EP3440502A1 - Screen for a free viewing mode and a restricted viewing mode - Google Patents

Abstract

The invention relates to a screen (1) which can be operated in at least two operating modes Bl for a free viewing mode and B2 for a restricted viewing mode, comprising a planar-like backlight (2), which radiates light in a restricted angular range, in the viewing direction arranged in front of the backlight (2) transmissive imager (5), a between the imager (5) and the backlight (2) located, plate-shaped light guide (3), which consists of a transparent, thermoplastic or thermoelastic plastic, and which on at least one the large surfaces and / or within its volume Auskoppelelemente (6), wherein laterally on narrow sides of the light guide (3) bulbs (4) are arranged, the light guide (3) for the backlight (2) outgoing light to at least 70% transparent is, the decoupling elements (6) in their number per area e and in their extent are chosen such that the optical waveguide (3) has an average haze value of less than 7% over at least 80% of its area, whereby the light emitted by the backlight (2) at least in the operating mode B2 in a limited angular range Light is only slightly scattered when passing through the light guide (3), wherein furthermore the decoupling elements (6) are distributed on at least one of the large surfaces and / or within the volume of the light guide (3) such that the coupling out of the light sources (4 ) originating light from the light guide to at least 80% on one of the large surfaces of the light guide (3) in the direction of the imager (5) is performed, and wherein in the operating mode B2, the backlight (2) on and the lighting means (4) are turned off , and wherein in the operating mode Bl at least the lighting means (4) are switched on.

Description

 title

 Screen for a free and restricted view mode

Field of the invention

In recent years, great progress has been made in broadening the viewing angle of LCDs. However, there are often situations in which this very large viewing area of a screen can be disadvantageous. Increasingly, information is also becoming available on mobile devices such as notebooks and tablet PCs, such as bank details or other personal information, and sensitive data. Accordingly, people need control over who can see this sensitive data; they must be able to choose between a wide viewing angle to share information on their display with others, e.g. when viewing holiday photos or for promotional purposes. On the other hand, they need a small viewing angle if they want to treat the image information confidentially. A similar problem arises in the vehicle industry: There, the driver must not be distracted by image content, such as digital entertainment programs, with the engine on, while the passenger would like to consume the same while driving. Thus, a screen is needed, which can switch between the corresponding display modes.

State of the art

Supplementary films based on micro-blades have already been used for mobile displays to achieve their optical data protection. However, these slides were not (re) switchable, they always had to be placed by hand and then removed again. Also you have to transport them separately to the display, if you do not need them right now. A major disadvantage of the use of such lamellar films is also associated with the accompanying loss of light. US Pat. No. 6,765,550 describes such a screen by micro-blades. The biggest disadvantage here is the mechanical removal or mechanical attachment of the filter as well as the loss of light in the protected mode. No. 5,993,940 describes the use of a film which has evenly arranged, small prism strips on its surface in order to achieve a privacy mode. Development and production are quite expensive. In WO 2012/033583, the switchover between free and restricted vision is generated by means of the activation of liquid crystals between so-called "chromonic" layers, resulting in a loss of light and the expense is quite high.

The document US 2009/00671 56 discloses a variety of ideas for designing a lighting system and a display device. The variant shown there in FIGS. 3A and 3B uses in particular two backlights, so-called backlights, consisting of wedge-shaped light guides, and an LCD panel, wherein the rear backlight 40 is bound to produce a wide illumination angle and the front backlight 38 is required to produce a narrow illumination angle , However, it remains unclear here how the backlight 38 should produce a narrow illumination angle, without the light having a wide illumination angle, which originates from the backlight 40, being substantially converted into light with a narrow illumination angle when passing through the backlight 38.

For the embodiment according to Fig. 5 of US 2009/0067156 it is to be noted that both light guides 46 and 48 produce "narrow light" in each case, ie light with a narrow illumination angle The light of the light guide 48 only becomes complicated by prismatic structures to be created partial mirror 50 in "wide light", ie light with a wide illumination angle converted. This conversion extremely curtails the light intensity, since the light initially emitted in a narrow illumination angle, which is available as the only light, then in a large illumination angle, i.d. R. the half-space, fanned out. As a result, depending on the parameters, the brightness is reduced by a factor of 5 or more (in terms of luminance). It is therefore a less relevant design. In the embodiment according to FIG. 7 of US 2009/0067156, a phosphor layer is absolutely necessary; it is intended to convert UV light into visible light. This effort is great and in the desire for sufficient light from the backlight to illuminate a LCD panel readable, very large intensities of UV light are needed. Thus, this is expensive, expensive and even from the shielding of the required UV radiation ago not practicable.

The US 2012/0235891 describes a very elaborate backlight in a screen. There, not only a plurality of optical fibers are used according to FIGS. 1 and 15, but also other complex optical elements, such as microlens elements 40 and prismatic structures 50, which transform the light from the rear illumination on the way to the front illumination. This is expensive and expensive to implement and also associated with loss of light. According to the variant according to FIG. 7 in the US 2012/0235891, both light sources 4R and 18 produce light with a narrow illumination angle, wherein the light from the rear light source 18 is first converted consuming into light with a large illumination angle. This complex transformation is - as noted above - strongly brightness-reducing.

According to JP 2007-1 55783, special optical surfaces 19, which are difficult to calculate and to produce, are used, which then deflect light into different narrow or broad regions depending on the angle of incidence of the light. These structures are similar to Fresnel lenses. There are also interfering edges which deflect light in undesired directions. Thus, it remains unclear whether really meaningful light distributions can be achieved.

According to the teachings of GB 2428128 A, to provide a limited view, additional light sources which are clearly remote from the screen and illuminate a hologram mounted on the screen are used to superimpose the side view with specific wavelengths. The disadvantage here is the required distance of the light sources from the screen and the effort to produce appropriate holograms.

In US 2013/0308185 a special step-shaped optical fiber is described which emits light on a large area in different directions, depending on which direction it is illuminated from a narrow side. In cooperation with a transmissive image display device, e.g. an LC display, a screen switchable between free and limited viewing mode can thus be generated. The disadvantage here u.a. That the limited visual effect either only for left / right or up / down, but not for left / right / up / down can be generated simultaneously, as it is necessary for certain payment transactions. In addition, even in the restricted viewing mode, blocked light is still visible from blocked viewing angles.

Applicant's WO 2015/121398 describes a screen of the type described in the introduction. There, scattering particles in the volume of the corresponding optical waveguide are essential for switching the operating modes. However, the scattering particles selected there from a polymer generally have the disadvantage that light is decoupled from both large areas, whereby about half of the useful light in the wrong direction, namely the backlight, emitted and there due to the structure not to a sufficient extent can be recycled. Moreover, the polymer scattering particles distributed in the volume of the light guide may, under certain circumstances, in particular at a higher concentration, lead to scattering effects which reduce the privacy protection effect in the protected operating mode. The above-mentioned methods and arrangements generally have the disadvantage that they significantly reduce the brightness of the basic screen and / or require an active, but at least a special, optical element for mode switching and / or require costly and expensive manufacture and / or or reduce the resolution in freely viewable mode.

Description of the invention

 It is therefore an object of the invention to describe a screen through which a secure display of information by means of an optionally restricted viewing angle can be realized, in a further mode of operation, a free, if possible in the viewing angle unrestricted vision should be possible. The invention should be as inexpensive as possible to implement with simple means. In both modes, the highest possible resolution, particularly preferably the native resolution of the screen used, should be visible. Furthermore, should be introduced by the solution only the least possible loss of light.

This object is achieved according to the invention by a screen which can be operated in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode, comprising

 an areally extended backlight which emits light in a restricted angular range (as a limited angular range, basically any range can be considered that is smaller than the half space in front of the backlight, however, an angle range of +/- 30 degrees is preferred, for example horizontal, meaning vertical or cone around the surface normal or a selectable directional vector on the backlight, small amounts of light of less than 3% to 5% peak brightness may be disregarded when defining the restricted angle range), one in the viewing direction from the backlight arranged transmissive imagers,

 a lying between the imager and the backlight, plate-shaped light guide, which consists of a transparent, thermoplastic or thermoelastic plastic or glass, and which has on at least one of the large surfaces and / or within its volume Auskoppelelemente, wherein

 Illuminants are arranged laterally on narrow sides of the light guide, preferably on one or both long sides of the light guide,

the light guide for the light emitted by the backlighting light is at least 70%, preferably at least 85% transparent, the decoupling elements are selected in their number per area and in their extent such that the optical waveguide has an average haze value of less than 7% over at least 80% of its area, preferably less than 2%, particularly preferably less than 1%, measured according to FIG ASTM D1003, whereby the light emitted by the backlight at least in the operating mode B2 in a limited angular range is only slightly scattered when passing through the light guide,

 wherein furthermore the decoupling elements are distributed on at least one of the large areas and / or within the volume of the light guide such that the decoupling of the light originating from the light sources from the light guide is performed at least 80% on one of the large areas of the light guide in the direction of the imager is (the light is preferably distributed over the entire large area, as homogeneous as possible, coupled), and wherein in the operating mode B2, the backlight on and the bulbs are switched off at the narrow sides of the light guide, and wherein in the

Mode B1 m at least the bulbs are switched on the narrow sides of the light guide.

In the operating mode B1, as described above, at least the light sources are switched on at the narrow sides of the light guide. It is possible that the backlight is on or off.

The decoupling of the light originating from the light sources from the light guide to at least 80% on one of the large surfaces of the light guide implies that a maximum of 20% of the total decoupled light is output on the correspondingly large area. This circumstance does not necessarily mean that in each case more than 80% of the light coupled into the optical waveguide by the light sources is coupled out of the one large surface but refers to more than 80% of the total coupled-out light. This clarification is important because, as a rule, the entire light coupled into the light guide is never coupled out across the large areas due to losses. However, in advantageous embodiments of the invention, it is actually possible, although not a condition, that more than 80% of the light coupled into the optical waveguide by the illuminants is coupled out in a planar manner over or over a large area. To the feature that the decoupling elements are distributed on at least one of the large areas and / or within the volume of the light guide, that the coupling of the light originating from the light sources from the light guide is performed to at least 80% on one of the large surfaces of the light guide is also Note that this just not as in the prior art, such as the use of nanoparticles such as Titanium dioxide in the optical fiber volume, the light is coupled out about half of each on both large surfaces. Because the light, which is radiated in the prior art backlight, can hardly be returned to the imager, and it is therefore largely lost for the balance of use. By virtue of the above-described 80% light extraction on only one large area, improved light efficiency is achieved because at least 80% of useful light is coupled out.

If the decoupling elements are not applied within the volume of the light guide, but on one of the large surfaces of the light guide in the invention, the outcoupling of the light from the light guide occurs primarily (just to at least 80%) usually on that large surface of the light guide, on the decoupling elements are applied, or on the opposite large area. It is also possible that decoupling elements are mounted on both large areas and additionally optionally in the volume.

The decoupling elements have maximum dimensions of ^" Ι ΟΟμιη, preferably between 1 μιη and 15 μπτι, on.

The decoupling elements for decoupling light at at least one of the large areas of the light guide preferably consist of microlenses and / or microprisms and / or diffractive structures and / or structural elements and / or scattering elements having a maximum extent in their largest dimension, which is smaller than 35 micrometers, preferably less than 15 microns, is. In the case of diffractive structures, it may be, for example, a hologram or a grating / diffraction grating.

However, the Auskoppelemente themselves can also have the outer shape of microlenses, microprisms, scattering elements and / or diffractive structures. They can then be designed in particular as cavities, which are then formed in the volume of the light guide. The cavities may be evacuated, but are preferably filled with a gaseous, liquid or solid material. The material has a refractive index which differs from that of the material used for the optical waveguide; it is preferably lower. By filling with material and by the choice of material, one can take a greater influence on the light pipe, as would be the case with evacuated cavities. Alternatively or additionally, the haze value of the material preferably deviates from that of the material used for the light guide, is preferably higher. Advantages of these embodiments are higher efficiency in light extraction.

Alternatively and technically simpler, the cavities can also be formed by forming the optical waveguide from two interconnected substrate layers, the substrate layers are preferably similar. The compound can be chemically done, for example by gluing. The cavities are then formed as material recesses on at least one of the boundary surfaces of the substrate layers. If, therefore, the decoupling elements are mounted on at least one of the large areas of the light guide, they are advantageously formed from a plastic structured with a tool, the structure of which has been embossed by means of a tool. This is possible, for example, in mass production by applying to a light guide substrate a UV-curing material (eg a paint, a monomer, etc.), which is structured by means of a tool and cured by UV radiation, eg. B. is polymerized. Other radiation curing materials may also be used. The formation of the recesses for the realization of the decoupling elements can be realized, for example, mechanically, lithographically or by printing, or else material-applying, converting, ablating or dissolving.

Dam it can e.g. Lattice structures, microprisms (either convex m with plastic portion on the surface facing outwards, and / or concave as imprint or recess within the surface layer of the structured plastic) or microlenses cost and mass-produced suitable.

Finally, the optical waveguide or its substrate may comprise at least 40% by weight of polymethyl methacrylate, preferably at least 60% by weight of polymethyl methacrylate, based on its weight. Alternatively, it may be, for example, polycarbonate (PC).

A further advantageous embodiment of the invention provides that for the operating mode B1, the light originating from the light sources and emerging from the light guide at each point of its surface at angles β> γ and / or β <-σ, with 10 ° <γ <80 ° and 10 ° <σ <80 °, preferably γ = σ = 40 ° or γ = σ = 20 °, measured perpendicularly - ie at an angle of ß = 0 ° - to the surface of the optical fiber and in a vertical orientation to the surface of the optical fiber - Orientation here is the orientation of the light guide and dam it inherently meant by the imager, ie in particular a portrait or landscape orientation -, much less of the light intensity, preferably at most 50% of the light intensity, which has the light, which emerges at such a point of the surface of the light guide perpendicular to its surface. As a result, for example, a Verm modification of disturbing reflections in the windshield, especially when driving at night, achieved when the screen according to the invention is installed in a vehicle. Another useful embodiment of the screen according to the invention is that in the viewing direction in front of the imager, a further light guide is arranged with means for coupling out of light, which can be supplied laterally by Leuchtm itteln m with light. The means for decoupling used here are, for example, those described above, or as known in the art, such as nanoparticles such as titanium dioxide, barium sulfate, etc. in suitable sizes and amounts, which are homogeneously distributed in the volume of the light guide. By means of this embodiment, a possibly unintentionally existing residual light in the mode B2 in the actually protected from view angle ranges still be superimposed or outshone that no contrast is more perceptible and thus no Bildwahrnehm out of the non-shared angles longer possible. The decoupling elements can also be embodied here in the form of cavities or at interfaces which, when used in a vehicle, ensure, for example, that only the front passenger receives information, but the driver is not limited by limiting the radiation to the corresponding subspace.

A particularly advantageous, stable and suitable for vehicles variant of a screen also includes another, plate-shaped light guide with large areas, which is arranged in the viewing direction in front of the imager, which, however, is made of a glass, for example, can be formed as a simple glass plate. This further light guide can also be fed with light from the side of light sources, as already described. The large areas of the further light guide adjoin materials having a smaller refractive index, i. Both materials include a material with a lower refractive index. The materials may be different, for example, the large area facing the imager may be an adhesion medium layer, an adhesive layer via which the further optical fiber is connected to the imager. On the other large surface may be present as a medium air, or also an adhesive layer for connection to a cover glass, in which, for example, touchscreen functions can be integrated. If the further optical waveguide is made of glass, it is not absolutely necessary to form the further optical waveguide with means for decoupling light, i. it can be dispensed with. Nevertheless, in order to further improve the desired effects, it is also possible to attach or form outcoupling elements in or on the further optical waveguide made of glass; the corresponding optically active structures can be made e.g. be produced on the large surfaces by material processing, for example, be etched into this, or be produced by applying a corresponding lacquer layer, to name just two examples.

The corresponding illuminants are designed to emit colored or white light. In this case, the luminescent means can emit light in a color which does not occur in the image represented by the transmissive imager. Alternatively, it is possible for the light sources to emit light in a color which occurs in the image represented by the transmissive imager or lies close to such a color in the color spectrum. Finally, it is conceivable that the light emitting means emit light in a color which corresponds approximately to the complementary color of a color which occurs in the image represented by the transmissive imager.

By "colored light" is meant, in particular, visible light which is not white, eg, light in the colors red, green, blue, turquoise, yellow, cyan, magenta, or yellow, and this light can be selectively radiated in different brightness levels It is also possible for the color of the light emanating from the light sources to be modulated in terms of time, for example in terms of color and / or brightness Moreover, the light bulbs can also be implemented with different individual light sources, such as RGB LEDs in LED rows simultaneously or offset in time and / or spatially offset each radiate light of different colors and / or different brightness.

Furthermore, it is possible that said limited angular range is formed symmetrically or asymmetrically about the surface normal of the imager. This is particularly helpful in applications in the vehicle, such as when the screen is arranged as a so-called center information display in the dashboard approximately in the middle between the driver and front passenger. Then in the operating mode two, the restricted angle range for the view, released exclusively for the passenger, must be asymmetrical, ie directed towards the front passenger. For example, the backlight may consist of

 a flat radiator, preferably a light guide with laterally or on the back arranged bulbs,

 at least one light collimator integrated into the planar radiator and / or in front of it, such as 3M ™ Optical Lighting Film ™ or prismatic grids, and / or privacy filters, e.g. from 3M ™.

Accordingly, the backlight can basically be constructed like a backlight, for example a side-light, edgelight, direct LED backlight, edge LED backlight, OLED or another surface radiator, onto which e.g. at least one permanent privacy filter (with micro-blades) is applied. Other variants provide for the use of so-called "directed backlights", ie directed backlighting.

On top of the imager and / or on at least one of the large areas of the light guide as well as on at least one of the privacy filters, if present, means for Reflex reduction or control, for example, a Antiglare- and / or an antireflection coating, be arranged.

The screen according to the invention is particularly advantageously used in a vehicle for selectively displaying image contents only for the front-seat passenger in the operating mode B2 or simultaneously for the driver and the front-seat passenger in the operating mode B1. The former is e.g. helpful if the passenger looks at entertainment content that may distract the driver. An inventive screen can be used as it were to enter or display confidential data, such as PIN PIN numbers, e-mails, SMS or passwords, ATMs, payment terminals or mobile devices.

In all the aforementioned embodiments, the said light sources can be LEDs or LED rows or laser diodes. Other variants are conceivable and are within the scope of the invention.

Furthermore, the desired restricted angle ranges for the restricted view mode B2 can be independently defined and translated for the horizontal and vertical directions, respectively. For example, in the vertical direction, a larger angle (or possibly no restriction) might be useful than in the horizontal direction, such as when ATMs of different sizes should see an image, while the side insight should remain strong or completely restricted. For POS payment terminals, on the other hand, due to security regulations, visibility restrictions in mode B2 are often necessary in both horizontal and vertical directions.

In the context of the invention is also a lighting device for a screen, as described above. It differs from the screen in that it does without the image generator.

Basically, the performance of the invention is maintained when the parameters described above are varied within certain limits.

It is understood 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 alone, without departing from the scope of the present invention. Brief description of the drawings

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

1 is a schematic diagram of the coupling of light, which is laterally coupled into a light guide, from the lower large surface of the light guide, on which the Auskoppelemente are, the light leaving the optical fiber at the upper large area,

 2 is a schematic diagram for coupling out light, which is laterally coupled into an optical waveguide, from the upper large area of the optical waveguide, on which the Auskoppelemente are, the light leaving the optical fiber at the upper large area,

 3 is a schematic diagram for the passage of light, which results from a backlight, through a light guide,

Fig. 4 is a schematic diagram of the screen according to the invention in the mode B1 for a free

Overview mode

 5 shows a schematic diagram of the screen according to the invention in the mode B2 for a restricted viewing mode,

Fig. 6 is a schematic representation for defining the vertical direction of the measured

Angle ß,

 7 shows a diagram of the relative brightness of the light coupled out of the optical waveguide, measured in the vertical direction, as well as FIG

8 shows an embodiment of the screen according to the invention, in which in

Viewing direction in front of the imager another light guide with means for

Coupling of light is arranged, which can be fed laterally from light sources with light.

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

Detailed description of the drawings

In Fig. 1 is a schematic diagram for coupling out of light, which is laterally coupled by light sources 4 in a light guide 3, from the lower large surface of the light guide 3, on which the Auskoppelemente 6 are shown. In the horizontal direction, the light is coupled out here at a large angle from the upper large area of the light guide 3. The location of the decoupling elements 6 is indicated by the number 6, but the actual decoupling elements 6 are not shown here, because they must be microscopic. Thus, light from the lighting means 4, for example from LEDs, is coupled laterally into the light guide 3. Due to total reflection, rays of the coupled light (bold Rays) thrown back into the light guide 3 on the outer wall until finally (possibly repeatedly) hit a decoupling element 6 to the desired coupling. The output is stylized by the thin rays. The illustration in Figure 1 is highly stylized for better visibility; In reality, a very large number of beam paths in the light guide 3 is implemented.

Fig. 2 shows a schematic diagram for coupling out of light, which is coupled laterally by light sources 4 in a light guide 3, from the upper large surface of the light guide 3, on which the Auskoppelemente 6 are located. The light also leaves the light guide 3 through the upper large area. The statements relating to FIG. 1 apply mutatis mutandis.

Technically different here is only the location and possibly the design of the decoupling elements 6, which are now on the top of the light guide 3 and thus decouple the light directly upwards, without it to leave the light guide 3, as shown in Fig. 1 , first the optical fiber 3 would have to cross once again.

Fig. 3 shows a schematic diagram for the passage of light, which results from a backlight 2, through a light guide 3, through the two large surfaces of the light guide 3 and transversely through its volume. The Auskoppelemente 6 thereby play a substantially negligible role, since the light comes from the backlight 2, i. is not laterally coupled by a narrow side of bulbs 4 in the light guide 3 and therefore is not or hardly controlled by total reflection in the light guide 3 back and forth. In this respect, the Auskoppelemente 6 are not shown here, because their effect is negligible.

FIG. 4 shows a schematic diagram of the screen according to the invention in operating mode B1 for a free viewing mode.

This screen 1 includes

 an areally extended backlighting 2 which emits light in a restricted angular range (a restricted angular range here is, for example, an angular range of +/- 30 degrees to the left and right to the surface normal of the backlight 2; small amounts of light of less than 3 to 5% peak Brightness may be disregarded when defining the restricted angle range),

 a transmissive imager 5 arranged in the viewing direction in front of the backlight 2,

a lying between the imager 5 and the backlight 2, plate-shaped light guide 3, which consists of a transparent, thermoplastic or thermoelastic plastic or glass, and which has at least one of the large areas and / or within its volume not graphically illustrated decoupling elements 6,

 in which

 are arranged laterally on narrow sides of the light guide 3 luminescent medium 4, (preferably on one or both long sides of the light guide 3),

 the light guide 3 is at least 70%, preferably at least 85%, transparent to the light emitted by the backlight 2,

 the decoupling elements 6 (not illustrated in the drawing) are selected in their number per area and in their extent such that the optical waveguide 3 has an average haze value of less than 7% over at least 80% of its area, preferably less than 2%, particularly preferably less than 1%, measured in accordance with ASTM D1003, whereby the light radiated by the backlight 2 m at least in the operating mode B2 into a restricted angular range is only slightly scattered when passing through the optical waveguide 3, as was also explained with reference to FIG.

 Furthermore, the decoupling elements 6 are distributed on m at least one of the large surfaces and / or within the volume of the light guide 3, that the coupling of the Leuchtm itteln 4 originating light from the light guide 3 to at least 80% on one of the large surfaces of the light guide. 3 4 (this is stylized in Fig. 4 in that the thin light arrows embodying the upwardly coupled light show only in one direction, more preferably even more than 90% of the light is on only one Large area decoupled, whereby the luminous efficacy and efficiency of the arrangement is substantially enhanced over the prior art), and

 wherein in the mode of operation B1 m at least the bulbs 4 are turned on.

It is possible that for the operating mode B1, the backlight 2 is switched on or off. In Fig. 4, the backlight 2 is turned off by way of example. If a particularly bright mode is desired for the front view, then in the operating mode B1, the backlight 2 can also be switched on, which is not shown in the drawing.

5 now shows a schematic diagram of the screen 1 according to the invention in the operating mode B2 for a limited viewing mode, wherein now the backlight 2 on and the Leuchtm means 4 are turned off.

The light emitted by the backlight 2 only to a limited angle, represented in the drawing by the thick arrows, then penetrates the light guide 3 essentially without scattering or deflection, as also described with reference to FIG. 3, and then illuminates the imager 5 due to its angular restriction such that it can be perceived substantially only from a limited angular range. The limitation of the angle range can apply horizontally and / or vertically. To the feature that the decoupling elements 6 are distributed on at least one of the large areas and / or within the volume of the light guide 3, that the coupling of the light originating from the light sources 4 out of the light guide to at least 80% on one of the large surfaces of the light guide 3 In the prior art, for example when using nanoparticles such as titanium dioxide or polymer in the optical fiber volume, the light is decoupled approximately halfway on both large surfaces. This is just not to be implemented in the invention, because the light, which is radiated in the prior art backlight 2, can hardly be returned to the imager 5 and is largely lost in the balance of use. If the decoupling elements 6 are not applied within the volume of the optical waveguide 3, but on one of the large surfaces of the optical waveguide 3, the coupling of the light from the optical waveguide 3 takes place primarily (just at least 80%), as a rule, on that large surface of the optical waveguide 3, which is turned to the imager 5. This also applies in the case of the decoupling elements 6 distributed in the volume of the optical waveguide 3.

The decoupling elements 6 have maximum dimensions of 100 μιτι, preferably between 1 μιη and 15 μιτι on. Typically, the decoupling elements 6 vary in number per area over the surface of the light guide 3 in order to achieve the desired decoupling properties, such as the output characteristics of the decoupling elements. Homogeneity, to achieve.

The decoupling elements 6 for decoupling light on at least one of the large areas of the optical waveguide 3 preferably consist of microlenses and / or microprisms and / or diffractive structures and / or structural elements having a maximum extent in their largest dimension, which is less than 35 μιτι, preferably less than 15 μιτι, is.

Thus, when the decoupling elements 6 are mounted on at least one of the large surfaces of the light guide 3, they are advantageously formed from a structured plastic with a tool whose structure was embossed by means of a tool. This is possible, for example, in mass production by applying to a light guide substrate a UV-curing material (eg a lacquer, a monomer, etc.) which is structured by means of a tool and cured by UV radiation, eg polymerized. Other possibilities of production include injection molding, hot stamping and lithography. Finally, the optical waveguide 3 or its substrate can comprise at least 40% by weight of polymethyl methacrylate, preferably at least 60% by weight of polymethyl methacrylate, based on its weight. Alternatively, it may be, for example, polycarbonate (PC).

A further advantageous embodiment of the invention provides that for the operating mode B1, the light originating from the light sources 4 and emerging from the light guide 3 at each point of its surface in angles β> 40 ° and / or β <-40 ° - preferably even in Angles ß> 20 ° and ß <-20 ° -, measured perpendicular to the surface of the light guide 3 and in a vertical orientation to the surface of the light guide 3 (with orientation here the orientation of the light guide 3 and thus inherently also the imager 5 is meant, ie in particular a portrait or landscape orientation), at most 50% of the light intensity having the light emerging from such a point of the surface of the light guide 3 perpendicular to its surface. This will e.g. a reduction of disturbing reflections in the windshield, especially when driving at night, achieved when the screen according to the invention is installed in a vehicle.

In this regard, Fig. 6 shows a schematic representation for defining the vertical direction of the angle to be measured ß, wherein the optical fiber 3 (as well as the imager 5, not shown) is arranged in landscape mode, ie the long sides are up and down. The dash-dot line stylizes a direction perpendicular to the surface of the light guide 3, to which the angle β is measured in a vertical orientation or plane, here indicated by the double arrow labeled "V." Finally, FIG The abscissa represents the angle β and the ordinate a relative luminance, which was measured in the vertical direction respectively at the corresponding angle angle .beta .. It can be clearly seen that .differential brightness of the light coupled out from the optical waveguide 3. FIG as described above for the operating mode B1, the light originating from the light sources 4 and emerging from the light guide 3 at the measuring point of its surface selected here in angles β> 40 degrees and / or β <-40 degrees, at most 50% (here even approx less than 25%) of the luminous intensity exhibiting the light coming from the selected point of the upper surface of the light guide 3 emerges perpendicular to its surface. Another useful embodiment of the screen 1 according to the invention, as shown in Fig. 8, is that in the viewing direction in front of the imager 5, a further light guide 5a is arranged with means for coupling out of light, which can be fed laterally by bulbs 4a with light. The decoupling means used here are, for example, those described above for the optical waveguide 3. By means of this embodiment, a possibly still inadvertently existing residual light in the mode B2 in the actually protected from view angle ranges still be superimposed or outshined - see in Fig. 8, the narrow oblique arrows 7 - that no contrast is more perceptible and thus no image perception from the non-shared Angles more is possible.

The corresponding lighting means 4a are designed to emit colored or white light. In this case, the light emitting means 4a can emit light in a color which does not occur in the image represented by the transmissive imager 5. Alternatively, it is possible that the lighting means 4a emit light in a color which occurs in the image represented by the transmissive imager 5 or in the color spectrum is close to such a color. Finally, it is conceivable that the lighting means 4a emit light in a color which corresponds approximately to the complementary color of a color which occurs in the image represented by the transmissive imager 5. By "colored light" is meant in particular visible light which is not white, for example light in the colors red, green, blue, turquoise, yellow, cyan, magenta or yellow.

Furthermore, this light can optionally be emitted in different brightness levels. It is also possible that the color of the outgoing light from the bulbs 4a is also modulated in time, such as color and / or brightness. In addition, the light sources can also be implemented with different individual light sources 4a, for example RGB LEDs in LED rows, which emit light of different colors and / or different brightness simultaneously or at different times and / or spatially offset. The light guide 5a, in particular if it uses similar coupling elements 6 as described for the light guide 3 in a suitable manner, also coupling light only in a selected direction, for example to the left or right, but almost not or negligibly perpendicular to its surface. This has the advantage that the image contrast for the person looking frontally in the mode B2 on the screen is almost or not reduced, while the visual protection effect to the side as described above is significantly improved.

Furthermore, it is possible for the said limited angular range to be formed symmetrically or asymmetrically around the surface normal of the imager 5. This is particularly useful in applications in the vehicle, such as when the screen 1 is arranged as a so-called center information display in the dashboard approximately in the middle between the driver and front passenger. Then, in the operating mode B2, the restricted angular range, which has been approved for the passenger only, must be asymmetrical, ie directed towards the front passenger. The backlight 2 may consist, for example

 a flat radiator, preferably a light guide with laterally or on the back arranged Leuchtm itteln, e. LEDs,

 two light-collimators crossed at right angles, integrated in the planar radiator and / or arranged in front of them, such as 3M ™ Optical Lighting Film ™ or prismatic grids, and at least one privacy filter, e.g. from 3M ™.

 The use of a directed backlight 2, ie a "directed backlight" is also possible.

Particularly advantageously, the screen according to the invention 1 is used in a vehicle for selectively displaying image content only for the passenger in the mode B2 or simultaneously for the driver and the passenger in the mode B1. The former is e.g. the case when the passenger looks at entertainment content that might distract the driver.

In all the aforementioned embodiments, the said illuminants 4 or 4 a may be LEDs or LED rows or laser diodes. Other variants are conceivable and are within the scope of the invention.

Furthermore, the desired restricted angle ranges for the restricted view mode B2 can be independently defined and translated for the horizontal and vertical directions, respectively. For example, in the vertical direction, a larger angle (or possibly no restriction) might be useful than in the horizontal direction, such as when ATMs of different sizes should see an image, while the side insight should remain strong or completely constrained. For POS payment terminals, on the other hand, due to security regulations, visibility restrictions in mode B2 are often necessary in both horizontal and vertical directions.

The screen according to the invention described above solves the problem posed: it allows practically well implementable solutions in order to realize a secure display of information through an optionally restricted viewing angle, while in another mode a free, unobstructed viewing angle is possible. The invention can be realized inexpensively by simple means. In both modes, the native resolution of the image display device used can be used. In addition, only a small loss of light is introduced through the solution. The invention described above can advantageously be applied everywhere where confidential data is displayed and / or input, such as PIN entry or data display at ATMs or payment terminals or for password entry or reading emails on mobile devices. The invention can also be used in cars, as described above.

Claims

claims A screen (1) operable in at least two modes B1 for a free viewing mode and B2 for a restricted viewing mode  an areally extended backlight (2) that emits light in a restricted angular range,  a transmissive imager (5) arranged in the viewing direction in front of the backlight (2),  a plate-shaped optical waveguide (3) located between the imager (5) and the backlight (2), which consists of a transparent, thermoplastic or thermoelastic plastic or glass, and which has outcoupling elements on at least one of the large areas and / or within its volume ( 6), wherein  Illuminants (4) are arranged laterally on narrow sides of the light guide (3), the light guide (3) is at least 70% transparent to the light emerging from the backlight (2),  the decoupling elements (6) are selected in their number per area and in their extent such that the optical waveguide (3) has an average Haze value of less than 7% over at least 80% of its area, preferably less than 2%, particularly preferably less than 1%, measured in accordance with ASTM D1003, whereby the light emitted by the backlight (2) at least in the operating mode B2 in a restricted angular range is only slightly scattered when passing through the optical waveguide (3),  wherein furthermore the decoupling elements (6) are distributed on at least one of the large areas and / or within the volume of the light guide (3) such that the decoupling of the light originating from the light sources (4) from the light guide is at least 80% on one of the large areas the light guide (3) in the direction of the imager (5) is performed, and  wherein in the operating mode B2 the backlight (2) is on and the lighting means (4) are switched off, and wherein in the operating mode B1 at least the lighting means (4) are switched on. 2. Screen (1) according to any one of the preceding claims, characterized in that in the viewing direction in front of the imager (5), a further light guide (5a) is arranged with means for coupling of light, which are fed laterally by light sources (4a) with light can, wherein the further optical fiber (5a) is preferably formed with outcoupling elements (6). 3. Screen (1) according to any one of the preceding claims, characterized in that said limited angular range sym metric or asymmetrical about the surface normal of the imager (5) is formed, preferably in the horizontal direction. 4. Screen (1) according to any one of the preceding claims, characterized in that on the upper side of the imager (5) and / or on at least one of the large surfaces of the light guide (3) and / or the light guide (5a), if present, means for Reflexm change, for example, a Antiglare- and / or an antireflective coating are arranged. 5. Screen (1) according to any one of the preceding claims, characterized in that the decoupling elements (6) maximum dimensions of 100 μιτι, preferably between 1 μιη and 15 μιη have. 6. Screen (1) according to any one of the preceding claims, characterized in that the decoupling elements (6) consist of microlenses and / or microprisms and / or diffractive structures and / or structural elements and / or scattering elements. 7. Screen (1) according to one of claims 1 to 6 with within the volume of the light guide (3) formed outcoupling elements, characterized in that the Decoupling elements are designed as cavities, which preferably have the outer shape of microlenses, microprisms or diffractive structures. 8. screen (1) according to claim 7, characterized in that the cavities are filled with a gaseous, liquid or a solid material, wherein the material has a refractive index which differs from that of the light guide (3) used material, preferably is lower, or that the cavities are evacuated. 9. Screen (1) according to claim 7 or 8, characterized in that the cavities m filled with a gaseous, liquid or a solid material, wherein the Material has a Haze value, which differs from that of the light guide (3) used material, is preferably higher. 10. Screen (1) according to any one of claims 7 to 9, characterized in that the light guide (3) of two m connected to one another at interfaces, preferably similar substrate layers is formed and the cavities as material recesses on at least one of the interfaces, preferably the outer Form of microlenses, microprisms or diffractive structures, are formed. 1 1. Screen (1) according to one of claims 1 to 10, characterized in that the decoupling elements (6), if they are mounted on at least one of the large surfaces or interfaces of the light guide (3), from a m it tool, preferably mechanically, lithographically , printing or material applying, material removal, -umwandelnd or -auflösend, structured plastic are formed. 12. Screen (1) according to any one of the preceding claims, characterized in that for the operating mode B1 from the light sources (4) originating from the light guide (3) at each point of its surface exiting light in angles ß> γ and / or ß <-σ, with 10 ° <γ <80 ° and 10 ° <σ <80 °, preferably γ = σ = 40 °, measured perpendicular to Surface of the light guide (3) and in a vertical orientation to the surface of the light guide (3), preferably at most 50% of the light intensity, which has the light emerging from such a point of the surface of the light guide (3) perpendicular to its surface. 13. Screen (1) according to any one of the preceding claims, characterized in that the backlight (2) consists of  a planar radiator, preferably a light guide with laterally or on the back arranged Leuchtm means,  At least one light collimator integrated in the planar radiator and / or arranged in front of it. 14. Screen (1) according to any one of the preceding claims, characterized in that in the viewing direction in front of the imager (5), a further, plate-shaped light guide (5a) is arranged with large areas, the side of Leuchtm itteln (4a) are fed with light can, wherein the further optical fiber (5a) is made of glass, wherein the large surfaces of materials m with smaller refractive index adjoin, and wherein the further optical fiber (5a) is preferably formed m with coupling-out elements (6). 15. Lighting device for a screen (1), which can be operated in at least two operating modes B1 for a free viewing mode and B2 for a restricted viewing mode, comprising  an areally extended backlight (2) that emits light in a restricted angular range, - A in a viewing direction in front of the backlight (2) located, plate-shaped light guide (3), which consists of a transparent, thermoplastic or thermoelastic plastic or glass, and which m at least one of the large surfaces and / or within its volume Auskoppelelemente (6 ), wherein Illuminants (4) are arranged laterally on narrow sides of the light guide (3), the light guide (3) is at least 70% transparent to the light emerging from the backlight (2),  the decoupling elements (6) are selected in their number per area and in their extent such that the optical waveguide (3) has an average Haze value of less than 7% over at least 80% of its area, preferably less than 2%, particularly preferably less than 1%, measured in accordance with ASTM D1003, whereby the light emitted by the backlight (2) at least in the operating mode B2 in a restricted angular range is only slightly scattered when passing through the optical waveguide (3),  wherein furthermore the decoupling elements (6) are distributed on at least one of the large areas and / or within the volume of the light guide (3) such that the decoupling of the light originating from the light sources (4) from the light guide is at least 80% on one of the large areas the light guide (3) is performed, and  wherein in the operating mode B2 the backlight (2) is on and the lighting means (4) are switched off, and wherein in the operating mode B1 at least the lighting means (4) are switched on. 16. Use of a screen (1) according to any one of claims 1 to 14 in a vehicle for selectively displaying image content only for the passenger in the mode B2 and at the same time for the driver and the passenger in the mode B1.