EP3440503A1

EP3440503A1 - Screen for a free viewing mode and a restricted viewing mode

Info

Publication number: EP3440503A1
Application number: EP17822296.4A
Authority: EP
Inventors: Uwe Schroeter; Juergen Schwarz; Ambrose Peter Nari; Markus Klippstein; Stepan Alkhimenko; André HEBER
Original assignee: SiOptica GmbH
Current assignee: SiOptica GmbH
Priority date: 2017-06-30
Filing date: 2017-12-21
Publication date: 2019-02-13
Also published as: KR102265117B1; WO2019002496A1; JP2020525972A; WO2019001755A1; WO2019001756A1; KR20200022438A; EP3545359B1; BR112019025000A2; EP3440502A1; US20190353838A1; IL270947B; DE102017006285A1; AU2018292146A1; AU2018292146B2; IL270947A; JP6839397B2; CN110692011A; TWI705284B; TW202001378A; EP3545359A1

Abstract

The invention relates to 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. The screen (1) comprises an image display unit (2), at least one plate-shaped transparent light guide (3) positioned in front of the image display unit (2) in the viewing direction, and lamps (4) which are arranged laterally on narrow sides of the light guide (3). The lamps (4) are switched off in operating mode (B1), such that the light that is emitted from the image display unit (2) passes through the light guide (3) substantially unaffected. The lamps (4) are switched on in operating mode (B2). Due to the decoupling elements (5) of the light guide (3) on the large surface of the light guide (3) facing away from the image display unit (2), a light radiation characteristic is generated, in which the average luminance - measured at angles α to the surface normal of this large surface of the light guide (3), where 0° ≤ α ≤ θ, where 10° ≤ θ ≤ 60° - is lower by at least one factor X, where X ≥ 1.2, than the highest measurable luminance of the same large surface of the light guide (3) radiated at angles α > θ to the surface normal. The light passing through the light guide (3) is only minimally scattered. As a result, in operating mode (B2), the light emitted by the image display unit (2) is superimposed by light that is extensively emitted by the light guide (3) over a large angular range, whereby the visibility of the image information represented on the image display unit (2) is reduced or even prevented from viewing angles α > θ.

Description

title

Screen for a free and restricted view mode

Field of the invention

In recent years, much 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.

State of the art

Supplementary films based on micro-fins have already been used for mobile displays in order to achieve their optical privacy - a so-called privacy mode. 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 and 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. US 2009/0067156 discloses a variety of ideas for designing a lighting system and a display device. The variant depicted 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 compellingly generates a wide illumination angle and the front backlight 38 compellingly produces a narrow illumination angle should. 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 transformed 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", ie light with a narrow illumination angle, The light of the light guide 48 only becomes complicated by prismatic structures to be created sub-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. This has the consequence that, depending on the parameters, the brightness - with respect to the luminance - is reduced by a factor of 5 or more. 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. 17 in 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 already noted above - greatly brightness-reducing. According to JP 2007-1 55783, special optical surfaces 19 that are difficult to calculate and to be produced are used, which then deflect light into different narrow or wide regions depending on the angle of light incidence. 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 teaching of GB 2428128 A, additional light sources, which are clearly removed from the screen and illuminate a hologram mounted on the screen, are used to superimpose the side view with specific wavelengths in order to obtain a restricted view. The disadvantage here is the required distance of the light sources from the screen and the effort to produce appropriate holograms.

US 2013/0308185 describes a special optical fiber designed with steps, which emits light in a large area in different directions, depending on which direction it is illuminated from a narrow side. In interaction with a transmissive imager, 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 for top / bottom, but not for left / right / up / down can be generated simultaneously, as it is necessary for determi mt payment transactions. In addition, even in the restricted viewing mode from blocked viewing angles still a residual light is visible.

Finally, DE 10 2014 003 298 A1 describes a method and arrangement for optionally limiting the recognizability of images. For this purpose, a special optical element is necessary, which is at least 70% transparent to the light emanating from the screen, and which deflects laterally incident light from light sources into a restricted angular range in such a way that in directions α greater than γ with γ> 20 ° to the surface normal of the screen, the light emanating from the screen is superimposed with the light deflected by the optical element, whereby substantially the image displayed on the screen only from angles β <γ to the surface normal of the screen is fully visible.

The abovementioned methods and arrangements generally have the disadvantage that they significantly reduce the brightness of the basic screen and / or require an active, but for the time being a special, optical element for mode switching and / or require complex and expensive manufacture and / 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 reliable display of information can be realized by an optionally restricted viewing angle, wherein in a second 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, only the least possible or no loss of light should be introduced through the solution. The solution should also preferably be placeable in front of the screen so that it can be used for as many types of screens as possible, such as LCD and OLED.

This object is achieved 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. Such a screen comprises an image display unit, one or more in the viewing direction in front of the image display unit located, plate-shaped and transparent optical fibers, which consist of a transparent, thermoplastic or thermoelastic plastic or glass, as well as light sources, which usually laterally on at least one of Narrow sides of the light guide are arranged. The image display unit is arranged behind the light guide in the viewing direction.

In operating mode B1, the lighting means are switched off, so that the light emanating from the image display unit, onto which image information is modulated, passes through the light guide substantially unaffected. In mode B2, the bulbs are switched on. In this case, due to arranged on at least one of the large surfaces and / or in the volume of the light guide decoupling elements on at least one of the major surfaces of the light guide generates a light emission characteristic in which the average luminance measured at angles α to the surface normal of at least one large area of the light guide with 0 ° <α <Θ, with 10 ° <Θ <60 ° by at least a factor X, with X> 1, 2, smaller than the highest measurable luminance of the same large area F1 of the optical fiber, which at angles α> Θ to the surface normal is emitted. In other embodiments, the factor X may be> 2.5 and / or the angle Θ may be 10 °, 30 °, 30 °, 45 ° or other reasonable value. In preferred embodiments, the haze value of the light guide (s) is less than 2%. The number of outcoupling elements is selected in their number per area and in their extent such that the light guide has an average Haze value of at least 80% of its area 7%, preferably less than 2%, measured in accordance with ASTM D1003, whereby the light emanating from the image display unit and passing through the light guide (3) is only slightly scattered; Furthermore, the decoupling elements are distributed on at least one of the large surfaces and / or in the volume of the light guide, that the extraction of the light originating from the light sources from the light guide to at least 80% on or from one of the large surfaces of the light guide is performed.

As a result, in the operating mode B2, the light emanating from the image display unit, onto which image information is modulated, is superimposed by light which the optical waveguide broadcasts over a large angular range, whereby the visibility of the image information represented on the image display unit is reduced from viewing angles α> Θ even prevented.

The size X can be chosen differently here and in the following embodiments of the invention, such as X> 4, 5, 6, 1 0, 20, 50, 1 00 or even larger. It is a measure of how much more the light guide emits light compared to the light radiated in the surface normal direction in "lateral" viewing angles, in particular, the angle Θ can also be predetermined as a function of the amount of light, ie the angle Θ can be influenced by the incident light quantity ,

In an advantageous embodiment of the screen according to the invention, the bulbs switched on in mode B2 generate at least one of the narrow sides of the light guide on at least one of the large surfaces F1 of the light guide a light emission characteristic which in the angular range 0 ° <α <30 °, an average luminance which is smaller by a factor X with X> 2.5 (or also greater than 4, 5, etc.) than the highest measurable (individual) luminance in the angular range 30 ° <α <90 ° to the surface normal. Ideally, at least one of the large surfaces F1 of the optical waveguide would have a light emission characteristic in which almost no light is coupled out in the angular range 0 ° <α <30 ° to the surface normal and at 30 ° <α <90 ° in the angular range Surface normal light with a luminance that is as nearly as high or even higher than the luminance of the screen in this direction is radiated. This ideal case is practically impossible to realize.

The angle α can be measured in any embodiment of the invention along the horizontal, the vertical and / or another direction of the screen, but always to the surface normal. For example, if the default conditions are for horizontal and vertical angle measurement, the screen in B2 mode can not be viewed from oblique angles from left, right, top and bottom. However, if the given conditions apply only to a horizontal angle measurement, the screen may be in the operating mode B2 only from oblique angles are not seen from left and right. From above and below, however, viewing is usually possible.

The Auskoppelemente - they have maximum dimensions of 100 μιη in each room direction, preferably the dimensions between 1 μιη and 15 μιη - preferably consist of microlenses and / or microprisms and / or diff raktive structures and / or structural elements and / or scattering elements.

However, the decoupling elements can also have only the outer shape of microlenses, microprisms 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; he is preferably higher. Technically, the cavities can also be formed if one forms the light guide of 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 interfaces. Thus, if the decoupling elements are mounted on at least one of the large surfaces of the light guide, they are advantageously formed from a plastic structured with a tool whose structure has been embossed by 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 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, -umwandelnd, -abtragend or -auflösend. For example, lattice structures, microprisms (either convex with plastic component on the surface facing outward, and / or concave as an imprint or recess within the surface layer of the structured plastic) or else microlenses can be implemented inexpensively and with mass production capability. Overall, a higher (relative) brightness of the light originating from the optical waveguide with respect to the light originating from the image reproducing unit at angles which are to be blocked for the view is essential for the invention, whereas the ratios should be exactly the opposite with non-blocked angles That is, from such viewing directions, the light of the image display unit should be stronger than the overlapping light from the light guide.

Further, the plate-shaped light guide has at least two opposing large surfaces, which are arranged parallel or inclined to each other. A wedge-shaped structure is also possible, although parallel large areas are advantageous. Sensible thicknesses of the light guide are typically between 0, 1 mm and 4 mm inclusive. Other thicknesses may also be appropriate case-related.

For all embodiments, the image display unit may be, for example, an LCD, OLED, plasma display, FED screen, SED screen, VFC screen or other type of screen. The image display unit - also referred to as an imager - but can also be static in nature, such as a backlit slide or even a printed image. Other variants are possible. Furthermore, it can bring advantages if on the upper side of the image display unit and / or on at least one of the large surfaces of the light guide means for reflection reduction, such as an antiglare and / or an antireflective coating, are arranged. In particular, an anti-glare coating in connection with the invention not only serves to reduce the direct reflections of external light spots, but rather also permits the scattered back reflection of the light, if any, emitted to the image display unit by the light guide in front of the image display unit.

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

In a preferred embodiment, the screen comprises further optical fibers. Particularly advantageously, at least one further light guide is arranged in front of the light guide in the direction of observation. Extending elements are arranged or formed on one of the large surfaces and / or in the volume of the optical waveguide and of the further optical waveguide, illuminants being arranged on a narrow side of the optical waveguide and on the narrow side of the further optical waveguide opposite this narrow side, and an asymmetrical light through the decoupling elements -Abstrahlcharakteristik is given such that the light from that large surface of the light guide and the other light guide, which in each case is in front of viewing, is emitted in the lying in the beam direction quarter space. Although this asymmetrical light emission characteristic requires at least two light guides for the optional blocking of the oblique view in mode B2, it can under certain circumstances be implemented favorably in relation to the outcoupling elements.

As decoupling elements it is generally possible, for example, to use holographic structures or other microstructures which, for example, can also be etched into the surface of the optical waveguide. The asymmetrical light emission characteristic manifests itself, for example, in the fact that, in the case of light radiated into the light guide from a left narrow side, light is radiated into the quarter space formed by the surface normal of the respective large surface of the light guide and the irradiation direction, ie away from the light source, however (almost) not in the backward direction. The emission range can be, for example, in the range of 20 ° to 80 ° to the surface normal. In a further, preferred embodiment, the lighting means are designed to emit colored light. By colored light is meant, in particular, visible light which is not white, e.g. Light in the colors red, green, blue, turquoise, yellow, cyan or magenta. 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 is also time modulated, such as in color and / or brightness. In addition, the bulbs can also be implemented with different individual light sources or luminous elements, such as RGB LEDs in LED rows, the same time or offset in time and / or spatial Lich each radiate light of different colors and / or different brightness.

In operating mode B2, the visible image, depending on the design of the lighting means, is a correspondingly colored surface, but usually not just a black or white surface, because the colored light emitted by the light guide is oblique, blocked by the angle restriction. From oblique viewing direction even a bright picture content visible outshines. Without the use of colored Leuchtm itteln the perceptible image depending on the design of the light source and the light guide is a gray or white surface, but usually not a black area, since the light emitted by the light guide, even a black image content outshines visible , The bulbs can emit light in a color that does not occur in the image displayed by the transmissive imager. Alternatively, the luminescent means can emit light in a color which is present in the image represented by the transmissive image reproduction unit or in the color spectrum is close to such a color. In addition, the illuminants can light in one Blend color that corresponds approximately to the complementary color of a color that occurs in the image displayed by the image display unit.

The screen according to the invention is particularly advantageously used for entering or displaying confidential data, for example PIN PIN numbers, e-mails, SMS or passwords, at ATMs, payment terminals or mobile devices.

For all embodiments, it holds true that each available light guide has at least one light entry surface and at least one light exit surface, wherein the ratio of light exit surface to light entry surface is at least 4.

Basically, the performance of the invention is maintained when the parameters described above are varied within certain limits. 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 could be a larger angle or possibly no restriction sense, as in the horizontal direction, such as when ATMs with different sizes should see something, while the page view should remain severely limited. For POS payment terminals, on the other hand, due to safety regulations, visual restrictions are often necessary in operating mode B2 both in the horizontal and in the vertical direction.

The invention works particularly well when, in the restricted-mode B2, i. when the bulbs are on, the image displayed on the screen is dimmed to some degree. Thereby, the superimposing effect of the light originating from the image, because it now has a lower light intensity, is amplified by the light emitted by the light guide, so that the visual impairment effect is improved. In order to further improve the visual restriction in this case, e.g. text displayed as a picture on the screen instead of black and white in black and gray.

Furthermore, the optical waveguides can contain at least 40% by weight, preferably at least 60% by weight, of polymethyl methacrylate, based on their weight. 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 for example with reference to the accompanying drawings, which also disclose characteristics essential to the invention. Show it

1 is a sectional view for the extraction of light, which is laterally coupled into an optical waveguide, with a defined radiation characteristic,

2 is a sectional view for the passage of light, which results from an image display unit, through a light guide,

3 shows a sectional view of a screen in the operating mode B2 for a restricted viewing mode, in which the light modulated by the imager is superimposed by light from a light guide in order to achieve the visual protection effect.

Fig. 4 is a sectional view of the screen in the mode B1 for a free viewing mode, wherein the light modulated by the imager is not superimposed by light from the optical fiber, and

Fig. 5 is a luminance curve for ideal Auskoppelverhältnisse of the light guide.

The drawings are not to scale and represent only schematic representations, including sectional representations, again.

Detailed description of the drawings

In Fig. 1 is a schematic diagram for decoupling of light, the side of light sources 4 in a light guide 3 - shown here only as a small section in sectional view - is coupled, with a defined radiation characteristic represented. The small dots stylize decoupling elements 5 for the light, which is coupled laterally from the bulbs 4. Due to total reflection, rays of the coupled-in light (bold lines) are thrown back into the light guide 3 on the outer wall, until they finally encounter decoupling elements 5 for the desired decoupling. The decoupling is stylized by the cluster of five thin beams per decoupling elements 5: The long beams are at angles to the side for a stronger light decoupling in angular ranges, which are stronger from the surface normal of the optical fiber 3 away. The shorter rays stylize that even less light is coupled out in angular regions that are closer to the surface normal of the optical waveguide 3, while the minimum of light in the surface normal direction of the optical waveguide 3 is coupled out, indicated here by the shortest upward arrow. The illustration in Figure 1 is highly stylized for better visibility; In reality, a very large number of beam paths and scattering particles 5 in the light guide 3 is implemented. Fig. 2 shows a schematic diagram for the passage of light, which originates from a (not shown here) image display unit 2, through a light guide 3. The decoupling elements 5 in the light guide 3 play a substantially negligible role, since the light from the backlight the image display unit 2 is derived, that is not laterally coupled by a narrow side of Leuchtm itteln 4 and therefore not or hardly by total reflection in the light guide 3 is directed back and forth. Similarly, in the mode B1, the image information modulated onto the light from the image display unit 2 is passed through the light guide 3 almost unaffected.

3 shows a schematic diagram of a screen 1 in the operating mode B2 for a restricted viewing mode, in which the light modulated by the image display unit 2 is superimposed by light from the light guide 3 to obtain the privacy effect. Shown in FIG. 3 is an image display unit 2, for example an LCD or OLED display, a plate-shaped, transparent optical waveguide 3 located in the viewing direction in front of the image display unit 2 with an average haze value of less than 7%, measured according to ASTM D1003, and illuminant 4, FIG are arranged laterally on a narrow side of the light guide 3, advantageously more Leuchtm means 4 are mounted on the opposite narrow side. As illuminants, for example, preferably cool white LEDs, eg. B. in line arrangement, in question.

In the operating mode B2, the illuminants 4 are switched on, so that, due to decoupling elements 5 arranged or formed on at least one of the large surfaces and / or in the volume of the light guide 3, at least one of the large surfaces - in this case the upper large surface area - of the light guide 3 a light emission characteristic is produced in which the average luminance measured at angles α to the surface normal of at least one large surface of the light guide 3 with 0 ° <α <Θ, with 10 ° <Θ <60 ° at least a factor X, With X> 1, 2, smaller than the highest measurable luminance - this means the highest measurable single value - the same large area of the light guide 3, which is radiated at angles α> Θ to the surface normal. The angle α may, for example, be 10 °, 20 °, 30 °, 45 ° or any other meaningful value. The decoupling elements 5 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%, preferably less than 2%, at least 80% of its area, measured in accordance with ASTM D1003. whereby the light emanating from the image display unit 2 and passing through the light guide 3 is only slightly scattered; Furthermore, the decoupling elements 5 are distributed on m at least one of the large surfaces and / or in the volume of the light guide 3, that the coupling out of the light originating from the light sources 4 from the light guide 3 is carried out to at least 80% on one of the large surfaces of the light guide 3.

As a result, in the operating mode B2, the light emanating from the image reproduction unit 2-shown in FIG. 3 as thick, light arrows-to which image information has been modulated, is superimposed by light, which the light guide 3 radiates in a planar manner, based on FIG. 2 here shown with thin arrows of different lengths. Thus, the visibility of the image information displayed on the image display unit is reduced or even prevented from viewing angles α> Θ.

The angle α can be measured here along the horizontal, the vertical and / or another direction of the screen 1, but always to the surface normal. For example, if the predetermined conditions for a horizontal and vertical angle measurement apply, the screen 1 in the operating mode B2 can not be viewed from oblique angles from left, right, up and down. However, if the predetermined conditions apply only to a horizontal angle measurement, the screen 1 in the B2 mode can only be viewed from oblique angles from the left and right. From above and below, however, viewing is usually possible. In contrast, Fig. 4 shows a schematic diagram of the screen 1 in the mode B1 for a free viewing mode, wherein the modulated by the image display unit 2 light (thick, bright arrows) is not superimposed by light from the light guide 3, because now the Leuchtm mediate 4 off are. In order for the light of the image display unit 2 to pass through the light guide 3 substantially uninfluenced, it reaches the viewer (s) substantially unaffected.

The o.g. Size X can be chosen differently here and in other embodiments, such as X> 2.5 or X> 4, 5, 6, 10, 20, 50, 100 or even larger. It is a measure of how much more the light guide emits light in "lateral" viewing angles compared to light radiated in surface normal.

5 shows by way of example the profile of the relative luminance as a function of the angle to the surface normal for ideal outcoupling ratios of the optical waveguide 3 in this case, for an angle Θ = 30 °. In such an ideal case, a light emission characteristic would prevail on at least one of the large surfaces of the light guide 3, in which almost no light is coupled out in the angular range 0 ° <α <30 ° to the surface normal, and in the angular range 30 ° <α <90 ° to the surface normal light with a luminance as nearly as possible or preferably even higher than luminance of the screen 1 in this direction, is emitted. This ideal case is practically impossible to realize.

In the operating mode B1, the lighting means 4 are switched off, so that the light emanating from the image reproduction unit, onto which image information is modulated, passes through the light guide 3 substantially uninfluenced.

In the operating mode B2, however, which is not shown separately in the drawing, the illuminants 4 are switched on, so that the light emanating from the image reproduction unit, onto which image information is modulated, is superimposed by light which the light guide 3 emits flatly, as a result the visibility of the image information displayed on the image display unit 2 is reduced or even prevented from viewing angles α> Θ. All in all, a higher relative brightness of the light originating from the light guide 3 relative to the light originating from the image reproduction unit 2 at angles which are to be blocked for the view, while at non-blocked angles, the conditions are exactly the opposite, that is. From such viewing directions, the light of the image display unit 2 should be stronger than the overlapping light from the light guide 3.

Furthermore, the plate-shaped light guide 3 has at least two opposing large surfaces, which are arranged parallel or inclined to each other. A wedge-shaped structure is also possible, although parallel large areas are advantageous. Sensible thicknesses of the optical fiber 3 are typically between 0.1 mm and 4 mm inclusive. Other thicknesses may also be appropriate case-related. For all embodiments, the image display unit 2 can be, for example, an LCD, OLED, plasma display, FED screen, SED screen, VFC screen or another type of screen 1. However, the image display unit 2 may also be static in nature, such as a backlit foil or even a printed image. Other variants are possible. In all embodiments of the invention, the said bulbs 4 LEDs or LED rows or laser diodes can be. Other variants are conceivable and are within the scope of the invention. The light guides 3 described as part of a screen 1 can be placed on the front of the screen, so that it can be used for as many types of screens as possible, such as LCD and OLED. An intervention about in the backlight of LCDs is not necessary.

The screens described above allow solutions that are practical and well practicable in order to ensure secure presentation of information through an optionally limited viewing angle to realize while in another mode, a free, if possible in the viewing angle unrestricted view is possible. The invention can be realized inexpensively by simple means. In both modes, the native resolution of the imager used can be used. In addition, only a small or depending on the embodiment even almost no 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.

LIST OF REFERENCES

1 screen

2 image playback unit

3 light guides

3a, 3b layers of the light guide

4 bulbs

5 decoupling element

6 lamella shape

7 microlamels

B1 Operating mode for a free viewing mode

B2 Operating mode for a restricted viewing mode

Claims

claims

A screen (1) which can be operated in at least two modes B1 for a free viewing mode and B2 for a restricted viewing mode, comprising a picture display unit (2),

at least one in the viewing direction in front of the image display unit (2) located, plate-shaped, transparent light guide (3), which consists of a transparent, thermoplastic or thermoelastic plastic or glass, and

Illuminants (4) which are arranged laterally on narrow sides of the light guide (3), characterized in that

the image display unit (2) is arranged behind the light guide (3) in the viewing direction,

wherein in the operating mode B1 the lighting means (4) are switched off, so that the light emanating from the image display unit (2) onto which image information is modulated passes through the light guide (3) substantially uninfluenced, and in the operating mode B2 the lighting means (4) are turned on, and on at least one of the large surfaces and / or in the volume of the light guide (3) arranged or trained decoupling elements (5) on at least one of the major surfaces of the light guide (3) a light emission characteristic is generated, wherein the average luminance measured in angles α to the surface normal of the at least one large surface of the light guide (3) with 0 ° <α <Θ, with 10 ° <Θ <60 ° by at least a factor X, with X> 1,

2, smaller than the highest measurable luminance of the same large area F1 of the light guide (3), which is radiated at angles α> Θ to the surface normal,

wherein the decoupling elements (5) 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% on at least 80% of its area, measured in accordance with ASTM D1003, whereby the image display unit (2) outgoing and passing through the light guide (3) light is only slightly scattered, and

wherein furthermore the decoupling elements (5) are distributed on at least one of the large surfaces and / or in the volume of the light guide (3) such that the decoupling of the light originating from the light sources (4) from the light guide (3) amounts to at least 80% on one the large surfaces of the light guide (3) is performed,

such that in the operating mode B2 the light emanating from the image display unit (2) onto which image information is modulated is superimposed by light which the optical waveguide (3) radiates over a large angular range, whereby the visibility of the image display unit (2) displayed image information from viewing angles α> Θ reduced or even prevented. Screen (1) according to claim 1, characterized in that the Haze value of the light guide

(3) is less than 2%, and / or the angle Θ is 10 °, 30 °, 30 °, 45 °, and / or the factor X> 2.5.

Screen (1) according to one of claims 1 or 2, characterized in that the angle Θ can be predetermined as a function of the incident light quantity.

4. screen (1) according to one of claims 1 to 3, characterized in that the decoupling elements (5) maximum dimensions of 100 μιτι, preferably between 1 μιη and 15 μιη have.

5. Screen (1) according to one of the preceding claims, characterized in that the decoupling elements (5) consist of microlenses and / or microprisms and / or diffractive structures and / or structural elements and / or scattering elements.

6. screen (1) according to one of claims 1 to 5 with within the volume of the light guide (3) formed outcoupling elements (5), characterized in that the decoupling elements (5) are formed as cavities, which preferably the outer shape of microlenses, Have microprisms or diffractive structures.

7. screen (1) according to claim 6, 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.

8. screen (1) according to claim 6 or 7, characterized in that the cavities are filled with a gaseous, liquid or a solid material, wherein the material has a Haze value, which of the used for the light guide (3) Material deviates, preferably higher.

9. Screen (1) according to any one of claims 1 to 8, characterized in that the light guide (3) consists of two interconnected at interfaces, preferably similar substrate layers is formed and the cavities as material recesses on at least one of the interfaces, preferably the outer shape microlenses, microprisms or diffractive structures, are formed.

10. screen (1) according to one of claims 1 to 9, characterized in that the decoupling elements (5), if they are mounted on at least one of the large surfaces or interfaces of the light guide (3), from a with a tool, preferably mechanically, lithographically, by printing or material application, material removal, -um- converting or -auflösend, structured plastic are formed.

1 1. Screen (1) according to claim 1, characterized in that at least one further light guide is arranged in front of the light guide (3) in the direction of observation, and at one of the large surfaces and / or in the volume of the light guide (3) and the further light guide Decoupling elements (5) are arranged or formed, wherein lighting means (4) are arranged on a narrow side of the light guide (3) and on the opposite narrow side of this narrow side of the further light guide, and wherein predetermined by the decoupling (5) an asymmetric light emission characteristic is that the light in each case from that large surface of the light guide (3) and the further light guide, which in each case in the viewing direction is located in front, in the direction of incidence

Quarter space is radiated.

12. Screen (1) according to one of claims 1 to 1 1, characterized in that the lighting means (4) radiate light in a color which does not occur in the image display unit (2) represented image.

13. Screen (1) according to one of claims 1 to 1 1, characterized in that the lighting means (4) radiate light in a color which occurs in the image displayed by the image display unit (2) or in the color spectrum close to such a color lies.

14. Screen (1) according to one of claims 1 to 1 1, characterized in that the lighting means (4) emit light in a color which is approximately the complementary color of a color, which occurs in the image displayed by the image display unit (2), equivalent.