Lighting device for a free and a restricted view mode and screen with such a lighting device and method for producing light guides

Abstract

The invention relates to a lighting device (1a) for a screen (1b), which can be operated at least in two sections in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode, comprising a backlight (2) which emits light in the restricted angular range, a first and a second plate-shaped light guide (3a, 3b) adjacent thereto, a first illuminating means (4a) arranged laterally on at least one narrow side of the first light guide (3a), a second illuminating means (4b) arranged laterally on at least one narrow side of the second light guide (3b), wherein in operating mode B2 the backlight (2) is switched on and at least one of the two illuminating means (4a, 4b) is switched off, and wherein in operating mode B1 at least one of the two illuminating means (4a, 4b) is switched on, wherein an opaque layer (7) is provided which prevents direct penetration of light,which the first illuminant (4a) emits into the second light guide (3b) and of light which the second illuminant (4b) emits into the first light guide (3a), so that the lighting device (1a) can optionally have different luminance curves in at least two sections which correlate with the dimensions of the two light guides (3a, 3b) in the operating modes B1 and B2. The invention further discloses a screen (1b) with a lighting device (1a) and a method for producing light guides (3a, 3b).

Description

Technical 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.Additional 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.Prior ArtU.S. Pat. No. 5,956,107 A discloses a switchable light source with which a screen can be operated in a plurality of modes. A disadvantage here is that all light decoupling is based on scattering and therefore only low efficiency and nonoptimal light direction effects are achieved. In particular, the achievement of a focused light cone is not disclosed in more detail.CN 107734118 A describes a screen which makes the viewing angle of a screen controllable by means of two backlightings. The upper of the two background illuminations is intended to emit focused light for this purpose. A refinement mentioned for this purpose is, in particular, a grating having opaque and transparent sections. However, the same presumably also leads to the light of the second backlighting, which must penetrate the first in the direction of an LCD panel, also being focused and therefore the public viewing mode actually provided for a wide viewing angle being subject to a significant angular narrowing.US 2007 / 030240 A1 describes an optical element for controlling the light propagation direction of light originating from a background illumination. This optical element requires, for example, liquid crystals in the form of PDLCs, which is firstly expensive but secondly particularly critical to safety for end-use applications, since PDLC liquid crystals generally require voltages higher than 60 V for their circuit.Furthermore, US 2018 / 0267344 A1 describes a structure with two flat lighting modules. In this case, the light of the illumination module lying at the rear in the viewing direction is focused by a separate structure. After focusing, the light still has to pass through the front lighting module, which has scattering elements. Thus, a strong light focusing for a visual protection cannot be optimally implemented.Finally, US 2007 / 0008456 A1 discloses the division of a light emission angle into at least 3 regions, wherein light is generally applied to two regions thereof. It follows from this that a visual protection, in which a display illuminated in this way is used, cannot be viewed from one direction alone.WO 2015 / 121398 A1 by the applicant describes a screen of the type described at the beginning. Particles of scattering that are essential for switching over 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.US2020 / 012129 A1 discloses a lighting device and a screen which describe two lights for switching between a narrow and a wide viewing mode. In this case, on the one hand, one of the light guides is formed with fibers. Secondly, the scattering coupling-out structure of a light guide in the projection direction is restricted to specific strips. This is disadvantageous for homogeneous image illumination and generally also causes unwanted moire effects in the structure, for example in interaction with the pixel columns or rows of an LCD panel lying above.DE 10 2017 007 669 A1 by the applicant describes a screen for a free and a restricted viewing mode, which also allows a partial changeover between the at least two modes. However, it is disadvantageous here that light from one of the two backlights may penetrate into an undesired partial region when using a relatively thick light guide (arranged in front of the backlights) and may thus cause disturbing light.Finally, EP 3 545 359 B1 of the applicant describes an illumination device for a screen with a free and a restricted viewing mode. Detailed information on special features for a partial switching capability of the lighting device cannot be gathered from this publication.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 and / or generate optical artifacts. In particular, however, in the aforementioned illumination-based solutions, a partial area switching of the viewing modes is not readily possible.DESCRIPTION OF THE INVENTIONIt is therefore the object of the invention to describe a lighting device which can be operated in at least two sections in at least two operating modes B 1 for a free viewing mode and B 2 for a restricted viewing mode. 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. Furthermore, a screen is to be specified which uses a corresponding illumination device.This object is achieved according to the invention by an illumination device for a screen which can be operated at least in two sections in at least two operating modes B 1 for a free viewing mode and B 2 for a restricted viewing mode, in which light is emitted by the illumination device in an angle range restricted with respect to the free viewing mode, comprisinga planar backlight emitting light in the restricted angular range,a first and a second plate-shaped light guide adjacent thereto, both of which are situated in front of the backlighting in the viewing direction, each of the two light guides having in each case two large surfaces and narrow sides which connect the large surfaces at their edges, whereinboth light guides have output elements on at least one of their large surfaces and / or within their volume, andeach coupling-out element has at least one functional surface for defined coupling-out of light, at which light is coupled out of the respective light guide,a first lighting means arranged laterally on at least one narrow side of the first light guide,a second lighting means arranged laterally on at least one narrow side of the second light guide,wherein in operating mode B 2 the backlighting is switched on and at least one of the two lighting means is switched off, and wherein in operating mode B 1 at least one of the two lighting means is switched on,at least one opaque layer is also provided, which is arranged at least between the first lighting means and the second lighting means and which prevents a direct penetration of light, which emits the first lighting means, into the second light guide and of light, which emits the second lighting means, into the first light guide,and wherein light coupled into the first light guide from the first illuminant is not passed directly into the second light guide and light coupled into the second light guide from the second illuminant is not passed directly into the first light guide,so that the illumination device can optionally have different luminance curves in the operating modes B 1 and B 2 in at least two sections which correlate with the extents of the two light guides.It is possible in principle to extend the invention also to more than two light guides and more than the first and second lighting means in order to switch the lighting device into more than two sections.Advantageously, the background illumination can be switched on and off in at least two separate regions. Alternatively, it is possible for the background illumination to be able to be switched on and off with respect to its entire light-emitting surface. In both cases, the background lighting can optionally also be dimmed.The at least one opaque layer, which is arranged at least between the first lighting means and the second lighting means, prevents crosstalk of the light emitted in each case, i.e. the opaque layer prevents a direct penetration of light which emits the first lighting means into the second light guide and of light which emits the second lighting means into the first light guide. Such an opaque layer can consist, for example, of a metal, a reflective film or a cured polymer with opaque particles.In addition, the at least one opaque layer can be arranged at least (also) between the first light guide and the second light guide, so that light coupled into the first light guide from the first illuminant is not forwarded directly into the second light guide and light coupled into the second light guide from the second illuminant is not forwarded directly into the first light guide.Furthermore, it is possible for an air gap to exist between the two light guides in order to prevent the transmission of light from one light guide into the other light guide.The invention further comprises a screen operable in at least two modes B1 for a free view mode and B2 for a restricted view modean illumination device as described above,a transmissive imager, preferably an LCD panel, in front of the illumination device in the viewing direction.Moreover, the invention also includes a method of manufacturing two light guides for use in a lighting device as described above, comprising the following stepsin a first alternative: producing two optical waveguides in an injection molding method (e.g. variotherm or isothermal injection molding or injection stamping) using a mold insert which in each case has the structure inverse to the decoupling elements of the two optical waveguides and molds this structure into the respective optical waveguide,in a second alternative: manufacturing two light guides using a nano imprint method (e.g. in plate-to-plate, roller-to-plate or roller-to-roller methods; the latter with subsequent application to a substrate) using a structural insert (e.g. a roller or a plate) which has the structure inverse to the decoupling elements of the two light guides and molds this structure into the respective light guide,optionally: removing edge regions, for example by cutting or sawing or punching out,mechanically connecting the two light guides, wherein between these facing narrow sides of the two light guides an opaque, preferably reflective, layer is inserted (e.g. by adhesive bonding).Alternatively, a two-component injection molding method is also possible for the production of two light guides for use in an illumination device.Advantageously, the respective first or second lighting means are arranged on at least one of the narrow sides of the first and second light guides, wherein this coupling side or these coupling sides can be located at the top, bottom, left and / or right of the respective light guide from the perspective of a seated or standing observer.In general, the decoupling elements can have a three-dimensional shape with a maximum extent in their largest dimension that is less than 100 micrometers, preferably less than 50 micrometers.Furthermore, the decoupling elements can be formed as depressions or elevations on one of the (or both) large areas of a light guide, wherein depressions and elevations can also be present on one and the same light guide or at least one of its large areas. Preferably, however, the decoupling elements are formed as depressions on one of the large surfaces of a light guide. It is also possible for decoupling elements to be attached on both large surfaces and / or additionally optionally in the volume.It is furthermore advantageous for the application if one light guide or both has a stronger scattering behavior in a selectable direction than in a direction perpendicular thereto. Preferably, this selectable direction corresponds to the vertical direction when a (stationary or sitting) observer is looking at the illumination device, so that the scattering behavior of the relevant light guide in the vertical direction is greater than in the horizontal direction, wherein the horizontal direction runs parallel to a line between the eyes of said observer.The two operating modes B 1 and B 2 finally differ in that in the operating mode B 2 the background lighting is switched on and at least one of the two lighting means is switched off, and wherein in the operating mode B 1 at least one of the two lighting means is switched on. In general, therefore, it applies that on sections of the lighting device in which the background lighting is switched on and one of the two lighting means is switched off, the operating mode B 2 is present for a restricted viewing mode. In contrast, on sections of the lighting device in which at least one of the two lighting means is switched on, the operating mode B 1 is present for a free viewing mode.In the above consideration of the operating modes, only light is taken into account, which was originally radiated by the lighting means into one of the light guides and was subsequently radiated again by the latter via the decoupling elements, wherein the light decoupling (except for losses) takes place almost exclusively via the decoupling elements.Each of the two light guides preferably consists of a transparent, thermoplastic or thermoelastic polymer, e.g. plastic, or of glass. For example, a 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 can be polycarbonate (PC), for example.Furthermore, it is possible to mitigate any optical artifacts that may occur, which originate, for example, from the production of the light guide or its decoupling structures, by means of an anisotropic diffuser which is located in front of one or both light guides in the viewing direction of a viewer. According to the definition of the directions described above, such an anisotropic diffuser should scatter significantly less in the horizontal direction than in the vertical direction, if possible, in order to scatter light horizontally only slightly or, in the best case, not at all, in the operating mode B 2 for a restricted viewing mode.A restricted angular range can be understood to mean in principle any range which is smaller than the half space in front of the background illumination; however, an angular range of + / -20° or + / -30°, horizontal and / or vertical or as a cone around the surface normal or a selectable direction vector on the background illumination is preferred here; small light amounts of less than 1% to 5% of the maximum brightness can be disregarded in defining the restricted angular range.The illumination device can additionally also contain a collimating film at a suitable point in the structure, for example a lens or prism grid above or below a light guide.During the production of the light guide, the decoupling elements can be distributed in principle in different ways in or on a 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, (dual) brightness-enhancing, collimating (brightness enhancement film - BEF) or else polarization-recycling layers, such as for example polarization-selective Bragg mirrors (dual) brightness enhancement film - (D)BEF) or wire grid polarizers. These additional layers, which do not fall under the term "decoupling element", are connected-if at all-to a light guide only at the edges, but usually lie only loosely in the region of the large areas and do not form a physical unit with the light guide. In contrast, lacquers applied to the large surfaces, which are connected to the light guide by chemical reactions or other forces (e.g. van der Waals forces), form a physical unit, and are no longer to be separated from one another; such lacquers therefore do not count as an additional layer in the above-mentioned sense.The number of decoupling elements per area and the extent thereof are selected such that each of the light guides has an average haze value of less than 20%, preferably less than 15%, particularly preferably less than 10%, over at least 50%, preferably over 80% of its area, particularly preferably over its entire area, measured according to ASTM D1003-wherein the measurement according to the more common procedure A with a hazemeter is used as a basis here as a reference. As a result, light which penetrates one of the light guides through its large surfaces is at most slightly scattered. By "slight" is meant, for example, that (due to the low haze value) in an angle range of, for example, horizontal + / -40° from the surface normal, a maximum of 1% to 5% of the luminance is added by scattering the relevant light guide from light which is radiated into the light guide at a perpendicular angle over a large surface.Alternatively, it is possible that the number of decoupling elements per area and the extent thereof are selected such that the corresponding light guide scatters over at least 80% of its area at most 25 percent, but preferably at most ten percent, of the light penetrating it through its large areas by more than ten degrees (preferably only 7°, particularly preferably only 5°).In a further configuration, the large area of a light guide from which the light exits can be divided into subareas of a predefined size and the ratio of the (summed) area contents of the functional areas in a subarea to the area contents of the respective subarea can be different for different subareas, such that the scattering behavior of the corresponding light guide varies over the large area from which the light exits from the relevant light guide. It should be noted here that the large surface from which the light passes does not necessarily have to correspond to the large surface on which the decoupling elements are located. Rather, for example, a large surface can have the decoupling elements as decoupling elements directed towards the volume of the light guide, which then deflect and thus decouple the coupled-in light, wherein however light beams thus decoupled still pass through the volume of the light guide or parts thereof in order then to leave the light guide at the other large surface. In general, the scattering behavior of the decoupling elements is defined in particular by their shape and size, but in particular their functional surface, which is taken into account in the optical design.The backlighting consists, for example, of a planar radiator, preferably a further light guide having further lighting means arranged laterally or on the rear side, and at least one light collimator integrated into the planar radiator and / or arranged in front thereof, such as, for example, at least one prism film and / or at least one privacy filter (leaf filter). Alternatively, instead of a lamella filter, an optical element with absorption dipole moments, the plurality of which are aligned with a tolerance of at most 20° to the perpendicular on the surface of the optical element, can also be used in order to restrict the light direction in cooperation with a linear polarization filter, for example a rear-side polarization filter of an LCD panel used with the illumination device. In addition, a so-called focused backlight unit can be used as a backlight, in which light is already coupled out from a (different) light guide into a restricted angular range and, if appropriate, is still directed, deflected or transformed.Accordingly, the backlighting can therefore be basically constructed like an LED backlight, for example as a so-called direct lit LED backlight, edge LED backlight, OLED or as another planar emitter, to which e.g. at least one optical element for limiting the light angles is applied.However, the decoupling elements themselves can also be configured, for example, as cavities which are formed in the volume of a light guide. The cavities can be air-empty, but 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 respective 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 light guide, is preferably higher. Advantages of these configurations are higher efficiency in the coupling out of light.Alternatively and more simply in terms of technology, the cavities can also be formed if an optical waveguide 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, physically or 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 a 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. In particular, variants of injection molding (variotherm / isothermal, injection stamping / injection molding) can be used with the aid of corresponding structural inserts (see also DE102020134055 B4 of the applicant).Thus, three-dimensional structural elements-either convexly with plastic portion pointing outward on the surface, and / or concavely as an impression or recess within the surface layer of the structured plastic can be implemented cost-effectively and with mass production capability. Concave and convex structures can likewise be used.Other variants are conceivable and are within the scope of the invention. Advantageously, each light guide is at least 50% transparent to light penetrating through its large surfaces. The lighting means can be, for example, LEDs (preferably) or LED lines or laser diodes, the emission surface of which is particularly preferably at least approximately rectangular. Other variants are conceivable and are within the scope of the invention.The structure of the decoupling elements is predefined according to the aforementioned criteria, as described above, wherein the effect of each decoupling element is at least approximately known and properties of the relevant light guide or of the light emerging from the corresponding light guide can be defined in a targeted manner by a predefinable structure and distribution of the decoupling elements, wherein the ratio of the sum of the area contents of the functional areas to the area contents of the total area of the large area from which light is decoupled, and the shapes of the functional areas are important in particular.The required properties for the decoupling elements with regard to their number per unit area, their shape including the functional area, their orientation and extension in three dimensions and their distribution on at least one of the large areas and / or within the volume of the 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. Furthermore, the parameters for the decoupling elements on the first and the second light guide can be identical, i.e. both light guides have identical (or almost identical) design structures for the defined decoupling of light.Advantageously, the distribution of the decoupling elements on at least one of the large surfaces and / or within the volume of the light guides is predefined such that the decoupled light reaches a luminance homogeneity (in particular with respect to white light) of at least 50%, preferably at least 60%, over at least 50% (preferably 95% or 100%) of the entire (light-decoupling region of the) light guide. The luminance homogeneity can be defined for this purpose as L Vmin / L Vmax i.e. as a ratio of the smallest value of the luminance to the largest value of a surface under consideration (so-called "area scan" approach, in which each ascertained value on the surface under consideration enters into the evaluation).Furthermore, it is advantageous for some applications if said restricted angular range is formed asymmetrically about the surface normal of the backlighting. The asymmetrical formation is preferably effected in one of the preferred directions. 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.Particularly advantageously, the lighting device according to the invention with a screen is used in a vehicle for the selective display of image contents only for the passenger in the operating mode B 2 on the first or second section (or both simultaneously) or simultaneously for the driver and the passenger in the operating mode B 1 on the first or second section (or both simultaneously). The former is helpful, for example, when the passenger is watching entertainment contents that could divert the driver.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.A lighting device according to the invention with a screen 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, payment terminals or mobile devices.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 on the basis of exemplary embodiments with reference to the appended drawings, which likewise disclose features essential to the invention. These exemplary embodiments are intended merely for illustrative purposes and should not be interpreted as restrictive. For example, a description of an embodiment having a plurality of elements or components should not be construed as requiring all of these elements or components for implementation. Rather, other embodiments may also include alternative elements and components, fewer elements or components, or additional elements or components. Elements or components of various embodiments may be combined with each other unless otherwise indicated. Modifications and variations described for one of the exemplary embodiments may also be applicable to other exemplary embodiments. To avoid repetitions, identical or mutually corresponding elements are denoted by identical reference symbols in different figures and are not explained multiple times. Moreover, none of the drawings are to scale. The following are shown: FIG. 1 shows a schematic diagram of an exemplary illumination device with a transmissive imager, FIG. 2 shows a two-dimensional schematic diagram as a plan view of exemplary light guides and lighting means, FIG. 3 shows a two-dimensional schematic diagram as a sectional view of exemplary light guides and lighting means, and FIG. 4 shows a two-dimensional schematic diagram as a plan view of exemplary decoupling elements.DETAILED DESCRIPTION OF THE DRAWINGSFIG. 1 shows a schematic diagram of an exemplary illumination device 1 afor a screen 1 b, which can be operated at least in two sections in at least two operating modes B 1 for a free viewing mode and B 2 for a restricted viewing mode, in which light is emitted by the illumination device in an angle range restricted with respect to the free viewing mode, comprisinga surface-like extended backlight 2 which emits light in the restricted angular range,a first and a second plate-shaped light guide 3 a, 3 badjacent thereto, both of which are situated in front of the backlight 2 in the viewing direction, wherein each of the two light guides 3 a, 3 bhas in each case two large areas and narrow sides which connect the large areas at their edges, whereinboth light guides 3 a, 3 bhave output coupling elements 6 (which are not illustrated in FIG. 1 ) on at least one of their large surfaces and / or within their volume, andeach coupling-out element 6 has at least one functional surface for defined coupling-out of light, at which light is coupled out of the respective light guide 3 a, 3 b,a first lighting means 4 aarranged laterally on at least one narrow side of the first light guide 3 a(here e.g. an LED line),a second lighting means 4 barranged laterally on at least one narrow side of the second light guide 3 b(here e.g. an LED line),wherein in operating mode B 2 the backlight 2 is switched on and at least one of the two lighting means 4 a, 4 bis switched off, and wherein in operating mode B 1 at least one of the two lighting means 4 a, 4 bis switched on,an opaque layer 7 is also provided, which is arranged at least between the first lighting means 4 aand the second lighting means 4 band which prevents a direct penetration of light, which the first lighting means 4 aradiates, into the second light guide 3 band of light, which the second lighting means 4 bradiates, into the first light guide 3 a,and wherein light (at least) not directly coupled into the second light guide 3 bfrom the first illuminant 4 aand light (at least) not directly coupled into the second light guide 3 bfrom the second illuminant 4 band light (at least) not directly coupled into the first light guide 3 bfrom the second illuminant 4 b,so that the illumination device 1 acan optionally have different luminance curves in the operating modes B 1 and B 2 in at least two sections which correlate with the extents of the two light guides 3 a, 3 b.Advantageously, the background illumination 2 can also be switched on and off in at least two separate regions, which is not shown in the drawing. Alternatively, it is possible for the background illumination 2 to be able to be switched on and off with respect to its entire light-emitting surface. In both cases, the backlight 2 is optionally also dimmable in order to adapt the brightness to the ambient light conditions.The at least one opaque layer 7, which is arranged at least between the first lighting means 4 aand the second lighting means 4 b, prevents crosstalk of the light emitted in each case, i.e. the opaque layer 7 prevents direct penetration of light which emits the first lighting means 4 ainto the second light guide 3 band of light which emits the second lighting means 4 binto the first light guide 3 a. Such an opaque layer 7 can consist, for example, of a metal, a reflective film or a cured polymer with opaque particles.In addition, the at least one opaque layer 7 can be arranged at least (also) between the first light guide 3 aand the second light guide 3 bso that light coupled into the first light guide 3 afrom the first illuminant 4 ais not directly forwarded into the second light guide 3 band light coupled into the second light guide 3 bfrom the second illuminant 4 bis not directly forwarded into the first light guide 3 a. For this purpose, FIG. 2 shows a two-dimensional schematic diagram as a plan view of exemplary light guides 3 a, 3 band lighting means 4 a, 4 b, while FIG. 3 reproduces a two-dimensional schematic diagram as a sectional view thereof.Said opaque layer 7 can be particularly advantageously formed as a component which extends both between the first and the second lighting means and between the first and the second light guide.The invention further comprises a screen 1b operable in at least two modes B1 for a free view mode and B2 for a restricted view mode, which can also be explained with reference to Fig. 1a lighting device 1a as described above,a transmissive imager 1, preferably an LCD panel, in front of the illumination device 1 ain the viewing direction.Advantageously, the respective first or second lighting means 4 a, 4 bare arranged on at least one of the narrow sides of the first and second optical waveguides 3 a, 3 b, wherein this coupling side or these coupling sides can be located at the top, bottom, left and / or right of the respective optical waveguide 3 a, 3 bfrom the view of a seated or standing observer.In general, the decoupling elements 6 can have a three-dimensional shape with a maximum extent in their largest dimension which is less than 100 micrometers, preferably less than 50 micrometers. For this purpose, FIG. 4 shows a greatly enlarged two-dimensional schematic diagram as a plan view of exemplary decoupling elements 6.Furthermore, the decoupling elements 6 can be formed as depressions or elevations on one of the (or both) large areas of the two light guides 3 a, 3 b, wherein depressions and elevations can also be present on one and the same light guide 3 a, 3 bor at least one of its large areas. Preferably, however, the decoupling elements 6 are formed as depressions on one of the large surfaces of each of the light guides 3 a, 3 b. It is also possible for decoupling elements 6 to be attached on both large surfaces and / or additionally optionally in the volume.Accordingly, the backlight 2 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 planar emitter, on which e.g. at least one permanent privacy filter (e.g. with micro-lamellae or else polarization-sensitive) and / or other light-focusing optical components (e.g. BEF, DBEF, lens grid etc.) are applied.The two operating modes B 1 and B 2 differ finally in that in the operating mode B 2 the background lighting 2 is switched on and at least one of the two lighting means 4 a, 4 bis switched off, and wherein in the operating mode B 1 at least one of the two lighting means 4 a, 4 bis switched on. In general, therefore, it applies that on sections of the lighting device in which the backlight 2 is switched on and one of the two lighting means 4 a, 4 bis switched off, the operating mode 2 is present for a restricted viewing mode. In contrast, on sections of the lighting device 1 a, in which at least one of the two lighting means 4 a, 4 bis switched on, the operating mode B 1 is present for a free viewing mode.When the operating modes are considered above, only light is taken into account, which was originally radiated from the lighting means 4 a, 4 binto one of the light guides 3 a, 3 band was subsequently radiated again from the latter via the decoupling elements 6, wherein the decoupling of light-apart from losses-takes place almost exclusively via the decoupling elements 6.Overall, there are therefore various variations of the operating modes, as listed by way of example in the following table, wherein the background illumination is assumed to be switchable over the full area in the configuration considered here:AnAnAnB1B1AnOffAnB1B2OffAnAnB2B1OffOffAnB2B2AnAnOffB1B1AnOffOffB1(Out)OffAnOff(Out)B1OffOffOff(Out)(Out)The above table of operating modes can be varied even further, because, as already mentioned, the background lighting 2 can also be switched in sections.Each of the two light guides 3 a, 3 bis preferably made of a transparent, thermoplastic or thermoelastic polymer, e.g. plastic, or of glass. For example, a 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 can be polycarbonate (PC), for example.A restricted angular range can be understood to mean in principle any range which is smaller than the half space in front of the backlight 2; however, an angular range of + / -20° or + / -30° horizontal and / or vertical or as a cone around the surface normal or a selectable direction vector on the backlight is preferred here; small light amounts of less than 1% to 5% in each case of the maximum brightness can be disregarded in defining the restricted angular range.During the production of the light guides 3 a, 3 b, the decoupling elements 6 can be distributed in principle in different ways in or on a light guide 3 a, 3 b, according to adaptable and predeterminable conditions for decoupling the light. The decoupling elements 6 are locally limited structural changes in the volume and / or on the surfaces of the light guide 3 a, 3 b.The number of decoupling elements 6 per area and the extent thereof are selected such that each of the light guides 3 a, 3 bhas an average haze value of less than 20%, preferably less than 15%, particularly preferably less than 10%, measured according to ASTM D 1003 over at least 50%, preferably over 80% of its area, particularly preferably over its entire area-wherein the measurement according to the more common procedure A with a hazemeter is used as a basis here as a reference. As a result, light which penetrates one of the light guides 3 a, 3 bthrough its large areas is at most slightly scattered. By "slight" is meant, for example, that (due to the low haze value) in an angle range of, for example, horizontal + / -40° from the surface normal, a maximum of 1% to 5% of the luminance is added by scattering the relevant light guide 3 a, 3 bfrom light which is radiated into the light guide 3 a, 3 bat a perpendicular angle over a large surface.If the decoupling elements 6 are attached to at least one of the large surfaces of a light guide 3 a, 3 b, 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 6 can be formed, for example, mechanically, lithographically or by printing, or else by material application, conversion, removal or dissolution.The structure of the decoupling elements 6 is predefined according to the aforementioned criteria, as described above, wherein the effect of each decoupling element 6 is at least approximately known and properties of the light guide 3 a, 3 bor of the light emerging from the corresponding light guide 3 a, 3 bcan be defined in a targeted manner by a predefinable structure and distribution of the decoupling elements 6, wherein the ratio of the sum of the area contents of the functional surfaces to the area contents of the total area of the large area from which light is decoupled and the shapes of the functional surfaces are important in particular.The required properties for the decoupling elements 6 with regard to their number per unit area, their shape including the functional area, their orientation and extension in three dimensions and their distribution on at least one of the large areas and / or within the volume of each light guide 3 a, 3 bmay be determined, for example, with an optical simulation software such as, for example, "LightTool" from the company Synopsis or other supplier and then implemented physically accordingly. Furthermore, the parameters for the decoupling elements 6 on the first and the second light guide 3 a, 3 bmay be identical, i.e. both light guides 3 a, 3 bhave identical (or virtually identical) design structures for the defined decoupling of light.Particularly advantageously, the lighting device 1 aaccording to the invention with an imager 1 is used in a vehicle for the selective display of image contents only for the passenger in the operating mode B 2 on the first or second section (or both simultaneously) or simultaneously for the driver and the passenger in the operating mode B 1 on the first or second section (or both simultaneously). The former is helpful, for example, when the passenger is watching entertainment contents that could divert the driver.Other variants are conceivable and are within the scope of the invention. Each light guide 3 a, 3 bis advantageously at least 50% transparent to light penetrating through its large surfaces. The first and second lighting means 4 a, 4 bmay be, for example, LEDs (preferred) or LED lines or laser diodes, the emission surface of which is particularly preferably at least approximately rectangular. Other variants are conceivable and are within the scope of the invention.Of course, a corresponding control is present for all the components required (e.g. image generator 1, lighting means 4 a, 4 b, backlighting 2, etc.).The above-described illumination device according to the invention and the screen which can be implemented therewith achieve the stated object: Solutions which can be implemented practically well are disclosed and can be operated in at least two sections in at least two operating modes B 1 for a free viewing mode and B 2 for a restricted viewing mode. The invention can be implemented at low cost using simple means. In both operating modes, a high resolution, in particular 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. As described above, the invention can also be used in a car.

Claims

Lighting device (1a) for a screen (1b) which can be operated at least in two sections in at least two modes of operation B1 for a free viewing mode and B2 for a restricted viewing mode, in which light is emitted by the lighting device in an angle range restricted with respect to the free viewing mode, comprising - a surface-like extended backlight (2) which emits light in the restricted angle range, - a first and a second plate-shaped light guide (3a, 3b) which are adjacent thereto and are both situated in front of the backlight (2) in the viewing direction, wherein each of the two light guides (3a, 3b) has in each case two large areas and narrow sides which connect the large areas at their edges, wherein - both light guides (3a, 3b) have output elements (6) on at least one of their large surfaces and / or within their volume, and - each output element (6) has at least one functional surface for defined output of light, at which light is output from the respective light guide (3a, 3b), - a first lighting means (4a) arranged laterally on at least one narrow side of the first light guide (3a), - a second lighting means (4b) arranged laterally on at least one narrow side of the second light guide (3b), - wherein in operating mode B2 the background lighting means (2) is switched on and at least one of the two lighting means (4a, 4b) is switched off, and wherein in operating mode B1 at least one of the two lighting means (4a, 4b) is switched on, - wherein further at least one opaque layer (7) is provided, which is arranged at least between the first lighting means (4a) and the second lighting means (4b) and which prevents direct penetration of light, which the first lighting means (4a) emits, into the second light guide (3b) and of light, which the second lighting means (4b) emits, into the first light guide (3a), - and wherein light, which is coupled into the first light guide (3a) from the first lighting means (4a), is not passed directly into the second light guide (3b) and light, which is coupled into the second light guide (3b) from the second lighting means (4b), is not passed directly into the first light guide (3a), - so that the lighting device (1a) is not passed on directly into the first light guide (3a) in at least two sections, which correlate with the extents of the two light guides (3a, 3b), in the operating modes B 1 and B 2, different luminance curves can optionally be provided.Lighting device (1a) according to Claim 1, characterized in that the background lighting (2) can be switched on and off in at least two separate regions.Lighting device (1a) according to Claim 1, characterized in that the backlighting (2) can be switched on and off with respect to its entire surface emitting light.Lighting device (1a) according to one of the preceding claims, characterized in that the at least one opaque layer (7) is also arranged between the first light guide (3a) and the second light guide (3b).Lighting device (1a) according to one of Claims 1 to 4, characterized in that an air gap exists between the two light guides (3a, 3b).Lighting device (1a) according to one of the preceding claims, characterized in that at least one of the two light guides (3a, 3b) has a stronger scattering behavior in a selectable direction than in a direction perpendicular thereto.Lighting device (1a) according to claim 6, characterised in that the selectable direction when a viewer looks at the lighting device (1a) corresponds to the vertical direction, so that the scattering behavior of at least one of the two light guides (3a) is greater in the vertical direction than in the horizontal direction, wherein the horizontal direction runs parallel to a line between the eyes of the viewer.Screen (1b) which can be operated in at least two modes of operation B1 for a free viewing mode and B2 for a restricted viewing mode, comprising - an illumination device (1a) according to one of the preceding claims, - a transmissive imager (1), preferably an LCD panel, in front of the illumination device (1a) in the viewing direction.Method for producing two light guides (3a, 3b) for use in an illumination device (1a) according to one of Claims 1 to 7, comprising the following steps - in a first alternative: producing two light guides (3a, 3b) in an injection molding method, using a mold insert which in each case has the structure which is the inverse of the decoupling elements (6) of the two light guides (3a, 3b) and molds this structure into the respective light guide (3a, 3b), - in a second alternative: producing two light guides (3a, 3b) using a nano-imprint method, using a structure insert which in each case has the structure which is the inverse of the decoupling elements (6) of the two light guides (3a, 3b) and molds this structure into the respective light guide (3a, 3b), 3b), optionally: removing edge regions, mechanically connecting both light guides (3a, 3b), wherein between narrow sides of both light guides (3a, 3b) facing each other an opaque, preferably reflective, layer (7) is inserted.

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