DE102020006110B3 - Switchable light filter with variable transmission and screen with such a switchable light filter and use of such a screen - Google Patents

Abstract

The invention relates to a switchable light filter. This includes, inter alia, an optical element (1) which comprises at least one, preferably more than five, layers (S1, S2, ...), each layer (S1, S2, ...) having a large number of light-absorbing material comprises electrical absorption dipoles which are aligned at least in a first state parallel to a selectable preferred direction or fluctuate around this, said preferred direction enclosing an angle between 0 ° and 45 ° to the surface normal of the layer S1, so that light which the optical element penetrates, is transmitted or partially or wholly absorbed depending on its direction of incidence with respect to the layers (S1, S2, ...) and its polarization properties. The light-absorbing electrical absorption dipoles in each layer (S1, S2, ...) can optionally be varied in their orientation and / or their absolute value and / or their density in order to make the respective layer (S1, S2, ...) in to be able to set at least two different states. In conjunction with at least one polarization filter (P) and / or means for varying the polarization properties of light, such as liquid crystals, the optical element (1) can be used in a switchable light filter (5), which in turn can be used in combination with an image display device - and switchable privacy effect enabled.

Description

Field of invention

In recent years, great advances have been made in widening the viewing angle in LCDs. However, there are often situations in which this very large viewing area of a screen can be a disadvantage. Information is also increasingly available on mobile devices such as notebooks and tablet PCs, such as bank details or other personal details and sensitive data. Accordingly, people need control over who can see this sensitive data; You have to be able to choose between a wide viewing angle in order to share information on your display with others, e.g. when looking at vacation photos or for advertising purposes. On the other hand, you need a small viewing angle if you want to treat the image information confidentially. A similar problem arises in vehicle construction: When the engine is switched on, the driver must not be distracted by image content, such as digital entertainment programs, while the front passenger wants to consume it while driving. A screen is therefore required that can switch between the corresponding display modes.

State of the art

Additional films based on micro-lamellas have already been used for mobile displays in order to achieve their visual data protection. However, these foils were not switchable, they always had to be put on by hand and then removed again. You also have to transport them separately to the display when you don't need them. A major disadvantage of using such lamellar foils is also associated with the associated loss of light.

the US 6,765,550 B2 describes such a privacy screen through micro-slats. The greatest disadvantage here is the mechanical removal or mechanical attachment of the filter as well as the loss of light in protected mode.

In the U.S. 5,993,940 A describes the use of a film with evenly arranged, small prism strips on its surface in order to achieve a privacy mode. Development and production are quite complex.

In the WO 2012/033583 A1 the switch between free and restricted view is generated by controlling liquid crystals between so-called "chromonic" layers. This results in a loss of light and the effort involved is quite high.

the US 2012/0235891 A1 describes a very complex backlight in a screen. There come according to 1 and 15th Not only several light guides are used, but also other complex optical elements such as microlens elements 40 and prism structures 50 that transform the light from the rear lights on its way to the front lights. This is expensive and time-consuming to implement and also associated with loss of light. According to the variant after 17th in the US 2012/0235891 A1 both produce light sources 4R and 18th Light with a narrow angle of illumination, the light from the rear light source 18th is only converted into light with a large angle of illumination in a complex manner. This complex transformation is - as already noted above - strongly reducing the brightness.

According to the JP 2007-155783 A are special optical surfaces that are complex to calculate and manufacture 19th which then divert light into various narrow or wide areas depending on the angle of incidence. These structures are similar to Fresnel lenses. There are also interference edges that deflect light in undesired directions. It therefore remains unclear whether really sensible light distributions can be achieved.

In the US 2013/0308185 A1 describes a special, stepped light guide that emits light over a large area in different directions, depending on the direction from which it is illuminated from a narrow side. In interaction with a transmissive image display device, for example an LC display, a screen that can be switched between free and restricted viewing mode can thus be generated. The disadvantage here is, among other things, that the restricted visual effect can be generated either only for left / right or for up / down, but not for left / right / up / down at the same time, as is necessary for certain payment transactions, for example. In addition, residual light is still visible from blocked viewing angles in restricted viewing mode.

the DE 600 22 081 T2 discloses nonlinear optical bodies and devices. In particular, non-linear optical properties of an object come into play here. Diffraction patterns from regions with different refractive indices within particles are also used. However, an optional angle-dependent transmission cannot be generated with this.

the WO 2015/121398 A1 the applicant describes a screen with two operating modes, in which there are scattered particles in the volume of the corresponding light guide for switching the operating modes. The scattering particles selected there from a polymer, however, usually have the disadvantage that light is coupled out from both large surfaces, so that about half of the useful light is emitted in the wrong direction, namely towards the background lighting, and is not there to a sufficient extent due to the structure can be recycled. In addition, the polymer scattering particles distributed in the volume of the light guide can, under certain circumstances, especially at a higher concentration, lead to scattering effects which reduce the visual protection effect in the protected operating mode.

The approach of the technology of "electrical birefringence (EDB)" is based on the idea of using the switchable liquid crystals of an additionally applied LC panel to "filter" all light rays that do not exit the imaging layer at a certain angle. Disadvantages of this technology are a high additional energy and cost expenditure and the difficult to change +/- 40 ° sweet spot. The degree of absorption of the LC structures is also insufficient, since the attenuation of the light intensity increases again for viewing angles greater than the sweet spot, so that the light intensity for viewing angles greater than +/- 40 ° is up to 3% of the maximum light intensity.

The aforementioned methods and arrangements usually have the disadvantage that they significantly reduce the brightness of the basic screen and / or require a complex and expensive optical element for mode switching and / or reduce the resolution in freely viewable mode and / or visual artifacts with very high resolution displays.

Description of the invention

It is therefore the object of the invention to describe a switchable light filter with the aid of which the transmission of light can be influenced as a function of the angle (optionally perpendicular), it being possible here to switch between at least two operating states. In particular, it should be possible to switch angle restrictions in the transmission in certain directions. The switchable light filter or systems based on it should be inexpensive to implement and, in particular, universally usable with different types of screen in order to enable switching between a privacy screen that exists at least in the horizontal direction and a free viewing mode, the resolution of such a screen being essentially not should be reduced.

• - mindestens eine, bevorzugt mehr als fünf, Schichten S1, S2, ..., (eine Schicht S1, S2, ... kann im Rahmen der Erfindung beispielsweise einer Moleküllage entsprechen; es kann sich aber auch um eine mechanisch separate Lage eines geeigneten Materials handeln),
• - wobei jede Schicht S1, S2, ... Material mit einer Vielzahl Licht absorbierender elektrischer Absorptionsdipole umfasst, welche mindestens in einem ersten Zustand parallel zu einer wählbaren Vorzugsrichtung ausgerichtet sind oder um diese herum fluktuieren, wobei die besagte Vorzugsrichtung einen Winkel zwischen 0° und 45° zur Flächennormale der Schicht S1 einschließt,
• - so dass Licht, welches in das optische Element einfällt, in Abhängigkeit von seiner Einfallsrichtung gegenüber den Schichten S1, S2, ... und seinen Polarisationseigenschaften transmittiert oder teilweise oder ganz absorbiert wird.

First of all, an optical element required to achieve this object will be described. This includes

• - At least one, preferably more than five, layers S1 , S2 , ..., (a layer S1 , S2 , ... can correspond, for example, to a molecular layer in the context of the invention; but it can also be a mechanically separate layer of a suitable material),
• - taking each layer S1 , S2 , ... comprises material with a plurality of light-absorbing electrical absorption dipoles, which are aligned parallel to a selectable preferred direction or fluctuate around this at least in a first state, said preferred direction being an angle between 0 ° and 45 ° to the surface normal of the layer S1 includes
• - so that light which falls into the optical element, depending on its direction of incidence with respect to the layers S1 , S2 , ... and its polarization properties is transmitted or partially or completely absorbed.

The extinction (i.e. the absorption) of the light depends on the absolute number of absorption dipoles (and thus inherently also on the layer thickness of the absorption dipoles) and the alignment between the absorption dipole and the electric field of the incident light. Depending on the implementation, the density of said electrical absorption dipoles, their strength or the refractive index in the layers S1 , S2 , ... vary. In the case of a passive, i.e. non-switchable optical element, the volume density of the absorption dipoles can approach 100%.

For the modeling of the transmission it is assumed that the absorbing absorption dipoles are oriented parallel to the plane of incidence. The filter only absorbs the polarization that is polarized - p-polarized light - in the plane of incidence of the light. Light that is polarized - s-polarized light - perpendicular to the plane of incidence is completely transmitted. This property is essential in all embodiments of the invention and represents an essential inventive means-effect relationship. In the following, the transmission of p-polarized light with an irradiated intensity l ₀ (α) is modeled. The transmission of light through an absorbing layer is described by the Lambert-Beer law: $$\mathrm{I.}\left(\alpha \right)={\mathrm{I.}}_0\left(\alpha \right)e^{-d\left(\alpha \right)N{\sigma }_{abs}\left(\alpha \right)}$$

Here, α is the direction of propagation relative to the surface normal, d (α) is the optical path length depending on the direction of propagation, N is the number of absorbing molecules and σ _abs (α) is the absorption cross section depending on the angle of incidence. With the help of Snell's law of refraction, the angle of propagation in the medium α can be calculated from the angle of incidence β. This then results from the equation of the dipole and the change in the optical path: $$\mathrm{I.}\left(\alpha \right)={\mathrm{I.}}_0\left(\alpha \right)e^{-d/N{\sigma }_{abs}\text{sin}{\left(\alpha \right)}^2}$$

Depending on the application, each of the layers ( S1 , S2 , ...) built up periodically or non-periodically in their structure.

Furthermore, such an optical element can be produced by lamination of a large number of polymer film polarizers and / or by photo-alignment of molecules or particles, which then each have one or more layers S1 , S2 , ... form, be produced. However, other manufacturing options are within the scope of what is possible.

The micro-lamellar filters described in the prior art (also called "View Control Filter - VCF" or "Light Control Filter - LCF") make use of the geometric optics. Due to the alternating periodic arrangement of transparent and absorbent layers, (almost) all incident light is absorbed here, which propagates at large angles relative to a defined direction. The position of the absorbers is checked there.

In contrast, in the optical elements described above, the transmission of light changes with different directions of propagation, since the absorption cross-section of the molecules changes with the direction of propagation. In the case of the invention, it is not the position but rather the orientation (alignment) of the absorber that is checked.

In other words: the procedure is based on a direction-dependent absorption of the light rays as they pass through an optical element, regardless of the position of the light rays.

This applies both to non-switchable optical elements as described above and to switchable configurations described below.

For a switchability of the optical effect of such an optical element, i.e. for a switchable optical element, the light-absorbing electrical absorption dipoles in each layer ( S1 , S2 , ...) can be varied in their alignment (orientation) and / or their absolute value and / or their density in order to achieve the respective layer ( S1 , S2 , ...) to be able to put at least two different states.

Possible configurations of a switchable optical element or of each layer S1 , S2 , ... therein are based, for example, on liquid crystals or fluorophores, which are arranged in a so-called “vertical alignment cell” or in a liquid crystal cell with homogeneous alignment on the surfaces and can be rotated between at least two states. The light-absorbing electrical absorption dipoles are also rotated and can thus assume at least two states of action. In particular, in such configurations it is conceivable that more than two states, for example three or eight states, each with different optical effects are achieved. Other configurations of the liquid crystal cells are also conceivable.

In the case of such active, that is to say switchable optical elements, volume densities of the absorption dipoles between 0.1% and 90% based on liquid crystals are conceivable.

Alternatively, there are configurations of a switchable optical element or of each layer S1 , S2 , ... are conceivable in which the absorption dipoles are embedded in a liquid that is subjected to an electro-wetting process. In this way, in particular, but not alone, the density of the absorption dipoles can be varied.

In general, a polarization filter can advantageously be located in front of or behind the optical element in the viewing direction.

• - zwei nicht-schaltbare vorstehend beschriebene optische Elemente, bei denen sich die Vorzugsrichtungen der Absorptionsdipole um weniger als 10° voneinander unterscheiden,
• - eine zwischen den optischen Elementen angeordnete schaltbare Flüssigkristallschicht, die in Abhängigkeit von einem auf sie wirkenden elektrischen Feld EF1 oder EF2 die Polarisationseigenschaften durch sie hindurchdringenden Lichtes beeinflusst,
• - optional einen oberhalb oder unterhalb der optischen Elemente angeordneten Polarisationsfilter P,
• - Mittel zum wahlweisen Erzeugen der besagten elektrischen Felder EF1 und EF2, beispielsweise durch transparente ITO-Elektroden E1 und E2,
• - so dass bei Vorhandensein des besagten Polarisationsfilters P in einer ersten Betriebsart B1H oder B1V bei einem elektrischen Feld EF1 unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters in diesen einfällt, zu mindestens 85% absorbiert wird, wobei diese Absorption ausschließlich in horizontaler (Betriebsart B1H) oder in vertikaler (Betriebsart B1V) Richtung gilt und parallel zur Polarisationsrichtung des Polarisationsfilters P liegt, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist,
• - so dass bei Abwesenheit eines Polarisationsfilters P in einer zweiten Betriebsart B3 bei einem elektrischen Feld EF1 unpolarisiertes Licht, welches in einem beliebigen Winkel in den schaltbaren Lichtfilter einfällt, zu mindestens 24% transmittiert wird,
• - und so dass schließlich in einer weiteren Betriebsart B2 bei einem elektrischen Feld EF2 unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters in diesen einfällt, zu mindestens 85% absorbiert wird, wobei dies gleichzeitig sowohl in horizontaler als auch in vertikaler Richtung gilt, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist.

The object of the invention is achieved according to the invention by a switchable light filter. In a first embodiment, this includes:

• - two non-switchable optical elements described above in which the preferred directions of the absorption dipoles differ from one another by less than 10 °,
• - a switchable liquid crystal layer arranged between the optical elements, which influences the polarization properties of light penetrating through it as a function of an electric field EF1 or EF2 acting on it,
• - optionally a polarization filter P arranged above or below the optical elements,
• - Means for optionally generating said electric fields EF1 and EF2, for example by means of transparent ITO electrodes E1 and E2 ,
• - so that when said polarization filter P is present in a first operating mode B1H or B1V with an electric field EF1, unpolarized light which is incident perpendicular to the switchable light filter, transmits at least 24% and so that unpolarized light which is at an angle of about 30 degrees to the center perpendicular of the switchable light filter falls into it, is absorbed to at least 85%, whereby this absorption applies exclusively in the horizontal (operating mode B1H) or in the vertical (operating mode B1V) direction and is parallel to the polarization direction of the polarization filter P if the horizontal is parallel to the bottom edge and the vertical parallel to the left or right side edge of the layer S1 is oriented
• - So that in the absence of a polarization filter P in a second operating mode B3 in the case of an electric field EF1, unpolarized light which falls into the switchable light filter at any angle is transmitted to at least 24%,
• - and so that finally in a further operating mode B2 In the case of an electric field EF2, unpolarized light that falls perpendicular to the switchable light filter is transmitted by at least 24% and so that unpolarized light that falls into the switchable light filter at an angle of more than 30 degrees to the central perpendicular of the switchable light filter is absorbed by at least 85% this applies simultaneously in both the horizontal and vertical directions if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented.

Thus, the switchable light filter according to the invention of the first embodiment, in conjunction with an image display unit, allows switching between either a two-sided and a four-sided privacy screen (e.g. top / bottom B1V vs. top / bottom / left / right protected B2) if a polarization filter P is present, or, if there is no polarization filter P, the switchover either between a view that is free in all directions and a four-sided privacy screen (e.g. unobstructed view B3 vs. top / bottom / left / right protected B2).

It is possible, for example, that either the electric field EF1 or the electric field EF2 describes a field-free state, the respective other electric field EF2 or EF1 having an absolute field strength greater than zero, for example 0.5 MV / m. The field-free state can mean, depending on the configuration of the two optical elements, that the operating mode B2 is present. However, it is also possible that one of the operating modes B1H, B1V or B3 is present in the field-free state.

• - zwei schaltbare optische Elemente, wie oben beschrieben, wobei für jedes der optischen Elemente die beiden besagten Zustände durch an beide optische Elemente anliegende elektrische Felder EF1 oder EF2 erzeugt werden (d.h., EF1 und EF2 liegen gleichzeitig an beiden optischen Elementen an),
• - optional einen oberhalb oder unterhalb der optischen Elemente angeordneten Polarisationsfilter P (Dieser ist nicht notwendig, kann aber die Leistungsfähigkeit dieses schaltbaren Lichtfilters verbessern. Die Polarisation des Polarisationsfilters P und die des einfallenden Lichtes müssen kongruent sein.),
• - eine zwischen den optischen Elementen angeordnete Schicht zur Rotation der Polarisationsrichtung des die besagte Schicht durchdringenden Lichts um 90 Grad, z.B. bestehend aus uniaxial-gedrehtem (analog zu einer TN-Zelle im feldfreien Zustand) und/oder aus optisch aktivem Material,
• - Mittel zum Erzeugen besagter elektrischer Felder EF1 oder EF2 (typischerweise stellt eines der Felder EF1 oder EF2 einen feldfreien Zustand dar),
• - so dass in einer Betriebsart B3 bei Anliegen des elektrischen Feldes EF1 unpolarisiertes Licht, welches in einem beliebigen Winkel zum schaltbaren Lichtfilter in diesen einfällt, zu mindestens 24% transmittiert wird, wobei in dieser Betriebsart B3 die Absorptionsdipole der beiden optischen Elemente senkrecht zueinander ausgerichtet sind, und die Absorptionsdipole des Polarisators P, wenn vorhanden, parallel zu dem ihm nächstliegenden schaltbaren optischen Element zueinander ausgerichtet sind,
• - und so dass in einer zweiten Betriebsart B2 bei Anliegen des elektrischen Feldes EF2 unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters in diesen einfällt, zu mindestens 85% absorbiert wird, wobei dies gleichzeitig sowohl in horizontaler als auch in vertikaler Richtung gilt, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist, wobei in dieser Betriebsart B2 die Absorptionsdipole von Polarisator P, wenn vorhanden, und zu dem ihm nächstliegenden schaltbaren optischen Element senkrecht und von den beiden optischen Elementen jeweils parallel zueinander ausgerichtet sind.

A second embodiment of a switchable light filter according to the invention comprises

• - two switchable optical elements, as described above, whereby for each of the optical elements the two said states are generated by electrical fields EF1 or EF2 applied to both optical elements (ie, EF1 and EF2 are applied simultaneously to both optical elements),
• - optionally a polarization filter P arranged above or below the optical elements (this is not necessary, but can improve the performance of this switchable light filter. The polarization of the polarization filter P and that of the incident light must be congruent.),
• - a layer arranged between the optical elements for rotating the polarization direction of the light penetrating said layer by 90 degrees, e.g. consisting of uniaxially rotated (analogous to a TN cell in the field-free state) and / or of optically active material,
• - Means for generating said electric fields EF1 or EF2 (typically one of the fields EF1 or EF2 represents a field-free state),
• - so that in one mode of operation B3 when the electric field EF1 is applied, at least 24% of unpolarized light which falls into this at any angle to the switchable light filter is transmitted, in this operating mode B3 the absorption dipoles of the two optical elements are aligned perpendicular to each other, and the absorption dipoles of the polarizer P, if present, are aligned parallel to the switchable optical element closest to it,
• - and so that in a second operating mode B2 when the electric field EF2 is applied, unpolarized light which falls into the switchable light filter perpendicularly to it is transmitted to at least 24% and so that unpolarized light which falls into the switchable light filter at an angle of more than 30 degrees to the central perpendicular of the switchable light filter is at least 85% is absorbed, this applies simultaneously both in the horizontal and in the vertical direction when the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented, in this mode of operation B2 the absorption dipoles of polarizer P, if present, and are perpendicular to the switchable optical element closest to it and each of the two optical elements is aligned parallel to one another.

Thus, the switchable light filter according to the invention of this second embodiment, in interaction with an image display unit, allows switching between viewing in all directions and a four-sided privacy screen (unobstructed view B3 vs. top / bottom / left / right protected B2).

• - ein nicht schaltbares optisches Element, wie oben beschrieben,
• - einen Polarisationsfilter P, der dem optischen Element vor oder nachgeordnet ist,
• - eine zwischen dem optischen Element und dem Polarisationsfilter P angeordnete Flüssigkristallschicht, die in Abhängigkeit von einem auf sie wirkenden elektrischen Feld EF1 oder EF2 die Polarisationseigenschaften des durch sie hindurchdringenden Lichtes beeinflusst,
• - Mittel zum wahlweisen Erzeugen der besagten elektrischen Felder EF1 und EF2,
• - so dass in einer Betriebsart B1V oder B1H bei Anliegen des elektrischen Feldes EF1 unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters in diesen einfällt, zu mindestens 85% absorbiert wird, wobei diese Absorption ausschließlich in horizontaler (Betriebsart B1H) oder ausschließlich in vertikaler Richtung (Betriebsart B1V) gilt, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist,
• - und so dass in einer zweiten Betriebsart B1H oder B1V bei Anliegen des elektrischen Feldes EF2 unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters in diesen einfällt, zu mindestens 85% absorbiert wird, wobei dies entweder ausschließlich in vertikaler (Betriebsart B1V) oder ausschließlich in horizontaler Richtung (Betriebsart B1H) gilt, so dass die Absorptionsrichtung zwischen der ersten und der zweiten Betriebsart B1 jeweils um 90 Grad gedreht ist, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist.

A third embodiment of a switchable light filter according to the invention comprises

• - a non-switchable optical element, as described above,
• - a polarization filter P, which is arranged upstream or downstream of the optical element,
• - A liquid crystal layer arranged between the optical element and the polarization filter P, which influences the polarization properties of the light penetrating through it as a function of an electric field EF1 or EF2 acting on it,
• - means for optionally generating said electric fields EF1 and EF2,
• - so that in an operating mode B1V or B1H when the electric field EF1 is applied, at least 24% of unpolarized light that falls perpendicular to the switchable light filter is transmitted and so that unpolarized light that is at an angle of over 30 degrees to the central perpendicular of the switchable Light filter falls into this, is absorbed to at least 85%, whereby this absorption applies exclusively in the horizontal (operating mode B1H) or exclusively in the vertical direction (operating mode B1V) if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented
• - and so that in a second operating mode B1H or B1V, when the electric field EF2 is applied, at least 24% of unpolarized light which falls perpendicular to the switchable light filter is transmitted and so that unpolarized light which is at an angle of more than 30 degrees to the perpendicular of the switchable light filter is absorbed by at least 85%, whereby this applies either exclusively in the vertical direction (operating mode B1V) or exclusively in the horizontal direction (operating mode B1H), so that the direction of absorption is between the first and the second operating mode B1 is rotated by 90 degrees if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented.

The configuration of this third embodiment of a switchable light filter according to the invention can switch between the operating modes B1V and B1H by rotating the polarization filter P by 90 degrees.

Here, too, it is possible that, for example, either the electric field EF1 or the electric field EF2 describes a field-free state, the respective other electric field EF2 or EF1 having an absolute field strength greater than zero, for example 0.5 MV / m.
The field-free state can mean, depending on the configuration of the optical element and the polarization filter P, that the operating mode B1H is present. However, it is also possible that the operating mode B1V is present in the field-free state.
Thus, the switchable light filter of this third embodiment, in conjunction with an image display unit, allows switching between a privacy screen in the vertical direction and a privacy screen in the horizontal direction (up / down protected B1V vs. left / right protected B1H). In a laptop, for example, this would mean that a user can view the content in operating mode B1V together with other people who are next to the user and are essentially arranged at the same eye level, while in operating mode B1H the people who are next to each other can view the image content can't see.

The switchable light filter according to the invention of this third embodiment can be varied in its construction.
In the following table 1 some essential construction variants are given. In each case, the first-mentioned component is on top in the viewing direction and the others follow below. In this case, the abbreviation “L / R” means that the optical effect is active in the horizontal effect (with the horizontal direction already defined above). For the polarization filter P this means that it transmits horizontally (linearly) polarized light and (essentially) absorbs vertical light. Correspondingly, “O / U” for the polarization filter P means that it transmits vertically (linearly) polarized light and horizontally (essentially) absorbs light
For the resulting effect of this switchable filter in conjunction with an image display unit, which can be arranged in front of or behind the switchable filter, the abbreviation "L / R" means that the screen effect works horizontally, so that a view from the left and right is prevented . Ultimately, this corresponds to operating mode B1H of the switchable filter.

Similarly, "O / U" for the switchable filter in conjunction with an image display unit means that the screen effect works vertically, so that a view from above and below is prevented. This corresponds to the B1V operating mode of the switchable filter. Table 1: construction Field-free (e.g. EF1 means no electrical field is present): Effect in conjunction with an image display unit Field adjacent (e.g. EF2 means an electrical field is adjacent): Effect in interaction with an image display unit Polarization filter P (L / R) liquid crystal layer 3 optical element 1 Privacy effect (L / R) - B1 H Privacy effect (O / U) - B1V Polarization filter P (O / U) liquid crystal layer 3 optical element 1 Privacy effect (O / U) - B1V Privacy effect (L / R) - B1 H optical element 1 liquid crystal layer 3 polarization filter P (L / R) Privacy effect (O / U) - B1V Privacy effect (L / R) - B1 H optical element 1 liquid crystal layer 3 polarization filter P (O / U) Privacy effect (L / R) - B1 H Privacy effect (O / U) - B1V

It should be pointed out again here that the "O / U" screen effect allows normal viewing for several viewers in many practical cases if they look sideways at the image display unit from approximately the same height.

• - ein schaltbares optisches Element, wie oben beschrieben,
• - einen oberhalb oder unterhalb des optischen Elementes angeordneten Polarisationsfilter P,
• - Mittel zum Erzeugen elektrischer Felder EF1 oder EF2, wobei für das optische Element mindestens zwei Zustände durch das jeweils anliegende elektrische Feld EF1 oder EF2 erzeugt werden,
• - so dass in einer Betriebsart B3, bei welcher die Absorptionsdipole der Schichten (S1, S2, ..) des schaltbaren optischen Elements parallel zur Substratoberfläche des schaltbaren optischen Elements und senkrecht zur Transmissionsrichtung des Polarisators ausgerichtet sind, unpolarisiertes Licht, welches in einem beliebigen Winkel zum optischen Element in dieses einfällt, zu mindestens 25% transmittiert wird,
• - und so dass in einer Betriebsart B1H oder B1V, bei welcher die Absorptionsdipole der Schichten (S1, S2, ..) des schaltbaren optischen Elements entlang der besagten Vorzugsrichtung ausgerichtet sind, unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters in diesen einfällt, zu mindestens 85% absorbiert wird, wobei dies entweder in vertikaler (Betriebsart B1V) oder horizontaler in Richtung (Betriebsart B1H) gilt, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist.

Furthermore, a fourth embodiment of a switchable light filter according to the invention comprises

• - a switchable optical element, as described above,
• - a polarization filter P arranged above or below the optical element,
• - Means for generating electrical fields EF1 or EF2, with at least two states being generated for the optical element by the respectively applied electrical field EF1 or EF2,
• - so that in one mode of operation B3 , at which the absorption dipoles of the layers ( S1 , S2 , ..) of the switchable optical element are aligned parallel to the substrate surface of the switchable optical element and perpendicular to the direction of transmission of the polarizer, unpolarized light which is incident at any angle to the optical element is transmitted to at least 25%,
• - and so that in an operating mode B1H or B1V, in which the absorption dipoles of the layers ( S1 , S2 , ..) of the switchable optical element are aligned along the said preferred direction, unpolarized light, which is incident perpendicular to the switchable light filter, at least 24% transmitted and so that unpolarized light, which is at an angle of over 30 degrees to the central perpendicular of the switchable Light filter that falls into it is absorbed to at least 85%, whereby this applies either in the vertical (operating mode B1V) or horizontal in the direction (operating mode B1H), if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented.

Here, too, it is again possible, for example, for either the electric field EF1 or the electric field EF2 to describe a field-free state, the respective other electric field EF2 or EF1 having an absolute field strength greater than zero, for example 0.5 V / m .
The field-free state can mean, depending on the configuration of the optical element and the polarization filter P, that the operating mode B3 is present. However, it is also possible that one of the operating modes B1H or B1V is present in the field-free state.
Thus, the switchable light filter according to the invention of this fourth embodiment, in conjunction with an image display unit, allows switching between a screen in the vertical or the horizontal direction and no screen effect (upper / lower protected B1V or left / right protected B1H vs. no screen B3 ).
For special applications, a switchable light filter according to the invention can be subdivided into several, separately switchable segments, regardless of the aforementioned configuration, so that local switchability between the respectively possible operating states is made possible. In interaction with an image display unit, this would mean that, for example, only part of the image area is between a privacy screen (e.g. operating mode B1H or B2) and no privacy effect (e.g. operating mode B3 , possibly also B1V) can be switched for a clear view, while the complementary part of the screen is permanently in a privacy mode (e.g. operating mode B1H or B2) or in no privacy mode (e.g. operating mode B3 , possibly also B1V) is located.
There can even be several segments of this type that are geometrically separated from one another and can be switched between the operating modes separately or together.

• - einen wie vorstehend beschriebenen schaltbaren Lichtfilter einer der vier genannten Ausgestaltungen, und
• - eine dem schaltbaren Lichtfilter von einem Betrachter aus gesehen nach- oder vorgeordnete Bildwiedergabeeinheit.

As already noted above, the invention acquires particular importance through the combination of a switchable light filter according to the invention as described above with an image display unit to form a screen.
Such a screen which can be operated in at least one first operating state B1V and / or B3 for a viewing mode that is free in the horizontal direction and in at least one second operating state B1H and / or B2 for a viewing mode restricted in the horizontal direction

• - A switchable light filter of one of the four mentioned configurations, as described above, and
• - An image display unit arranged downstream or upstream of the switchable light filter as seen by a viewer.

The image display unit advantageously corresponds to an LCD panel, one polarization filter of which corresponds to the polarization filter P. This can be the front or rear polarizer in the LCD structure. In addition, the switchable light filter can advantageously be arranged between the LCD panel and its background lighting in order to switch between a first operating state B3 (or B1V) for a free viewing mode and a second operating state B1H or B2 for a restricted viewing mode, because the light from the background lighting is focused once in the horizontal direction due to the switchable light filter (B2 or B1H) and once not focused (B3 or B1V). B1V). “Focusing” does not mean focusing in the manner of lenses, but rather a narrowing of the emission area or transmission area over the angle.

The image display unit can alternatively be an OLED, an SED display, an FED display, a microLED display or a VFD display, in front of which a switchable light filter is arranged. Since the switchable light filter is effective regardless of the type of image display unit, any other types of screen are also possible.

Such a screen is advantageously used in a mobile device, a motor vehicle, aircraft or watercraft, in a payment terminal or in an access system. It is possible to switch between the mentioned operating modes in order to protect sensitive data, ie to display it in a way that is perceptible for only one viewer, or alternatively to display image content simultaneously for several viewers.

Furthermore, a switchable or non-switchable optical element in the configurations described above can be used together with a static image or also a dynamic image display unit such as an LCD panel, for example to make advertising content visible only in a restricted field of vision.

However, the variety of uses of the optical element does not end with applications for displaying image content with or without visual protection effects. Rather, other applications are possible, for example when special properties of a lighting device are desired. Configurations of the optical element in which defined polarization contrasts are generated are conceivable. These in turn can be used in the context of optical sensors.

In principle, the performance of the invention is retained if the parameters described above are varied within certain limits.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the specified combinations, but also in other combinations or on their own, without departing from the scope of the present invention.

• 1a die Prinzipskizze eines nicht schaltbaren optischen Elements,
• 1b die Prinzipskizze eines schaltbaren optischen Elements in einem ersten Zustand,
• 1c die Prinzipskizze eines schaltbaren optischen Elements in einem zweiten Zustand,
• 2 die Prinzipskizze eines schaltbaren Lichtfilters in einer ersten Ausgestaltung mit einem Polarisationsfilter P,
• 3 die Prinzipskizze eines schaltbaren Lichtfilters in einer ersten Ausgestaltung ohne Polarisationsfilter,
• 4a bis 4c Skizzen zur Beeinflussung des Lichtes aufgrund eines schaltbaren Lichtfilters gemäß der 3,
• 5 die Prinzipskizze eines schaltbaren Lichtfilters in einer zweiten Ausgestaltung,
• 6 die Prinzipskizze eines schaltbaren Lichtfilters in einer dritten Ausgestaltung,
• 7 die Prinzipskizze eines schaltbaren Lichtfilters in einer vierten Ausgestaltung, sowie
• 8-12 optische Simulationen zur Veranschaulichung der optischen Wirkung eines optischen Elements.

The invention is explained in more detail below with reference to drawings, which also show features essential to the invention. It shows

• 1a the basic sketch of a non-switchable optical element,
• 1b the schematic diagram of a switchable optical element in a first state,
• 1c the schematic diagram of a switchable optical element in a second state,
• 2 the schematic diagram of a switchable light filter in a first embodiment with a polarization filter P,
• 3 the schematic diagram of a switchable light filter in a first embodiment without a polarization filter,
• 4a until 4c Sketches for influencing the light due to a switchable light filter according to 3 ,
• 5 the schematic diagram of a switchable light filter in a second embodiment,
• 6th the schematic diagram of a switchable light filter in a third embodiment,
• 7th the schematic diagram of a switchable light filter in a fourth embodiment, as well as
• 8-12 optical simulations to illustrate the optical effect of an optical element.

The drawings are not true to scale and only represent basic representations.

• - mindestens eine Schicht S1,
• - wobei diese Schicht S1 Material mit einer Vielzahl Licht absorbierender elektrischer Absorptionsdipole (die hier vereinfacht als kleine vertikale Striche dargestellt sind) umfasst, welche mindestens in einem ersten Zustand parallel zu einer wählbaren Vorzugsrichtung ausgerichtet sind (hier senkrecht zur Oberfläche der Schicht S1) oder um diese herum fluktuieren, wodurch die besagte Vorzugsrichtung einen Winkel zwischen 0° und 45° zur Flächennormale der Schicht S1 einschließt,
• - so dass Licht, welches in das optische Element 1 einfällt, in Abhängigkeit von seiner Einfallsrichtung gegenüber der Schicht S1 und seinen Polarisationseigenschaften transmittiert oder teilweise oder ganz absorbiert wird.

the 1a shows the schematic diagram of an exemplary non-switchable optical element 1 , which can be used in the context of the invention. The same includes

• - at least one shift S1 ,
• - taking this layer S1 Material with a plurality of light-absorbing electrical absorption dipoles (which are shown here in simplified form as small vertical lines), which are aligned at least in a first state parallel to a selectable preferred direction (here perpendicular to the surface of the layer S1 ) or fluctuate around it, whereby said preferred direction forms an angle between 0 ° and 45 ° to the surface normal of the layer S1 includes
• - so that light entering the optical element 1 incident, depending on its direction of incidence with respect to the layer S1 and its polarization properties is transmitted or partially or wholly absorbed.

An optical element 1 can be made, for example, by lamination of a variety of polymer film polarizers and / or by photo-alignment of molecules or particles. Depending on the implementation, the density of said electrical absorption dipoles in the layer S1 vary. With a passive polarizer, the volume density can approach 100%. The optical element 1 represents a privacy filter for linearly polarized light. A polarizer P is therefore provided here, which polarizes incident light from below linearly parallel to the surface of the drawing. However, the polarizer P does not change the directions of light propagation. Two possible directions of light propagation are indicated by the two thick arrows.

Due to the effect of the absorption dipoles, the light is now through the optical element 1 absorbs, which is an (oblique) direction of about 30 degrees from the perpendicular to the layer S1 having. Ultimately, all that remains is essentially that which is perpendicular to the optical element 1 Incident light remains after passing through it, as shown with the single arrow in the drawing above. Depending on the application, each of the layers ( S1 , S2 , ...) built up periodically or non-periodically in their structure.

The extinction (i.e. the absorption) of the light depends on the layer thickness of the absorption dipoles. The drawings show this 8th until 12th optical simulations to illustrate the optical effect of an optical element 1 .
the 8th shows a diagram for the normalized transmission of the light when passing through an optical element 1 according to 1 , here plotted over horizontal measuring angles from -90 ° to + 90 °. The strong absorption effect at angles over +/- 25 ° is clearly visible. The simulations are based on an assumed layer thickness of an optical element 1 of d = 0.5mm, a refractive index of the material of n = 1.5, the molarity M = 0.01 mol m ^-3 and an exemplary molar extinction of ε = 12700 m ² mol ^-1 .
In 9 are the proportions after 8th plotted logarithmically on the ordinate for the value range essential for use. It can be seen that with such parameters at +/- 25 ° the transmission is already reduced to about one percent and at +/- 40 ° to only about 0.001 percent. In 10 were the for 8th assumed conditions with regard to the refractive index n for values n = 1.0; 1.3; 1.5 and n = 1.7 calculated. It can be seen that the transmission in the angle is more restricted, the lower the refractive index of the material of the layer S1 is.
Furthermore, the 11 a variation of the normalized transmission through an optical element 1 according to the circumstances 8th in terms of the thickness of an optical element 1 . Layer thicknesses of d = 0.1 mm; 0.2 mm; 0.3mm; 0.4 mm and 0.5 mm are calculated. As expected, a greater layer thickness consequently ensures a greater restriction of the transmission across the angles.

Finally shows 12th the angle-dependent, standardized transmission for three selected parameter sets (1. n = 1.0 and d = 0.2 mm; 2. n = 1.5 and d = 0.5 mm; 3. n = 1.7 and d = 0.65 mm). All three parameter sets produce very similar optical effects.

In contrast, the micro-lamellar filters known in the prior art (also called "View Control Filter - VCF" or "Light Control Filter - LCF") make use of the geometric optics. Due to the alternating periodic arrangement of transparent and absorbing layers, (almost) all light is absorbed that spreads at large angles relative to a defined direction. The position of the absorbers is checked there. In contrast, in the case of the optical elements described here, the transmission of light changes with different directions of propagation, since the absorption cross-section of the molecules changes with the direction of propagation. It is not the position, but rather the orientation of the absorber in particular that is checked.

In other words: the mode of operation is based on a direction-dependent absorption of the light rays as they pass through an optical element, and in principle independently of the position of the light rays. This applies both to non-switchable optical elements as described above and to switchable configurations described below.

For a switchability of the optical effect of the optical element 1 , i.e. for a switchable optical element 1 , the light absorbing electrical absorption dipoles in each layer ( S1 , S2 , ...) can be varied in their orientation and / or their absolute value in order to achieve the respective layer ( S1 , S2 , ...) to be able to put at least two different states. Possible configurations of a switchable optical element or of each layer S1 , S2 , ... therein are based, for example, on liquid crystals or fluorophores, which are arranged in a so-called "vertical alignment cell" or in a liquid crystal cell with homogeneous alignment on the surfaces and are rotated between at least two states can. The light-absorbing electrical absorption dipoles are also rotated and can thus assume at least two states of action. In particular, in such configurations it is conceivable that more than two states, for example three or eight states, each with different optical effects are achieved. Other configurations of the liquid crystal cells are also conceivable.

To do this shows 1b the schematic diagram of a switchable optical element in a first state and 1c the schematic diagram of a switchable optical element in a second state.

For this exemplary case, it should be assumed that the incident light is p-polarized, i.e. polarized parallel to the plane of incidence (see 1b) is. Are the transparent electrodes E1 , E2 uncharged, ie they generate the electric field EF1 with 0 V / m (field-free), then the liquid crystal molecules shown here as dots align themselves (which here, for example, as layers S1 , S2 and S3 are formed) along the surface of the electrodes E1 , E2 the end. This can be achieved by a suitable combination of surface functionalization and liquid crystals and is known in the prior art. For light that propagates in the plane of the drawing and is s-polarized, the polarization of the light and absorption dipoles of the liquid crystals are always oriented perpendicular to one another. Therefore, no absorption takes place, so that the directions of light propagation shown above and below the substrates S with s-polarization are the switchable optical element 1 penetrate unhindered.

Will, as in 1c shown the electrodes E1 and E2 charged, ie they generate the electric field EF2> 0 V / m, so the liquid crystals rotate in the layers S1 , S2 and S3 . If the voltage and thus the field strength EF2 exceeds a certain threshold value, liquid crystal molecules and thus - if present - also dye molecules are aligned parallel to the field lines of the electric field EF2. As a result, light is generated as a function of the angle α, the angle between the direction of propagation of the light and the surface normal of the surface of the layer S1 , absorbed. The absorption increases with the angle α. The extinction of the electric field of light is proportional to sin (α).

In principle, it is advantageous to check the alignment of the dye molecules in order to control the axis of the privacy screen or to carry out a defined beam deflection.

In the state according to 1 b the dipoles are aligned perpendicular to the polarization of the incident light and in the state according to 1c parallel to the vertical incidence of light.

With such switchable optical elements, volume densities between 0.1% and 90% based on liquid crystals are conceivable.

• - zwei nicht-schaltbare optische Elemente 1, 2, wie vorstehend beschrieben, bei denen die Vorzugsrichtungen der Absorptionsdipole sich um weniger als 10° voneinander unterscheiden,
• - eine zwischen den optischen Elementen 1, 2 angeordnete schaltbare Flüssigkristallschicht 3, die in Abhängigkeit von einem auf sie wirkenden elektrischen Feld EF1 oder EF2 die Polarisationseigenschaften des durch sie hindurchdringenden Lichtes beeinflusst,
• - einen unterhalb der optischen Elemente 1, 2 angeordneten Polarisationsfilter P (oberhalb wäre auch möglich),
• - zeichnerisch nicht dargestellte Mittel zum wahlweisen Erzeugen der besagten elektrischen Felder EF1 und EF2, beispielsweise oberhalb und unterhalb der Flüssigkristallschicht 3 angeordnete Elektroden,
• - so dass in einer ersten Betriebsart B1H oder B1V bei einem elektrischen Feld EF1 unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter 5 in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters 5 in diesen einfällt, zu mindestens 85% absorbiert wird, wobei diese Absorption ausschließlich in horizontaler (Betriebsart B1H) oder in vertikaler (Betriebsart B1V) Richtung gilt, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist,
• - und so dass schließlich in einer weiteren Betriebsart B2 bei einem elektrischen Feld EF2 unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter 5 in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters 5 in diesen einfällt, zu mindestens 85% absorbiert wird, wobei dies gleichzeitig sowohl in horizontaler als auch in vertikaler Richtung gilt, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist.

The invention is used as a switchable light filter 5 implemented. Such a switchable light filter according to the invention 5 is in a first embodiment in 2 shown. It includes:

• - two non-switchable optical elements 1 , 2 , as described above, in which the preferred directions of the absorption dipoles differ from one another by less than 10 °,
• - one between the optical elements 1 , 2 arranged switchable liquid crystal layer 3 which, depending on an electric field EF1 or EF2 acting on it, influences the polarization properties of the light penetrating through it,
• - one below the optical elements 1 , 2 arranged polarization filter P (above would also be possible),
• - Means, not shown in the drawing, for selectively generating said electric fields EF1 and EF2, for example above and below the liquid crystal layer 3 arranged electrodes,
• - so that in a first operating mode B1H or B1V with an electric field EF1 unpolarized light which is perpendicular to the switchable light filter 5 incident in this, at least 24% transmitted and so that unpolarized light, which is at an angle of more than 30 degrees to the perpendicular of the switchable light filter 5 is absorbed by at least 85%, whereby this absorption only applies in the horizontal (operating mode B1H) or in the vertical (operating mode B1V) direction if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented
• - and so that finally in a further operating mode B2 with an electric field EF2 unpolarized light, which is perpendicular to the switchable light filter 5 incident in this, at least 24% transmitted and so that unpolarized light, which is at an angle of over 30 degrees to the perpendicular of the switchable light filter 5 falls into this, is absorbed to at least 85%, this applies simultaneously both in the horizontal and in the vertical direction if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented.

• - in einer zweiten Betriebsart B3 bei einem elektrischen Feld EF1 unpolarisiertes Licht, welches in einem beliebigen Winkel in den schaltbaren Lichtfilter 5 einfällt, zu mindestens 24% transmittiert wird,
• - und so dass schließlich in einer weiteren Betriebsart B2 bei einem elektrischen Feld EF2 unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter 5 in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters 5 in diesen einfällt, zu mindestens 85% absorbiert wird, wobei dies gleichzeitig sowohl in horizontaler als auch in vertikaler Richtung gilt, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist.

Furthermore, the 3 in modification of the 2 the schematic diagram of a switchable light filter 5 in a first embodiment, but this time without a polarization filter. This configuration is used to ensure that

• - in a second operating mode B3 in the case of an electric field EF1, unpolarized light which enters the switchable light filter at any angle 5 incident, is transmitted to at least 24%,
• - and so that finally in a further operating mode B2 with an electric field EF2 unpolarized light, which is perpendicular to the switchable light filter 5 incident in this, at least 24% transmitted and so that unpolarized light, which is at an angle of over 30 degrees to the perpendicular of the switchable light filter 5 falls into this, is absorbed to at least 85%, this applies simultaneously both in the horizontal and in the vertical direction if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented.

Thus, the switchable light filter allows 5 In the first embodiment, in conjunction with an image display unit, switching between a two-sided and a four-sided privacy screen (e.g. top / bottom B1V vs. top / bottom / left / right protected B2) if a polarization filter P is present, or if no polarization filter P is present is available, the switchover either between a view that is free in all directions and a four-sided privacy screen (e.g. unobstructed view B3 vs. top / bottom / left / right protected B2).

It is possible, for example, that either the electric field EF1 or the electric field EF2 describes a field-free state, the respective other electric field EF2 or EF1 having an absolute field strength greater than zero, for example 0.5 MV / m. The field-free state can be depending on the configuration of the optical elements 1 and 2 mean that the mode of operation B2 is present. However, it is also possible that one of the operating modes B1H, B1V or B3 is present in the field-free state.

the 4a until 4c show a sketch of the polarization state of the light due to a switchable light filter 5 according to the 3 . the 4a shows the polarization state of the public mode, in which the light is tangentially polarized for viewing angles greater than 30 ° and light with perpendicular incidence is linearly polarized. the 4c shows the polarization state in restricted viewing mode. Here, light is very much attenuated for an angle of incidence of, for example, greater than 30 °, while light with perpendicular incidence is transmitted unpolarized.

Due to the alignment or orientation of the absorption dipoles, the light is polarized for angles of incidence, ie the linear polarization of the light is always oriented perpendicular to the direction of the origin. This state is in 4a shown and applies after the light has passed through the non-switchable optical element 1 . The light with small angles is only weakly polarized. Ideally, light that is emitted perpendicularly is not absorbed, ie it is polarized.

The light now emerges from the optical element 2 into the liquid crystal layer 3 about, it depends on the state of the liquid crystal layer 3 whether and how the polarization state of the light is changed or whether it remains unchanged. Is, for example, in the field-free state EF1, the polarization rotation in the liquid crystal layer 3 switched off, nothing changes in the state described above. After passing through the liquid crystal layer 3 and further through the non-switchable optical element 1 the transmission remains essentially unchanged. Is a polarizer P above the optical element 1 or below the optical element 2 available, an operating mode B1H or B1V, depending on the configuration, is achieved. If this polarizer does not exist, the operating mode is B3 realized.

In contrast, if an electric field is applied EF2> 0 V / m, the polarization rotation in the liquid crystal layer 3 switched on, the polarization is rotated by 90 ° everywhere. The polarization state is in 4b shown: there is the polarization state after passing through the optical element 2 and the polarization rotating liquid crystal layer 3 shown. This is in the context of the further light propagation due to the optical element 1 extinguished all light that spreads at an angle greater than 25 ° or about 30 °. This corresponds to the operating mode B2 and is in 4c shown.

• - zwei schaltbare optische Elemente 1, 2, wie oben beschrieben, wobei für jedes der optischen Elemente 1, 2 die beiden besagten Zustände durch an beide optische Elemente 1, 2 anliegende elektrische Felder EF1 oder EF2 erzeugt werden (EF1 liegt am Element 1 und EF2 am Element 2 an),
• - optional einen oberhalb oder unterhalb der optischen Elemente 1, 2 angeordneten Polarisationsfilter P (Dieser ist nicht notwendig, kann aber die Leistungsfähigkeit des schaltbaren Lichtfilters verbessern. Die Polarisation des Polarisationsfilters P und die des einfallenden Lichtes müssen kongruent sein.),
• - eine zwischen den schaltbaren optischen Elementen 1, 2 angeordnete Schicht 4 zur Rotation der Polarisationsrichtung (z.B. Flüssigkristalle oder eine schaltbare Halbwellenplatte) des die besagte Schicht 4 durch-dringenden Lichts um 90 Grad,
• - zeichnerisch nicht dargestellte Mittel zum Erzeugen besagter elektrischer Felder EF1 oder EF2 (typischerweise stellt eines der Felder EF1 oder EF2 einen feldfreien Zustand dar),
• - so dass in einer Betriebsart B3 bei Anliegen des elektrischen Feldes EF1 unpolarisiertes Licht, welches in einem beliebigen Winkel zum schaltbaren Lichtfilter 5 in diesen einfällt, zu mindestens 24% transmittiert wird, wobei in dieser Betriebsart B3 die Absorptionsdipole der beiden schaltbaren optischen Elemente 1, 2 senkrecht zueinander ausgerichtet sind und die Absorptionsdipole des Polarisators P, wenn vorhanden, parallel zu den Absorptionsdipolen des dem Polarisator P nächstliegenden schaltbaren optischen Elements 1 oder 2 zueinander ausgerichtet sind,
• - und so dass in einer zweiten Betriebsart B2 bei Anliegen des elektrischen Feldes EF2 unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter 5 in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters 5 in diesen einfällt, zu mindestens 85% absorbiert wird, wobei dies gleichzeitig sowohl in horizontaler als auch in vertikaler Richtung gilt, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist, wobei in dieser Betriebsart B2 die Absorptionsdipole von Polarisator P, wenn vorhanden, und zu dem ihm nächstliegenden schaltbaren optischenElement 1 senkrecht und von den beiden optischen Elementen 1 und 2 jeweils parallel zueinander ausgerichtet sind.

Furthermore shows 5 the schematic diagram of a switchable light filter 5 in a second embodiment. This includes

• - two switchable optical elements 1 , 2 as described above, where for each of the optical elements 1 , 2 the two said states through to both optical elements 1 , 2 applied electrical fields EF1 or EF2 are generated (EF1 is on the element 1 and EF2 on the element 2 at),
• - optionally one above or below the optical elements 1 , 2 arranged polarization filter P (This is not necessary, but can improve the performance of the switchable light filter. The polarization of the polarization filter P and that of the incident light must be congruent.),
• - one between the switchable optical elements 1 , 2 arranged layer 4th to rotate the direction of polarization (eg liquid crystals or a switchable half-wave plate) of the said layer 4th penetrating light by 90 degrees,
• - Means, not shown in the drawing, for generating said electric fields EF1 or EF2 (typically one of the fields EF1 or EF2 represents a field-free state),
• - so that in one mode of operation B3 when the electric field EF1 is applied, unpolarized light, which is at any angle to the switchable light filter 5 incident in this, at least 24% is transmitted, in this mode of operation B3 the absorption dipoles of the two switchable optical elements 1 , 2 are aligned perpendicular to each other and the absorption dipoles of the polarizer P, if present, parallel to the absorption dipoles of the switchable optical element closest to the polarizer P. 1 or 2 are aligned with each other,
• - and so that in a second operating mode B2 when the electric field EF2 is applied, unpolarized light which is perpendicular to the switchable light filter 5 incident in this, at least 24% transmitted and so that unpolarized light, which is at an angle of more than 30 degrees to the perpendicular of the switchable light filter 5 falls into this, is absorbed to at least 85%, this applies simultaneously both in the horizontal and in the vertical direction if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented, in this mode of operation B2 the absorption dipoles of polarizer P, if present, and perpendicular to the switchable optical element 1 closest to it and from the two optical elements 1 and 2 are each aligned parallel to one another.

Thus, the switchable light filter allows 5 In this second embodiment, in interaction with an image display unit, the switchover between a view that is free in all directions and a four-sided privacy screen (unobstructed view B3 vs. top / bottom / left / right protected B2).

• - ein nicht schaltbares, optisches Element 1, wie oben beschrieben,
• - einen Polarisationsfilter P, der dem optischen Element 1 vor oder nachgeordnet ist,
• - eine zwischen dem optischen Element 1 und dem Polarisationsfilter P angeordnete Flüssigkristallschicht 3, die in Abhängigkeit von einem auf sie wirkenden elektrischen Feld EF1 oder EF2 die Polarisationseigenschaften des durch sie hindurchdringenden Lichtes beeinflusst,
• - zeichnerisch nicht dargestellte Mittel zum wahlweisen Erzeugen der besagten elektrischen Felder EF1 und EF2,
• - so dass in einer Betriebsart B1V oder B1H bei Anliegen des elektrischen Feldes EF1 unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter 5 in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters 5 in diesen einfällt, zu mindestens 85% absorbiert wird, wobei diese Absorption ausschließlich in horizontaler (Betriebsart B1H) oder ausschließlich in vertikaler Richtung (Betriebsart B1V) gilt, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist,
• - und so dass in einer zweiten Betriebsart B1H oder B1V bei Anliegen des elektrischen Feldes EF2 unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter 5 in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilter 5 in diesen einfällt, zu mindestens 85% absorbiert wird, wobei dies entweder ausschließlich in vertikaler (Betriebsart B1V) oder ausschließlich in horizontaler Richtung (Betriebsart B1H) gilt, so dass die Absorptionsrichtung zwischen der ersten und der zweiten Betriebsart B1 jeweils um 90 Grad gedreht ist, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist.

A third embodiment of a switchable light filter 5 , which are shown as a schematic diagram in 6th is shown includes

• - a non-switchable, optical element 1 , as described above,
• - A polarization filter P, the optical element 1 is before or after,
• - one between the optical element 1 and the liquid crystal layer disposed on the polarizing filter P. 3 which, depending on an electric field EF1 or EF2 acting on it, influences the polarization properties of the light penetrating through it,
• - Means, not shown in the drawing, for the optional generation of said electric fields EF1 and EF2,
• - so that in an operating mode B1V or B1H, when the electric field EF1 is applied, unpolarized light which is perpendicular to the switchable light filter 5 incident in this, at least 24% transmitted and so that unpolarized light, which is at an angle of over 30 degrees to the perpendicular of the switchable light filter 5 is absorbed by at least 85%, whereby this absorption applies exclusively in the horizontal (operating mode B1H) or exclusively in the vertical direction (operating mode B1V) if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented
• - and so that in a second operating mode B1H or B1V, when the electric field EF2 is applied, unpolarized light which is perpendicular to the switchable light filter 5 incident in this, at least 24% transmitted and so that unpolarized light, which is at an angle of over 30 degrees to the perpendicular of the switchable light filter 5 falls into these, is absorbed to at least 85%, this being applies either exclusively in the vertical direction (operating mode B1V) or exclusively in the horizontal direction (operating mode B1H), so that the absorption direction is between the first and the second operating mode B1 is rotated by 90 degrees if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented.

The configuration of this third embodiment of a switchable light filter 5 can switch between operating modes B1V and B1H by rotating the polarization filter P by 90 degrees.

Here, too, it is possible that, for example, either the electric field EF1 or the electric field EF2 describes a field-free state, the respective other electric field EF2 or EF1 having an absolute field strength greater than zero, for example 0.5 MV / m.
The field-free state can be depending on the configuration of the optical element 1 and the polarization filter P mean that the operating mode B1H is present. However, it is also possible that the operating mode B1V is present in the field-free state.
Thus, the switchable light filter allows 5 In this third embodiment, in conjunction with an image display unit, the switchover between a privacy screen in the vertical direction and a privacy screen in the horizontal direction (up / down protected B1V vs. left / right protected B1H). In a laptop, for example, this would mean that a user can view the content in operating mode B1V together with other people who are next to the user and are essentially arranged at the same eye level, while in operating mode B1H the people who are next to each other can view the image content can't see.

The switchable light filter 5 this third embodiment can be varied in its construction, as has been described above.

• - ein schaltbares optisches Element 1, wie oben beschrieben,
• - einen oberhalb oder unterhalb des optischen Elementes 1 angeordneten Polarisationsfilter P,
• - zeichnerisch nicht dargestellte Mittel zum Erzeugen elektrischer Felder EF1 oder EF2, wobei für das optische Element 1 mindestens zwei Zustände durch das jeweils anliegende elektrische Feld EF1 oder EF2 erzeugt werden,
• - so dass in einer Betriebsart B3, bei welcher die Absorptionsdipole der Schichten (S1, S2, ..) des optischen Elements 1 parallel zur Substratoberfläche des optischen Elements 1 und senkrecht zur Transmissionsrichtung des Polarisators ausgerichtet sind, unpolarisiertes Licht, welches in einem beliebigen Winkel zum schaltbaren Lichtfilter 5 in diesen einfällt, zu mindestens 25% transmittiert wird,
• - und so dass in einer Betriebsart B1H oder B1V, bei welcher die Absorptionsdipole der Schichten S1, S2, .. des optischen Elements 1 entlang der besagten Vorzugsrichtung ausgerichtet sind, unpolarisiertes Licht, welches senkrecht zum schaltbaren Lichtfilter 5 in diesen einfällt, zu mindestens 24% transmittiert und so dass unpolarisiertes Licht, welches in einem Winkel von über 30 Grad zur Mittelsenkrechten des schaltbaren Lichtfilters 5 in diesen einfällt, zu mindestens 85% absorbiert wird, wobei dies entweder in vertikaler (Betriebsart B1V) oder horizontaler in Richtung (Betriebsart B1H) gilt, wenn die Horizontale parallel zur Unterkante und die Vertikale parallel zur linken oder rechten Seitenkante der Schicht S1 orientiert ist.

Furthermore, a fourth, as a basic sketch in 7th Shown, embodiment of a switchable light filter 5

• - a switchable optical element 1 , as described above,
• - one above or below the optical element 1 arranged polarization filter P,
• - Means, not shown in the drawing, for generating electrical fields EF1 or EF2, wherein for the optical element 1 at least two states are generated by the applied electric field EF1 or EF2,
• - so that in one mode of operation B3 , at which the absorption dipoles of the layers ( S1 , S2 , ..) of the optical element 1 parallel to the substrate surface of the optical element 1 and aligned perpendicular to the direction of transmission of the polarizer, unpolarized light, which is at any angle to the switchable light filter 5 occurs in this, is transmitted to at least 25%,
• - and so that in an operating mode B1H or B1V, in which the absorption dipoles of the layers S1 , S2 , .. of the optical element 1 are aligned along the said preferred direction, unpolarized light which is perpendicular to the switchable light filter 5 incident in this, at least 24% transmitted and so that unpolarized light, which is at an angle of over 30 degrees to the perpendicular of the switchable light filter 5 is absorbed by at least 85%, whereby this applies either in the vertical (operating mode B1V) or horizontal in the direction (operating mode B1H) if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the layer S1 is oriented.

Here, too, it is again possible, for example, for either the electric field EF1 or the electric field EF2 to describe a field-free state, the respective other electric field EF2 or EF1 having an absolute field strength greater than zero, for example 0.5 MV / m.
The field-free state can be depending on the configuration of the optical element 1 and the polarization filter P mean that the operating mode B3 is present. However, it is also possible that one of the operating modes B1H or B1V is present in the field-free state.
Thus, the switchable light filter allows 5 In this fourth embodiment, in interaction with an image display unit, the switchover between a privacy screen in the vertical or horizontal direction and no privacy screen effect (upper / lower protected B1V or left / right protected B1H vs. no privacy screen B3 ).

A switchable light filter can be used for special applications 5 -independent of the aforementioned configuration- be subdivided into several, separately switchable segments, so that local switchability between the respectively possible operating states is made possible. In interaction with an image display unit, this would mean that, for example, only part of the image area is between a privacy screen (e.g. operating mode B1H or B2) and no privacy effect (e.g. operating mode B3 , possibly also B1V) can be switched for a clear view, while the complementary part of the screen is permanently in a privacy mode (e.g. operating mode B1H or B2) or in no privacy mode (e.g. operating mode B3 , possibly also B1V) is located. There can even be several segments of this type that are geometrically separated from one another and can be switched between the operating modes separately or together.

• - einen wie vorstehend beschriebenen schaltbaren Lichtfilter 5 einer der vier genannten Ausgestaltungen, und
• - eine dem schaltbaren Lichtfilter 5 von einem Betrachter aus gesehen nach- oder vorgeordnete Bildwiedergabeeinheit.

As already noted above, the invention is of particular importance through the combination of a switchable light filter described above with an image display unit to form a screen. Such a screen which can be operated in at least one first operating state B1V and / or B3 for a viewing mode that is free in the horizontal direction and in at least one second operating state B1H and / or B2 for a viewing mode restricted in the horizontal direction

• - a switchable light filter as described above 5 one of the four configurations mentioned, and
• - one of the switchable light filters 5 A downstream or upstream image display unit seen from a viewer.

The image display unit advantageously corresponds to an LCD panel, one polarization filter of which corresponds to the polarization filter P. This can be the front or rear polarizer in the LCD structure. In addition, the switchable light filter can advantageously be arranged between the LCD panel and its background lighting in order to switch between a first operating state B3 (or B1V) for a free viewing mode and a second operating state B1H or B2 for a restricted viewing mode, because the light from the background lighting is focused once in the horizontal direction due to the switchable light filter (B2 or B1H) and once not focused (B3 or B1V). B1V).

In this context, “focusing” does not mean focusing in the manner of lenses, but rather a narrowing of the emission area or transmission as a function of the angle of incidence.

Such a screen is advantageously used in a mobile device, a motor vehicle, aircraft or watercraft, in a payment terminal or in an access system. It is possible to switch between the mentioned operating modes in order to protect sensitive data, i.e. to display it in a way that is perceptible to only one viewer, or alternatively to display image content for several viewers at the same time.

In principle, additional retardation films can also be used within the scope of the invention in order to be able to further adapt the polarization states. This applies to the aforementioned and also to the embodiment of the invention described below.

The switchable light filter described above solves the problem: A switchable light filter that influences the transmission of light as a function of the angle (optionally perpendicular) has been described, whereby it is possible to switch between at least two operating states. In particular, angle restrictions in the transmission can be switched in certain directions. The switchable light filter or systems based on it can be implemented inexpensively and can be used universally, in particular with different types of screen, in order to enable switching between a privacy screen - at least in the horizontal direction - and a free viewing mode, whereby the resolution of such a screen is fundamentally not reduced . The invention described above can advantageously be used in conjunction with an image display device wherever confidential data is displayed and / or entered, such as when entering a PIN or for displaying data at ATMs or payment terminals or for entering passwords or when reading emails on mobile phones Devices. As described above, the invention can also be used in a car in order to either withhold disruptive image content from the driver or front passenger.

Claims (9)

Switchable light filter (5), comprising - two optical elements (1, 2), each comprising, - at least one, preferably more than five, layers (S1, S2, ...), - each layer (S1, S2,. ..) material with a plurality of light-absorbing electrical absorption dipoles, which are aligned parallel to a selectable preferred direction or fluctuate around this at least in a first state, said preferred direction at an angle between 0 ° and 45 ° to the surface normal of the at least one layer (S1) includes - so that light which falls into the optical element (1, 2), depending on its direction of incidence with respect to the layers (S1, S2, ...) and its polarization properties, is transmitted or partially or completely absorbed, the respective preferred directions of the Differentiate absorption dipoles between the optical elements (1, 2) by less than 10 °, - a switchable liquid crystal layer (3) arranged between the optical elements (1, 2) which, depending on an electric field acting on it, EF1 or EF2 the Polarization properties influenced by light penetrating them, - optionally a polarization filter (P), which is arranged above or below the optical elements (1, 2) - means for optionally generating said electrical fields EF1 and EF2, - so that when said polarization filter is present (P) unpolarized in a first operating mode B1H or B1V with an electric field EF1 At least 24% of light that falls perpendicular to the switchable light filter (5) is transmitted and so that unpolarized light, which falls into the switchable light filter (5) at an angle of more than 30 degrees to the center perpendicular, is absorbed by at least 85% This absorption only applies in the horizontal direction, operating mode B1H, or in the vertical direction, operating mode B1V, if the horizontal is oriented parallel to the lower edge and the vertical is oriented parallel to the left or right side edge of the at least one layer (S1), - see above that in the absence of said polarization filter (P) in a second operating mode B3 with an electric field EF1 unpolarized light which is incident at any angle in the switchable light filter (5) is transmitted to at least 24%, - and so that finally in a further operating mode B2 with an electric field EF2 unpolarized light, which is switchable perpendicular to the en light filter (5) falls into it, at least 24% is transmitted and so that unpolarized light which falls into the switchable light filter (5) at an angle of more than 30 degrees to the center perpendicular is absorbed to at least 85%, and this at the same time It applies both in the horizontal and in the vertical direction if the horizontal is oriented parallel to the lower edge and the vertical is oriented parallel to the left or right side edge of the at least one layer (S1). Switchable light filter (5), comprising - each comprising two optical elements (1, 2), - at least one, preferably more than five, layers (S1, S2, ...), - each layer (S1, S2, ..) .) Material with a multiplicity of light-absorbing electrical absorption dipoles which are aligned parallel to a selectable preferred direction or fluctuate around this at least in a first state, said preferred direction being an angle between 0 ° and 45 ° to the surface normal of the at least one layer ( S1) includes - so that light which falls into the optical element (1, 2) is transmitted or partially or completely absorbed depending on its direction of incidence with respect to the layers (S1, S2, ...) and its polarization properties, with the light-absorbing electrical absorption dipoles in each layer (S1, S2, ...) can be varied in their orientation and / or their absolute value in order to achieve the respective layer (S1, S2, ...) i n to be able to set at least two different states, - where for each of the optical elements (1, 2) the two said states are generated by electric fields EF1 or EF2 applied to the optical elements (1, 2), - optionally a polarization filter ( P), which is arranged above or below the optical elements (1, 2), - a layer (4) arranged between the optical elements (1, 2) for rotating the direction of polarization of the light penetrating said layer (4) by 90 degrees - Means for generating said electric fields EF1 or EF2, - so that in an operating mode B3, when the electric field EF1 is applied, at least 24% of unpolarized light which is incident on it at any angle to the switchable light filter (5) is transmitted, wherein in this operating mode B3 the absorption dipoles of the two switchable optical elements (1, 2) are aligned perpendicular to each other and the absorption dipoles of the Polari sators (P), if present, are aligned parallel to the absorption dipoles of the switchable optical element (1 or 2) closest to the polarizer (P), - and so that in a second operating mode B2 when the electric field EF2 is applied, unpolarized light which perpendicular to the switchable light filter (5) falls into this, at least 24% transmitted and so that unpolarized light which falls into the switchable light filter (5) at an angle of more than 30 degrees to the center perpendicular is absorbed by at least 85%, whereby this applies simultaneously both in the horizontal and in the vertical direction if the horizontal is oriented parallel to the lower edge and the vertical is oriented parallel to the left or right side edge of the at least one layer (S1), whereby in this operating mode B2 the absorption dipoles of the polarizer (P), if present, and the absorption dipoles of the polarizer (P) closest switchable optical element (1) are perpendicular to one another and the absorption dipoles of the two optical elements (1, 2) are each aligned parallel to one another. Switchable light filter (5), comprising - An optical element (1) comprising, - at least one, preferably more than five, layers (S1, S2, ...), - wherein each layer (S1, S2, ...) comprises material with a plurality of light-absorbing electrical absorption dipoles, which at least in a first state are aligned parallel to a selectable preferred direction or fluctuate around this, said preferred direction being an angle between 0 Includes ° and 45 ° to the surface normal of the at least one layer (S1), - so that light which falls into the optical element (1) is transmitted or partially or completely absorbed depending on its direction of incidence with respect to the layers (S1, S2, ...) and its polarization properties, - A polarization filter (P), which is arranged upstream or downstream of the optical element (1), - A liquid crystal layer (3) arranged between the optical element (1) and the polarization filter (P), which influences the polarization properties of the light penetrating through it as a function of an electric field EF1 or EF2 acting on it, - means for optionally generating said electric fields EF1 and EF2, - so that in an operating mode B1V or B1H when the electric field EF1 is applied, at least 24% of unpolarized light that falls perpendicular to the switchable light filter (5) is transmitted and so that unpolarized light that is at an angle of over 30 degrees to the The central perpendicular of the switchable light filter (5) is incident on it, is absorbed to at least 85%, whereby this absorption applies exclusively in the horizontal direction, operating mode B1H, or exclusively in the vertical direction, operating mode B1V, if the horizontal is parallel to the lower edge and the vertical is parallel to the left or right side edge of the at least one layer (S1), - and so that in a second operating mode B1H or B1V, when the electric field EF2 is applied, it is unpolarized At least 24% of light that falls perpendicular to the switchable light filter (5) is transmitted and so that unpolarized light, which falls into the switchable light filter (5) at an angle of more than 30 degrees to the center perpendicular, is absorbed by at least 85% , whereby this applies either exclusively in the vertical direction, operating mode B1V, or exclusively in the horizontal direction, operating mode B1H, so that the absorption direction between the first and the second operating mode B1 is rotated by 90 degrees if the horizontal is oriented parallel to the lower edge and the vertical is oriented parallel to the left or right side edge of the at least one layer (S1). Switchable light filter (5) comprising - an optical element (1) comprising - at least one, preferably more than five, layers (S1, S2, ...), - each layer (S1, S2, ...) Comprises material with a plurality of light-absorbing electrical absorption dipoles, which are aligned at least in a first state parallel to a selectable preferred direction or fluctuate around this, said preferred direction being an angle between 0 ° and 45 ° to the surface normal of the at least one layer (S1) - so that light which falls into the optical element (1), depending on its direction of incidence opposite the layers (S1, S2, ...) and its polarization properties is transmitted or partially or completely absorbed, the light absorbing electrical Absorption dipoles in each layer (S1, S2, ...) can be varied in their orientation and / or their absolute value to the respective layer (S1, S2, ...) in at least z white to be able to set different states, - a polarization filter (P) arranged above or below the optical element (1), - means for generating electrical fields EF1 or EF2, whereby for the optical element (1) the two said states through the respectively applied electric fields EF1 or EF2 are generated - so that in an operating mode B3, in which the absorption dipoles of the layers (S1, S2, ..) of the optical element (1) parallel to the substrate surface of the optical element (1) and perpendicular to the direction of transmission of the Polarizer (P) are aligned, unpolarized light, which is incident at any angle to the switchable light filter (5) in this, at least 25% is transmitted, - and so that in an operating mode B1H or B1V, in which the absorption dipoles of the layers ( S1, S2, ..) of the optical element (1) are aligned along the said preferred direction, unpolarized light, which is vertically switchable Li chtfilter (5) falls into it, at least 24% is transmitted and so that unpolarized light which falls into it at an angle of more than 30 degrees to the central perpendicular of the switchable light filter (5) is absorbed to at least 85%, whereby this is either in vertical direction, Operating mode B1V, or in the horizontal direction, operating mode B1H, applies if the horizontal is oriented parallel to the lower edge and the vertical parallel to the left or right side edge of the at least one layer (S1). Switchable light filter (5) according to one of the Claims 1 until 4th , characterized in that each of the layers (S1, S2, ...) of the optical element (1) and / or, if present, of the second optical element (2) has a non-periodic structure. Switchable light filter (5) according to one of the Claims 1 until 5 , characterized in that the switchable light filter (5) is divided into several, separately switchable segments, so that local switchability between the respectively possible operating modes is made possible. Screen that can be operated in at least one first operating mode B1V and / or B3 for a viewing mode free in the horizontal direction and in at least one second operating mode B1H and / or B2 for a viewing mode restricted in the horizontal direction - A switchable light filter (5) according to one of the preceding claims, and - An image display unit arranged downstream or upstream of the switchable light filter (5) as seen by a viewer. Screen after Claim 7 , characterized in that the image display unit is an LCD panel, one polarization filter of which corresponds to the polarization filter (P), if present. Using a screen after Claim 7 or 8th in a mobile device, a motor vehicle, aircraft or watercraft, in a payment terminal or in an access system.

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