Lighting device for free and restricted viewing modes

Abstract

The present invention relates to an illumination device (1a) for a screen (1) capable of operating in at least two modes, namely, a mode B1 for a free viewing mode and a mode B2 for a restricted viewing mode, in which light is emitted from the illumination device within a restricted angular range relative to the free viewing mode. The illumination device includes a planar backlight element (2) emitting light within a restricted angular range; and a plate-shaped light guide (3) located in front of the backlight element (2) in the viewing direction, the light guide having two large faces and a narrow face, the narrow face connecting to the large faces at its edges, wherein the light guide (3) has a coupling output element (6) on at least one large face and / or within its volume, the light guide (3) being at least 50% transparent to light emitted by the backlight element (2), wherein each coupling output element (6) has at least one functional surface for definingly coupling output light, at which light is coupled out from the light guide (3). Furthermore, the lighting device also includes a light-emitting mechanism (4) arranged laterally on a narrow surface of the light guide (3). In operation mode B2, the backlight illuminating element (2) is turned on and the light-emitting mechanism (4) is turned off, while in operation mode B1, at least the light-emitting mechanism (4) is turned on. According to the invention, at least a portion of the coupling output element (6) has a special structure such that the light guide (3) has a scattering characteristic in a predetermined preferred direction that is at least 1.2 times the scattering characteristic in a direction perpendicular to the preferred direction, thus the overall scattering characteristic is anisotropic.

Description

Technical Field

[0001] Significant progress has been made in recent years in terms of viewing angle extension for LCDs. However, there are often situations where this very large viewing area of ​​the screen can be disadvantageous. Mobile devices such as laptops and tablet PCs also provide an increasing amount of information, such as banking data or other personal and sensitive data. Therefore, there is a need to monitor who can see this sensitive data; people must be able to choose between wide viewing angles to share information with others on their displays, such as when viewing vacation photos, or also for advertising purposes. On the other hand, if they want to handle image information confidentially, they need a narrow viewing angle.

[0002] A similar problem arises in vehicle architecture: the driver should not be distracted by visual content, such as digital entertainment programs, while the passenger wants to consume that content while driving. Therefore, a screen capable of switching between appropriate display modes is needed.

[0003] Microlayer-based additional films have been used in mobile displays to achieve their optical data protection. However, these films cannot be (re)switched; they must always be applied by hand and then removed. If they are not needed, they must also be transferred to the display separately. Furthermore, a major drawback of using such thin films is associated with the resulting light loss. Background Technology

[0004] Document US5,956,107A discloses a switchable light source that enables a screen to operate in multiple modes. However, a disadvantage is that all optically coupled outputs are based on scattering, resulting in low efficiency and suboptimal light direction effects. Furthermore, the method of achieving a focused light cone is not disclosed in detail.

[0005] CN107734118A describes a screen whose viewing angle can be controllably designed by means of two backlight illuminators. The upper backlight illuminator of the two backlight illuminators is intended to emit focused light for this purpose. As a construction for this, a grille having opaque and transparent sections is specifically mentioned. However, the same situation leads to the result that the light from the second backlight illuminator (which must pass through the first backlight illuminator in the direction of the LCD panel) is also focused, and therefore the common viewing mode originally designed for a wide viewing angle suffers a significant reduction in angle.

[0006] US2007 / 030240A1 describes an optical element for monitoring the direction of light propagation originating from a backlight illumination element. This optical element, for example, requires a liquid crystal in the form of a PDLC, which is expensive on the one hand, but important for safety, especially for consumer applications, because PDLC liquid crystals typically require voltages higher than 60V for their conversion.

[0007] CN1987606A further describes a screen whose viewing angle can be controllably designed using two backlighting elements. Here, a "first light plate" is specifically used, which must be wedge-shaped to achieve intentionally focused light-coupled output. Precise details regarding achieving focused light-coupled output with the corresponding angular conditions are not disclosed.

[0008] Furthermore, US2018 / 0267344A1 describes a structure with two flat illumination modules. Here, light from the rear-mounted illumination module along the viewing direction is focused by a separate structure. After focusing, the light must also pass through the front illumination module with scattering elements. Therefore, the strong light focusing is not optimal for visual protection.

[0009] Finally, US2007 / 0008456A1 discloses dividing the light emission angle into at least three regions, of which light is typically applied to two. Therefore, visual protection using a display illuminated in this manner cannot be achieved by viewing from only one direction.

[0010] The applicant's WO2015 / 121398A1 describes a screen of the type described at the beginning. Here, to switch operating modes, necessary scattering particles are present in the volume of the corresponding light guide. However, the scattering particles, composed of polymers, chosen there typically have the disadvantage that light is coupled out from two large surfaces, resulting in approximately half of the effective light being emitted in the wrong direction, i.e., toward the backlight element, and thus not being able to be recovered within a sufficient range due to the construction. Furthermore, the scattering particles, composed of polymers, distributed in the volume of the light guide can cause scattering effects, especially at higher concentrations, which reduce the viewing protection effect in the protected operating mode.

[0011] US2020 / 012129A1 discloses an illumination device and a screen, which describes two lights for switching between a narrow viewing mode and a wide viewing mode. Here, one of the light guides is constructed with fibers. On the other hand, the scattering coupling output structure of the light guide is confined to a specific strip in the projection direction. This is detrimental to uniform image illumination and generally also causes undesirable moiré effects in the construction, such as interactions with the pixel columns or rows of the LCD panel located thereon.

[0012] The methods and apparatus described above typically have the following drawbacks: they significantly reduce the brightness of the base screen and / or require active, at least special, optical elements for mode switching, and / or require costly and expensive manufacturing and / or reduce the resolution in freely viewable modes. Summary of the Invention

[0013] Therefore, the object of this invention is to introduce a lighting device that, in conjunction with a screen, enables reliable display of information with a selectively limited viewing angle, while in another operating mode, allows for free and as unrestricted viewing as possible. This invention should be achievable with simple means and at the lowest possible cost. In both operating modes, the highest possible resolution should be visible, particularly preferably the native resolution of the screen used. Furthermore, this solution should introduce only the least possible light loss, and the limited viewing angle should provide the most comprehensive possible viewing protection.

[0014] According to the invention, this objective is achieved by an illumination device for a screen, which is capable of operating in at least two modes: mode B1 for a free viewing mode and mode B2 for a restricted viewing mode, in which light is emitted by the illumination device within a limited angular range relative to the free viewing mode. Here, the illumination device includes a planar backlight element and a plate-shaped light guide located in front of the backlight element in the viewing direction. The backlight element emits light within a limited angular range. The light guide has two large surfaces and a narrow surface, with the narrow surface connecting to the large surfaces at its edges. The light guide has a coupling output element on at least one of the large surfaces and / or within its volume, and is at least 50% transparent to light emitted by the backlight element, but preferably at least 70%. A light-emitting mechanism is laterally disposed on the narrow surface of the light guide, which also includes the light-emitting mechanism being disposed only on one side of the light guide. In mode B2, the backlight element is turned on and the light-emitting mechanism is turned off, while in mode B1, at least the light-emitting mechanism is turned on. The shape, number per unit area, orientation, and / or extension of the coupling output element are selected such that the light guide (adjusted via the coupling output element or at least a portion thereof) has anisotropic scattering characteristics for light passing through a large surface area of ​​the light guide.

[0015] Specifically, this means that each coupling output element has at least one functional surface for defining the coupling of output light, on which light is correspondingly coupled out from the light guide. These functional surfaces are, in their simplest case, flat or have at least flat surface segments, but can also be surfaces curved in one or two linearly independent directions. Now, an orientation vector is defined for the functional surface, which is parallel to the large surface from which the light is emitted, that is, located in a plane parallel to said large surface. This orientation vector is a vector that maximizes the integral of the dot product of the vector and the position-dependent normal vector of the functional surface with respect to the functional surface. For a flat surface, the normal vector is, of course, constant at every position of the functional surface; however, for a curved surface, the normal vector varies, thus involving the normal vector of the tangent at the corresponding position. Specifically, the orientation vector... Make integration Maximize, where This is the normal vector of functional surface A, dependent on its position at coordinates x and y. This orientation vector now forms an angle of up to 45° with a predetermined preferred direction. The normal vector here forms an angle of up to 85° with the associated large surface from which light is emitted, however, preferably with a lower limit of 30° and / or an upper limit of 60°.

[0016] If the coupled output element is designed in this way, it results in the light guide having a scattering characteristic in the preferred direction that is at least 1.2 times that in the direction perpendicular to the preferred direction, and therefore, anisotropic scattering characteristics for light passing through the two large surfaces of the light guide in general.

[0017] As a limited angle range, in principle each of the following ranges can be considered, said range being less than half the space in front of the backlight illuminator; however, preferably, for example, an angle range of + / -20° or 30° is horizontal and / or vertical or as a cone around the surface normal or as a selectable direction vector on the backlight illuminator; when defining the limited angle range, a small amount of light less than 1% to 5% of the maximum brightness can be disregarded.

[0018] The lighting device can also additionally include a collimating film at an appropriate location in the structure, such as a lens grating or prism grating above or below the plate-shaped light guide.

[0019] Advantageously, the relevant portion of the coupled output element comprises at least 30% of all coupled output elements, preferably at least 50%, 70%, or 90% of all coupled output elements. Additionally or alternatively, for the average of all coupled output elements, the orientation vector and the preferred direction form an angle with a maximum value of 45°, that is, an angle between -45° and +45°.

[0020] Preferably, the light guide has stronger scattering characteristics in the preferred direction than in the opposite direction. This is achieved by a correspondingly asymmetrically shaped coupling output element. More precisely, if the scattering characteristics are the same in the preferred direction and perpendicular to the preferred direction without a coupling output element, then the cross-section of the coupling output element should be asymmetrical in a section parallel to the preferred direction; in the case of achieving even stronger scattering characteristics in the preferred direction, a coupling output element with a symmetrical cross-section can also be used. An asymmetrical cross-section in the preferred direction is also a prerequisite for achieving different scattering characteristics in and opposite to the preferred direction.

[0021] The anisotropic scattering characteristics of the coupled output element are characterized by measurements of scattering characteristics along at least two mutually perpendicular directions (the preferred direction and the direction perpendicular to it). Here, the scattering characteristics caused by the coupled output element when light passes approximately perpendicularly through the optical guide should be considered.

[0022] Advantageously, when an observer views the lighting device, the preferred direction corresponds to the vertical direction, thus the scattering characteristics of the light guide in the vertical direction are greater than those in the horizontal direction. The terms "vertical" and "horizontal" here primarily refer, first and foremost, to two mutually perpendicular directions on the surface of the backlighting element or the large surface of the light guide, which, in operation, correspond to the actual horizontal or vertical direction with respect to the observer's position and, consequently, the position of the ground, depending on the orientation of the screen, which is typically fixed and used with the lighting device. The horizontal direction generally extends parallel to the line connecting the observer's eyes, that is, ultimately depends on the observer's orientation in space.

[0023] Particularly preferred is that the ratio of the area of ​​the functional surface to the area of ​​the large surface of the aforementioned portion of the coupled output element is determined such that the scattering characteristics of the coupled output element in the preferred direction are at least two or three times greater than the scattering characteristics in the direction perpendicular to the preferred direction. However, this anisotropy can vary on the surface of the plate-shaped light guide. The anisotropy at high-density locations of the coupled output element is generally higher than that at low-density locations. For this purpose, the large surface from which light exits is divided into sub-regions of predetermined size, wherein the ratio of the area of ​​the functional surface to the area of ​​the corresponding sub-region is different for different sub-regions, thereby varying the scattering characteristics of the light guide on the large surface from which light exits.

[0024] In a preferred design of the lighting device, the light emitted by the backlight element, at least in operating mode B2, is emitted in a limited angular range in the horizontal direction, such that the light experiences less scattering in the horizontal direction than in the vertical direction when passing through the light guide. Thus, the light emitted within the limited angular range is typically scattered at most slightly outside the limited angular range, which is beneficial for visual protection. This is a significant advantage of the invention.

[0025] "Slightly" can be understood, for example, as meaning that due to the small scattering characteristics, the light density increases by a maximum of 3% due to scattering by the light guide at an angle of, for example, 40° horizontally to the surface normal or in other predetermined directions measured along the horizontal direction, while the illumination device emits light at an angle of 0°. In another design that can be combined with the first design, "slightly" means that less than 10% of the light is scattered within a spatial angle range of + / -20° in the preferred direction and within a spatial angle range of + / -10° in the direction perpendicular to the preferred direction. The haze value should also preferably be less than 15%.

[0026] However, the opposite can also be true: if the light originating from the backlight is too strongly focused within a limited horizontal angle range, then selectively fanning out the light can result in stronger scattering characteristics in the horizontal direction (compared to the vertical direction). Furthermore, the anisotropic scattering characteristics of at least a portion of the coupled output elements (or all coupled output elements) can contribute to visible superposition (e.g., the moiré effect), which can occur in the interaction between the components of the lighting device and / or with the screen.

[0027] To quantify the scattering characteristics along the two preferred axes, a "bidirectional transmission distribution function" (BTDF) is used. The BTDF quantifies how scattering occurs at a specific incident angle (H). i V i Light that is considered scattered. All light that is considered scattered has a deflection greater than 5°. Therefore, in order to determine the metric S of horizontal scattering... H (That is, the horizontal scattering characteristics), the measured BTDF is integrated accordingly. Similarly, the metric S for vertical scattering is determined. V (i.e., vertical scattering characteristics). The lower limit of integration, i.e., the angle at which light is considered to be scattered, should be chosen to be greater than 1.8° of the usual haze measurement value, because BTDF measurements can be performed with a laser beam that typically has a divergence of 4°.

[0028] The following is given for determining parameter S. H and S V Integrals:

[0029]

[0030]

[0031] Where H is the horizontal angle and V is the vertical angle, used to measure transmittance. i V i and are the angles at which the light beam is incident on the object being measured (here, and are respectively 0°). Therefore, in this scheme, the scattering characteristic S V / S H The anisotropy required by the present invention can be expressed as follows: S V / S H ≠1 or for frequently used applications S V / S H >1.

[0032] Table 1 below shows the normalized scattering S at different measurement points P1 to P5 on the plate-shaped light guide. H and S V Example values ​​for (i.e., scattering characteristics):

[0033] Table 1: Scattering S H and S V Exemplary standardized values

[0034] P1 0.037 0.139 3.757 P2 0.030 0.210 7.000 P3 0.054 0.372 6.889 P5 0.066 0.490 7.424 P4 0.083 0.598 7.205

[0035] The anisotropy S V / S H This indicates the intensity of the scattering characteristics along the vertical direction. As mentioned above, scattering here is understood as a deflection greater than 5°. The anisotropic scattering characteristics are evident in this example.

[0036] Coupling output elements can, in principle, be matched to and pre-defined conditions for the coupling output of light during the fabrication of the light guide, and can be distributed in different ways within or on the light guide. Coupling output elements involve locally confined structural variations within and / or on the surface of the light guide. Therefore, the term "coupling output element" explicitly excludes additional optical layers applied to the surface of the light guide, i.e., such as diffuse layers, reflective layers, (dual) brightness enhancement layers, collimation layers (brightness enhancement films BEF), or polarization recycling layers, such as polarization-selective Bragg mirrors ((dual) brightness enhancement films (D)BEF) or wire-grid polarizers. These additional layers, which are not part of the term "coupling output element" (if present), are connected to the light guide only at the edges, and are mostly loosely arranged over large areas and do not form physical units with the light guide. Conversely, varnish applied to the large surface area and connected to the light guide by chemical reactions or other forces (e.g., van der Waals forces) forms physical units, and the varnish can no longer be separated from each other; therefore, such varnish is not considered an additional layer in the aforementioned sense.

[0037] The structure of the coupling output element is preset according to the standard as described above, wherein the function of each coupling output element is at least approximately known and the characteristics of the light guide or the light emitted from the light guide can be specifically determined by the preset structure and distribution of the coupling output element, wherein, in particular, the light is coupled out from the large surface, depending on the ratio of the sum of the areas of the functional surfaces to the total area of ​​the large surface.

[0038] The characteristics required for the coupling output element, which are important to the present invention, in terms of their number per unit area, their shape, their orientation and extension in three dimensions, and their distribution on at least one large surface of the light guide and / or within the volume of the light guide, can be determined, for example, using optical simulation software, such as Synopis' "LightTools" or other vendors, and then physically implemented accordingly.

[0039] Advantageously, the distribution of the coupling output elements on at least one large surface and / or within the volume of the light guide is preset such that the coupled output light achieves a brightness uniformity of 70% over at least 70% of the surface of the light guide. Brightness uniformity can here be defined as L... V min / L V max In other words, it is defined as the ratio of the minimum brightness to the maximum area. Another applicable rule for measuring brightness uniformity is defined in the "Uniform Measurement Standard for Displays V1.3" of the German Automotive OEM WorkGroup Display.

[0040] The difference between the two operating modes B1 and B2 is that in operating mode B2, the backlight illumination element is turned on and the light-emitting mechanism (on the narrow face of the light guide) is turned off, while in operating mode B1, at least the light-emitting mechanism (on the narrow face of the light guide) is turned on. Here, only light initially emitted into the light guide by the light-emitting mechanism and subsequently emitted by the light guide through the coupling output element is considered, where emission is achieved almost solely through the coupling output element.

[0041] It is feasible to place the coupled output element on two large surfaces and / or additionally optionally in the volume.

[0042] The light guide is preferably made of a transparent, thermoplastic, or thermoelastic polymer, such as plastic, or of glass. For example, the light guide or its substrate may comprise at least 40% by weight of polymethyl methacrylate, preferably at least 60% by weight. Alternatively, it may be, for example, polycarbonate (PC).

[0043] Furthermore, for some applications, it is advantageous that the defined angle range is designed asymmetrically with respect to the surface normal of the backlight element. Preferably, the asymmetrical construction takes place in one of the preferred directions. This is particularly advantageous in vehicle applications, for example, when a screen to be combined with the lighting device according to the invention is arranged in the dashboard as a so-called central information display, approximately midway between the driver and passenger. Thus, the limited angle range released only for the passenger in operating mode B2 must be designed asymmetrically for viewing, i.e., directed towards the passenger. The asymmetrical structure here corresponds to the horizontal direction along the preferred direction in which it is formed.

[0044] The coupling output element for coupling output light onto at least one large surface of the light guide preferably comprises microlenses and / or microprisms and / or diffraction structures and / or three-dimensional structural elements and / or scattering elements, wherein the coupling output element has a maximum extension of less than 100 micrometers, preferably less than 50 micrometers, in its maximum dimension. In the case of a diffraction structure, for example, a hologram or a grating / diffraction grating may be involved.

[0045] However, the coupling output element itself can also simply have the external shape of a microlens, microprism, scattering element, and / or diffraction structure. Thus, the coupling output element can be designed in particular as a cavity, which is then constructed within the volume of the light guide. The cavity can be airless, but is preferably filled with a gaseous, liquid, or solid material having a different refractive index than the material used for the light guide; the refractive index is preferably lower. The light conduction or optical coupling output can be influenced by the filling material and by the material selection. Alternatively or supplementarily, the haze value of the material is also preferably different from that of the material used for the light guide, preferably a higher haze value. The advantage of these embodiments is the high efficiency of the optical coupling output.

[0046] Alternatively, if the light guide is formed from two interconnected substrate layers, the cavity can also be formed more simply technically, preferably of the same type. This connection can be achieved chemically, physically, or adhesively. The cavity is then constructed as a material recess at at least one interface of the substrate layers.

[0047] When the coupled output element is mounted on at least one large surface of the light guide, these large surfaces are advantageously formed from plastic or glass structured using a tool, the structure being pressed by means of the tool. This can be achieved, for example, in mass production by applying a UV-curable material, such as varnish, monomer, etc., to the light guide substrate, which is structured by means of the tool and cured by UV radiation, such as polymerization. Other radiation-cured materials can also be used. The construction of the recesses for realizing the coupled output element can be achieved, for example, mechanically, photolithographically, or by printing techniques, or by coating, depositing, scraping, or decomposing the material.

[0048] Therefore, for example, grid structures, microprisms (or protruding plastic portions pointing outwards on a surface, and / or recessed portions or depressions within a structured plastic surface layer) can be realized inexpensively and with mass production capabilities as other three-dimensional structural elements of other shapes, or microlenses. Both concave and convex structures can also be used.

[0049] A backlight illumination element, such as I, consists of a planar emitter, preferably another light guide (with additional light-emitting mechanisms disposed laterally or on the back side), and at least one light collimator integrated into and / or disposed before the planar emitter (e.g., at least one prism film and / or at least one privacy filter (slab filter)). Furthermore, a so-called focused backlight unit can be used as the backlight illumination element, wherein light from the (other) light guide has already been coupled out within a limited angular range and, if necessary, also oriented, deflected, or superimposed.

[0050] Accordingly, the backlighting element can in principle be constructed like an LED backlight, for example as a so-called direct-lit LED backlight, an edge LED backlight, an OLED, or as another surface emitter, on which at least one permanent privacy filter (with a microfilm) is applied, for example.

[0051] Of particular advantage to all the aforementioned variations of the lighting device is that the lighting device also includes a transmissive screen, preferably in the form of an LCD panel, positioned in front of the lighting device along the viewing direction, which is based on the fact that the lighting device can operate in at least two modes, wherein B1 is for a free viewing mode and B2 is for a restricted viewing mode.

[0052] In some cases, it may be advantageous when the screen also exhibits anisotropic scattering characteristics for light passing through its large surface area. Here, the preferred direction for stronger scattering characteristics of the screen should correspond to the preferred direction for stronger scattering characteristics in the light guide. This is typically the vertical direction. Furthermore, it is feasible to place an anisotropic scattering layer between the screen and the light guide, for example, to mask optical artifacts on the light guide, while minimizing or even eliminating any impact on the viewing protection effect. Anisotropic scattering layers are known in the prior art, such as holographic diffusers or binary (computer-generated) holograms.

[0053] If present, a device for reducing or controlling reflection, such as an anti-reflective coating, may be provided on the upper side of the screen and / or on at least one of the large surfaces of the light guide and on at least one of the privacy filters.

[0054] Another design for the lighting device extending around the screen involves placing another light guide (e.g., made of glass or plastic) in front of the screen in the viewing direction, with a device for coupling the output light. This light guide can be supplied with light from the side of the light-emitting mechanism. The device used here for coupling the output is, for example, the device described above, or a device known in the prior art, such as nanoparticles of suitable size and quantity (e.g., titanium dioxide, barium sulfate, etc.), as described in WO2015 / 121398A1 and WO2017 / 089482A1, where the nanoparticles are uniformly distributed within the volume of the light guide. With this design, any residual light that may not have been intentionally present can be superimposed or illuminated in operating mode B2 within the angle range that was originally protected from being seen, in such a way that contrast is no longer perceptible, and therefore the corresponding light-emitting mechanism for the other light guide is designed to emit colored or white light. Here, the light-emitting mechanism can emit light in a color that appears or does not appear in the image displayed by the transmissive screen. No image perception is possible at angles that are never released.

[0055] Particularly advantageously, the lighting device with a screen according to the invention is used in a vehicle to selectively display image content only for the co-driver in operating mode B2 or simultaneously for both the driver and co-driver in operating mode B1. For example, the former (displaying image content only for the co-driver in operating mode B2) is advantageous when the co-driver is watching entertainment content that may distract the driver.

[0056] The lighting device with a screen according to the invention can similarly be used to input or display confidential data, such as PIN codes, emails, SMS messages, or passwords, on ATMs, payment terminals, or mobile devices.

[0057] In all the above-described designs, the light-emitting mechanism can be an LED, an LED array, or a laser diode. Other variations are conceivable and within the scope of this invention.

[0058] Furthermore, the desired range of restricted viewing angles in Mode B2, for the horizontal and vertical directions respectively, can be defined and implemented independently. For example, it is meaningful to have a larger angle (or perhaps no restriction) in the vertical direction than in the horizontal direction, such as when a person should see the image at a different size in the case of an ATM, and to maintain significant or complete restriction during lateral viewing. Conversely, for POS terminals, based on security regulations, line-of-sight restrictions are often necessary in Mode B2 not only in the horizontal direction but also in the vertical direction.

[0059] If the above parameters change within a certain range, then in principle the working efficiency of the present invention remains unchanged.

[0060] It goes without saying that, without departing from the scope of the invention, the above features and the features to be explained below can be used not only in the combination described, but also in other combinations or individually. Attached Figure Description

[0061] The invention will now be described in more detail with reference to the accompanying drawings and embodiments, which also disclose important features of the invention. These embodiments are for illustrative purposes only and should not be construed as limiting. For example, the description of embodiments having multiple elements or components should not be construed as indicating that all such elements or components are necessary for implementation. Preferably, other embodiments may include alternative elements and components, fewer elements or components, or additional elements or components. Unless otherwise stated, elements or components of different embodiments may be combined with each other. Modifications and variations described with respect to one embodiment may also be applicable to other embodiments. To avoid repetition, the same or corresponding elements are indicated by the same reference numerals in different drawings and will not be described again. Wherein:

[0062] Figure 1 A schematic diagram is shown for coupling light that is laterally coupled into the light guide from the lower large surface of the light guide where the coupling output element is located, wherein the light leaves the light guide on the upper large surface.

[0063] Figure 2 A schematic diagram is shown for coupling light that is laterally coupled into the light guide from the upper large surface of the light guide where the coupling output element is located, wherein the light leaves the light guide on the upper large surface.

[0064] Figure 3 The schematic diagram of the lighting device in the first design scheme combined with the screen for free viewing mode in mode B1 is shown.

[0065] Figure 4 The schematic diagram shows the lighting device in the first design scheme combined with the screen for the restricted viewing mode in mode B2.

[0066] Figure 5A A schematic diagram of a light guide is shown in top view to illustrate the anisotropic scattering characteristics, through which a light beam passes.

[0067] Figures 5B to 5C It shows crossing along two mutually orthogonal directions. Figure 5A A cross-sectional view of the optical guide in the image.

[0068] Figures 6A to 6C The schematic diagrams show different designs of the coupled output element.

[0069] Figure 7A A top view of the coupled output element is shown, with a general beam orientation.

[0070] Figure 7B Show Figure 7A A cross-sectional view of the coupling output element, showing the beam direction for light passing through the optical guide and the coupling output element, and

[0071] Figure 7C A cross-sectional view of another coupled output element is shown, with the indicated beam direction for light passing through the optical guide and coupled output element. Detailed Implementation

[0072] exist Figure 1 The diagram shows a schematic of light coupling output from the light-emitting mechanism 4, coupled to the light source on the lower surface of the light guide 3, where the coupling output element 6 is located. However, the coupled output light primarily, i.e., more than 50%, leaves the light guide 3 at the upper surface. In the horizontal direction (here located in the plane of the page and extending from right to left; conversely, the vertical direction points into the page), the light is coupled out from the upper surface of the light guide 3 at a wide angle (greater than 60°). The position of the coupling output element 6 is indicated by the reference numeral 6; however, the actual coupling output element 6 is not shown here because it is very small under a microscope. Therefore, light from the light-emitting mechanism 4 (e.g., an LED) is coupled into the light guide 3 from the side. Due to total internal reflection, the rays of the coupled input light (represented by thick lines) on the outer wall are reflected back into the light guide 3 until they finally (repeated once if necessary) strike the coupling output element 6 for the desired coupling output. The coupling output is represented by a sparse beam. For better identification, Figure 1 The diagram in bold shows this; in practice, a very large number of optical paths are implemented in optical guide 3. Furthermore, light refraction at the refractive index transition surface is not considered.

[0073] Figure 2 This diagram illustrates a principle for coupling light input from the side of the light-emitting mechanism 4 into the light guide 3, and then coupling it out from the upper large surface of the light guide 3, where the coupling output element 6 is located. The light also exits the light guide 3 primarily through the upper large surface. This is meaningfully applicable here. Figure 1 The implementation scheme is as follows. Technically, the only difference here is the position of the coupling output element 6 and, if necessary, the design scheme; the coupling output element is now located on the upper side of the light guide 3, thus coupling the light directly upwards for output. Here, compared with the implementation scheme... Figure 1 Compared to the previous case, the coupled output light does not need to pass through the optical guide 3 again.

[0074] Figure 3 and Figure 4 An illumination device 1a is shown, which is capable of operating in at least two modes: mode B1 for a free viewing mode and mode B2 for a restricted viewing mode, in which light is emitted from the illumination device within a limited angular range relative to the free viewing mode. Here, the illumination device 1a includes a planar backlight illuminating element 2 and a plate-shaped light guide 3 located in front of the backlight illuminating element 2 in the viewing direction. The backlight illuminating element emits light within the restricted angular range. The light guide has two large surfaces and a narrow surface, the narrow surface connecting to the large surfaces at its edges. The light guide 3 has a coupling output element 6 on at least one of the large surfaces and / or within its volume, and is at least 50%, however preferably at least 70%, of the light emitted by the backlight illuminating element 2. A light-emitting mechanism is laterally disposed on the narrow surface of the light guide, which also includes the light-emitting mechanism being disposed only on one side of the light guide. In mode B2, the backlight illuminating element is turned on and the light-emitting mechanism is turned off, while in mode B1, at least the light-emitting mechanism is turned on.

[0075] The shape, number per unit area, orientation and / or extension of the coupling output element 6 are selected in such a way that the light guide 3 (through the coupling output element 6 or at least a portion thereof) has anisotropic scattering characteristics for light passing through the large surface of the light guide 3.

[0076] Specifically, this means that each coupling output element 6 has at least one functional surface 5 for the defined coupling output of light, on which light is correspondingly coupled out from the light guide. In the simplest case, these functional surfaces 5 are flat or at least have flat surface segments, or they may be surfaces curved in one or two linearly independent directions. Now, an orientation vector is defined for the functional surface 5, which is parallel to the large surface from which the light is emitted, that is, it lies in a plane parallel to said large surface. This orientation vector is a vector that maximizes the integral of the dot product of this vector and the position-dependent normal vector of the functional surface 5 with respect to the functional surface 5. For a flat surface, the normal vector is of course constant at every position of the functional surface 5; however, for a curved surface, the normal vector varies, thus involving the normal vector of the tangent at the corresponding position. Specifically, the orientation vector... Make the integral Maximize, where This is the normal vector of functional surface 5 in coordinates x and y, denoted here as "A". This orientation vector now forms an angle of up to 45° with the predetermined preferred direction. The normal vector here forms an angle between a minimum of 5° and a maximum of 85° with the associated, light-emitting large surface, however preferably, a lower limit of 30° and / or an upper limit of 60°. The calculated orientation vector is a measure of the rotation of functional surface 5 relative to the preferred direction for coupling output element 6, but does not necessarily correspond to the "average" of all possible surface normals on functional surface 5 or their projection onto the large surface of the light guide 3.

[0077] If the coupled output element 6 is designed in this way, the light guide 3 has a scattering characteristic in the preferred direction that is at least 1.2 times, preferably even at least 2 or 3 times, greater than the scattering characteristic in the direction perpendicular to the preferred direction, and thus has anisotropic scattering characteristics for light passing through the two large surfaces of the light guide 3 as a whole.

[0078] The large surface from which light emanates can also be divided into multiple sub-regions with predetermined sizes. The ratio of the area of ​​the functional surface in a sub-region to the area of ​​the corresponding sub-region is different for different sub-regions, thus causing the scattering characteristics of the light guide 3 on the large surface from which light emanates to change.

[0079] exist Figure 3The diagram shows a schematic of the lighting device 1a in the first design embodiment integrated with screen 1 in mode B1 for free viewing mode. As a limited angle range, each of the following ranges can be considered in principle, said range being smaller than the half-space in front of the backlight illuminator; preferably, this angle range is represented horizontally and / or vertically, or as a cone around the surface normal, or as a selectable directional vector on the backlight illuminator 2, for example, + / -20° or 30°; when defining the limited angle range, a small amount of light less than 1% to 5% of the maximum brightness can be disregarded.

[0080] Figure 3 and Figure 4 The schematic diagram is a cross-sectional view.

[0081] In contrast, Figure 4 The diagram shows the schematic of the lighting device in the first design scheme combined with the screen in mode B2 for a limited viewing mode. Thick arrows represent light limited in the angular range, while dashed thin arrows represent very little light being horizontally scattered compared to the light from the backlight illuminator 2. (The following is a continuation of the diagram.) Figures 5A to 5C The anisotropy of the coupled output element 6 on the optical guide 3 and its stronger scattering characteristics in the vertical direction relative to the horizontal direction are further elaborated in detail.

[0082] In a preferred design of the lighting device 1a, the light emitted by the backlight element 2, at least in operating mode B2, is emitted in the horizontal direction at a limited angular range, such that the light experiences less scattering in the horizontal direction than in the vertical direction when passing through the light guide 3, as in Figure 4 As shown in the diagram. Therefore, light emitted within a limited angular range is scattered only slightly outside of that limited angular range.

[0083] The difference between the two operating modes B1 and B2 is that in operating mode B2, the backlight illuminating element 2 is turned on and the light-emitting mechanism 4 (on one or more narrow faces of the light guide 3) is turned off, while in operating mode B1, at least the light-emitting mechanism (on a narrow face of the light guide) is turned on. The light-emitting mechanism 4 directs light into the light guide 3. Then, the coupling output element 6 couples out light from the light guide 3, where emission is achieved almost entirely through the coupling output element 6.

[0084] The backlight illuminating element 2 consists, for example, a planar emitter, preferably another light guide (with an additional light-emitting mechanism disposed laterally or on the back side), and at least one light collimator integrated into the planar emitter and / or disposed in front of the emitter on the planar surface, such as at least one prism film and / or at least one privacy filter (e.g., a sheet filter).

[0085] Therefore, in principle, the backlight illuminating element 2 can be constructed as an LED backlight, for example, as a so-called direct-lit LED backlight, edge-lit LED backlight, OLED or other surface emitter, on which at least one permanent privacy filter (e.g., with a microchip) and / or other light collimator is applied or disposed.

[0086] The light guide 3 is preferably made of a light-transmitting, thermoplastic or thermoelastic polymer, such as plastic, or made of glass. For example, the light guide 3 can be made of polycarbonate.

[0087] Advantageously, if the portion of the coupling output element 6 comprises at least 30%, preferably at least 50%, and particularly preferably greater than 90%, then the coupling output element is selected in such a way as to have anisotropic scattering characteristics for light, such that light passes through the large surface of the light guide 3. Alternatively or additionally, for all coupling output elements on average, the orientation vector forms an angle with the preferred direction having a maximum value of 45°. In particular, the light guide 3 may have stronger scattering characteristics in the preferred direction than in the direction perpendicular to the preferred direction.

[0088] The anisotropic scattering characteristics of the coupled output element 6 are characterized by measuring the scattering characteristics along at least two mutually perpendicular directions, a preferred direction, and a direction perpendicular to it. In particular, the scattering characteristics caused by the coupled output element 6 when light passes approximately perpendicularly through the optical guide 3 should be considered. Other reference directions can also be considered as perpendicular lines on the optical guide 3.

[0089] The terms "vertical" and "horizontal" here generally refer first to the preferred direction on the surface of the backlight element or the large surface of the light guide and the direction perpendicular to said preferred direction. Advantageously, the preferred direction when an observer observes the lighting device 1a is equivalent to the vertical direction, and the direction perpendicular to the preferred direction is equivalent to the vertical direction, wherein the scattering characteristics of the coupled output element 6 in the vertical direction are greater than those in the horizontal direction. Generally, the horizontal direction also corresponds to a horizontal line on the ground surface, at least in the case of a screen with a light guide that does not change its orientation therein. However, generally, the horizontal direction should be understood as the direction parallel to the extension of the line connecting the observer's eye, where it is assumed that the position of the observed screen changes when the observer or the line moves, for example in mobile terminal devices. Finally, for the coordinate system of the moving screen, "which direction is horizontal and which direction is vertical" is arbitrarily determined; the two directions only need to be orthogonal to each other.

[0090] In this regard, Figure 5AThe schematic diagram is shown in top view of the light guide 3. To illustrate the anisotropic scattering characteristics, the light guide 3 is through which a beam passes in its large surface. A dot in the circle represents a beam of light entering vertically from below onto the light guide 3, passing from large surface to large surface and also striking the coupling output element 6 (not shown in the figures). The shorter dashed arrow in the horizontal direction, compared to the longer dashed arrow in the vertical direction, indicates that the scattering characteristics in the horizontal direction are smaller than those in the vertical direction due to the anisotropic scattering characteristics of the corresponding coupling output element 6.

[0091] Figure 5B The diagram shows a cross-sectional view of the optical guide 3 in a direction perpendicular to the preferred direction, i.e., in the horizontal direction. Figure 5C The diagram shows a cross-sectional view of the light guide 3 in the preferred direction, i.e., the vertical direction. Coupling output elements are not shown here. The thick arrows represent light passing through the two large surfaces (upper and lower in this case) of the light guide 3, emitted by a backlight illuminating element 2 (not shown). The dashed arrows indicate the maximum scattering angle range, showing that the maximum scattering angle range is within... Figure 5C The preferred direction in is compared to in Figure 5B It is larger in the direction perpendicular to the preferred direction.

[0092] The coupling output element for coupling output light onto at least one large surface of the light guide preferably comprises microlenses and / or microprisms and / or diffraction structures and / or three-dimensional structural elements and / or scattering elements, wherein the extension at its maximum dimension is at most 100 micrometers, preferably at most 50 micrometers. In the case of diffraction structures, for example, holograms or gratings / diffraction gratings may be involved.

[0093] In response Figure 6A A schematic diagram depicting an exemplary shape of the coupling output element 6 is shown, here in the shape of a microprism. This type of coupling output element can be uniformly, or preferably non-uniformly (i.e., in greater quantities as the spacing of the light-emitting mechanisms 4 on each face increases, except for the recesses) distributed on one or two large faces and / or in the volume of the light guide 3, for example as an air-filled recess. Of course, other shapes of the coupling output element 6 are also feasible and... Figure 6B and Figure 6C As shown in the diagram. The functional surfaces are those that slope upwards. Figure 6A The coupling output element 6 shown has a simplified shape; the functional surface, typically shown flat here, is rounded at its upper and lower edges and can also have curvature in one or two dimensions throughout its orientation, as it is in... Figure 6B and Figure 6CAs shown in the figure. Typical dimensions are between 1 μm and 100 μm in each spatial dimension, preferably between 2 μm and 40 μm, wherein the height—in the vertical direction in the drawing plane—is preferably no greater than 20 μm.

[0094] Figure 7A The coupled output element 6 is shown in a top view, as in Figure 6A As exemplarily shown, and for example, a recess can be formed on the light incident surface, i.e., on such a large surface as the light guide, in which light emitted by the backlight element enters the backlight element. The light (not shown here) strikes the light incident surface from below, i.e., from below the page plane, perpendicular to the page plane. Due to the deflection on functional surface 5, the light is deflected by a maximum of 45° in the preferred direction (here, the vertical direction pointing upwards in the page plane), which... Figure 7B This can be seen more clearly in the image. Perpendicular to the preferred direction, functional surface 5 has no effect, so the scattering effect is significantly smaller in that direction.

[0095] Figure 7B Show Figure 7A A cross-sectional view of the coupling output element, which is constructed as a material recess in the light guide, the material of which is indicated by a corresponding shading line. Due to the presence of functional surface 5, light is redirected in the preferred direction (in this case, the horizontal direction within the page plane) by refraction and scattering, characterized by two arrows. Perpendicular to this, that is, perpendicular to the page plane, functional surface 5 has no effect; however, due to the residual effect of the three-dimensional extension of the coupling output element, an undesirable scattering component perpendicular to the preferred direction is formed in principle.

[0096] at last, Figure 7C A cross-sectional view of another coupled output element is shown, which is relative to... Figure 7B The coupling output element 6 has two functional surfaces 5. The coupling output element 6 is also similarly constructed as a recess in the material. The function of the functional surfaces 5 corresponds to... Figure 7B Its role in.

[0097] Of particular advantage to all the aforementioned variations of the lighting device 1a is that the lighting device 1a further includes a transmissive image generator disposed in front of the lighting device 1a along the viewing direction as a screen 1, which is preferably in the form of an LCD panel, the screen being based on the fact that the lighting device 1a can operate in at least two modes of operation, namely mode B1 for a free viewing mode and mode B2 for a restricted viewing mode.

[0098] In some cases, this may also be advantageous when screen 1 also has anisotropic scattering characteristics for light passing through its large surface area. Here, the preferred direction with smaller scattering characteristics of screen 1 should be equivalent to the preferred direction with smaller scattering characteristics even in the light guide. This is usually the horizontal direction.

[0099] Devices for reducing or controlling reflections, such as anti-glare and / or anti-reflective coatings, may be provided on the upper side of screen 1 and / or on at least one of the large surfaces of light guide 3 and on at least one of privacy filters (if present).

[0100] In all the above-described designs, the light-emitting mechanism 4 can be an LED, an LED array, or a laser diode. Other variations are conceivable and within the scope of this invention.

[0101] The lighting device and screen achievable by means of the present invention achieve the proposed objective: to allow a practically feasible solution for reliable display of information with a selectively limited viewing angle, while in another mode of operation, free and unrestricted viewing is possible. The invention can be implemented in a simple and inexpensive manner. The native resolution of the screen used is available in both modes of operation. Furthermore, this solution introduces only minimal light loss and achieves the most comprehensive possible viewing protection with a limited viewing angle.

[0102] Advantageously, the invention can be applied anywhere that displays and / or inputs confidential data, such as for PIN input or displaying data on ATMs or payment terminals, or for password input or reading emails on mobile devices. As mentioned above, the invention can also be applied to automobiles.

[0103] List of reference numerals

[0104] 1 screen

[0105] 1a lighting fixture

[0106] 2 Backlighting components

[0107] 3 optical guides

[0108] 4 Light-emitting mechanism

[0109] 5 functional aspects

[0110] 6 Coupled Output Components

Claims

1. A lighting device (1a) for a screen (1), the lighting device being capable of operating in at least two operating modes, namely, an operating mode B1 for a free viewing mode and an operating mode B2 for a restricted viewing mode, wherein in the restricted viewing mode, light is emitted by the lighting device at an angle range limited relative to the free viewing mode, the lighting device comprising: A planar extended backlight illuminator (2), the backlight illuminator emitting light within a limited angular range, A plate-shaped light guide (3) is disposed in front of the backlight illuminator (2) along the observation direction. The light guide has two large surfaces and a narrow surface, the narrow surface connecting to the large surfaces at its edges. The light guide (3) has a coupling output element (6) on at least one of the large surfaces and / or within the volume of the light guide. The light guide (3) is at least 50% transparent to light emitted by the backlight illuminator (2). Each coupling output element (6) has at least one functional surface for definingly coupling out light, on which light is coupled out from the light guide (3). The light-emitting mechanism (4) is arranged laterally on the narrow surface of the light guide (3). In operation mode B2, the backlight illumination element (2) is turned on and the light-emitting mechanism (4) is turned off, and in operation mode B1, at least the light-emitting mechanism (4) is turned on, characterized in that... For at least a portion of the coupled output element (6), the orientation vector of each functional surface parallel to the large surface from which light is emitted forms an angle with a maximum value of 45° with the preferred direction parallel to the large surface from which light is emitted, wherein the orientation vector is a vector that maximizes the integral of the dot product of the vector and the position-dependent normal vector of the functional surface on the functional surface, and each normal vector forms an angle between 5° and 85° with the corresponding large surface, thereby the scattering characteristics of the light guide (3) along the preferred direction are at least 1.2 times that in the direction perpendicular to the preferred direction, wherein the scattering characteristics are measured along at least two mutually perpendicular directions, the at least two mutually perpendicular directions including the preferred direction and the direction perpendicular to the preferred direction, and the scattering characteristics are the scattering characteristics caused by the coupled output element (6) when light passes through the light guide (3) approximately perpendicularly, and therefore have anisotropic scattering characteristics for light passing through the two large surfaces of the light guide (3) in general.

2. The lighting device (1a) according to claim 1, characterized in that, The portion of the coupled output element (6) comprises at least 30% of all coupled output elements, and / or, on average for all coupled output elements, the orientation vector forms an angle with the preferred direction having a maximum value of 45°.

3. The lighting device (1a) according to claim 1 or 2, characterized in that, The light guide (3) has stronger scattering properties along the preferred direction than along the opposite direction.

4. The lighting device (1a) according to claim 3, characterized in that, When an observer observes the lighting device (1a), the preferred direction is equivalent to the vertical direction, such that the scattering characteristics of the light guide (3) in the vertical direction are greater than those in the horizontal direction, wherein the horizontal direction extends parallel to the line connecting the observer's eyes.

5. The lighting device (1a) according to any one of claims 1 to 4, characterized in that, The ratio of the area of ​​the functional surface of the portion of the coupled output element to the area of ​​the large surface is determined such that the scattering characteristics of the coupled output element (6) in the preferred direction are at least 2 or 3 times the scattering characteristics in the direction perpendicular to the preferred direction.

6. The lighting device (1a) according to any one of claims 1 to 5, characterized in that, The large surface from which light emanates is divided into sub-regions of a predetermined size, and the ratio of the area of ​​the functional surface in a sub-region to the area of ​​the corresponding sub-region is different for different sub-regions, causing the scattering characteristics of the light guide (3) on the large surface from which light emanates to change.

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