Switchable light filters, illuminators, and screens

Abstract

The present invention relates to a switchable optical filter (5) comprising a first optical element (1) with a plurality of optical absorption transition dipole moments, whereby light incident on the first optical element (1) is transmitted or at least partially absorbed as a function of its direction of incidence relative to the first optical element (1) and its polarization state, means for optionally generating a first electric field (EF1) or a second electric field (EF2), and a liquid crystal layer (3) on which the first electric field (EF1) or the second electric field (EF2) acts, wherein the transmission characteristics of the switchable optical filter (5) differ during a first operating mode B1. Furthermore, the present invention discloses a lighting device and a screen using the above-mentioned switchable optical filter (5).

Description

[Technical Field]

[0001] Significant progress has been made in recent years to increase the viewing angle of LCDs. However, there are often situations where this extremely wide viewing angle of a screen can be a disadvantage. Information such as bank details, personal information, and confidential data are increasingly available on mobile devices such as notebooks and tablet PCs. Therefore, people need control over who can see this confidential data and must be able to select a wide viewing angle, i.e., public mode, to share information on their display with others, for example, when viewing vacation photos or for advertising purposes. On the other hand, a small viewing angle is required when image information is desired to be kept confidential, i.e., in private mode.

[0002] A similar problem arises in vehicle construction, where the driver must not be distracted by visual content, such as digital entertainment programs, when the vehicle is powered on, but passengers want to enjoy them while traveling. Therefore, a screen that can switch between the respective display modes is required.

[0003] Microlouver-based additional films have already been used for mobile displays to achieve visual data protection. However, these films cannot be turned on / off or switched on, and must always be manually installed and then removed. Furthermore, if they are not currently needed, they must be transported separately from the display. Furthermore, a significant drawback of using such louver films relates to the associated light loss.

[0004] US Patent No. 6,765,550 describes such visual protection by microlouvers, the main drawbacks of which are the mechanical removal or attachment of the filters and the light loss in the protection mode.

[0005] To achieve a private mode, i.e., a limited viewing mode with a small viewing angle range, the use of a film with small strip-shaped prisms uniformly arranged on the surface is described in U.S. Pat. No. 5,993,940. The development and production are technically very complex.

[0006] Switching between free view and limited view by controlling liquid crystals between so-called "chromonic" layers is produced in WO 2012 / 033583, which causes light losses and is very technically challenging.

[0007] US Patent Application Publication No. 2012 / 0235891 describes a highly complex backlighting, i.e., background illumination, for a screen. According to FIGS. 1 and 15, it uses not only several light guides but also additional complex optical elements, such as microlens elements 40 and prism structures 50, that convert the light from the rear illumination into forward illumination along the way. This implementation is expensive and technically complex, and also involves light losses. According to a variant according to FIG. 17 of US Patent Application Publication No. 2012 / 0235891, both light source 4R and light source 18 generate light with a narrow illumination angle, and the light from rear light source 18 is first converted in a complex manner into light with a large illumination angle. This complex conversion significantly reduces brightness, as already mentioned above.

[0008] U.S. Patent Application Publication No. 2013 / 0308185 describes a special light guide that is stepped and emits light in various directions across a large surface depending on the direction of illumination from the narrow side. This allows it to be combined with a transmissive image reproduction device, such as an LC display, to create a screen that can be switched between free-view and limited-view modes. This has the disadvantage that, for example, limited visual effects can only be generated for either left / right or top / bottom, but not simultaneously for left / right / top / bottom, as may be necessary for certain payment processes. Furthermore, residual light remains visible from blocked viewing angles even in limited-view mode.

[0009] The present applicant's WO 2015 / 121398 describes a screen with two operating modes, in which scattering particles are present in the corresponding volume of the light guide for switching between operating modes. However, the polymeric scattering particles selected there generally have the disadvantage that light is separated from both large surfaces, and about half of the available light is emitted in the wrong direction, i.e., towards the background lighting, and cannot be recycled there to a sufficient extent due to the configuration. Furthermore, polymeric scattering particles distributed in the volume of the light guide can cause scattering effects, especially in high concentrations, which can hinder the eye protection effect in the protective operating mode.

[0010] The "electric birefringence (EB)" technology approach is based on the idea of ​​using switchable liquid crystals in an additionally applied LC panel to "filter" all light beams so that they do not leave the image-forming layer at a certain emission angle. The drawbacks of this technology are the large additional energy and cost expenditures, as well as the difficulty of changing the sweet spot of + / - 40°, i.e., the best possible observation position. Similarly, the absorption of the LC structure is insufficient due to the weakening of the light intensity for observation angles greater than the sweet spot, resulting in a light intensity of up to 3% of the maximum light intensity for observation angles greater than + / - 40°.

[0011] The above-mentioned methods and configurations generally have the common drawbacks of significantly reducing the brightness of the original screen, and / or requiring complex and expensive optical elements for mode switching, and / or reducing the resolution in freely viewable public mode, and / or having visual artifacts in the case of very high resolution displays. Summary of the Invention

[0012] The object of the present invention is therefore to describe a light filter comprising an optical element, in which light incident on the optical element is transmitted or partially or completely absorbed, not primarily as a function of its position, but rather as a function of its direction of incidence and its polarization properties. A light filter using an optical element should allow the light transmission to be influenced in an angle-dependent manner, optionally vertically with respect to a seated or standing observer, and be capable of switching between at least two operating states. In particular, the transmission behavior for a specific direction should thereby be switchable.

[0013] This object is solved in a first design according to the invention by an optical filter, which comprises: a first optical element, a plurality of optical absorption transition dipole moments arranged in a layer having a thickness of at least 0.2 micrometers, the absorption transition dipole moments being preferably formed by dichroic dyes, in which case the dye mass density is typically greater than 1%, or even greater than 10%, the majority of the transition dipole moments, at least in a first state (in this context, the property "at least in a first state" includes several options: on the one hand, exactly one state can exist, which is a permanent design. However, this expression also explicitly includes the possibility of two or more states being present. In this case, the transition dipole moments can be varied, for example, via a so-called guest-host liquid crystal cell), are aligned parallel to a first preferred direction that can be selected for the first optical element, with a tolerance of up to 20° (other tolerance values ​​are also possible, for example, 5° or 10°), or vary around this, the first preferred direction being arranged at an angle α with respect to the perpendicular bisector of the first optical element, for example α=0°, α=+ / -2°, or amount(α)>2°, the angle α being measured in a first plane that can be selected containing the perpendicular bisector, the angle α being preferably measured parallel to an edge, for example the lower edge, of the first optical element, light incident on the first optical element is therefore transmitted or at least partially absorbed as a function of its direction of incidence on the first optical element and its polarization state, a first optical element; and means for optionally generating a first electric field EF1 or a second electric field EF2; a liquid crystal layer arranged behind or in front of the first optical element in the viewing direction, on which a first electric field EF1 or a second electric field EF2 acts, which influences the polarization state of the light passing through it as a function of the electric field; a first linear polarizing filter (X) in case the liquid crystal layer is arranged in front of the first optical element in the viewing direction, the first linear polarizing filter (X) being located in front of the liquid crystal layer in the viewing direction and whose preferred polarization transmission direction is preferably aligned parallel to an edge, preferably a lower edge, of the first optical element; Equipped with the transmission characteristics of the switchable optical filter differ between a first operating mode B1 in which a first electric field EF1 is applied (with a field strength of 0 V / μm) and a second operating mode B2 in which a second electric field EF2 is applied (for example as a 10 kHz square wave, with a field strength not equal to 0 V / μm, for example with a magnitude of 1 V / μm), such that the relative transmissions in the two operating modes B1 and B2 at at least one point on the first optical element (preferably at a plurality of points, particularly advantageously at least half of the surface of the optical element) are in each case equal to or greater than the transmission T for the operating mode B1, except for a selectable tolerance, for example 3% or 5%; B1 (β) or the transmittance T for the operating mode B2 B2 (β), each of which is described by T B1 (α)=1 and T B2 Standardized so that (α)=1 holds, -Light, In a first operating mode B1 in which a first electric field EF1 is applied when the s-polarized part of the light is incident on the first optical element 1 at an angle β, α-60°≦β≦α-40° or α+40°≦β≦α+60°, the s-polarized part of the light has a normalized transmittance value T B1 (β) ≥ 0.25, preferably T B1 (β) ≧ 0.3 In a second operating mode B2, in which a second electric field EF2 is applied when the p-polarized part of the light is incident on the first optical element at an angle β such that α-60°≦β≦α-40° or α+40°≦β≦α+60°≦ (and advantageously also for all angles β such that β≦α-40° or α+40°≦β), the p-polarized part of the light has a normalized transmittance value T B2 (β)≦0.2, preferably T B2 (β)≦0.1, particularly preferably T B2 It transmits up to (β)≦0.05.

[0014] Thereby, an important means-effect relationship exists in the fact that by switching between a first operating mode B1, in which a first electric field EF1 is applied (at a field strength of 0 V / μm), and a second operating mode B2, in which a second electric field EF2 is applied (for example as a 10 kHz square wave, for example at a field strength not equal to 0 V / μm, with a magnitude of 1 V / μm), only in operating mode B2 is s-polarized light incident on the liquid crystal layer essentially converted to p-polarized light which is then incident on the first optical element, and vice versa. In combination with a layer of the first optical element at least 0.2 micrometers thick having an absorbing transition dipole moment, the above-mentioned variation in transmission is due to the T of the above-mentioned operating modes. B1 (β) or T B2 (β), respectively. When the absorption transition dipole moment is additionally formed by a dichroic dye, in which case the dye mass density is generally greater than 1%, which is a supporting factor.

[0015] The means for selectively generating at least the first electric field EF1 or the second electric field EF2 can comprise two or more transparent ITO (indium tin oxide, known in the art) layers between which the liquid crystal layer 3 is disposed. Such ITO layers can be connected to a signal generator that applies a DC electric signal, or preferably an AC electric signal, such as a sine wave or rectangular (or other) electric signal, as required for the first electric field EF1 or the second electric field EF2. The ITO layers can then exhibit the respective first electric field EF1 or second electric field EF2, which affects the state of the liquid crystal in the liquid crystal layer 3. In an exemplary embodiment, the signal used for the first mode B1 is a rectangular or sinusoidal signal with a frequency between 1 kHz and 10 kHz, and the maximum voltage applied is in the range of -20 V to +20 V. In the second mode, the second electric field EF2 can have a field strength of 0 V / m, i.e., no electric field. Alternatively, the no field condition may be for a first mode B1, and a second mode B2 represents the field condition.

[0016] Other embodiments are possible, for example using the same principles as those used to drive pixels in FFS (Fringe Field Switching) or IPS (In-Plane Switching) LCD panels. However, the invention is not limited to the above-described embodiments, which merely show possible examples of exemplary implementations of the invention.

[0017] Furthermore, the means for selectively generating at least the first electric field EF1 or the second electric field EF2 may be embodied to enable partial switching of the switchable optical filter 5 into different modes by generating the first electric field EF1 and the second electric field EF2 simultaneously, but at different positions of the switchable optical filter 5.

[0018] Furthermore, the means for selectively generating at least the first electric field EF1 or the second electric field EF2 may be embodied by a person skilled in the art to not only generate the first electric field EF1 and the second electric field EF2, but also to generate third, fourth etc. electric fields EF3, EF4 etc., if necessary, to enable additional operating modes for the entire area or only a portion of the switchable optical filter 5.

[0019] Further operating modes B3, B4 etc. can also be explicitly provided by electric fields EF3, EF4 etc. that deviate from the electric fields EF1 and EF2. Furthermore, the operating modes B1, B2 etc. can also be locally different on the switchable optical filter.

[0020] Normalization of transmittance, i.e., T B1 (α)=1 and T B2 For (α)=1, it should be noted that the angles β and α are obviously measured in the same above-mentioned plane. In general, T B1 (α)>1 and / or T B2 It is also possible that (α)>1 holds for angle β≠α. Then, in many cases, T B1 (α)<1 and / or T B2 (α)<1 holds for angle β≠α.

[0021] If the transition dipole moment is variable, for example, via a so-called guest-host liquid crystal cell, such a guest-host liquid crystal cell can, but need not, correspond directly to the liquid crystal layer described above.

[0022] In a preferred design, light through the liquid crystal layer travels essentially unchanged when a first electric field EF1 is applied, while when a second electric field EF2 is applied, the incident light becomes circularly or elliptically polarized, or the polarization of the light is rotated by 90°. In this context, this essentially means that the orientation of the liquid crystal molecules at the interface is determined by the electric field and surface-induced forces, resulting in a non-ideal alignment of the liquid crystal molecules, leading to undesirable small changes in polarization.

[0023] The following applies to designs using TN liquid crystals: the alignment of the liquid crystal molecules typically differs by 90° across the large surface area that bounds the liquid crystal layer. Such alignment is supported by PMI or PVA, and may be further supported by mechanical or optical treatments of the surface. It is also true for TN liquid crystal layers that, in general, in response to switching between electric fields EF1 and EF2, the majority of the liquid crystals in the liquid crystal layer rotate 75-90 degrees out-of-plane. For IPS and FFS liquid crystal layers, the rotation of the LC molecules is less than 45°, typically about 20-30°.

[0024] When the liquid crystal layer is arranged behind the first optical element in the viewing direction, linearly or elliptically polarized light is preferably incident, in which case the ratio of the semimajor axis to the semiminor axis is at least 4:1 (preferably 5:1 or more). This can be achieved, for example, by a linear polarizing filter in the light path, or also by a λ / 4 layer in the case of incident circularly polarized light.

[0025] Conveniently, the first optical element (and each further such optical element, if present) and / or the liquid crystal layer are divided into a plurality of separately switchable segments to allow local switchability between respective possible operating states.

[0026] In a further design, the switchable optical filter comprises at least two first optical elements, optionally with a retarder disposed between the at least two such first optical elements, and the at least two first optical elements may, but need not, optionally have different thicknesses of respective layers comprising the plurality of optical absorption transition dipole moments.

[0027] In certain designs of the invention, there can be at least one angle β1 at which the transmittance of the p-polarized part of the light is not equal to the transmittance of the s-polarized part of the light, this condition preferably applies over the entire angular range of angle β1, and particularly preferably applies for all angles α≠β.

[0028] In yet another design of the invention, in both operating modes B1 and B2, there can be at least one angle β2 for which the transmittance of the s-polarized part of the light is greater than the transmittance of the p-polarized part of the light, this condition preferably applies over the entire angular range of angle β2, and particularly preferably applies for all angles α≠β.

[0029] Furthermore, the present invention provides an illumination device in a first design for a screen that can be operated in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted into a limited viewing angle range for the observer compared to the free view mode, comprising: - a background light that spreads in a flat manner, emits light and is optionally configured to be illuminated directly (for example with an LED matrix); a switchable light filter according to the invention as described above, arranged in front of the background illumination in the observation direction; The lighting device includes:

[0030] In addition, the present invention provides a screen in a first design that can operate in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted to the user in a limited range of viewing angles compared to the free view mode, a lighting device as described above, - a second linear polarizing filter P, when the first linear polarizing filter is not arranged in the switchable optical filter of the lighting device, which is arranged in front of the background illumination in the observation direction and limits the propagation direction of light coming from the background illumination and passing through the second linear polarizing filter P; a transmissive image reconstructor arranged in front of a switchable optical filter in the observation direction; Equipped with - further comprising a screen to which a second electric field EF2 is applied in operating mode B2 and to which a first electric field EF1 is applied in operating mode B1.

[0031] The term background lighting is synonymous with backlighting or background illumination.

[0032] Thereby, preferably the first or second linear polarizing filter P is arranged in or is part of a transmissive image reproducing device.

[0033] Furthermore, the present invention provides a screen in a second design that can operate in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted into a limited viewing angle range for the observer compared to the free view mode, - an image reproduction device (e.g., LC panel, OLED, micro LED, etc., but here any type of image reproduction device is generally possible), a switchable optical filter according to the invention in front of the image reproducing device in the observation direction as further described above, and Equipped with - a screen to which a second electric field EF2 is applied in the first operating mode B2 and to which a first electric field EF1 is applied in the operating mode B1.

[0034] Optionally, the switchable light filter may be subsequently and / or reversibly attached to the image reproduction device by the user, in which case the light filter may be sold as a so-called "aftermarket product".

[0035] Furthermore, the present invention provides screens in third and fourth designs that can operate in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted to a viewer in a limited viewing angle range compared to the free view mode, a transmissive image reproduction device, preferably an LC panel; - a background illumination arranged downstream of the transmission image reproduction device in the observation direction and having a light density distribution whose peak luminance is emitted in a direction forming an angle of at least 3°, advantageously 5° or 8°, with the first preferred direction (the background illumination may have a permanent or variable light density curve); a switchable optical filter according to the invention as further described above in front (third design) or behind (fourth design) the image reproducing device in the viewing direction; Equipped with - further comprising a lighting device, wherein in the operating mode B2 a second electric field EF2 is applied and in the operating mode B1 a first electric field EF1 is applied.

[0036] Background illumination with such characteristics can be produced, for example, if it further includes a turning film and / or a partially mirrored or asymmetric prismatic grating above the light guide with a diffuser, BEF, or DBEF.

[0037] More advantageously, in the case of such a screen of the third or fourth design, for at least one partial surface, in the second operating mode B2, for at least the angular range α-4°≦β≦α+4° (preferably also for α-6°≦β≦α+6° or α-8°≦β≦α+8°, and at most for α-20°≦β≦α+20°), for all angles β included in this angular range, T B2 (β) and the light density of the background lighting at angle β, L V (β) and the transmittance T of the image reproduction device at angle β BW The product with (β) may deviate by a maximum of + / - 10% from the value of said product for the angle α=β.

[0038] Due to compliance with this product as part of the above-mentioned tolerances, the perceived uniformity is improved for the observer, for example when looking directly at the center of the screen, since if the transmittance of the first optical element or image reproduction device drops significantly when, for example, an oblique line of sight is present in the lateral areas of the screen, this is again compensated for by the corrective light density distribution of the background illumination.

[0039] Alternatively, optionally, in the case of such a screen of the third or fourth design, in the second operating mode B2, for at least one partial surface, for an angular range of at least α-4°≦β≦α+4° (preferably α-6°≦β≦α+6° or α-8°≦β≦α+8°, at most α-20°≦β≦α+20°), for all angles β included in this angular range, T B2 (β) and the light density of the background lighting at angle β, L V The product with (β) may deviate by a maximum of + / - 10% from the value of said product for the angle α=β.

[0040] The balancing effect described above also applies here due to the countervailing light density distribution of the background illumination, but by ignoring the transmission behavior of the image reproduction device.

[0041] Finally, the invention provides a screen in a fifth design that can operate in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted in a limited angular range for the observer compared to the free view mode, wherein: a transmissive image reproduction device, preferably an LC panel; a background illumination arranged downstream of the transmission image reproduction device in the observation direction and having an asymmetric light density distribution, the asymmetry preferably existing in the horizontal direction from the observer's point of view; and a switchable optical filter according to the invention as further described above in front of or behind the image reproducing device in the viewing direction; Equipped with - further comprising a lighting device, wherein in the operating mode B2 a second electric field EF2 is applied and in the operating mode B1 a first electric field EF1 is applied.

[0042] Thereby, the background lighting does not have any inherently symmetric light density distribution (e.g., around a vertical centerline—from the observer's point of view), but is, in contrast, designed to embody an asymmetric light density distribution (e.g., in the horizontal direction). In other words, this background lighting 8a has an asymmetric light density distribution, and this asymmetry preferably exists with respect to the horizontal direction from the observer's point of view. Such a design is possible, for example, by using light guides that separate the light in a deterministic way and / or turning films that shift the peak brightness.

[0043] This variant is particularly advantageous for use in vehicles, since the light that would otherwise be emitted in the direction of the passenger window can be significantly reduced by the design of the background lighting, for example to less than 10%, preferably less than 2.5%, of the peak brightness, starting from a horizontal angle of 25 degrees or more (relative to the perpendicular bisector), while there is an intentionally high light density in the direction of the driver. In this way, annoying reflections on the passenger window or, optionally, on the outside mirror closest to the passenger are reduced or avoided. Nevertheless, thanks to a light filter mounted in front of the image reproduction device, the screen can be selectively operated so that image content, for example relating to moving images, is visible only to the passenger (operating mode B2), or so that image content, for example relating to navigation map material, is visible to both the driver and passenger (operating mode B1).

[0044] For some of the above-mentioned screens of the first to fourth designs, when used in a passenger vehicle, it may be advantageous for a second optical element to be arranged in front of the transmission image reproducing device in the viewing direction, the second optical element comprising: a plurality of optical absorption transition dipole moments, whereby the dye mass density is greater than 1%, or greater than 10%; the majority of the transition dipole moments, at least in the first state, are aligned parallel to or fluctuating about a selectable second preferred direction for the second optical element with a tolerance of up to 20° (alternatively 10°), the second preferred direction being disposed at an angle α1 with respect to a perpendicular bisector of the second optical element (whereby, for example, α1=0°, α1=+ / -2°, or amount(α1)>2°), the angle α1 being measured in a selectable second plane containing the perpendicular bisector, the second plane preferably being perpendicular to the first plane of the first optical element; Light incident on the second optical element is therefore transmitted or at least partially absorbed as a function of its direction of incidence and its polarization state relative to the second optical element.

[0045] This last-mentioned design advantageously ensures a reduced vertical transmission and therefore reduces or completely avoids reflections on the windshield of the image content displayed on this screen in the vehicle.

[0046] Furthermore, the present invention provides an illumination device for a screen in a second design that can operate in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode, in which light is emitted in a limited angular range compared to the free view mode, comprising: - a background light that extends in a flat manner, emits light in a limited angular range, and is optionally configured to shine directly; a plate-shaped light guide located in front of the background illumination in the observation direction and having a separation element in at least one of its major surfaces and / or in its volume; - lighting means arranged laterally towards at least one narrow side of the light guide; an optional linear polarizing filter; a switchable light filter according to the invention as further described above, arranged in front of the background illumination in the direction of observation (this also includes a position in front of a screen used together with the illumination device); Equipped with in operating mode B2 the background lighting is switched off and the lighting means is switched on, and in operating mode B1 at least the lighting means is switched on; - further comprising a lighting device, wherein in the operating mode B2 a second electric field EF2 is applied and in the operating mode B1 a first electric field EF1 is applied.

[0047] In the context of the present invention, particularly with regard to background lighting, a "limited angular range" means that the corresponding light density is concentrated in the specified angular range by at least 80% or 90%. However, in practice, typically for technical reasons, residual light outside the specified limited angular range may still exist. Ideally, such residual light is minimal and decreases toward larger angles. To achieve particularly strong minimization, a corresponding light filter that emits light in a limited angular range is used in addition to the background lighting. This also applies to the later-described variants with light guides that emit or separate light primarily in a limited angular range. In contrast to this design of the present invention, the light density curve of the background lighting is typically bell-shaped, especially in the horizontal (and optionally also vertical) angular range, although actual concentration of light density in smaller angular ranges may not exist.

[0048] Finally, the invention provides an illumination device for a screen in a third design that can operate in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode, in which light is emitted in a limited angular range compared to the free view mode, comprising: background lighting that is spread in a flat manner, emits light over an unlimited range of angles, and is optionally configured to be illuminated directly (for example by means of a locally dimmable LED matrix lighting unit); - a plate-shaped light guide located in front of the background illumination in the observation direction and having a separation element in at least one of its major surfaces and / or in its volume, which separates the light coupled laterally into at least one narrow side of the light guide substantially (i.e. more than half, preferably more than 80% or 90%) into a limited angular range; - lighting means arranged laterally towards at least one narrow side of the light guide; an optional linear polarizing filter; a switchable light filter according to the invention as described above, arranged in front of the background illumination in the observation direction; Equipped with in operating mode B2 the background lighting is switched off and the lighting means is switched on, and in operating mode B1 at least the background lighting is switched on (optionally the lighting means may also be switched on), - further comprising a lighting device, wherein in the operating mode B2 a second electric field EF2 is applied and in the operating mode B1 a first electric field EF1 is applied.

[0049] The illumination devices of the first, second and third designs may be advantageously combined with a transmissive screen, such as an LC panel, to produce a screen that can operate in at least two operating modes: an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted into a limited angular range compared to the free view mode.

[0050] Advantageously, the transition dipole moment of the first optical element (or, optionally, the second or further optical element, if present) is formed as one or more dichroic dyes mixed with the liquid crystal in a guest-host configuration. In the case of a permanent transition dipole moment, the liquid crystal can be fixed, preferably by a curing process.

[0051] In contrast, the transition dipole moments can be embedded in a non-fixed manner in a guest-host configuration in a liquid crystal layer, so that the transition dipole moments can change their alignment and / or their magnitude between a first state and at least one second state in response to the influence of the liquid crystal layer.

[0052] The dichroic dye molecules generally align parallel to the liquid crystal molecules.

[0053] Alternatively, the first optical element can be formed as a stack of layers of polymeric film polarizers.

[0054] The above design further ensures that the first optical element is aperiodic in its structure, which is highly advantageous since in combination with the pixel structure of the screen there is no risk of artifacts such as Moiré effects.

[0055] The first preferred direction may in each case subtend an angle of, for example, 0° to 45° with respect to the surface normal of the first optical element. The first preferred direction may also vary across the surface of the first optical element. In that case, an average weighted preferred direction applies in the context of the present invention.

[0056] Furthermore, it is possible that at least two such preferred directions in the selectable plane differ by more than 10° and / or that each preferred direction of the transition dipole moment is selectable as a function of its position within the first optical element.

[0057] In addition, the first optical element can conveniently be divided into different regions (A1, A2,...) along selectable reference lines, and for each region (A1, A2,...) a separate preferred direction can be selected that applies to all transition dipole moments within the region (A1, A2,...), the preferred directions of all regions being different in pairs and pointing towards the observer 3 except for a tolerance of up to + / - 10 degrees. This arrangement has the advantage that the observer perceives the screen with the light filter in limited view mode as uniformly illuminated.

[0058] A transition dipole moment, also called a transition matrix element, corresponds to the quantum mechanical vector GROESSE and a specific transition between an initial (generally, ground) and final (generally, excited) state of a system, i.e., an atom, molecule, or solid, and the electric dipole moment associated with this transition. The direction of the vector defines the polarization of the transition, which determines how the system interacts with electromagnetic waves having a particular polarization; for example, light of the corresponding polarization is absorbed in response to the transition from the ground state to the excited state. The quantity of the vector corresponds to the strength of the interaction or the transition probability.

[0059] Thereby, the first (second) preferred direction corresponds to the alignment of the transition dipole moment of the first (second) optical element for a particular light propagation direction, in which case the absorption is the same for all polarizations of light.

[0060] The first and second preferred directions may be identical or may differ in alignment by only a few degrees (up to 10°), and may in particular be perpendicular on the respective optical elements. This is the preferred case. However, depending on the application, it is also possible for the first and second preferred directions to differ from each other by more than 10°.

[0061] The optical filter may further comprise a polarizing filter arranged in front of or behind the first or second optical element in the direction of incidence. Alternatively or additionally, a λ / 4 layer is also conceivable, e.g., in response to incident circularly polarized light, which is converted into (essentially) linearly polarized light in this layer.

[0062] A first exemplary manufacturing variant of the first or second optical element by using the guest-host principle is based on a mixture of a dichroic dye or dichroic dye mixture with a liquid crystal mixture or compound and comprises the following steps for manufacturing (see U.S. Pat. No. 9,481,658 or WO 2021 / 177308, paragraphs 37 et seq.): A weakly or non-birefringent substrate is coated with a film that determines the alignment of the molecules with respect to the surface, generally parallel or perpendicular to the surface. For this purpose, polymers are used, preferably polyvinyl alcohol or polyimides. - Optional: optical or mechanical treatment of the surface to improve the quality of the subsequent molecular alignment. - Application of mixtures of dichroic dyes with thermotropic liquid crystal compounds or polymers. - Irradiation with light causes the side chains to locally condense in a way that ensures birefringence along the surface. An alternative second manufacturing variant uses a thermotropic liquid crystal dichroic dye (see JP 2011-237513 A) and includes the following steps: - Preparation of the corresponding dyes and addition of polar groups. - Application of the pigment mixture and photo-alignment and curing of the pigment mixture with polarized light.

[0063] For example, the following materials may be used in various manufacturing variations, although this list does not claim to be exhaustive. as a polymer substrate with low or no birefringence: preferably TAC, as dichroic substances or mixtures: dichroic dyes (preferably azo dyes) or dichroic metal nanoparticles (preferably gold, silver, copper and aluminum); these are generally individual dyes or mixtures of typically up to three different dyes to provide absorption across the entire spectrum, for surface treatment by alignment of dyes or liquid crystal substances: polymers, preferably polyvinyl alcohol or polyimides, With regard to thermotropic liquid crystal compounds or polymers, reference is made, for example, to JP 2011-237513 A. As chemical groups for crosslinking (crosslinking) to thermotropic liquid crystal compounds or polymers: methacryloyl groups, epoxy groups, oxetanyl groups, and styrene groups, preferably methacrylic acid groups. Alternatively, they may be polymerizable liquid crystal compounds, as described, for example, in Japanese Patent No. 6268730. -polymerizable liquid crystal dichroic dyes, e.g. azo dyes

[0064] At least one dye molecule, in which a transition dipole or transition dipole moment is associated with each dye molecule, i.e., each dye molecule corresponds to a transition dipole or transition dipole moment. The dye typically has a mass fraction of at least 0.01%, preferably 1% to 15%, in the material of each layer of each optical element. In special cases, the concentration in the case of liquid crystal dichroic dyes can even reach 95%. The layer thickness is preferably in the range of 0.2 μm to 50 μm, preferably 0.5 μm to 20 μm, all limits being included. The dyes or dye mixtures in different layers within the optical element may or may not be different.

[0065] The above-mentioned light filters, lighting devices or such screens are advantageously used in mobile devices, automobiles, aircraft or ships, payment terminals or access systems, which allow switching between the above-mentioned operating modes in order to protect sensitive data, i.e. to display it in a way that is only perceptible to one observer, or to display image content to several observers simultaneously.

[0066] The performance of the present invention is generally maintained when the above-mentioned parameters are varied within certain limits.

[0067] It goes without saying that the features mentioned above and those to be described below can be used not only in the combinations specified, but also in other combinations or alone without departing from the scope of the invention. [Brief explanation of the drawings]

[0068] The present invention will be described in more detail below based on exemplary embodiments and with reference to the accompanying drawings, which also disclose essential features of the present invention. These exemplary embodiments are for illustrative purposes only and should not be construed as limiting. For example, a description of an exemplary embodiment having multiple elements or components should not be construed to mean that all of those elements or components are required for implementation. In contrast, other exemplary embodiments may include alternative elements and components, fewer elements or components, or additional elements or components. Elements or components of different exemplary embodiments may be combined with each other unless otherwise specified. Changes and variations described with respect to one of the exemplary embodiments may also be applied to the other exemplary embodiments. To avoid repetition, identical or corresponding elements in different figures are identified with the same reference numerals and will not be described multiple times. [Figure 1a] 1A-1C show schematic diagrams of aspects of operation of an exemplary switchable optical filter in operating modes B1 and B2. [Figure 1b] 1 is an exemplary normalized transmission graph of an optical element in combination with a linear polarizing filter without (left) and with (right) a wave plate (B-plate). [Figure 2] 1 shows a schematic diagram of an exemplary configuration of a switchable optical filter in a first design. [Figure 3] 1 shows an exemplary normalized transmission graph (schematic based on measurements) versus horizontal angle range of a switchable optical filter in a first operating mode B1. [Figure 4] 1 shows an exemplary normalized transmission graph (schematic based on measurements) versus horizontal angle range for a switchable optical filter in a second operating mode B2. [Figure 5] 10 shows a schematic diagram of an exemplary configuration of a switchable optical filter in a second design. [Figure 6] 1 shows a schematic diagram of an exemplary configuration of an illumination device in a first design with a switchable optical filter. [Figure 7] 1 shows a schematic diagram of an exemplary configuration of a screen in a first design that can operate in at least two operating modes B1 and B2 with a switchable optical filter. [Figure 8] 10 shows a schematic diagram of an exemplary configuration of a screen in a second design that can operate in at least two operating modes B1 and B2 with a switchable optical filter. [Figure 9a] 10 shows a schematic diagram of an exemplary configuration of a screen in a third design that can operate in at least two operating modes B1 and B2 with a switchable optical filter. [Figure 9b] 10 shows a schematic diagram of an exemplary configuration of a screen in a fourth design that can operate in at least two operating modes B1 and B2 with a switchable optical filter. [Figure 9c] 10 shows an exemplary normalized light density distribution of background lighting that can be used in a screen of, for example, the third or fourth design. [Figure 10a] In particular, but not by way of limitation, exemplary optical density or transmission graphs for screens of third or fourth designs are shown. [Figure 10b] In particular, but not by way of limitation, exemplary optical density or transmission graphs for screens of third or fourth designs are shown. [Figure 10c] In particular, but not by way of limitation, exemplary optical density or transmission graphs for screens of third or fourth designs are shown. [Figure 10d] In particular, but not by way of limitation, exemplary optical density or transmission graphs for screens of third or fourth designs are shown. [Figure 11] 10 shows a schematic diagram of an exemplary configuration of a screen in a fifth design that can operate in at least two operating modes B1 and B2 with a switchable optical filter. [Figure 12]10 shows a schematic diagram of an exemplary configuration of an illumination device in a second design with a switchable optical filter. [Figure 13] 10 shows a schematic diagram of an exemplary configuration of an illumination device in a third design with a switchable optical filter. DETAILED DESCRIPTION OF THE INVENTION

[0069] The drawings are not to scale and represent only schematic diagrams. For example, with respect to the exemplary drawings in Figures 1b, 3, 4, 9c, and 10b-10d, which represent one- or two-dimensional angle-dependent diagrams of the transmittance of an optical filter, the numbers assigned to the lines in each case represent the transmittance normalized to "1" for the corresponding pair of angles in polar coordinates. Thus, for example, in Figure 1b, the number "0.90" corresponds to a transmittance of 90% in the corresponding direction.

[0070] 1a shows a schematic diagram of an exemplary switchable optical filter 5 operating in a first mode (B1) and a second mode (B2) of operation. a first optical element 1, arranged in a layer having a thickness of at least 0.2 micrometers, preferably formed by a dichroic dye, in which case the dye mass density is greater than 1%, or alternatively greater than 10%, and has a plurality of optical absorption transition dipole moments, the majority of the transition dipole moments, at least in a first state (with respect to the design examples described below on the basis of the drawings, the characteristic "at least in a first state" includes exactly one option, i.e., the existence of exactly one state, i.e., this is a permanent design), are aligned parallel to a first selectable preferred direction for the first optical element 1 with a tolerance of up to 20° (other tolerance values ​​are possible, e.g., 5° or 10°), or vary thereabout, the first preferred direction being disposed at an angle α with respect to the perpendicular bisector of the first optical element, e.g., α=0°, α=+ / -2°, or amount(α)>2°, the angle α being measured in a selectable first plane containing said perpendicular bisector, the angle α being preferably measured parallel to an edge, e.g., the upper edge, of the first optical element 1; light incident on the first optical element 1 is therefore transmitted or at least partially absorbed as a function of its direction of incidence and its polarization state relative to the first optical element 1, a first optical element 1; - means for optionally generating the first electric field EF1 or the second electric field EF2 (not shown, but see for example paragraph

[0068] ); a liquid crystal layer 3, which is arranged in this example behind the first optical element 1 in the viewing direction and which influences the polarization state of the light passing through it as a function of the action of a first electric field EF1 or a second electric field EF2; Equipped with the transmission characteristics of the switchable optical filter 5 differ between a first operating mode B1 in which a first electric field EF1 is applied (with a field strength of 0 V / μm) and a second operating mode B2 in which a second electric field EF2 is applied (for example as a 10 kHz square wave, with a field strength not equal to 0 V / μm, for example with a magnitude of 1 V / μm), such that the relative transmissions in the two operating modes B1 and B2, respectively, at at least one point on the optical element 1 (preferably at a plurality of points, particularly advantageously at least half of the surface of the optical element) are in each case equal to or greater than the transmission T for the operating mode B1, except for a selectable tolerance, for example 3% or 5%; B1 (β) or the transmittance T for the operating mode B2B2 (β), each of which is described by T B1 (α)=1 and T B2 Standardized so that (α)=1 holds, -Light, In a first operating mode B1 in which a first electric field EF1 is applied when the s-polarized part of the light is incident on the optical element 1 at an angle β, with α-60°≦β≦α-40° or α+40°≦β≦α+60°, the s-polarized part of the light has a normalized transmittance value T B1 (β) ≧ 0.25 (preferably, T B1 (β) ≧ 0.3) In a second operating mode B2 in which a second electric field EF2 is applied when incident on the optical element 1 at an angle β with α-60°≦β≦α-40° or α+40°≦β≦α+60° (and advantageously also for all angles β with β≦α-40° or α+40°≦β), the p-polarized part of the light has a maximum normalized transmittance value T B2 (β)≦0.2 (preferably T B2 (β)≦0.1, particularly preferably T B2 (β)≦0.05) and transmits.

[0071] Normalization of transmittance, i.e., T B1 (α)=1 and T B2 For (α)=1, it should be noted that the angles β and α are obviously measured in the same above-mentioned plane. In general, T B1 (α)>1 and / or T B2 It is also possible that (α)>1 holds for angle β≠α. Then, in many cases, T B1 (α)<1 and / or T B2 (α)<1 holds for angle β≠α.

[0072] The means for selectively generating at least the first electric field EF1 or the second electric field EF2 can comprise two or more transparent ITO (indium tin oxide, known in the art) layers between which the liquid crystal layer 3 is disposed. Such ITO layers can be connected to a signal generator that applies a DC electric signal, or preferably an AC electric signal, such as a sine wave or rectangular (or other) electric signal, as required for the first electric field EF1 or the second electric field EF2. The ITO layers can then exhibit the respective first electric field EF1 or second electric field EF2, which affects the state of the liquid crystal in the liquid crystal layer 3. In an exemplary embodiment, the signal used for the first mode B1 is a rectangular or sinusoidal signal with a frequency between 1 kHz and 10 kHz, and the maximum voltage applied is in the range of -20 V to +20 V. In the second mode, the second electric field EF2 can have a field strength of 0 V / m, i.e., no electric field. Alternatively, the no field condition may be for a first mode B1, and a second mode B2 represents the field condition.

[0073] Other embodiments are possible, for example using the same principles as those used to drive pixels in FFS (Fringe Field Switching) or IPS (In-Plane Switching) LCD panels. However, the invention is not limited to the above-described embodiments, which merely show possible examples of exemplary implementations of the invention.

[0074] Furthermore, the means for selectively generating at least the first electric field EF1 or the second electric field EF2 may be embodied to enable partial switching of the switchable optical filter 5 into different modes by generating the first electric field EF1 and the second electric field EF2 simultaneously, but at different positions of the switchable optical filter 5.

[0075] Furthermore, the means for selectively generating at least the first electric field EF1 or the second electric field EF2 may be embodied by a person skilled in the art to not only generate the first electric field EF1 and the second electric field EF2, but also to generate third, fourth etc. electric fields EF3, EF4 etc., if necessary, to enable additional operating modes for the entire area or only a portion of the switchable optical filter 5.

[0076] An important means-effect relationship therefore resides in the fact that switching between a first operating mode B1, in which a first electric field EF1 is applied (at a field strength of 0 V / μm), and a second operating mode B2, in which a second electric field EF2 is applied (e.g., as a 10 kHz square wave, at a field strength not equal to 0 V / μm, e.g., of a magnitude of 1 V / μm), causes the s-polarized light illuminating the liquid crystal layer 3 only in operating mode B2 to be essentially converted to p-polarized light, which then enters the first optical element 1. This is illustrated in FIG. 1a: operating mode B1 is shown on the left, in which the s-polarized component of the light incident on the liquid crystal layer 3 remains s-polarized after passing through this liquid crystal layer. In contrast, the right side of FIG. 1a shows how the s-polarized component becomes p-polarized after passing through the liquid crystal layer. In combination with a layer of the first optical element at least 0.2 micrometers thick having an absorbing transition dipole moment, the above-mentioned variation in transmission leads to a significant increase in the T of the above-mentioned operating modes. B1 (β) or T B2 This is suggested by the arrows in FIG. 1a: on the left, i.e., in operating mode B1, the s-polarized light passes through the first optical element 1 even at oblique angles, whereas on the right, i.e., in operating mode B2, the p-polarized light component is transmitted laterally and is therefore stylized by vertically only arrows.

[0077] Thus, in a preferred design, light passing through the liquid crystal layer 3 travels in an essentially unchanged manner when a first electric field EF1 is applied, while when a second electric field EF2 is applied, the incident light is polarized in a circular or elliptical manner, or the polarization of the light is rotated by 90°. As mentioned above, Fig. 1 shows the operating mode B1 on the left. This means that light incident from below, indicated by "sss", when the first electric field E1 is applied, has its polarization essentially unchanged by the liquid crystal layer 3. Therefore, s-polarized light can pass through the optical element 1 with a transition dipole moment, i.e., in all directions (at least) suggested here in the plane of the paper. This allows the transmittance value T to be maintained even if there are losses in transmission. B1 The above condition on (β) holds for a corresponding angle β where α-60°≦β≦α-40° or α+40°≦β≦α+60°.

[0078] For clarity, the angle α is shown in FIG. 1 with a value greater than 0°. However, α=0° generally applies in all considerations. A value of α≠0° provides a preferred tilt in the transmission direction of the switchable optical filter 5.

[0079] 1 further shows, on the right side, an operating mode B2, whereby a second electric field E2 is applied, and the light incident from below, denoted "sss", has its polarization changed by the liquid crystal layer 3, i.e., is essentially converted to p-polarized light. Therefore, the p-polarized light thus generated can only be transmitted to a limited extent through the optical element 1, which has a transition dipole moment. Due to the alignment of the transition dipole moment and the limited transmission thereby applied, the transmittance value T B2 The above condition for (β) particularly holds for corresponding angles β with α-60°≦β≦α-40° or α+40°≦β≦α+60°. This condition also preferably holds for all angles β≦α-40° or α+40°≦β.

[0080] To further understand the mode of operation of the present invention, Figure 1b further shows exemplary normalized transmission graphs of the optical element 1 in combination with a linear polarizing filter, on the left without a wave plate (B-plate) and on the right with a wave plate (B-plate). It can be seen that the use of a wave plate (retarder, e.g. a B-plate as in the calculations here) ensures a reduction in the transmission and is therefore advantageous, especially for perpendicular angles with an absolute value of about 15° or more.

[0081] These figures are plotted in a polar coordinate system for the hemisphere through which the light is emitted. The straight lines in each case correspond to the horizontal and vertical. The transmittance is limited in each case, especially in the horizontal direction. For the circle shown, the polar angles from the inside (i.e., the intersection of the straight lines) to the outside are 25°, 45°, and 90°.

[0082] It is advantageously applied that the transition dipole moment is formed as one or more dichroic dyes mixed with the liquid crystal in a guest-host configuration. In the case of a permanent transition dipole moment, the liquid crystal can be fixed by a curing process. The dichroic dye molecules generally align parallel to the liquid crystal molecules.

[0083] The above-described design further ensures that the first optical element 1 is set aperiodic in its structure, which is highly advantageous since in combination with the pixel structure of the screen there is no risk of artifacts such as Moiré effects.

[0084] The first preferred direction may in any case subtend an angle between 0° and 45° with respect to the surface normal of the first optical element 1. The first preferred direction may also vary across the surface of the first optical element 1. In that case, an average weighted preferred direction applies in the context of the present invention.

[0085] 2 further shows a schematic diagram of an exemplary configuration of the switchable optical filter 5 in a first design, whereby the liquid crystal layer 3 is arranged in front of the first optical element 1 in the viewing direction (from above). This first design further comprises a first linear polarizing filter (X) arranged in front of the liquid crystal layer 3 in the viewing direction, with its preferred polarization transmission direction preferably aligned parallel to an edge, preferably the bottom edge, of the optical element 1.

[0086] 3 shows an exemplary normalized transmission graph (as a schematic diagram based on measurements) versus a range of horizontal angles for the switchable optical filter 5 in the first operating mode B1 with a first electric field EF1 applied. Due to the fact that α=0° has been assumed, it is now assumed that when light is incident on the optical element 1 (generally the switchable optical filter 5) at an angle β with α-60°≦β≦α-40° or α+40°≦β≦α+60°, as desired, the s-polarized part of this light will have at least one normalized transmission value T B1 (β)≧0.25 transmits.

[0087] In contrast, Figure 4 shows an exemplary normalized transmission graph (as a schematic diagram based on measurements) over a range of horizontal angles for the switchable optical filter 5 in the second operating mode B2 with a second electric field EF2 applied.

[0088] In a second operating mode B2 in which a second electric field EF2 is applied, when light is incident on the optical element 1 (or on the switchable filter 5) at an angle β, with α-60°≦β≦α-40° or α+40°≦β≦α+60°, the p-polarized portion of this light (p-polarization here originating in particular from the influence of the liquid crystal layer 3) has a maximum normalized transmittance value T B2 (β)≦0.2 (In this case, T B2 (β)≦0.15) and transmits.

[0089] In certain designs of the invention, there can be at least one angle β1 for which the transmittance of the p-polarized part of the light is not equal to the transmittance of the s-polarized part of the light, this condition preferably applies over the entire angular range of angle β1 (e.g., -60°≦β≦-40° and / or +40°≦β≦+60°), and particularly preferably applies for all angles α≠β.

[0090] In yet another design of the invention, in both operating modes B1 and B2, there can be at least one angle β2 for which the transmittance of the s-polarized part of the light is greater than the transmittance of the p-polarized part of the light, this condition preferably applies over the entire angular range of angle β2 (e.g., −60°≦β≦−40° and / or +40°≦β≦+60°), and particularly preferably applies for all angles α≠β.

[0091] A schematic diagram of an exemplary configuration of a switchable optical filter in the second design is shown in Fig. 5. Thereby, the switchable optical filter 5 comprises at least two first optical elements 1, 1', with a retarder R optionally arranged between at least two such first optical elements 1, 1'. Furthermore, the at least two first optical elements 1, 1' may optionally, but need not necessarily, have different thicknesses of respective layers comprising multiple optical absorption transition dipole moments. When a retarder R is arranged between the two first optical elements 1, 1', this retarder allows an improvement of the transmission limiting effect, particularly in the second operating mode B2.

[0092] A schematic diagram of an exemplary configuration of an illumination device in a first design with a switchable light filter 5 is shown in Figure 6. The illumination device in this first design for a screen that can be operated in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted into a limited viewing angle area for the observer compared to the free view mode, - a background light 8 that spreads in a flat manner, emits light and is configured to shine directly (for example with an LED matrix, for local dimming); a light filter 5 as described above, arranged in front of the background illumination 8 in the observation direction; Equipped with.

[0093] Therefore, in the first design, such an illumination device can also operate in the two aforementioned operating modes B1 and B2 when the switchable optical filter 5 inserted therein is used accordingly in the respective operating modes.

[0094] 7 further shows a schematic diagram of an exemplary configuration of a screen in a first design that can operate in at least two operating modes B1 and B2 with a switchable light filter 5. Such a screen that can operate in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted into a limited viewing angle area for the observer compared to the free view mode, can be in a first design: a lighting device as described above with reference to FIG. 6; a second linear polarizing filter P, when the first linear polarizing filter X is not arranged in the switchable light filter 5 of the lighting device, which is arranged in front of the background illumination 8 in the observation direction and which, in combination with the optical element 1 of the switchable light filter 5, limits the propagation direction of light coming from the background illumination and passing through the second linear polarizing filter P; a transmission type image reconstructor 11 arranged in front of the optical filter 5 in the observation direction; Equipped with - further comprising a screen to which a second electric field EF2 is applied in operating mode B2 and to which a first electric field EF1 is applied in operating mode B1.

[0095] Thereby, preferably the first or second linear polarizing filter P, X is arranged in or is part of the transmissive image reproducing device 11 .

[0096] Furthermore, the present invention includes a screen in a second design that can operate in at least two operating modes: an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted into a limited viewing angle range for the observer compared to the free view mode. To this end, Figure 8 shows a schematic diagram of an exemplary configuration of such a screen in the second design. The latter comprises: an image reproduction device 12 (for example, an LC panel, an OLED, a microLED, etc., but here any type of image reproduction device is generally possible), - an optical filter 5 as described above in front of the image reproducing device 12 in the observation direction; Equipped with - further comprising a lighting device, wherein in the operating mode B2 a second electric field EF2 is applied and in the operating mode B1 a first electric field EF1 is applied.

[0097] Thereby, optionally, the switchable optical filter 5 may be subsequently and / or reversibly attached to the image reproduction device 12 by a user, in which case the optical filter 5 may be sold as a so-called "aftermarket product".

[0098] Figures 9a and 9b show schematic diagrams of exemplary configurations of a screen in a third and fourth design that can operate in at least two operating modes B1 and B2 with a switchable optical filter. a transmissive image reproduction device 11, preferably an LC panel, a background illuminator 8a (which may have a permanent or variable light density curve) arranged downstream of the transmission image reproducing device 11 in the observation direction and having a light density distribution whose peak luminance is emitted in a direction forming an angle of at least 3°, advantageously 5° or 8°, with the first preferred direction; an optical filter 5 as further described above in front (see FIG. 9a, third design) or behind (see FIG. 9b, fourth design) the image reproduction device 11 in the viewing direction; Equipped with - further comprising a lighting device, wherein in the operating mode B2 a second electric field EF2 is applied and in the operating mode B1 a first electric field EF1 is applied.

[0099] Background illumination 8a with such characteristics can be produced, for example, if it further includes a turning film and / or a partially mirrored or asymmetric prism grating above the light guide with a diffuser, BEF, or DBEF.

[0100] To this end, Figure 9c shows an exemplary normalized light density distribution of background illumination 8a that can be used, for example, in a screen of the third or fourth design, where the peak luminance is shifted horizontally to the right by approximately 5°.

[0101] More advantageously, in the case of such a screen of the third or fourth design, for at least one partial surface, in the second operating mode B2, for at least the angular range α-4°≦β≦α+4° (preferably also for α-6°≦β≦α+6° or α-8°≦β≦α+8°, and at most for α-20°≦β≦α+20°), for all angles β included in this angular range, T B2 (β) and the light density L of the background lighting 8a at angle β V (β) and the transmittance T of the image reproduction device 11 at the angle β. BW The product with (β) may deviate by a maximum of + / - 10% from the value of said product for the angle α=β.

[0102] Due to compliance with this product as part of the aforementioned tolerances, the perceived uniformity is improved for the observer, for example when looking directly at the center of the screen, since if the transmittance of the first optical element 1 or the image reproduction device 11 drops significantly when, for example, an oblique line of sight is present in the lateral areas of the screen, this is again compensated for by the corrective light density distribution of the background illumination 8a.

[0103] In this context, reference should be made in particular, but not exclusively, to Figures 10a to 10d, which show exemplary optical density or transmission graphs of individual components or groups of components for screens of the third or fourth design. Two different parameter combinations are shown: optical density of background illumination 8a, transmittance of transmissive image reproduction device 11, and transmittance of optical element 1. At an angle β with α-4°≦β≦α+4°, T B2 (β), L V (β), and T BW The condition that the deviation of the product of (β) is at most 10% is met for both parameter sets. V (β) and the transmittance T of the image reproduction device BW (β) has no angle dependence.

[0104] In the second case (dashed line), T B2 The angular dependence of (β) is more pronounced, so the optical density L V The condition can be met if only (β) increases at least locally with the difference of the viewing angle β from the angle α.

[0105] Alternatively, optionally in the case of such a screen of a third design, at least for a partial surface, in the second operating mode B2 at least α-4°≦β≦α+4°, preferably α-6°≦β≦α+6° or α-8°≦β≦α+8°, at most For the angle range α-20°≦β≦α+20°, for all angles β included in this angle range, T B2 (β) and the light density L of the background lighting 8a at angle β V The product with (β) may deviate by a maximum of + / - 10% from the value of said product for the angle α=β.

[0106] The above-mentioned balancing effect is due to the countervailing light density distribution of the background illumination, but also to the transmission behavior T BW This also applies here by ignoring (β).

[0107] Finally, the present invention further comprises a screen in a fifth design that can operate in at least two operating modes: an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted into a limited angular range for the observer compared to the free view mode. To this end, Figure 11 shows a schematic diagram of an exemplary configuration of such a screen in the fifth alternative, which comprises: a transmissive image reproduction device 11, preferably an LC panel, a background illumination 8x arranged downstream of the transmission image reproduction device 11 in the observation direction and having an asymmetric light density distribution, this asymmetry preferably existing in the horizontal direction from the viewpoint of the observer; an optical filter 5 as further described above in front of or behind the image reproducing device 11 in the viewing direction; a second linear polarizing filter P, when no first linear polarizing filter X is arranged in the switchable optical filter 5, which is arranged in front of the background illumination 8x in the observation direction or in the image reproduction device 11 and which, in combination with the optical element 1 of the switchable optical filter 5, limits the propagation direction of light coming from the background illumination 8x through the second linear polarizing filter P; Equipped with - further comprising a lighting device, wherein in the operating mode B2 a second electric field EF2 is applied and in the operating mode B1 a first electric field EF1 is applied.

[0108] Thereby, the background illuminator 8x does not have any inherently symmetric light density distribution (e.g., around a vertical centerline—from the observer's point of view), but is, in contrast, designed to embody an asymmetric light density distribution (e.g., in the horizontal direction). In other words, this background illuminator 8a has an asymmetric light density distribution, the asymmetry preferably existing with respect to the horizontal direction from the observer's point of view. Such a design is possible, for example, by using light guides that separate the light in a deterministic manner and / or turning films that shift the peak brightness.

[0109] This variant is particularly advantageous for use in vehicles, where the light that would otherwise be emitted in the direction of the passenger window can be significantly reduced by the design of the background lighting, for example to less than 20%, preferably less than 2.5%, of the peak brightness, starting from a horizontal angle of 25 degrees or more (relative to the perpendicular bisector), while there is an intentionally high light density in the direction of the driver. In this way, annoying reflections on the passenger window or, optionally, on the outside mirror closest to the passenger are reduced or avoided. Nevertheless, thanks to the switchable light filter 5 mounted in front of the image reproduction device 11, the screen can be selectively operated so that image content, e.g., relating to moving images, is visible only to the passenger (operation mode B2), or so that image content, e.g., relating to navigation map material, is visible to both the driver and passengers (operation mode B1).

[0110] For some of the above-mentioned screens of designs 1 to 5, when used in a passenger car, it may be advantageous to arrange a second optical element 2 in front of the transmission image reproducing device 11 in the viewing direction (see also FIG. 11 ), which second optical element 2 comprises: a plurality of optical absorption transition dipole moments, whereby the dye mass density is greater than 1%, or greater than 10%; the majority of the transition dipole moments are, at least in the first state, aligned parallel to or fluctuating around a selectable second preferred direction for the second optical element 2 with a tolerance of up to 20° (alternatively 10°), the second preferred direction being disposed at an angle α1 with respect to a perpendicular bisector of the second optical element 2 (whereby, for example, α1=0°, α1=+ / -2°, or amount(α1)>2°), the angle α1 being measured in a selectable second plane containing said perpendicular bisector, the second plane 2 preferably being perpendicular to the first plane of the first optical element 1; Light incident on the second optical element 2 is therefore transmitted or at least partially absorbed as a function of its direction of incidence relative to the second optical element 2 and its polarization state.

[0111] This last-mentioned design advantageously ensures reduced vertical transmission and therefore reduces or completely avoids reflections of the image content displayed on this screen on the vehicle windshield.

[0112] Furthermore, the present invention includes an illumination device for a screen in a second design that can operate in at least two operating modes: an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted in a limited angular range compared to the free view mode. To this end, Figure 12 shows a schematic diagram of an exemplary configuration of an illumination device in such a second design. This is - a background light 8b extending in a flat manner and emitting light in a limited angular range, optionally configured to shine directly; a plate-like light guide 9 located in front of the background lighting 8b in the observation direction and having a separation element in at least one of its major surfaces and / or in its volume; - lighting means 10 arranged laterally towards at least one narrow side of the light guide 9; an optional linear polarizing filter P (not shown), a light filter 5 as further described above, arranged in front of the background illumination 8b in the viewing direction (this also includes a position in front of a screen used in conjunction with the illumination device); Equipped with in operating mode B2 the background lighting 8b is switched on and the lighting means 10 are switched off, and in operating mode B1 at least the lighting means 10 are switched on; - further comprising a lighting device, wherein in the operating mode B2 a second electric field EF2 is applied and in the operating mode B1 a first electric field EF1 is applied.

[0113] Furthermore, here also a transmission type image reproduction device 11, such as for example an LC panel, is present in the viewing direction (thus from above the plane of the sheet).

[0114] In the context of the present invention, particularly with regard to background lighting, a "limited angular range" means that the corresponding light density is concentrated in the specified angular range by at least 80% or 90%. However, in practice, typically for technical reasons, residual light outside the specified limited angular range may still exist. Ideally, such residual light is minimal and decreases toward larger angles. To achieve particularly strong minimization, a corresponding light filter that emits light in a limited angular range is used in addition to the background lighting. This also applies to the later-described variants having light guides that emit or separate light primarily in a limited angular range. In contrast to this design of the present invention, the light density curve of the background lighting is typically bell-shaped, especially over the horizontal (and optionally vertical) angular range, although actual concentration of light density in smaller angular ranges may not exist.

[0115] Finally, the present invention includes an illumination device for a screen in a third design that can operate in at least two operating modes: an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted in a limited angular range compared to the free view mode. To this end, Figure 13 shows a schematic diagram of an exemplary configuration of an illumination device in the third design, which: background lighting 8c, which is spread in a flat manner and emits light over an unlimited angular range, and which is optionally configured to be illuminated directly (for example by means of a locally dimmable LED matrix lighting unit); a plate-like light guide 9c located in front of the background illumination 8c in the observation direction and having a separation element in at least one of its major surfaces and / or in its volume, which separates the light coupled laterally into at least one narrow side of the light guide 9c substantially (i.e. more than half, preferably more than 80% or 90%) into a limited angular range; - lighting means 10 arranged laterally towards at least one narrow side of the light guide 9c; an optional linear polarizing filter P (not shown), a light filter 5 as described above, arranged in front of the background lighting 8c in the observation direction, preferably in front of the light guide 9c; Equipped with in operating mode B2 the background lighting 8c is switched off and the lighting means 10 is switched on, and in operating mode B1 at least the background lighting 8c is switched on (optionally the lighting means 10 may also be switched on), - further comprising a lighting device, wherein in the operating mode B2 a second electric field EF2 is applied and in the operating mode B1 a first electric field EF1 is applied.

[0116] The illumination devices of the first, second and third designs can be advantageously combined with a transmissive image reproduction device 11, such as an LC panel (see also, for example, Figures 12 and 13), to produce a screen that can operate in at least two operating modes: an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted into a limited angular range compared to the free view mode.

[0117] The present invention solves the set objectives and describes a light filter comprising an optical element, in which light incident on the optical element is transmitted or partially or completely absorbed, not primarily as a function of its position, but as a function of its direction of incidence and its polarization properties. Due to the use of an optical element, the light transmission is influenced as a function of angle, optionally with respect to a seated or standing observer, and can be switched between at least two operating states. In particular, the transmission behavior for a specific direction is thereby switchable.

[0118] The above-described invention can be advantageously used in combination with an image reproduction device wherever sensitive data is displayed and / or entered, for example when entering a PIN, displaying data on an automated teller machine or payment terminal, entering a password, or reading email on a mobile device. Furthermore, as mentioned above, the present invention can also be used in passenger vehicles, optionally without the image content distracting the driver or passengers. [Explanation of symbols]

[0119] 1. First Optical Element 2 Second Optical Element 3 Liquid crystal layer 5 Switchable Optical Filters 8. Background Lighting 8a background lighting 8b background lighting 8c background lighting 8x background lighting 9,9c Light guide 10 Lighting means 11 Image reproduction device P,X polarizing filter

Claims

1. A switchable optical filter (5), a first optical element (1), a plurality of optical absorption transition dipole moments arranged in a layer having a thickness of at least 0.2 micrometers; the majority of the transition dipole moments, at least in a first state, are aligned parallel to a selectable first preferred direction for the first optical element (1) with a tolerance of up to 20° or fluctuating thereabout, the first preferred direction being disposed at an angle α with respect to a perpendicular bisector of the first optical element (1), the angle α being measured in a selectable first plane containing the perpendicular bisector; - thus light incident on said first optical element (1) is transmitted or at least partially absorbed as a function of its direction of incidence on said first optical element (1) and its polarization state, a first optical element (1); - means for optionally generating a first electric field (EF1) or a second electric field (EF2); a liquid crystal layer (3) arranged behind or in front of said first optical element (1) in the viewing direction, on which said first electric field (EF1) or said second electric field (EF2) acts and which influences the polarization state of the light passing through it as a function of the electric field; a first linear polarizing filter (X) located in front of the liquid crystal layer (3) in the viewing direction when the liquid crystal layer (3) is arranged in front of the first optical element (1) in the viewing direction; Equipped with the transmission characteristics of the switchable optical filter (5) differ between a first operating mode B1 in which the first electric field (EF1) is applied and a second operating mode B2 in which the second electric field (EF2) is applied, such that the relative transmissions in the two operating modes B1 and B2 at at least one point on the switchable optical filter (5) are in each case equal to or greater than the transmission T Ｂ１ (β) or the transmittance T for the operating mode B2 Ｂ２ (β), each of which is described by T for the transmittance value. Ｂ１ (α)=1 and T Ｂ２ It is standardized so that (α) = 1 holds, -The light, In a first operating mode B1, in which the first electric field (EF1) is applied, the s-polarized portion of the light, when incident on the first optical element (1) at an angle (β) such that α-60°≦β≦α-40° or α+40°≦β≦α+60°, has a normalized transmittance value T Ｂ１ (β) ≧ 0.25, In a second operating mode B2 in which the second electric field (EF2) is applied, the p-polarized portion of the light, when incident on the first optical element (1) at an angle (β) such that α-60°≦β≦α-40° or α+40°≦β≦α+60°≦, has a maximum normalized transmittance value T Ｂ２ (β)≦0.2, and is transmitted through the switchable optical filter (5); Switchable optical filter (5).

2. 2. The switchable optical filter (5) of claim 1, wherein the first optical element (1) and / or the liquid crystal layer (3) are divided into a plurality of separately switchable segments to allow local switching capability between the respective possible operating states.

3. 2. A switchable optical filter (5) according to claim 1, characterized in that it comprises at least two first optical elements (1, 1'), optionally with a retarder arranged between at least two such first optical elements (1, 1').

4. At least one angle (β １ 2. The switchable optical filter (5) according to claim 1, characterized in that there is present a

5. In both operating modes B1 and B2, there is at least one angle (β ２ 2. The switchable optical filter (5) according to claim 1, characterized in that there is present a

6. 1. An illumination device for a screen which can be operated in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted in an angular range for a viewer that is limited compared to said free view mode, - a background light (8) configured to spread in a flat manner, to emit light and optionally to shine directly; a switchable light filter (5) according to claim 1, arranged in front of the background lighting (8) in the observation direction; A lighting device comprising:

7. A screen that can be operated in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted in an angular range for the observer that is limited compared to said free view mode, - a lighting device according to claim 6, - a second linear polarizing filter (P) when no first linear polarizing filter (X) is arranged in the switchable optical filter (5) of the lighting device, the second linear polarizing filter (P) being arranged in front of the background illumination (8) in the observation direction and limiting the propagation direction of light coming from the background illumination (8) and passing through the second linear polarizing filter (P); a transmission image reconstructor (11) arranged in front of the switchable optical filter (5) in the observation direction; Equipped with a screen, in which the second electric field (EF2) is applied in the operating mode B2 and the first electric field (EF1) is applied in the operating mode B1.

8. 8. A screen according to claim 7, characterized in that the first or second linear polarizing filter (P, X) is arranged in or is part of the transmissive image reproducing device (11).

9. A screen that can be operated in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted to a viewer in a limited angular range compared to said free view mode, an image reproduction device (12), a switchable optical filter (5) according to claim 1 in front of the image reconstructor (12) in the observation direction; and Equipped with a screen to which the second electric field (EF2) is applied in the first operating mode B2 and the first electric field (EF1) is applied in the operating mode B1.

10. 10. Screen according to claim 9, characterized in that the switchable light filter (5) is subsequently and / or reversibly attached to the image reproduction device (12) by a user.

11. A screen that can be operated in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted to a viewer in a limited angular range compared to said free view mode, a transmission type image reproduction device (11), a background illumination (8a) arranged downstream of said transmission image reproducing device (11) in the observation direction and having a light density distribution whose peak luminance is emitted in a direction forming an angle of at least 3° with the first preferred direction; a switchable optical filter (5) according to claim 1 in front of or behind the transmission image reconstructor (11) in the observation direction; Equipped with a screen, in which the second electric field (EF2) is applied in the operating mode B2 and the first electric field (EF1) is applied in the operating mode B1.

12. In the second operation mode B2, for at least the angle range of α-4°≦β≦α+4°, for all angles β included in the angle range, T Ｂ２ (β) and the light density L of the background illumination (8a) at angle β Ｖ (β) and the transmittance T of the transmission type image reproduction device (11) at the angle β ＢＷ 12. A screen according to claim 11, characterized in that the product with (β) deviates from the value of said product for an angle α=β by a maximum of + / −10%.

13. In the second operation mode B2, for at least the angle range of α-4°≦β≦α+4°, for all angles β included in the angle range, T Ｂ２ (β) and the light density L of the background illumination (8a) at angle β Ｖ 12. A screen according to claim 11, characterized in that the product with (β) deviates from the value of said product for an angle α=β by a maximum of + / −10%.

14. A screen that can be operated in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted to a viewer in a limited angular range compared to said free view mode, a transmission type image reproduction device (11), background illumination (8x), arranged downstream of the transmission image reproduction device (11) in the observation direction and having an asymmetric light density distribution, said asymmetry existing in the horizontal direction from the observer's point of view; a switchable optical filter (5) according to claim 1 in front of or behind the transmission image reconstructor (11) in the observation direction; Equipped with a screen, in which the second electric field (EF2) is applied in the operating mode B2 and the first electric field (EF1) is applied in the operating mode B1.

15. a second optical element (2) arranged in front of the transmission image reproducing device (11) in the observation direction, The second optical element (2) comprises: a plurality of optical absorption transition dipole moments; the majority of the transition dipole moments, at least in a first state, are aligned parallel to or vary about a second preferred direction selectable for the second optical element (2) with a tolerance of up to 20°, the second preferred direction being at an angle α with respect to the perpendicular bisector of the second optical element (2); １ and the angle α １ is measured in a selectable second plane containing the perpendicular bisector, - thus light incident on said second optical element (2) is transmitted or at least partially absorbed as a function of its direction of incidence and its polarization state relative to said second optical element (2); 8. A screen according to claim 7.

16. 1. An illumination device for a screen which can be operated in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted in a limited range of observation angles compared to the free view mode, - a background light (8b) extending in a flat manner and configured to emit light in a limited angular range and optionally to shine directly; a plate-like light guide (9) located in front of said background illumination (8b) in the observation direction and having a separation element in at least one of its major surfaces and / or in its volume; - lighting means (10) arranged laterally towards at least one narrow side of said light guide (9); an optional linear polarizing filter (P), a switchable light filter (5) according to claim 1, arranged in front of the background lighting (8b) in the observation direction; and Equipped with in the operating mode B2, the background lighting (8b) is switched on and the lighting means (10) are switched off, and in the operating mode B1, at least the lighting means (10) are switched on; A lighting device, wherein the second electric field (EF2) is applied in the operating mode B2 and the first electric field (EF1) is applied in the operating mode B1.

17. 1. An illumination device for a screen which can be operated in at least two operating modes, namely an operating mode B1 for a free view mode and an operating mode B2 for a limited view mode in which light is emitted in an angular range which is limited compared to the free view mode, - a background light (8c) extending in a flat manner, emitting light in an unlimited range of angles and optionally configured to shine directly; a plate-like light guide (9c) located in front of the background illumination (8c) in the observation direction and having a separation element in at least one of its major surfaces and / or in its volume, said separation element separating light coupled laterally into at least one narrow side of said light guide (9c) into a substantially limited angular range; - lighting means (10) arranged laterally towards at least one narrow side of said light guide (9c); an optional linear polarizing filter (P), a switchable light filter (5) according to claim 1, arranged in front of the background lighting (8c) in the observation direction; Equipped with in the operating mode B2, the background lighting (8c) is switched off and the lighting means (10) is switched on, and in the operating mode B1, at least the background lighting (8c) is switched on; A lighting device, wherein the second electric field (EF2) is applied in the operating mode B2 and the first electric field (EF1) is applied in the operating mode B1.

18. The first optical element (1) is a plurality of optical absorption transition dipole moments arranged in a layer having a thickness of from 0.2 microns to 50 microns, inclusive; 2. The switchable optical filter (5) of claim 1, wherein the majority of the transition dipole moments are, at least in a first state, aligned parallel to a first selectable preferred direction for the first optical element (1) with a tolerance of 5° or varying thereabout, the first preferred direction being disposed at an angle α with respect to a perpendicular bisector of the first optical element (1), the angle α being measured in a first selectable plane containing the perpendicular bisector.

19. A screen as claimed in claim 11 or 14, characterized in that the transmissive image reproduction device (11) is an LC panel.

Images