Optical waveguide and illumination device for a free and a restricted viewing mode with such an optical waveguide

Abstract

The invention relates to a flat optical waveguide (3) having two large surfaces and having narrow sides which connect the large surfaces at their edges. The optical waveguide (3) comprises a plurality of individual lighting means (4a, 4b, …) which are arranged in series and which have an average central spacing of p and have radiating surfaces, wherein one of the narrow sides of the optical waveguide (3) is formed as a coupling-in side (5) for light from the lighting means (4a, 4b, …). The optical waveguide (3) furthermore comprises coupling-out elements (6) which are arranged on at least one of the large surfaces of the optical waveguide (3) and / or within its volume, wherein each coupling-out element (6) has at least one functional surface for defined coupling-out of light from the optical waveguide (3), and in the event of projection onto one of its large surfaces, all coupling-out elements lie completely within a defined region (B) projected onto the large surface. At the end of the series, a final lighting means (4x) is arranged, wherein the narrow side closest to the final lighting means (4x) at the end of the series of lighting means (4a, 4b, …) has at least one straight-line portion, and wherein the final lighting means (4x) is oriented at the coupling-in side (5) in such a manner that the centroid of its radiating surface is arranged at a distance p / 2, with an orientation tolerance of at most + / -0.3*p, from an intersection point (S) of the projection of an imaginary extension of the longest straight-line portion of the narrow side having the coupling-in side (5) and closest to the final lighting means (4x) at the end of the series of lighting means (4a, 4b, …), wherein the distance p / 2 is measured in the direction of the longest expansion of the coupling-in side (5), as a result of which some of the light which is radiated from the final lighting means (4x) into the optical waveguide (3) is totally reflected there, and thus for at least half of an area of the defined region (B) of the optical waveguide (3) the luminance homogeneity of the light coupled out of at least one of the large surfaces, measured at three angles which each differ from one another by at least 20° and lie in a plane through the central vertical to the corresponding large surface of the optical waveguide (3), is in each case greater than 50%. 2c

Description

title

[0001] Light guide and lighting device for a free and a restricted view mode with such a light guide Technical field of the invention

[0002] In recent years, great strides have been made in widening the viewing angle of LCDs. However, there are often situations in which the very large viewing area of ​​a screen can be a disadvantage. Information such as banking details and other personal and sensitive data is also becoming increasingly available on mobile devices such as notebooks and tablet PCs. Accordingly, people need control over who can see this sensitive data; they need to be able to choose between a wide viewing angle in order to share information on their display with others, e.g. when looking at holiday photos or for advertising purposes. On the other hand, they need a narrow viewing angle if they want to keep the image information confidential.

[0003] A similar problem arises in vehicle construction: The driver must not be distracted by image content, such as digital entertainment programs, when the engine is running, while the passenger also wants to consume the same content while driving. Therefore, a screen that can switch between the corresponding display modes is required.

[0004] Additional films based on micro-louvres have already been used for mobile displays to achieve optical data protection. However, these films were not switchable; they always had to be applied and removed manually. They also had to be transported separately from the display when not in use. A major disadvantage of using such louvre films is the associated light loss. State of the art

[0005] US Pat. No. 5,956,107 A discloses a switchable light source that allows a display to be operated in multiple modes. The disadvantage here is that all light extraction is based on scattering, resulting in low efficiency and suboptimal light direction effects. In particular, the achievement of a focused light cone is not disclosed in detail.

[0006] CN 1077341 18 A describes a display that uses two backlights to control the viewing angle of a screen. The upper of the two backlights is intended to emit focused light. A grid with opaque and transparent sections is specifically mentioned as a design for this purpose. However, this presumably results in the light from the second backlight, which must penetrate the first toward an LCD panel, also being focused, thus significantly narrowing the viewing angle in the public viewing mode, which is actually intended for a wide viewing angle.

[0007] US 2007 / 030240 A1 describes an optical element for controlling the direction of light propagation from a backlight. This optical element requires liquid crystals in the form of PDLCs, for example, which are both expensive and safety-critical, especially for end-user applications, since PDLC liquid crystals typically require voltages higher than 60V for their circuitry.

[0008] CN 1987606 A, in turn, describes a screen that uses two backlights to control the viewing angle of a screen. In particular, a "first light plate" is used, which must be wedge-shaped to enable the intended focused light extraction. Precise details on how to achieve the focused light extraction with the corresponding angle conditions are not disclosed.

[0009] Furthermore, US 2018 / 0267344 A1 describes a setup with two flat lighting modules. The light from the rear lighting module 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 diffusing elements. Therefore, strong light focusing for privacy protection is not optimal.

[0010] Finally, US 2007 / 0008456 A1 discloses the division of a light beam angle into at least three areas, with two of these areas typically being illuminated. This means that a privacy screen using such an illuminated display cannot be viewed from one direction only.

[0011] WO 2015 / 121398 A1 by the applicant describes a screen of the type described above. There, scattering particles are present in the volume of the corresponding light guide, which are essential for switching between operating modes. However, the polymer scattering particles selected there generally have the disadvantage that light is coupled out of both large surfaces, causing approximately half of the useful light to be emitted in the wrong direction, namely toward the backlight, where it cannot be adequately recycled due to the design. Furthermore, the polymer scattering particles distributed throughout the volume of the light guide can, under certain circumstances, particularly at higher concentrations, lead to scattering effects that reduce the privacy effect in the protected operating mode.

[0012] US2020 / 012129 A1 discloses an illumination device and a display screen, which describe two lights for switching between a narrow and a wide viewing mode. One of the light guides is formed with fibers. The other is to limit the scattering output structure of a light guide to specific stripes in the projection direction. This is detrimental to homogeneous image illumination and generally also causes unwanted moiré effects in the structure, for example, in interaction with the pixel columns or rows of an LCD panel located above.

[0013] The aforementioned methods and arrangements generally have the disadvantage that they significantly reduce the brightness of the basic screen and / or require an active, or at least a special, optical element for mode switching and / or require complex and expensive production and / or reduce the resolution in the freely viewable mode and / or have brightness or homogeneity artifacts. Description of the invention

[0014] It is therefore an object of the invention to describe a light guide that has the most stable possible homogeneity of luminance over a wide viewing angle range. On the other hand, brightness artifacts, such as shadow formation, particularly in corners near the coupling edge, should be avoided as far as possible. A further object of the invention is to describe an illumination device which, in conjunction with a screen, can be used to reliably display information using an optionally restricted viewing angle, while in a further operating mode an unobstructed view with as little as possible of the viewing angle should be possible. The invention should be implementable as inexpensively as possible using simple means, while at the same time leveraging the advantages of the aforementioned desired light guide.In both operating modes, the highest possible resolution should be visible, preferably the native resolution of the screen in use. Furthermore, the solution should introduce as little light loss as possible, the image quality—especially in terms of homogeneity—should be high, and the restricted viewing angle should achieve the most comprehensive privacy effect possible.

[0015] This object is achieved according to the invention by a plate-shaped light guide with two large surfaces and with narrow sides that connect the large surfaces at their edges, which comprises a plurality of individual light sources arranged in a row. The light sources have an average center-to-center distance of p and emission surfaces, wherein at least one of the narrow sides of the light guide is designed as the input side for light from the light sources. The light guide has output coupling elements on at least one of the large surfaces and / or within its volume, i.e. the output coupling elements are arranged or formed there. Each output coupling element has at least one functional surface for a defined output of light from the light guide, i.e. light is output from the light guide at the functional surface.When the light guide is viewed in the direction of one of its large surfaces - in other words when projected vertically onto one of its large surfaces - all output coupling elements lie completely within a defined area B projected onto the large surface. The light guide also comprises at least one end illuminant located or arranged at one end of the row of illuminants, the end illuminant closest to the end illuminant at the end of the row of illuminants. Narrow side has at least one rectilinear section, and wherein the end illuminant is aligned on the coupling side such that the center of its radiating surface is arranged at a distance p / 2 with an alignment tolerance of at most + / -0.3*p from an intersection point S of the projection of an imaginary extension of the longest rectilinear section or portion of the narrow side closest to the end illuminant at the end of the row of illuminants (i.e. the closest narrow side which is not the coupling side) with the coupling side, wherein the said distance p / 2 is measured along the direction of the longest extent of the coupling side, whereby a portion of the light which is radiated into the light guide by the end illuminant is totally reflected there.As a result, for at least half of an area of ​​the defined area B of the light guide (preferably for three quarters or the entire area of ​​area B), the luminance homogeneity (depending on the color of the light from the illuminants, one color or several colors are taken into account with regard to their respective luminance homogeneity, but in particular this can be the white homogeneity) of the light coupled out from at least one of the large areas, measured at three angles each differing from one another by at least 20° and lying in a plane through the bisector of the corresponding large area of ​​the light guide, is in each case greater than 50%.

[0016] Advantageously, the light guide is at least 50% transparent to the light penetrating it due to its large surface area. The light sources can be, for example, LEDs (preferred) or LED arrays or laser diodes, whose radiation surface is particularly preferably at least approximately rectangular. Other variants are conceivable and within the scope of the invention.

[0017] The meaning of "intersection point S" should explicitly include not only the intersection of two straight lines, but also the mere touching of two straight lines. This touching point then corresponds to the intersection point S within the meaning of the invention. If the coupling side is not completely straight, the determination of the aforementioned intersection point S is also based on the fact that its longest straight portion conceptually defines the corresponding straight line.

[0018] Further embodiments provide for the optical fiber that the defined area B has (essentially) a rectangular shape, and that the distance of at least one edge of the defined area B from a narrow side of the optical fiber that does not correspond to the coupling side has the value p / 2 with a distance tolerance of is at most + / -0.3*p. Deviations of the defined area B from a rectangular shape are possible because often not the entire edge of area B is occupied by output coupling elements. In simplified terms, the narrowest rectangle within which all output coupling elements are located can generally be considered area B.

[0019] Preferably, any of the aforementioned tolerances, i.e. in particular both spacing tolerances and alignment tolerances of + / -0.3*p, are interpreted narrowly, namely with + / -0.2*p or even + / -0.1*p. The invention achieves particularly good results when a lamp located at one end of the row of lamps is aligned on the coupling side such that its center of surface is arranged at a distance p / 2 with a tolerance of at most + / -0.1*p from the intersection point S of the projection of an imaginary extension of the longest, most rectilinear portion of the narrow side closest to the lamp at the end of the row of lamps with the coupling side, wherein the said distance p / 2 is measured along the direction of the longest extent of the coupling side. The conditions according to the invention preferably apply at both ends of the row of lamps.

[0020] The coupling-out elements for coupling out light at at least one of the large surfaces of the light guide can generally consist of microlenses and / or microprisms and / or microprismatoids and / or diffraction structures and / or metastructures and / or three-dimensional structural elements with a maximum extension in their largest dimension that is less than 100 micrometers, preferably less than 50 micrometers. In the case of diffraction structures, this can be, for example, a hologram or a grating / diffraction grating. However, the coupling-out elements particularly preferably have the form of three-dimensional structural elements that comprise at least one curved functional surface.

[0021] It is important for the design of the invention that the targeted coupling of light from the light guide does not occur through scattering, as is common with most commercially available light guides. The invention would be ineffective for coupling using scattering elements that, in the prior art, damage the light guide surface, since the coupling of light in this case is not defined or deterministic, but primarily diffuse. Furthermore, coupling using scattering elements would have the negative consequence that the light guide would also have a strongly scattering effect on light penetrating through the large surfaces, which is particularly important for its use in privacy applications. represents an exclusion criterion. It can therefore be stated that the invention does not encompass any optical fibers whose primary approach to coupling out light is the principle of scattering. For this reason, (micro)prismatoids, three-dimensional structural elements, diffraction structures, or microlenses are particularly preferable because they enable deterministic coupling out of light—except for avoidable scattering within a predefined tolerance. In general, the scattering of the light penetrating the optical fiber should be as low as possible, as described in the following two sections.

[0022] The number of output elements per surface and their extent are selected such that the light guide has an average haze value of less than 20%, preferably less than 15%, particularly preferably less than 10%, measured according to ASTM D1003 over at least 50%, preferably 80% of its surface, particularly preferably over its entire surface - whereby the measurement according to the more common procedure A with a haze meter is used as a reference. As a result, light penetrating the light guide through its large surfaces is only slightly scattered. By "slightly" is meant, for example, that (due to the low haze value) in an angular range of, for example, horizontally + / -40 0A maximum of 1% to 5% of the luminance is added to the surface normal due to scattering of light from the light guide, which is radiated into the light guide at a perpendicular angle across a large area. Commercially available light guides that use scattering as their primary mechanism for coupling out the light typically do not achieve the aforementioned haze values.

[0023] Alternatively, the number of output elements per area and their size can be selected such that the optical fiber scatters at most 25%, but preferably at most 10%, of the light penetrating its large surfaces by more than 10° (preferably only 7°, particularly preferably only 5°) over at least 80% of the defined area B (preferably over the entire defined area B). Commercially available optical fibers that use scattering as their primary output mechanism typically do not achieve the aforementioned maximum scattering values.

[0024] The coupling elements themselves can also have the external form of microlenses, microprisms, microprismatoids, three-dimensional structural elements, and / or diffractive structures. They can then be designed, for example, as cavities formed within the volume of the light guide. can be airless, but are preferably filled with a gaseous, liquid, or solid material. The material has a refractive index that differs from that of the material used for the light guide; it is preferably lower. The filling with material and the choice of material can influence the light transmission or extraction. Alternatively or additionally, the haze value of the material preferably differs from that of the material used for the light guide and is preferably higher. Advantages of these designs include higher efficiency in light extraction.

[0025] Alternatively, and with greater technical simplicity, the cavities can also be formed by forming the light guide from two interconnected substrate layers. The substrate layers are preferably of the same type. The connection can be made chemically, physically, or by adhesive bonding. The cavities are then formed as material recesses at at least one of the interfaces between the substrate layers.

[0026] If the output coupling elements are attached to or formed on at least one of the large surfaces of the light guide, they are advantageously made from a plastic or glass whose structure has been embossed using 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 is then structured using a tool and cured, e.g. polymerized, by UV radiation. Other radiation-curing materials can also be used. The formation of the recesses for the output coupling elements can be realized, for example, mechanically, lithographically or printing-technically, or by material application, conversion, removal or dissolution.In particular, variants of injection moulding (variothermal / isothermal, injection compression moulding / injection moulding) can be used with the aid of appropriate structural inserts (see also DE 1020 201 340 55 B4 of the applicant).

[0027] This allows, for example, lattice structures, microprisms, Z-prismatoid or three-dimensional structural elements - either convex with plastic portion on the surface facing outwards, and / or concave as an embossing or recess within the surface layer of the structured plastic -, other three-dimensional structures Elements with other shapes, or even microlenses, can be implemented cost-effectively and with mass production capability. Concave and convex structures can be used equally.

[0028] The structure of the decoupling elements is specified as described above according to the criteria mentioned, whereby the effect of each decoupling element is at least approximately known and properties of the light guide or of the light emerging from the light guide can be specifically determined by a predeterminable structure and distribution of the decoupling elements, whereby the ratio of the sum of the surface areas of the functional areas to the surface area of ​​the total area of ​​the large area from which light is coupled out is particularly important.

[0029] The required properties of the output coupling elements, which are essential for the invention, with regard to their number per unit area, their shape, their orientation and extension in three dimensions as well as their distribution on at least one of the large surfaces and / or within the volume of the light guide can be determined, for example, using optical simulation software such as "LightTools" from Synopsis or other providers and then physically implemented accordingly.

[0030] Advantageously, the distribution of the output coupling elements on at least one of the large surfaces and / or within the volume of the light guide is specified such that the output light achieves a luminance homogeneity (particularly with regard to white light) of at least 50%, preferably at least 60%, on at least 50% (preferably 95% or 100%) of the entire defined area B of the light guide. The luminance homogeneity can be defined as Lv min / Lv maxbe defined, i.e. as the ratio of the smallest luminance value to the largest value of an observed area (so-called "area scan" approach, in which every determined value on the observed area is included in the evaluation). Within the scope of the invention, this should apply to three angles that differ from one another by at least 20° and lie in a plane through the perpendicular bisector to the corresponding large area of ​​the light guide, for example -20°, 0° and +20°, or 0°, +20° and +45°, or 0°, -20° and -45°, or even -45°, 0° and +45°, whereby the said plane is preferably horizontal in the perception of an observer.

[0031] The means-effect relationships of the invention consist, among other things, in the fact that due to the positioning of the end illuminant chosen according to the invention at the end the corresponding row of illuminants - and thus inherently also the positioning of all existing illuminants in relation to the geometry of the selected coupling side - at least the (partial) effect of another physically non-existent illuminant outside the row of illuminants is created by totally reflecting part of the light from the end illuminant, i.e. the last illuminant at the end of the row of illuminants, on the narrow side closest to the end illuminant, i.e. the side immediately adjacent to the coupling side of the end illuminant of the said row of illuminants. This creates a light beam combination in the light guide which is close to one as if another (virtual) illuminant followed the end illuminant, i.e. the said last illuminant at the end of the row of illuminants, at approximately the center-to-center distance p.For the coupling out by the coupling out elements in area B, this means that sufficient light is available to generate a good luminance homogeneity of the coupled out light even over a wide angular range, ie the luminance homogeneity is relatively stable from different viewing angles, which differ, for example, by at least 20° each.

[0032] Otherwise, if the center of the surface of the final illuminant is not arranged at a distance p / 2 with a tolerance of at most + / -0.3*p from the intersection point S described above (e.g. with a distance of >0.6*p from the intersection point S described above), the desired values ​​of at least 50% for the luminance homogeneity are generally not achieved, since strong luminance variations occur, particularly at the corners near the coupling side, at angles greater than or equal to + / -25° or greater than or equal to + / -45°.These in turn arise in particular from the fact that, due to the positioning of the final illuminant not chosen in accordance with the invention in this case, there is no effect of another, physically non-existent illuminant outside the row of illuminants, in which part of the light of the final illuminant would be totally reflected on the narrow side closest to this final illuminant, which adjoins the coupling side immediately near the said last illuminant of the said row of illuminants.

[0033] A reasonable range for the distance between the light source and the coupling side of the light guide is 200 pm to 700 pm, with a range of approximately 400 pm to 550 pm being preferable. This range also depends on the thickness of the light guide. Thicker light guides generally allow somewhat larger distances than the aforementioned. Overall, other distances are also conceivable within the scope of the invention.

[0034] For the average center-to-center distance p of the lamps, values ​​of 3 mm to approximately 8 mm are common. However, other values ​​are explicitly possible. Preferably, this center-to-center distance p is in the range of 5 mm to 6.5 mm.

[0035] A further part of the object of the invention is achieved by a lighting device for a screen, which can be operated in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode, in which light is emitted by the lighting device in an angular range that is restricted compared to the free viewing mode. This comprises a planar backlight that emits light in the restricted angular range, and a plate-shaped light guide located in front of the backlight in the viewing direction with illuminants arranged on a narrow side serving as the coupling side, as described above. In operating mode B2, the backlight is switched on and the illuminants are switched off, and in operating mode B1 at least the illuminants are switched on.

[0036] Advantageously, the light guide can be designed such that it exhibits greater scattering behavior in a selectable direction than in a direction perpendicular to it. This selectable direction can correspond to the vertical direction when an observer views the lighting device, so that the scattering behavior of the light guide is greater in the vertical direction than in the horizontal direction, with the horizontal direction running parallel to a line between the observer's eyes.

[0037] Furthermore, it is possible to mitigate any optical artifacts that may arise, for example, from the manufacturing of the light guide or its output structures, using an anisotropic diffuser. According to the previously described definition of directions, this diffuser should, if possible, scatter significantly less in the horizontal direction than in the vertical direction, in order to scatter light horizontally as little as possible, or ideally not at all, in the B2 operating mode for a restricted view.

[0038] In addition, the invention can be implemented in such a way that the defined area B is divided into sub-areas of a predetermined size and the ratio of the (on- summed) surface areas of the functional surfaces in a sub-area differ from the surface area of ​​the respective sub-area for different sub-areas, so that the scattering behavior of the light guide varies over the defined area B. It should be noted that the large surface from which the light emerges does not necessarily have to correspond to the large surface on which the output coupling elements are located. Rather, the latter large surface can, for example, have the output coupling elements as (micro-)prismatoids directed towards the volume of the light guide or three-dimensional structural elements with at least one straight or curved functional surface, which then deflect the coupled-in light and thus output it, whereby light rays coupled out in this way initially still traverse the volume of the light guide or parts thereof, in order to then leave the light guide at the first-mentioned, other large surface.

[0039] In principle, any area smaller than the half-space in front of the background illumination can be considered as a restricted angular range; however, an angular range of + / -20° or + / -30° is preferred. 0 horizontal and / or vertical or as a cone around the surface normal or a selectable directional vector on the backlight; small amounts of light of less than 1% to 5% of the maximum brightness can be disregarded when defining the restricted angular range.

[0040] The illumination device may additionally contain a collimation film at a suitable location in the structure, for example a lens or prism grid above or below the plate-shaped light guide.

[0041] During the manufacture of the light guide, the output coupling elements can be distributed in or on the light guide in various ways, depending on the adaptable and predeterminable conditions for the output of the light. Output coupling elements are locally limited structural changes in the volume and / or on the surfaces of the light guide. Therefore, the term output coupling element expressly excludes additional optical layers applied to the surfaces of the light guide, e.g., diffusion layers, reflection layers, (dual) brightness-enhancing, collimating brightness enhancement film (BEF), or polarization-recycling layers, such as polarization-selective Bragg mirrors (dual) brightness enhancement film (D)BEF) or wire mesh po- larisators. These additional layers, which do not fall under the term "outcoupling element," are connected to the light guide only at the edges, if at all. However, they are usually only loosely applied to the large surfaces and do not form a physical unit with the light guide. In contrast, lacquers applied to the large surfaces, which bond with the light guide through chemical reactions or other forces (e.g., van der Waals forces), form a physical unit and can no longer be separated; such lacquers are therefore not considered an additional layer in the above-mentioned sense.

[0042] Finally, the two operating modes B1 and B2 differ in that in operating mode B2, the backlight is switched on and the lamps (on the input side of the light guide) are switched off, while in operating mode B1, at least the lamps (on the input side of the light guide) are switched on. Only light originally emitted by the lamps into the light guide and subsequently re-emitted via the output elements is taken into account, with the emission occurring almost exclusively via the output elements.

[0043] It is possible that decoupling elements are mounted on both large surfaces and / or additionally optionally in the volume.

[0044] The light guide preferably consists of a transparent, thermoplastic or thermoelastic polymer, e.g., plastic, or glass. For example, the light guide or its substrate can comprise at least 40 percent by weight of polymethyl methacrylate, preferably at least 60 percent by weight of polymethyl methacrylate, based on its weight. Alternatively, it can be, for example, polycarbonate (PC).

[0045] Furthermore, for some applications, it is advantageous for said restricted angular range to be formed asymmetrically around the surface normal of the backlight. The asymmetrical formation preferably takes place in a direction specified by the application. This is particularly helpful for applications in vehicles, for example, when a screen to be combined with the lighting device according to the invention is arranged as a so-called center information display in the dashboard approximately midway between the driver and front passenger. In operating mode B2, the restricted angular range of vision, which is exclusively available to the front passenger, must be asymmetrical, i.e., directed toward the front passenger. The specified direction in which the asymmetry is formed corresponds to the horizontal.

[0046] The backlight consists, for example, of a planar radiator, preferably another light guide with additional light sources arranged to the side or on the back, as well as at least one light collimator integrated into the planar radiator and / or arranged in front of it, such as at least one prism film and / or at least one privacy filter (leaf filter). Alternatively, instead of a leaf filter, an optical element with absorption dipole moments, the majority of which are aligned with a maximum tolerance of 20° to the vertical on the surface of the optical element, can be used to limit the direction of the light. In addition, a so-called focused backlight unit can be used as backlighting, in which light from a (different) light guide is already coupled out into a restricted angular range and, if necessary, further directed, deflected, or reshaped.

[0047] Accordingly, the backlight can basically be constructed like an LED backlight, for example as a so-called direct-lit LED backlight, edge LED backlight, OLED or as another surface radiator, on which, for example, at least one permanent privacy filter (e.g. with micro-louvres or polarization-sensitive) is applied.

[0048] For all variants of the lighting device described above, it is particularly advantageous if they further comprise a transmissive screen arranged in front of the lighting device in the viewing direction as a screen, preferably in the form of an LCD panel, which, due to the lighting device, can be operated in at least two operating modes B1 for a free view mode and B2 for a restricted view mode.

[0049] The lighting device according to the invention with a screen is particularly advantageous for use in a vehicle for selectively displaying image content only for the front passenger in operating mode B2 or simultaneously for the driver and front passenger in operating mode B1. The former is helpful, for example, when the front passenger is watching entertainment content that could distract the driver.

[0050] A lighting device according to the invention with a screen can also be used for entering or displaying confidential data, for example PIN numbers, e-mails, SMS or passwords, at ATMs, payment terminals or mobile devices.

[0051] Furthermore, the desired restricted angle ranges for mode B2 for a restricted view can be defined and implemented independently for the horizontal and vertical directions. For example, a larger angle (or possibly no restriction at all) might be appropriate in the vertical direction than in the horizontal direction, such as when people of different heights need to see an image at ATMs, while the side view should remain severely or completely restricted. For POS payment terminals, however, visibility restrictions in mode B2 are often necessary in both the horizontal and vertical directions due to security regulations.

[0052] In principle, the performance of the invention is maintained if the parameters described above are varied within certain limits.

[0053] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations indicated, but also in other combinations or on their own, without departing from the scope of the present invention. Short description of the drawings

[0054] The invention will be explained in more detail below using exemplary embodiments with reference to the accompanying drawings, which also disclose features essential to the invention. These exemplary embodiments are for illustrative purposes only and are not to be interpreted as limiting. For example, a description of an exemplary embodiment with a plurality of elements or components should not be interpreted as meaning that all of these elements or components are necessary for implementation. Rather, other exemplary embodiments may also contain alternative elements and components, fewer elements or components, or additional elements or components. Elements or components of different exemplary embodiments may be combined with one another. unless otherwise stated. Modifications and variations described for one of the embodiments may also be applicable to other embodiments. To avoid repetition, identical or corresponding elements in different figures are designated by the same reference numerals and will not be explained more than once. They show: Fig. 1 a schematic diagram of a light guide with lamps, Fig. 2a-2c further schematic diagrams (in detail form) of a light guide with lamps, with illustration of different distances, Fig. 3a-3d Simulation results for the luminance distribution of a light guide section, shown from different viewing angles, for a first position of the illuminants, Fig. 4a-4d Simulation results for the luminance distribution of a light guide section, shown from different viewing angles, for a second position of the illuminants, Fig. 5a- 5d Simulation results for the luminance distribution of a light guide section, shown from different viewing angles, for a third position of the illuminants, Fig. 6 is a graph showing an overview of various simulation results, and Fig. 7 is a schematic diagram of a lighting device with a screen. Detailed description of the drawings

[0055] Fig. 1 shows a schematic diagram of a plate-shaped light guide 3 with illuminants 4a, 4b, ... and Fig. 2a to Fig. 2c show further schematic diagrams of a light guide 3 with illuminants 4a, 4b, ... in a top view of a section (top right corner from the viewpoint of an observer) with illustration of various distances.

[0056] This is a plate-shaped light guide 3 with two large surfaces and narrow sides that connect the large surfaces at their edges, wherein the light guide 3 comprises several individual illuminants 4a, 4b, ... arranged in a row (in Fig. 1, four illuminants 4a, 4b, 4c and 4x are shown as an example, although in a practical embodiment there may be considerably more, for example several dozen illuminants or more) and one of the narrow sides of the light guide 3 serves as the coupling side 5 for light from the said illuminants 4a, 4b, ..., wherein the illuminants means 4a, 4b, ... have an average center-to-center distance of p and radiating surfaces. The light guide 3 has output coupling elements 6 on at least one of the large surfaces and / or within its volume (this is only indicated in Fig. 2a; in reality, there are considerably more output coupling elements 6, and these are also significantly smaller in proportion than the lighting means 4a, 4b, ...). Each output coupling element 6 has at least one (not shown in the drawing) functional surface for a defined output of light from the light guide, i.e., light is output from the light guide 3 at the functional surface. When the light guide 3 is viewed in the direction of one of its large surfaces - in other words, when projected perpendicularly onto one of its large surfaces - all output coupling elements 6 lie completely within a defined area B projected (perpendicularly) onto the large surface.The light guide 3 also comprises at least one end illuminant 4x located or arranged at one end of the row of illuminants 4a, 4b, ..., wherein the narrow side closest to the end illuminant 4x at the end of the row of illuminants has at least one rectilinear section, and wherein the end illuminant is aligned with the coupling side 5 such that the center of its radiating surface is arranged at a distance p / 2 with an alignment tolerance of at most + / -0.3*p from an intersection point S of the projection of an imaginary extension of the longest rectilinear section or portion of the narrow side closest to the end illuminant 4x at the end of the row of illuminants 4a, 4b, ... with the coupling side 5, wherein the said distance p / 2 is measured along the direction of the longest extent of the coupling side 5, as shown in Fig.2a, whereby a portion of the light radiated by the end illuminant 4x into the light guide 3 is totally reflected there. As a result, for at least half of the area of ​​the defined region B of the light guide 3 (preferably for three-quarters or the entire area of ​​region B), the luminance homogeneity (depending on the color of the light from the illuminants 4a, 4b, ..., one color or several colors are taken into account with regard to their respective luminance homogeneity; in particular, however, this can be the white homogeneity) of the light coupled out from at least one of the large surfaces, measured at three angles each differing from one another by at least 20° and lying in a plane through the bisector of the corresponding large surface of the light guide 3 (see the dashed thick lines in Fig. 1, which indicate such exemplary angles), is in each case greater than 50%.

[0057] The meaning of "intersection point S" should explicitly include not only the intersection of two straight lines, but also the mere touching of two straight lines. This touching point then corresponds to the intersection point S within the meaning of the invention.

[0058] Fig. 2b shows another schematic diagram as a section of a light guide 3 with light sources 4a, 4b, ..., with an illustration of various distances. The explanations given for Fig. 2a apply here analogously. Here, too, an end light source 4x located at one end of the row of light sources 4a, 4b, ... is aligned with the coupling side 5 such that its center of surface of its radiating surface is arranged at a distance p / 2 with an alignment tolerance of at most + / -0.3*p from the intersection point S of the projection of an imaginary extension of the longest straight-line portion of the narrow side closest to the end light source 4x at the end of the row of light sources 4a, 4b, ... with the coupling side 5, wherein the said distance p / 2 is measured along the direction of the longest extent of the coupling side 5. However, this light guide 3 has a so-called stopper X. This corresponds to a protrusion on the right narrow side.Such stoppers are used in the prior art to anchor light guides in the backlight. Such stoppers can, in principle, take on any shape and do not necessarily have to have straight edges. At this point, it becomes clear why the intersection point S was defined as above: The imaginary extension of the longest straight-line portion of the narrow side closest to the end illuminant 4x at the end of the row of illuminants 4a, 4b, ... (i.e., the right-hand side here) is not influenced by the stopper X; rather, the said imaginary extension (shown here with the double-dotted dashed line) intersects (or touches) the coupling side 5 at the same intersection point S, as in the situation according to Fig. 2a.

[0059] Fig. 2c also shows another schematic diagram as a section of a light guide 3 with lamps 4a, 4b, ..., with an illustration of various distances. The explanations given for Figs. 2a and 2b apply analogously. However, the stopper X is now located directly at the end of the coupling side 5. Based on the definition given above for the intersection point S, the same also results clearly under the conditions shown in Fig. 2c.

[0060] Of course, one or more stoppers X can also be present at other and / or multiple positions and / or on multiple narrow sides. Furthermore, a stopper can also represent a recess on a narrow side.

[0061] The light sources 4a, 4b, etc. can preferably be LEDs whose radiation surface is at least approximately rectangular. Other variants are conceivable and within the scope of the invention.

[0062] Further embodiments provide for the light guide 3 that the defined region B has (essentially) a rectangular shape, as shown in Fig. 1.

[0063] Preferably, any tolerances, alignment tolerances, and spacing tolerances mentioned above and those mentioned below are narrowly defined, namely + / -0.3*p, namely + / -0.2*p or even + / -0.1*p. The invention achieves particularly good results if a lamp 4x located at the end of the row of lamps 4a, 4b, ... is aligned with the coupling side 5 such that its center of surface is arranged at a distance p / 2 with a tolerance of at most + / -0.1*p from the previously described intersection point S - measured along the direction of the longest extent of the coupling side 5.

[0064] Particularly preferably, the embodiment according to the invention applies to both ends of the row of illuminants 4a, 4b, ..., i.e. simultaneously to the first illuminant 4a, which is then designed as the initial illuminant, and the end illuminant 4x of the row of illuminants 4a, 4b, ...

[0065] The coupling-out elements 6 can advantageously have the shape of (micro)prismatoids. However, the coupling-out elements 6 particularly preferably have the shape of three-dimensional structural elements comprising at least one curved functional surface. Examples of three-dimensional structural elements comprising at least one curved functional surface are described, inter alia, in WO 2023 / 274541 A1 (e.g., in Fig. 3 and Fig. 4 or others) or US 2018 / 088270 A1 (e.g., Fig. 3A to 3D, Fig. 4B and Fig. 5A or others).

[0066] If the coupling-out elements 6 are mounted on at least one of the large surfaces of the light guide 3, they 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 A UV-curing material - e.g. a lacquer, a monomer, etc. - is applied to the light guide substrate, which is structured by means of a tool and cured, e.g. polymerized, by UV radiation.

[0067] Advantageously, the distribution of the output coupling elements 6 on at least one of the large surfaces and / or within the volume of the light guide (but within the area B) is specified such that the output coupled light achieves a luminance homogeneity (particularly with regard to white light) of at least 60% on at least 50% (preferably 95% or 100%) of the entire defined area B of the light guide. The luminance homogeneity can be defined as Lv min / Lv maxbe defined, i.e. as the ratio of the smallest value of the luminance to the largest value of an observed area. Within the scope of the invention, this should apply to three angles that differ from one another by at least 20° and lie in a plane through the bisector of the corresponding large area of ​​the light guide 3, for example -20°, 0° and +20°, or 0°, +20° and +45°, or 0°, -20° and -45°, or also -45°, 0° and +45°, wherein the said plane is preferably horizontal in the perception of an observer.

[0068] The number of output elements 6 per area and their extent are also selected such that the light guide 3 has an average haze value of less than 20%, preferably less than 15%, particularly preferably less than 10%, measured according to ASTM D1003 over at least 50%, preferably 80% of the defined area B, particularly preferably over its entire area - the measurement according to the more common procedure A with a hazemeter being used as a reference here. As a result, light penetrating the light guide 3 through its large areas or the defined area B is at most slightly scattered. By "slightly" is meant, for example, that (due to the low haze value) in an angular range of, for example, horizontally + / -40 0a maximum of 1% to 5% of the luminance is added from the surface normal by scattering of the light guide 3 from light which is radiated into the light guide 3 at an angle of 0° over a large area.

[0069] Alternatively, it is possible that the number of coupling elements 6 per area and their extent are selected such that the light guide 3 is at most 80% of the defined area B (preferably in the entire defined area B). at least 25%, but preferably at most 10%, of the light penetrating it through its large surfaces by more than 10° (preferably only 7°, particularly preferably only 5°).

[0070] The means-effect relationships of the invention consist, among other things - as illustrated in particular in Fig. 2a to Fig. 2c - in the fact that due to the positioning of the end illuminant 4x at the end of the corresponding row of illuminants 4a, 4b, ... as described, at least the (partial) effect of another physically non-existent, quasi "assumed", virtual illuminant 4imagine is created outside the row of illuminants 4a, 4b, ... by a part of the light of the end illuminant 4x at the end of the row of illuminants 4a, 4b, ... being totally reflected on the narrow side which is closest to the end illuminant, i.e. which adjoins the coupling side directly near the end illuminant 4x of the said row of illuminants (see the indicated light beam from the illuminant 4a with a solid line onto the right narrow side of the light guide 3). Furthermore, in Fig.2a is indicated by the dashed line for an exemplary light beam that would originate from the assumed virtual illuminant 4image and run to the right-hand narrow side of the light guide. In reality, however, there is only the imaginary extension of such a beam in the light guide 3, namely due to the totally reflected light from the final illuminant 4x, as described above. This creates a light beam combination in the light guide 3 that is close to that of another virtual illuminant 4imagine following the final illuminant 4x at the end of the row of illuminants 4a, 4b, ... For the outcoupling by the outcoupling elements 6 in area B, this in turn means that sufficient light is available to generate good luminance homogeneity of the outcoupled light even over a wide angular range.

[0071] Otherwise, if the center of the surface of the final illuminant 4x is not arranged at a distance p / 2 with a tolerance of at most + / -0.3*p from the previously described intersection point S (e.g. with a distance of >0.9*p from the previously described intersection point S), the desired values ​​of luminance homogeneity of at least 50% are generally not achieved, since especially at the corners near the coupling side at angles greater than + / -20 0 or greater than + / -45°, strong luminance variations occur. These in turn are due in particular to the fact that due to the positioning of the end illuminant 4x at the end of the corresponding row of illuminants 4a, 4b, ... not being chosen in accordance with the invention, the effect of a further, physically non-existent virtual illuminant 4imagine (see Fig.2a) still outside the row of illuminants 4a, 4b, ..., in which part of the light of the end illuminant 4x at the end of the row of illuminants 4a, 4b, ... would be totally reflected at the narrow side closest to the end illuminant 4x, which narrow side adjoins the coupling side immediately near the said last illuminant of the said row of illuminants.

[0072] All drawings Fig. 3a to Fig. 5d represent a (simulated) luminance distribution of a light guide section, more precisely of a sector of the defined area B of the light guide 3. To the right of each of the drawings mentioned is a legend of the grayscale values ​​for simulated brightnesses in the unit cd / m 2This sector of the defined area B is located close to the end illuminant 4x at the end of the corresponding row of illuminants 4a, 4b, ..., and its right edge simultaneously represents the right end of the defined area B, or a part thereof. Each sector simulates an approximately 15 mm wide and approximately 68 mm high area of ​​the defined area B of the light guide 3. Furthermore, the drawings Fig. 3a, Fig. 4a, Fig. 5a each show the corresponding luminance distribution for an angle H0°V0°, the drawings Fig. 3b, Fig. 4b, Fig. 5b each show the corresponding luminance distribution for an angle H-20°V0°, the drawings Fig. 3c, Fig. 4c, Fig. 5c each show the corresponding luminance distribution for an angle H-30°V0° and the drawings Fig. 3d, Fig. 4d, Fig. 5d each show the corresponding luminance distribution for an angle H-45°V0°.Therefore, all the above-mentioned angles satisfy the condition that they lie in a plane through the perpendicular bisector of the corresponding large surface of the light guide 3.

[0073] Further parameters for all results shown in Fig. 3a to Fig. 6 are: (a) Distance of the illuminants 4a, 4b, ... to the said coupling side 5 of the light guide 3: 500 pm; (b) Thickness of the light guide: 2 mm; (c) Average center-to-center distance p of the illuminants 4a, 4b, ...: 5 mm; (d) Size of the coupling-out elements 6 with three-dimensional structure: Maximum dimensions between 3 pm and 30 pm.

[0074] Fig. 3a-3d show simulation results for the luminance distribution of a light guide section, shown from different viewing angles, for a first position of the illuminants. In this first position, the end illuminant 4x located at the end of the row of illuminants 4a, 4b, ... is aligned with the coupling side 5 such that its center of surface is (exactly) at a distance p / 2 from the (as shown in the front) defined) intersection point S with that of the coupling side 5 - measured along the direction of the longest extension of the coupling side 5. The simulated luminance homogeneities here are:

[0075] It can be seen that the luminance homogeneity is very stable and always greater than 50 percent, even across larger viewing angles up to H-45°V0°. This is achieved due to the means-effect relationships of the invention described above.

[0076] Fig. 4a-4d show simulation results for the luminance distribution of a light guide section, shown from different viewing angles, for a second position of the illuminants. In this second position, the end illuminant 4x, located at the end of the row of illuminants 4a, 4b, ..., is aligned with the coupling side 5 such that its center of surface is located at a distance p / 2 + 0.2*p from the intersection point S (as defined above) with the coupling side 5 - measured along the direction of the longest extension of the coupling side 5. It can be seen, particularly in Fig. 4c and Fig. 4d, that the minimum luminances occur primarily at the upper right edge. However, these can still be acceptable. The simulated luminance homogeneities here are:

[0077] It can be seen that the luminance homogeneity remains largely stable, even at larger viewing angles up to H-45°V0°. All luminance homogeneity values, even at a strong oblique view below H-45°V0°, are, as desired, greater than 50%, and in this case even greater than 60%. This is achieved due to the means-effect relationships of the invention described above.

[0078] In Fig. 5a-5d simulation results for the luminance distribution of a light guide section, shown from different viewing angles, for a third position of the illuminants. In this third position, the end illuminant 4x, located at the end of the row of illuminants 4a, 4b, ..., is aligned with the coupling side 5 such that its center of surface is located at a distance p / 2+0.4*p from the intersection point S (as defined above) with that of the coupling side 5 - measured along the direction of the longest extension of the coupling side 5. It can be seen, in particular, in Figs. 5b to 5d that the minimum luminances occur primarily at the upper right edge. These have dropped so far here that a clear shadow is visible in the corner from these viewing angles, and the overall luminance homogeneity is no longer acceptable. The simulated luminance homogeneities here are:

[0079] It can be seen that the luminance homogeneity is not stable over larger viewing angle ranges. Luminance homogeneities below 60% or 50% are not permissible for various applications. This poor luminance homogeneity is due in particular to the fact that the above-described means-effect relationships of the invention are not realized here.

[0080] Figure 6 shows a graph providing an overview of the aforementioned simulation results. It is clear that stable homogeneity of the luminance distribution is achieved even across different angles for the first and second positions of the end illuminant 4x in the row of illuminants 4a, 4b, ..., while the third position, which explicitly lies outside the scope of the present invention, does not allow for stable homogeneity of the luminance distribution across different angles.

[0081] Fig.7 shows the schematic diagram of a lighting device 1 a for a screen 1 , which can be operated in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode, in which light is emitted by the lighting device in an angular range that is restricted compared to the free viewing mode, comprising a surface-like extended background lighting 2 that emits light in the restricted angular range, a plate-shaped light guide 3 located in front of the background lighting 2 in the viewing direction, with lighting means 4a, 4b, ... arranged on a narrow side serving as the coupling side 5, as described above, wherein the lighting means 4a, 4b, ... are not shown in the drawing here, wherein in operating mode B2 the background lighting 2 is switched on and the lighting means 4a, 4b, .. are switched off, and wherein in operating mode B1 at least the lighting means 4a, 4b, .. are switched on.

[0082] In principle, any area smaller than the half-space in front of the background illumination can be considered as a restricted angular range; however, an angular range of + / -20° or + / -30° is preferred. 0horizontal and / or vertical or as a cone around the surface normal or a selectable directional vector on the backlight; small amounts of light of less than 1% to 5% of the maximum brightness can be disregarded when defining the restricted angular range.

[0083] The illumination device 1 a can additionally contain a collimation film at a suitable location in the structure, for example a lens or prism grid above or below the plate-shaped light guide 3, or an anisotropic diffuser for concealing optical artifacts (such as production-related mura phenomena on the light guide 3 and / or other components in the structure).

[0084] Finally, the two operating modes B1 and B2 differ in that in operating mode B2, the background illumination 2 is switched on and the lamps 4a, 4b, ... (on the input side 5 of the light guide 3) are switched off, whereas in operating mode B1, at least the lamps 4a, 4b, ... (on the input side 5 of the light guide 3) are switched on. Only light originally emitted by the lamps 4a, 4b, ... into the light guide 3 and subsequently emitted from the light guide via the output elements 6 is taken into account, with the emission occurring almost exclusively via the output elements 6.

[0085] The light guide 3 is preferably made of a transparent, thermoplastic or thermoelastic polymer, e.g. plastic, or glass.

[0086] The background lighting 2 consists, for example, of a flat spotlight, preferably a further light guide with further light sources arranged laterally or on the rear, as well as at least one integrated into the flat spotlight integrated and / or arranged in front of it light collimator, such as at least one prism film and / or at least one privacy filter (e.g. louvre filter).

[0087] 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.

[0088] For all variants of the lighting device 1 a described above, it is particularly advantageous if they further comprise a transmissive screen 1 arranged in front of the lighting device 1 a in the viewing direction as a screen, preferably in the form of an LCD panel, which, due to the lighting device 1 a, can be operated in at least two operating modes B1 for a free view mode and B2 for a restricted view mode.

[0089] The above-described lighting device according to the invention and the screen that can be implemented with it solve the stated problem: Practically easy-to-implement solutions are described for a light guide that exhibits stable luminance homogeneity over a wide viewing angle range. At the same time, brightness artifacts, such as shadowing, particularly in corners near the coupling edge, are largely avoided. Furthermore, the invention describes a lighting device that, in conjunction with a screen, enables reliable display of information using an optionally restricted viewing angle, while in a further operating mode, a clear view with as little restriction as possible in terms of the viewing angle is possible. The invention can be implemented inexpensively using simple means, while simultaneously leveraging the advantages of the aforementioned desired light guide.In both operating modes, the highest possible resolution is visible, up to the native resolution of the screen in use. Furthermore, the solution introduces minimal light loss, the image quality—especially in terms of homogeneity—is high, and the limited viewing angle achieves the most comprehensive privacy effect possible.

[0090] The invention described above can be advantageously applied wherever confidential data is displayed and / or entered, such as when entering a PIN or displaying data at ATMs or payment terminals, entering a password, or reading emails on mobile devices. As described above, the invention can also be applied in cars. List of reference symbols Screen 1a Lighting device 2 Backlight 3 light guides 4a Light bulbs 4b Light bulbs 4m bulbs 4x end bulbs 4imagine Virtual Light Source 5 Coupling side 6 Decoupling element B Defined area S Intersection point X Stopper p Average center-to-center distance of the lamps 4a, 4b, ...

Claims

Patent claims 1 . Plate-shaped light guide (3) with two large surfaces and with narrow sides which connect the large surfaces at their edges, comprising a plurality of individual illuminants (4a, 4b, which have an average center-to-center distance of p and have radiating surfaces, wherein one of the narrow sides of the light guide (3) is designed as a coupling side (5) for light from the illuminants (4a, 4b, ...), Output elements (6) which are arranged on at least one of the large surfaces of the light guide (3) and / or within its volume, wherein each output element (6) has at least one functional surface for a defined output of light from the light guide (3), and all output elements (6), when projected onto one of its large surfaces, lie entirely within a defined area (B) projected onto the large surface, an end illuminant (4x) arranged at one end of the row of illuminants (4a, 4b, ...), wherein the output elements assigned to the end illuminant (4x) at the end of the row of illuminants (4a, 4b, ...) has at least one rectilinear section, and wherein the end illuminant (4x) is aligned on the coupling side (5) such that the center of its radiating surface is at a distance p / 2 with an alignment tolerance of at most + / -0.3*p from an intersection point (S) of the projection of an imaginary extension of the longest rectilinear section of the end illuminant (4x) at the end of the row of illuminants (4a, 4b, ...) closest narrow side with the coupling side (5), wherein the said distance p / 2 is measured along the direction of the longest extent of the coupling side (5), whereby a part of the light which is radiated by the end illuminant (4x) into the light guide (3) is totally reflected there and thereby for at least half of an area of ​​the defined region (B) of the light guide (3) the luminance homogeneity of the light coupled out from at least one of the large areas, measured under three distances from one another by at least 20° in each case. different angles lying in a plane through the perpendicular bisector to the corresponding large surface of the light guide (3), is each greater than 50%.

2. Optical fiber (3) according to claim 1, characterized in that the defined region (B) has a rectangular shape, and in that the distance of at least one edge of the defined region (B) from a narrow side of the optical fiber (3) which does not correspond to the coupling side is p / 2 with a distance tolerance of at most + / -0.3*p.

3. Light guide (3) according to claim 1 or 2, characterized in that the coupling-out elements (6) have the shape of prismatoids, prisms or three-dimensional structural elements, each with at least one curved or straight functional surface for the defined coupling-out of light.

4. Optical fiber (3) according to claim 1 or 2, characterized in that the coupling-out elements (6) comprise diffraction structures and / or meta-structures.

5. Optical fiber (3) according to one of the preceding claims, characterized in that the alignment tolerance is at most + / -0.1*p.

6. Optical fiber (3) according to one of the preceding claims, characterized in that the decoupling elements (6) are selected in their number per area and in their extent such that the optical fiber (3) scatters at most 25%, preferably at most 10%, of the light penetrating it through its large areas by more than 10° over at least 80% of the defined area (B).

7. Lighting device (1 a) for a screen (1 ), which can be operated in at least two operating modes B1 for a free view mode and B2 for a restricted view mode, in which light is emitted by the lighting device in an angular range that is restricted compared to the free view mode, comprising a surface-like extended backlight (2) that emits light in the restricted angular range, a plate-shaped light guide (3) located in front of the background lighting (2) in the viewing direction, with lighting means (4a, 4b, ...) according to one of the preceding claims arranged on a narrow side serving as the coupling side (5), wherein in operating mode B2 the background lighting (2) is switched on and the lighting means (4a, 4b) are switched off, and wherein in operating mode B1 at least the lighting means (4a, 4b) are switched on.

8. Lighting device (1 a) according to claim 7, characterized in that the light guide (3) has a stronger scattering behavior in a selectable direction than in a direction perpendicular thereto.

9. Lighting device (1 a) according to claim 8, characterized in that the selectable direction when an observer looks at the lighting device (1 a) corresponds to the vertical direction, so that the scattering behavior of the light guide (3) is greater in the vertical direction than in the horizontal direction, the horizontal direction running parallel to a line between the eyes of the observer.

10. Lighting device (1 a) according to one of claims 7 to 9, characterized in that the defined area (B) is divided into sub-areas of predetermined size and the ratio of the surface areas of the functional surfaces in a sub-area to the surface area of ​​the respective sub-area is different for different sub-areas, so that the scattering behavior of the light guide (3) varies over the defined area (B).

Images