mode B 1 corresponding to FIG. 1, FIG. 1 b shows an exemplary luminance distribution of the screen in the vertical direction in operating mode B 1 corresponding to FIG. 1, FIG. 2 shows a schematic diagram of a first embodiment of an exemplary screen, shown here in operating mode B 2, FIG. 2 ashows an exemplary luminance distribution of the screen in the horizontal direction in operating mode B 2 corresponding to FIG. 2, FIG. 2 b shows an exemplary luminance distribution of the screen in the vertical direction in operating mode B 2 corresponding to FIG. 2, FIG. 2 cshows an alternative luminance distribution of the screen in the horizontal direction in operating mode B 2 corresponding to FIG. 2, FIG. 3 shows a schematic diagram of a second embodiment of an exemplary screen, FIG. 4 shows a schematic diagram to illustrate the position of preferred directions, FIG. 5 shows a schematic diagram of a third embodiment of an exemplary screen, and FIG. 6 shows a schematic diagram of a fourth embodiment of an exemplary screen.The drawings are not true to scale and merely represent schematic representations.DETAILED DESCRIPTION OF THE DRAWINGSFIG. 1 shows a schematic diagram of a first configuration of an exemplary screen 1, which can be operated in at least two operating modes B 1 and B 2, in operating mode B 1. This isthe screen 1 in the operating mode B1 is visible from a wide angular range of at least 100 degrees along a first preferred direction and only visible from a restricted angular range of at most 60 degrees along a second preferred direction which is perpendicular to said first preferred direction, andthe screen 1 in the operating mode B 2 is visible only from a limited angular range of at most 60 degrees, both along the first and along the second preferred direction,and it is true here that the screen is visible from the above-defined angle ranges exactly when at least 4%, preferably only at least 2%, of the maximum brightness ("peak brightness") emitted by the screen 1 in any direction is emitted into such an angle range.In the following considered embodiment cases, it holds true that the lower edge of the screen 1 or of the image generator 5 (which can be an LCD panel, for example) forms the reference for the horizontal direction and the first preferred direction lies parallel to this horizontal direction. As a result, the vertical direction, i.e. the second preferred direction, is also inherently defined. This is shown in FIG. 4. The letter H stands for the horizontal and the letter V for the vertical direction.In the exemplary first embodiment of the screen 1 according to FIG. 1, it comprisesa planar background illumination 2 which emits light along the first preferred direction into a restricted angular range of at most 60 degrees,a plate-shaped first light guide 3 which is situated in front of the backlight 2 in the viewing direction and has output elements on at least one of the large surfaces and / or within its volume, and which outputs light which is coupled laterally into it along the first preferred direction into a wide angle range of at least 100 degrees, wherein the first light guide 3 is ideally transparent to the light emitted from the backlight 2 to an extent of at least 70%, more preferably to an extent of at least 80% or more,lighting means 4 arranged laterally on narrow sides of the first light guide 3,a transmissive imager 5, for example an LCD panel, which is located in front of the first light guide 3 in the viewing direction,a light filter 6, for example a lamella filter of the 3M™ Vikuiti™ type, which transmits light--apart from low residual light values--along the second preferred direction only in a limited angle range of at most 60 degrees, and which is arranged here behind the transmissive imager 5 in the viewing direction,wherein in operating mode B 2 the backlight 2 is switched on and the lighting means 4 are switched off, and wherein in operating mode B 1 at least the lighting means 4 are switched on.The operation is further illustrated in the drawings FIG. 1 a, which shows an exemplary luminance distribution of the screen in the horizontal direction in the operating mode B 1 corresponding to FIG. 1, and FIG. 1 bfor the vertical direction in the operating mode B 1.It can be seen in FIG. 1 a that there is no restriction in angle in the first preferred direction, here the horizontal direction. Therefore, the screen 1 is visible in this respect in a wide angular range of at least 100 degrees.At the same time, it can be seen in FIG. 1 bthat there is a distinct angular restriction in the second preferred direction, here the vertical direction. The screen 1 is therefore visible in the vertical only from a restricted angular range of at most 60 degrees.The two operating modes B 1 and B 2 (regarding operating mode B 2, see the drawings FIGS. 2, 2 aand 2 b ) differ in that in operating mode B 2 the backlighting is switched on and the lighting means 4 (on the narrow sides of the first light guide 3) are switched off, and wherein in operating mode B 1 at least the lighting means 4 (on the narrow sides of the first light guide 3) are switched on. Only light is taken into account here, which was originally radiated from the lighting means 4 into the first light guide 3 and was subsequently radiated again by the latter via the decoupling elements, wherein the radiation takes place almost exclusively via the decoupling elements.In operating mode B 1, as described above, at least the lighting means 4 on the narrow sides of the first light guide 3 are switched on. It is possible here for the background illumination to be switched on or off.Reflector bands can be attached to those narrow sides of the first light guide 3 on which no lighting means 4 are arranged, in order to increase the efficiency, or else to reduce uncontrolled light in the build-up absorber.Furthermore, FIG. 2 shows a schematic diagram of an exemplary screen 1, still in the first embodiment, but shown here in operating mode B 2. The basic configuration is here the same as described above for FIG. 1.For this purpose, FIG. 2 ashows an exemplary luminance distribution of the screen 1 in the horizontal direction in the operating mode B 2 corresponding to FIG. 2 and FIG. 2 bshows an exemplary luminance distribution of the screen 1 in the vertical direction in the operating mode B 2 corresponding to FIG. 2. The mode of operation is clearly evident.Furthermore, it is possible that at least one such restricted angle range of at most 60 degrees is oriented symmetrically about the perpendicular bisector onto the image-reproducing surface of the screen 1 (which was used as the basis for the drawings FIGS. 1 a, 1 b, 2 aand 2 b).Alternatively, at least one such restricted angular range of at most 60 degrees may be oriented asymmetrically about the perpendicular bisector onto the image-reproducing surface of the screen 1. To this end, FIG. 2 cshows an alternative luminance distribution of the screen in the horizontal direction in operating mode B 2 that corresponds to FIG. 2. Here, the axis of symmetry of said angular range is shifted by 15 degrees towards the right as an example. Other values for the displacement are of course conceivable.This is helpful in particular in applications in the vehicle, for example if a screen 1 to be combined with the lighting device according to the invention is arranged as a so-called center information display in the dashboard approximately in the middle between the driver and the passenger. Then, the restricted angular range released in operating mode B 2 exclusively for the passenger must be designed asymmetrically for vision, i.e. directed towards the passenger.Furthermore, a distribution of the decoupling elements on at least one of the large surfaces and / or within the volume of the first light guide 3 is predefined such that light radiated into the first light guide 3 by the lighting means 4 and decoupled from the first light guide 3 by the decoupling elements satisfies the following condition:at least 50% of the amount of light coupled out on one of the large surfaces between an angle range of -50° and +50° with respect to the surface normal of the large surface is radiated between an angle range of -20° and +20° with respect to the second preferred direction, and / or at least 70% of the amount of light coupled out on one of the large surfaces between an angle range of -50° and +50° with respect to the surface normal of the large surface is radiated between an angle range of -30° and +30° with respect to the second preferred direction.Furthermore, it is advantageous if at least 50% of the amount of light coupled out of the first light guide 3 is coupled out in the direction away from the backlight 2.The number of decoupling elements per area and the extent thereof are selected such that the first light guide 3 has an average haze value of less than 7% over at least 50%, preferably 80% of its area, preferably less than 2%, particularly preferably less than 1%, measured according to ASTM D1003 -wherein the measurement according to the more common procedure A with a hazemeter is used as a basis here-whereby the light emitted by the backlighting at least in the operating mode B2 into a restricted angular range is at most slightly scattered outside said angular range during passage through the first light guide 3. By "slight" is meant, for example, that, due to the small haze, a maximum of 1% of the luminance at an angle of, for example, horizontally 40° from the surface normal is added by scattering, which the illumination device emits at an angle of 0°.The structure of the decoupling elements can be predefined, so that the effect of each decoupling element is at least approximately known and properties of the first light guide 3 or of the light coming from the first light guide 3 can be defined in a targeted manner by a predefinable distribution of the decoupling elements.The required properties for the decoupling elements that are helpful for the invention with regard to their number per unit area, their shape and extent in three dimensions and their distribution on at least one of the large areas and / or within the volume of the first light guide 3 can be determined, for example, with an optical simulation software such as, for example, "LightTool" from Synopsis or other supplier and then correspondingly physically implemented.Finally, the decoupling elements 6 can have maximum dimensions of 100 μm, preferably between 1 μm and 30 μm.The decoupling elements for decoupling light at at least one of the large surfaces of the first light guide 3 preferably consist of microlenses and / or micro-prisms and / or diffractive structures and / or three-dimensional structural elements and / or scattering elements with a maximum extent in their largest dimension which is smaller than 35 micrometers, preferably smaller than 15 micrometers. In the case of diffractive structures, it can be a hologram or a grating / diffraction grating, for example.If the decoupling elements are attached to at least one of the large surfaces of the first light guide 3, these are advantageously formed from a plastic or glass structured with a tool, the structure of which has been embossed 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 a light guide substrate, which material is structured by means of a tool and cured, e.g. polymerized, by UV radiation. Other radiation curing materials may also be used. The recesses for realizing the decoupling elements can be formed mechanically, lithographically or by printing, for example, or else by applying, converting, removing or dissolving material.Thus, for example, grating structures, micro-prisms-either convexly with plastic content pointing outward on the surface, and / or concavely as an impression or recess within the surface layer of the structured plastic-other three-dimensional structure elements with other shapes, or else microlenses can be implemented cost-effectively and with mass-production capability. Concave and convex structures can likewise be used.FIG. 3 shows a schematic diagram of a second embodiment of an exemplary screen 1. In this case, the positions of the image generator 5 and of the light filter 6 (for example a lamella filter) are interchanged with respect to the first configuration of the screen 1 with reference to the drawings FIGS. 1 and 2. The above explanations regarding FIGS. 1 and 2 and also regarding FIGS. 1 a, 1 b, 2 a, 2 band 2 cmay be applied analogously to this, for which reason they will not be repeated here.In a development of the screen 1, a distribution of the decoupling elements on at least one of the large areas and / or within the volume of the first light guide 3 is predefined such that light radiated into the first light guide 3 by the lighting means 4 and decoupled from the first light guide 3 by the decoupling elements is radiated along the second preferred direction into a restricted angular range of at most 60 degrees. For this purpose, FIG. 5 shows a schematic diagram of a third exemplary embodiment of the exemplary screen 1. no light filter 6 (such as a lamella filter), which transmits light along the second preferred direction only in a limited angle range of at most 60 degrees, is present because the first light guide 3 already has the corresponding light decoupling profile for such an angle range entirely alone (as a directed light guide). In principle, the above explanations apply analogously to this.It is furthermore favorable if the surface-like extended backlight 2 also emits light along the second preferred direction in a restricted angular range of at most 60 degrees.The screen 1 according to the invention is particularly useful in that its brightness in both operating modes B 1 and B 2 is controlled in a sensor-controlled manner as a function of the intensity of the ambient light. That is, in the case of a rather dark environment such as at night, the screen 1 is dimmed in its brightness, while in the case of a light environment such as sunlight it is set as light as possible.The first light guide 3 can consist of a transparent, thermoplastic or thermoelastic plastic or of glass. Thus, the first light guide 3 or its substrate could comprise at least 40 percent by weight polymethyl methacrylate, preferably at least 60 percent by weight polymethyl methacrylate, based on its weight. Alternatively, it can be polycarbonate (PC), for example.In an exemplary embodiment of the screen 1 according to the invention, the background illumination 2 consists ofa planar radiator, preferably a second light guide with lighting means arranged laterally or on the rear side, wherein optionally (apart from a definable residual light, e.g. a maximum of 5% or 10% of the total coupled-out quantity of light) the second light guide operates in a directed manner, i.e. emits light along the first and optionally also the second preferred direction into a restricted angle range of a maximum of 60 degrees,optionally at least one light collimator integrated into the planar radiator and / or arranged in front thereof, which transmits light along the first and optionally also the second preferred direction in a restricted angle range of a maximum of 60 degrees, andoptionally at least one isotropic or anisotropic prism grid.A further advantageous embodiment of the invention provides that for operating mode B 1 depending on predefined limit angles σ, γ, the coupled-out light which exits from the first light guide 3 at an angle β has at each point of the surface of the first light guide 3 in angle ranges which satisfy the conditions 80°>β>γ and / or -80°<β<-σ, with 10°<γ<80° and 10°<σ<80°, preferably γ=σ=40°, measured perpendicularly to the surface of the first light guide 3 and in at least one of the two preferred directions at most 80%, preferably 60%, particularly preferably at most 50%, of the light intensity which the light which exits from such a point of the surface of the first light guide 3 along the normal of the surface. The preferred direction is often the vertical orientation. A negative angle is generally assigned (without any restriction of generality) to the side on which the light is coupled in, i.e., an angle of -90° corresponds to a direction from which the light is coupled in. The critical angles σ, γ are fixedly predefined here, specifically on the basis of the optical power desired for the respective application. In the case of the particularly preferred limit angles γ=σ=40°, the light intensity condition then applies only to angles between -40° and -80° and 40° and 80°. The smaller the critical angles σ, γ are in each case, the more the light is concentrated in the preferred direction or directions corresponding to the mean perpendicular. For example, in a car where the driver and the passenger look at a screen with the lighting device according to the invention at viewing angles that can be defined relatively well in operating mode B 1, the vertical limit angles σ, γ can be selected to be less than 40°. In contrast, values of about 40° or greater may be useful in a laptop on account of the foldability of the screen and the universal deployment scenario with regard to the viewing angles of different persons. The 80° limit may also be 70°. The angle β is also visible in FIG. 4.Finally, FIG. 6 shows a schematic diagram of a fourth embodiment of an exemplary screen 1. Here, compared to the third embodiment according to FIG. 5, the positions of the backlight 2 and the first light guide 3 are interchanged. Naturally, the background illumination 2 is then to be designed to be at least partially transmissive, for example as a directed light guide. Furthermore, further lighting means 4 aare present here for the backlight 2. Otherwise, the explanations given further above also apply analogously to this configuration.It is also advantageous for the invention if an imager 5 is used which is composed of pixels which in turn consist of subpixels, and each dimension of said decoupling elements in height, depth and width is smaller than the minimum of width and height of the subpixels of an imager used, i.e. smaller than the minimum of these two values. Preferably, each dimension of said decoupling elements in height, depth and width is even smaller by a factor of 1.3; 1.5 or 2.0 than the minimum of width and height of the subpixels of an image generator 5 used. The image becomes more homogeneous in this way and superposition phenomena of structure pattern and subpixel pattern can possibly be avoided.On the upper side of the image generator 5 and / or on at least one of the large surfaces of the first light guide 3, if present, of the second light guide, as well as on other components in the screen 1, means for reducing or controlling reflections, for example an anti-glare and / or an anti-reflection coating, can be arranged.In all of the aforementioned embodiments, the lighting means 4 can be LEDs or LED lines or laser diodes. Other variants are conceivable and are within the scope of the invention.Particularly advantageously, the screen 1 according to the invention is used in a vehicle for the selective display of image contents only for the passenger in the operating mode B 2 or simultaneously for the driver and the passenger in the operating mode B 1. The former is helpful, for example, when the passenger is watching entertainment contents that could divert the driver. Alternatively, the invention can also be designed such that in operating mode B 1 only the driver sees the image contents.In addition, a screen 1 according to the invention can be used in a mobile device for the selective display of image contents only for one viewer in operating mode B 2 and at the same time for a plurality of viewers in operating mode B 1.The screen according to the invention described above achieves the stated object: A screen has been described which realizes a secure display of information by means of an optionally restricted viewing angle in the horizontal and vertical directions, wherein in a further operating mode a view which is as unrestricted as possible in the viewing angle in one direction, for example the horizontal, is possible. This makes it possible to include the vertical direction permanently in the visual protection.The invention can also be implemented inexpensively with simple means. In both operating modes, the highest possible resolution, generally the native resolution of the screen used, is visible.The invention described above can be advantageously applied wherever confidential data is displayed and / or input, such as for PIN input or for data display to automated teller machines or payment terminals or for password input or for reading e-mails on mobile devices. The invention can also be used in a car as described above.

Claims

Screen (1) which can be operated in at least two operating modes B1 and B2, comprising - a surface-like extended background lighting (2) which emits light along a first preferred direction into a restricted angular range of at most 60 degrees, - a plate-shaped first light guide (3) which is situated in front of the background lighting (2) in the viewing direction and has output elements on at least one of the large surfaces and / or within its volume, and which outputs light which is coupled laterally into it along the first preferred direction into a wide angular range of at least 100 degrees, - lighting means (4) arranged laterally on narrow sides of the first light guide (3), - a transmissive image generator (5) which is situated in front of the first light guide (3) in the viewing direction, - a light filter (6) which outputs light along a second preferred direction which is perpendicular to said first preferred direction, Only in a restricted angular range of at most 60 degrees, and which is arranged in front of or behind the transmissive imager (5) in the viewing direction, - wherein the backlighting (2) is switched on and the lighting means (4) are switched off in the operating mode B2, and wherein at least the lighting means (4) are switched on in the operating mode B1, such that - the screen (1) is visible from a wide angular range of at least 100 degrees in the operating mode B1, and is visible only from a restricted angular range of at most 60 degrees in the second preferred direction, and such that - the screen (1) is visible only from a restricted angular range of at most 60 degrees in each case in the operating mode B2, both along the first and along the second preferred direction, - wherein it applies that the screen is visible from the angular ranges defined above exactly then, when at least 4% of the maximum brightness radiated from the screen (1) in any direction is radiated into such an angle range.Screen according to Claim 1, characterized in that the lower edge of the screen (1) forms the reference for the horizontal direction and the first preferred direction lies parallel to this horizontal direction.Screen according to Claim 1 or 2, characterized in that at least one such restricted angular range of at most 60 degrees is oriented symmetrically about the perpendicular bisector onto the image-reproducing surface of the screen (1).Screen according to claim 1 or 2, characterised in that at least one such restricted angular range of at most 60 degrees is oriented asymmetrically about the perpendicular bisector onto the image-reproducing surface of the screen (1).Screen (1) according to one of the preceding claims, characterized in that the surface-like extended backlighting (2) emits light along the second preferred direction in a restricted angular range of at most 60 degrees.Screen (1) according to one of the preceding claims, characterized in that its brightness in both operating modes B1 and B2 is controlled in a sensor-controlled manner as a function of the intensity of the ambient light.Screen (1) according to one of the preceding claims, characterized in that the decoupling elements of the light guide (3) consist of microlenses and / or micro-prisms and / or diffractive structures and / or three-dimensional structural elements and / or scattering elements.Screen (1) according to one of Claims 1 to 6 having output coupling elements formed within the volume of the first light guide (3), characterized in that the output coupling elements are formed as cavities which preferably have the outer shape of microlenses, micro-prisms or diffractive structures.Screen (1) according to one of the preceding claims, characterized in that the backlighting (2) comprises - a planar radiator, - at least one light collimator integrated into the planar radiator and / or arranged in front thereof, which collimator transmits light along the first and / or the second preferred direction into a restricted angular range of at most 60 degrees, and - at least one isotropic or anisotropic prism grid.Screen (1) according to one of the preceding claims, characterized in that a further, third light guide with means for decoupling light is arranged in front of the imager (5) in the viewing direction, which can be fed with light laterally by further lighting means, wherein the further, third light guide is preferably formed with decoupling elements.Use of a screen (1) according to one of the preceding claims in a vehicle for the selective display of image contents only for the passenger in the operating mode B2 and simultaneously for the driver and the passenger in the operating mode B1.Use of a screen (1) according to one of Claims 1 to 10 in a mobile device for the selective display of image contents only for one viewer in the operating mode B2 and at the same time for a plurality of viewers in the operating mode B1.

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