Device for backlighting an optical display unit

Abstract

The device for backlighting an optical display unit with a light-transparent cover plate (2) comprises at least one rod-shaped optical waveguide (1) arranged along a lateral outer edge (2a) of the cover plate (2). Light radiation can be coupled into the rod-shaped optical waveguide(s) (1) from an end face of the respective rod-shaped optical waveguide(s) (1), and the rod-shaped optical waveguide(s) (1) is in contact with the cover plate (2) on its outer surfaces, except for the surface area(s) that are in contact with the cover plate (2). One or more surface areas that are in contact with the cover plate (2) are reflective to coupled light.On the surface area(s) output structure elements (4) are provided which are designed to direct light, which is guided through the respective rod-shaped optical waveguide (1), into the cover plate (2) along the respective outer edge (2a) of the cover plate (2) to backlight the optical display unit in the cover plate (2).

Description

[0001] The invention relates to a device for backlighting an optical display unit, which can be used in particular on a wide variety of electronic devices. It can, for example, be used for backlighting a display unit in the form of a screen or display on mobile telecommunications devices, computers, measuring instruments, or control elements for a wide variety of devices and machines.

[0002] For example, computer displays or other electronic devices are usually backlit by artificial light sources such as LEDs or CFLs.

[0003] In cases where these known light sources are physiologically unusable for some people to backlight an optical display unit, or where light of a special spectral composition is to be used for an optical display unit for other reasons, this is not yet possible, at least not in a relatively simple way, and is not provided for in current systems.

[0004] A segment of the population has problems with artificial light and is therefore excluded from digital life, which is largely conducted via artificially illuminated screens. Artificial light is also psychologically and physiologically harmful for the average person, so even ordinary consumers benefit from the use of natural sunlight for lighting.

[0005] If light with different spectra and / or from different light sources is to be used for backlighting optical display elements, the required effort is quite high. A larger number of suitable light-emitting elements must then be used and emitted homogeneously across the display surface.

[0006] US 6 369 866 B1 is an LCD with a panel, light guide plate (LGP), backlight, and ambient light collecting optics. A novel feature is a light transmitter between the collecting lens and the LGP, whose top and bottom surfaces have reflective surfaces. This homogenizes the externally coupled light and feeds it evenly into the LGP, thus eliminating the periodic brightness maxima ("bands") observed in prior art along the panel width. The system switches on the external light collector during the day and the internal light source when ambient light is low; the goal is uniform luminance with lower energy consumption.

[0007] Additionally, DE 197 48 636 A1 describes area- or line-shaped illuminated displays for vehicle interiors where installation space is limited. Polymer-based optical fibers (POF) are used, the surface of which is selectively roughened or microstructured to locally refract total internal reflection and allow light to exit in a defined manner. Tapes / films with patterned and text-shaped exit zones can be produced from many fibers, which can be integrated very flatly without conventional backlighting (e.g., model or equipment logos, safety symbols).

[0008] WO 01 / 86 586 A1 integrates front / backlighting and an optical touch grid. A flat light guide illuminates the (reflective or transmissive) display; on two non-parallel sides are elongated radiation sources that emit parallel beams of light from the light guide across the display. The position is determined from the shadows cast by a pointer (finger / stylus) on lateral detectors. Each elongated source consists of a light tube with micro-optics, powered by a point-like emitter (LED), and forming an output window above the LGP plane (tangential dimension > LGP thickness). Particularly economical is its production from a single sheet – the LGP is cut to size, an elongated piece is rotated 90° and used as a coupling element; a single light source can simultaneously power the LGP and generate the parallel beams. Variants include compact corner powering and a backlight version.

[0009] Furthermore, US 2014 / 0300843A1 describes the problem of visible hotspots at the fiber outputs in ambient light-fed backlights. An ambient light gatherer feeds multiple optical fibers; a light diffusion element (preferably a double-concave, alternatively a plano-concave lens) is positioned between each fiber output and the LGP coupling edge. This widens the beam angle of the fiber output and levels the luminance along the edge. Geometric conditions ensure uniformity, e.g., W < P (lens width smaller than the distance between adjacent fiber outputs) or, in the case of alternating combinations of LEDs and fibers, W < P2 - L and W < P1 - L (with LED width L). Application in edge backlights and complete LCDs is demonstrated.

[0010] US 2014 / 0133176A1 discloses a side-illuminated backlight module with a conventional LED source and an additional solar light source. At its core is an optical connector (fiber coupler) attached to the backlight, to which an external light collector (e.g., on the device / product frame) is coupled via optical fibers. The fiber outputs are mounted on a holder / bracket and project into the coupling edge of the light guide plate; a switching unit selects the LED, solar, or both sources depending on the environment. Objectives: energy savings, improved use of daylight, and compatibility with standard optical film stacks. Design variants: LED and fiber outputs on opposite sides or on the same side, with the latter arranged alternately on a circuit board.

[0011] It is therefore an object of the invention to provide possibilities by which a simple and flexible method for backlighting optical display units can be achieved, which is simple in design and does not require a significant increase in space and opens up the possibility of achieving illumination with natural sunlight, among other things.

[0012] According to the invention, this problem is solved with a device having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features specified in dependent claims.

[0013] In the following, light shall be understood to mean electromagnetic radiation with wavelengths from the spectrum of visible and near-infrared light.

[0014] An optical display unit is typically a plate-shaped element whose transparency can be adjusted pixel by pixel to allow a person to focus their gaze and visually perceive a display or image. This plate-shaped element may also be equipped with color filter arrays. The respective display or image is usually generated using elements such as LCDs or TFTs. The light passing through these controllably light-absorbing or transparent elements appears as a view visible from the outside, forming a variety of visually recognizable displays.

[0015] The rear backlighting of such display units can be achieved by a planar light source consisting of a transparent cover plate equipped with rear diffuser structures into which light from at least one light source (such as LED) can be coupled laterally.

[0016] According to the invention, at least one rod-shaped optical waveguide is arranged along a lateral outer edge of the transparent cover plate. For better and more uniform illumination of the display unit, it is advantageous that rod-shaped optical waveguides are arranged on opposite edges of, for example, a polygonal cover plate.

[0017] A cover plate and one or more rod-shaped optical waveguides should preferably be made of the same transparent material, such as glass or an optically transparent plastic. If the cover plate and rod-shaped optical waveguides are made of different materials, their refractive indices should differ by a maximum of 20%.

[0018] Light radiation can be coupled into the rod-shaped optical waveguide(s), for example, via at least one optical fiber originating from one end face of the respective rod-shaped optical waveguide. The light guided through the optical fiber(s) can be emitted from a suitable radiation source and coupled into the optical fiber(s). Alternatively, light can also be coupled directly into a rod-shaped optical waveguide from a suitable radiation source.

[0019] For example, sunlight can be concentrated, particularly by means of a solar collector, and coupled into one or more optical fibers and guided through them to an end face of a rod-shaped optical waveguide, or, in particular, coupled out of the respective optical fiber and coupled into at least one end face of the rod-shaped optical waveguide. Alternatively, light emitted by an artificial light source can be coupled into one or more optical fibers and guided to a rod-shaped optical waveguide, or directly coupled into a rod-shaped optical waveguide from a corresponding radiation source.

[0020] For example, light from an artificial radiation source can be electromagnetic radiation from a sub-range of the wavelength spectrum of visible light, making it possible, for example, to backlight an optical display unit with a corresponding color.

[0021] The rod-shaped optical waveguide(s) can be reflective to coupled light on its outer surfaces, except for the area in contact with the cover plate and a surface area opposite this area. This allows the coupled light to be guided at least partially through the entire rod-shaped optical waveguide using total internal reflection.

[0022] Because coupling structure elements are located on the surface area(s) opposite the surface area of ​​the respective rod-shaped optical waveguide that is in contact with the cover plate, light guided through the rod-shaped optical waveguide can exit and, by the action of the coupling structure elements, be directed into the cover plate along the outer edge to illuminate the optical display unit.

[0023] The coupling structure elements are designed in such a way that light rays guided through the respective rod-shaped optical waveguide are reflected or scattered there in such a way that these light rays are directed towards the cover plate, so that they can enter the cover plate for illumination purposes through the surface of the outer edge, which is in contact with the rod-shaped optical waveguide.

[0024] It is also advantageous if light from opposite end faces is coupled into a rod-shaped waveguide, particularly one made of optical fibers. This is especially beneficial for uniform illumination across the entire surface of the display unit when the edge lengths of cover plates are longer.

[0025] In one embodiment of the invention, light-emitting elements for additional backlighting can be arranged at regular intervals on the outside of each rod-shaped optical waveguide at the output coupling structure elements, the emitted light of which can be directed through the respective rod-shaped optical waveguide into the cover plate. This allows backlighting to be achieved, for example, even when no natural sunlight is available that can be coupled into a rod-shaped optical waveguide.

[0026] However, it is also possible to change the illumination of an optical display unit with different colors by sequentially directing a mixture of different wavelengths of light or different wavelengths of light radiation onto a cover plate.

[0027] Coupling structural elements can be present as protrusions, depressions, structured coatings and / or combinations thereof on or in the surface of the respective rod-shaped optical waveguide, which is arranged opposite the surface area that is in contact with the cover plate.

[0028] The individual light-emitting elements for additional backlighting should advantageously be arranged along the length of the respective rod-shaped optical waveguide (at positions located between adjacent coupling structure elements). This allows the light emitted by them to be directed unimpeded from the respective light-emitting elements into the top panel. This also achieves improved, uniform backlighting across the entire surface of a display unit.

[0029] Light-emitting elements can also be present on the back of a cover plate, either alone or additionally, preferably in a regular arrangement, as is already common practice. They can form a regular pattern on this side to provide additional backlighting.

[0030] One or more rod-shaped optical waveguides should each have a length that corresponds to at least 80%, preferably at least 90%, of the length of the respective lateral edge of the cover plate on which the respective rod-shaped optical waveguide is arranged.

[0031] Rod-shaped optical waveguides can have various cross-sectional geometries, for example, polygonal, preferably triangular or quadrilateral, or even round. Only the surface area that is in contact with an outer edge of a cover plate should be shaped to be complementary to the surface of that outer edge. Thus, if the surface of an outer edge is flat and planar, the corresponding surface area of ​​the rod-shaped optical waveguide should also be planar and flat. If an outer edge of the respective cover plate is curved, the surface area that is to be in contact with this surface should be complementarily curved. In any case, at least almost the entire corresponding surface area of ​​the rod-shaped optical waveguide and the outer edge of the cover plate should be in direct contact.

[0032] The outer edges of a cover plate that are in contact with a surface area of ​​a rod-shaped optical waveguide can be bent or curved in one or two dimensions, which means that a surface area of ​​a rod-shaped optical waveguide should be complementary in shape.

[0033] An optical element that modifies the direction of radiation of the coupled light into the rod-shaped optical waveguide should be arranged at an end face where light can be coupled into the respective rod-shaped optical waveguide. This can be, for example, a suitably oriented reflective surface of an optical element or an optical prism. Alternatively, a beam-shaping optical element can also be arranged and used to couple light into a rod-shaped optical waveguide, either alone or additionally.

[0034] Cover plates, like the respective display units, can also be polygonal or fully or partially curved. Curved cover plate shapes have a partially curved outer contour or the shape of an ellipse or a circle. Rod-shaped optical fibers should then also be curved accordingly, so that surface areas of the respective rod-shaped optical fiber and the surface of an outer edge of the cover plate are in direct contact. An arc should have a minimum radius of 20 mm.

[0035] This principle allows light to be coupled into the backlight of an optical display unit in parallel with the existing light source. This makes it possible, for example, to couple sunlight or light from unusual light sources and use both types of light simultaneously for backlighting. This allows the very thin form factor of modern displays to be maintained.

[0036] For example, if natural sunlight is used for the backlighting of a display unit, then the simultaneous additional lighting with an existing LED source can also be used to maintain a constant brightness (darkening due to clouds and brightness fluctuations throughout the day).

[0037] The problem of sensitivity to artificial light affects only a minority of the population and was therefore not the focus of the development work. Nevertheless, the invention can contribute to ensuring that electronic devices can also be used without problems by people sensitive to artificial light.

[0038] The minority of the population who have problems with artificial light and are therefore excluded from digital life, which is largely conducted via artificially illuminated screens, can participate in digital society again through the inventive backlighting of an optical display unit by means of sunlight guided via a rod-shaped optical waveguide and optical fiber. Artificial light is also psychologically and physiologically harmful to the average population, so there is also an advantage for ordinary consumers.

[0039] Other areas of application, e.g., with the input of other light sources, e.g., by means of at least one optical fiber, are also conceivable with the aid of the principle according to the invention.

[0040] Flat designs, similar to existing optical display units, can be maintained, and light from an alternative source (e.g., sunlight) can be supplied via multimode fiber(s) and used for illumination. This light can be coupled into multimode optical fibers and guided through them using total internal reflection.

[0041] The backlighting of an optical display unit can be largely achieved by utilizing total internal reflection in rod-shaped optical waveguides and by directing the light in the direction relevant for illumination. This is accomplished by means of coupling elements arranged on or within the rod-shaped optical waveguide, or formed therein. These elements deflect the light towards the optical display unit and couple it out of the waveguide. The coupling elements should be designed to ensure homogeneous illumination of the side facing the optical display unit. The degree of coupling of each coupling element or their spacing from one another can be varied to achieve this.

[0042] Other areas of application, e.g. with the injection of light from other light sources, in particular through optical fibers, are conceivable with the help of the principle according to the invention.

[0043] The backlighting of an optical display unit can be achieved through a transparent cover plate using coupling elements. In the cover plate, the light is preferably guided by total internal reflection, with coupling elements arranged on or within the rod-shaped optical waveguide on the side facing away from the optical display unit. These elements deflect the light towards the optical display unit and couple it out of the waveguide. The coupling elements should be designed to ensure homogeneous illumination of the side facing the optical display unit.

[0044] The light from the light-emitting elements (usually several LEDs), which is used for additional lighting, can be coupled laterally into the transparent cover plate.

[0045] For backlighting the optical display unit, the light emitted by the light-emitting elements for illumination passes through the rod-shaped optical waveguide almost undisturbed.

[0046] As already mentioned, a rod-shaped optical waveguide can be fed from one or two ends, which should be arranged opposite each other, each by means of an optical fiber. All sides through which no light enters or exits can be designed to be reflective in order to increase efficiency.

[0047] For example, a single optical fiber with an LED array can be used on one side, or two corresponding rod-shaped optical fibers can be used on opposite sides of the optical display unit. This also depends on the specific lighting requirements and the required homogeneity.

[0048] Light coupled out from a rod-shaped optical waveguide can be directly fed as a typical backlight to an optical display unit and thereby distributed two-dimensionally.

[0049] The light, which is also supplied via one or more optical fibers, can be distributed across a rod-shaped multi-mode optical waveguide on one side or at one height of the top plate of a given optical display unit and fed into a conventional backlight system. Supplementary illumination by LEDs shines through the rod-shaped multi-mode optical waveguide without affecting its function. This allows a fiber-driven light source and LEDs as light-emitting elements to be used together or sequentially for backlighting, independently of each other, or even simultaneously for backlighting the optical display unit. No mechanical switching is required to change between different illumination types.

[0050] The invention advantageously results in a very small footprint and allows integration into existing optical display units without major modifications. This preserves the general form factor of current optical display units.

[0051] In short, the invention can be used to... a) Inclusion of highly sensitive people in digital life b) Relief for health-conscious individuals through healthier light at work c) Technical applications such as infrared lighting d) Lower electricity consumption can be achieved through direct use of solar radiation.

[0052] The invention will be explained in more detail below by way of example.

[0053] This shows: Fig. 1 a top view of an example of a device according to the invention; Fig. 2a a perspective partial representation of an example without and Fig. 2b a perspective partial representation of an example with light-emitting elements for illumination; Fig. 3 a schematic side view of an example with display unit and Fig. 4 A schematic side view of another example with a display unit and light-emitting elements arranged below a cover plate.

[0054] With Fig. Figure 1 shows a top view of an example of a device according to the invention. A transparent cover plate 2 is located on the side, behind an optical display unit 8 (not shown here).

[0055] A rod-shaped optical waveguide 1 is arranged on each of two opposing outer edges 2a of the cover plate 2, which is in direct contact with the surface on the outer edge 2a of the cover plate 2 and is transparent to light in this direction.

[0056] In the example shown, an optical fiber 3 is guided towards each of the two end faces of the rod-shaped optical waveguide 1, through which light is supplied and can be coupled into each end face of the rod-shaped optical waveguide 1. As already mentioned in the general part of the description, sunlight as well as light from artificial light sources can be supplied, in particular via at least one optical fiber 3.

[0057] On the surface of the rod-shaped optical waveguide 1, which is arranged opposite the surface that is in contact with the cover plate 2 and through which light is guided into the cover plate 2, there are coupling structure elements 4 (also not shown here) with the help of which light guided through the rod-shaped optical waveguide 1 can be deflected towards the cover plate 2 and coupled into it.

[0058] Additional light-emitting elements 5, such as LEDs in a row arrangement, can be provided on the surface where coupling structure elements 4 are arranged for additional backlighting, with the help of which backlighting of the respective optical display unit can be achieved alone or in addition to the light that can be supplied from the outside via the rod-shaped optical waveguides 1 or via optical fibers 3 into the rod-shaped optical waveguides 1.

[0059] In the examples shown, the cover plate 2 and the cross-sections of the rod-shaped optical waveguide 1 are also rectangular.

[0060] In Fig. 2a additionally shows how the individual coupling structure elements 4 can and should be arranged at uniform intervals along the outward-facing surface of a rod-shaped optical waveguide 1.

[0061] Fig. Figure 2b illustrates how additional light-emitting elements 5 are arranged in a row behind the outward-facing surface of the rod-shaped optical waveguide 1, which can be used for additional backlighting of the optical display unit 8. The individual light-emitting elements 5 are arranged such that they are positioned between two adjacent output coupling structure elements 4, thus ensuring that at least the largest proportion of the light emitted by them can be directed through the rod-shaped optical waveguide 1 into the cover plate 2.

[0062] In the Fig. It can also be seen from Figures 2a and b that the outer end faces of the rod-shaped optical waveguide 1 can be aligned at an angle, preferably 45°, with respect to the longitudinal axis of the rod-shaped optical waveguide 1. This allows for improved and simplified coupling of light from an optical fiber 3 into the rod-shaped optical waveguide 1, which requires little space and can therefore contribute to miniaturization.

[0063] With Fig. Figure 3 illustrates the invention from a different perspective, namely from one side. Below the transparent cover plate 2, elements 6 are provided for coupling the light towards a display 8. The coupling strength of these elements 6 can be varied laterally to achieve homogeneous backlighting of the display unit (display) 8.

[0064] In the Fig. 3 and Fig. In the four examples shown, a film 7 is present between the cover plates 2 and the display units 8 to increase the brightness of the display. A film 7 can be formed from several films that have structural elements in the form of microprisms oriented perpendicular to each other.

[0065] A rod-shaped optical waveguide 1 is arranged on each of two opposing outer edges 2a of the cover plate 2 such that light coupled in via optical fibers 3 can pass through it and be coupled into the cover plate 2 at the surface that is in contact with the outer edge of the cover plate 2. In this example as well, light-emitting elements 5 for additional backlighting are provided on the outward-facing surface of the rod-shaped optical waveguide 1 behind output coupling structure elements 4 (not shown here).

[0066] The two suggested eyes are meant to illustrate which surface a viewer is looking at in order to recognize the respective display.

[0067] In Fig. Figure 4 shows another possibility for using the proposed arrangement for directly backlit display units 8. In this case, the light-emitting elements 5' that can be used for additional backlighting are not arranged laterally next to the cover plate 2 and the rod-shaped optical waveguide 1, but rather the light-emitting elements 5' form a planar arrangement so that they directly illuminate the display unit 8. If, in this case, the output coupling structures 6 of the backlighting are positioned only between the light-emitting elements 5', the coupling of the light from the optical fibers 3 can be achieved, as in Figure 1. Fig. 3. This will take place.

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