Abstract:
This invention relates to uniform backlighting of surfaces by semiconductor light sources. Various semiconductor light sources are combined into identical illumination groups. These identical illumination groups are arranged so that uniform backlighting of a surface is made possible. For homogeneous color mixing to be achieved, especially at edges, each illumination group in the arrangement has at least one adjacent illumination group in a different orientation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the National Stage of International Application No. PCT/DE2006/001550, filed Sep. 4, 2006, which claims priority to German Patent Application No. 10 2005 042 066.4, filed Sep. 3, 2005, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates to a backlighting arrangement with semiconductor light sources arranged in illumination groups. The invention also relates to an illumination device that has such a backlighting arrangement. 
       BACKGROUND OF THE INVENTION 
       [0003]    This Patent Application claims the priority of German Patent Application 102005042066.4-54, the disclosure content of which is incorporated herewith by back reference. 
       SUMMARY OF THE INVENTION 
       [0004]    Cold cathode fluorescent tubes have been used primarily up to now for the backlighting of surfaces such as LCDs (Liquid Crystal Displays). These radiate mostly white light, but require considerable space and power. 
         [0005]    The use of semiconductor light sources in the backlighting of LCD or TFT image screens has been gaining more and more importance in recent years. For this purpose, it is necessary for a surface to be uniformly backlighted by semiconductor light sources. 
         [0006]    For uniform color rendition on the image screen to be illuminated, it is particularly necessary to achieve homogeneous color mixing of the light emitted by semiconductor light sources of various colors. First of all, the use of differently colored semiconductor light sources requires uniform color mixing of the individual emissions of the semiconductor light sources. This homogeneous color mixing can be achieved by a large separation of the individual light sources from the surface to be backlighted. In addition, diffusely scattering materials can be applied between the surface to be backlighted and the light sources. 
         [0007]    The increased separation, of course, causes undesirably large structural dimensions. Diffusers between the light sources and the surfaces to be backlighted typically lead to considerable losses of illuminating power. This impairs the overall efficiency of such backlighting and its feasibility. Overall efficiency of the backlighting here means the illuminating power relative to the energy consumed. 
         [0008]    WO 2004/031844 A1 provides an example of backlighting with semiconductor light sources. A plurality of semiconductor light sources of different colors are assembled there into subassemblies, and these illumination groups are arranged in a rectangular grid with identical orientations. It may be difficult to produce a homogeneous mixed color by using such a light source arrangement. Because of the identical orientation of the subassemblies, there is a tendency for regions within the backlighted surface, and especially at the edge, to show severe color deviations. 
         [0009]    The color mixture of a subassembly of semiconductor light sources, for one thing, is affected by the fact that the individual semiconductor light sources have different preferential directions in their emitted radiation. Similar behavior also occurs when multichip packages, i.e. LED units that contain a plurality of semiconductor chips of different colors, are used instead of subassemblies with semiconductor light sources of different colors. 
         [0010]      FIG. 5  shows details of a backlighting arrangement  1 . The dashed line is intended to represent the edge  3  of the backlighting arrangement  1 . There are four illumination groups there, at one of the illustrated edges. The individual illumination groups are of identical construction. In particular, they contain three semiconductor chips with different emission spectra. The semiconductor chips of each illumination group are arranged in the same way. This example involves a multichip package such as that sold by the Osram company under the name Multitopled. Illumination groups pursuant to the invention are of course not limited to such multichip packages, but include all types of arrangements of radiation-emitting semiconductor structural members. 
         [0011]    In such backlighting arrangements, identical illumination groups, or illumination groups of the same kind, are arranged on strip-shaped boards in identical orientation. Planar backlighting units are than assembled on the strip-shaped boards. 
         [0012]    Each of the illumination groups of the same kind is arranged in the same orientation in a rectangular grid arrangement. In this case, each illumination group contains a radiation-emitting semiconductor structural member with three radiation-emitting semiconductor chips. In this example of embodiment, in each case these are a blue-emitting (B), a green-emitting (G), and a red-emitting (R) semiconductor chip  32   a ,  32   b , and  32   c , respectively. Since adjacent illumination groups  31   a ,  31   b  in each case have the same orientation and the individual semiconductor light sources of each illumination group have preferential directions of radiation, there is only conditionally homogeneous color mixing of the individual spectral contributions of the semiconductor light sources. 
         [0013]    According to the Figure, adjacent illumination groups  31   a  and  31   b  have the same orientation. In this example of embodiment, only red-emitting semiconductor members  2   c ,  2   d , and  2   e  are adjacent on the edge along the vertical dashed line. Because of this, there can be inhomogeneous color effects at the edge of such backlighting units. The objective underlying this invention is to bring about an improvement of color mixing in a backlighting arrangement or an illumination device in an economical manner. 
         [0014]    This objective is reached by a backlighting arrangement or an illumination device pursuant to Patent claim  1  or Patent claim  18 . 
         [0015]    A backlighting arrangement or a backlighting module pursuant to the invention comprises a plurality of illuminating groups of the same kind, wherein each illuminating group has at least one adjacent illumination group with a different orientation. 
         [0016]    Different semiconductor light sources are assembled into illumination groups of the same kind. For example, these can be RGB light sources. The illumination groups can of course also contain various other colors. These illumination groups of the same kind are arranged so that a surface is backlighted uniformly. Each of the illumination groups is preferably of the same kind. In other words, each illumination group contains the same semiconductor light sources in the same arrangement. So that edge effects of inhomogeneous color mixing can be avoided, each illumination group with the same arrangement has at least one adjacent illumination group in a different orientation. 
         [0017]    Two illumination groups of a backlighting arrangement are adjacent if an imaginary path between the centers of the two illumination groups neither contacts nor intersects the envelope of any third illumination group of the backlighting arrangement. 
         [0018]    There is a different orientation of an illumination group relative to another illumination group, for example, when the distance between the centers of the identical semiconductor light sources of adjacent illumination groups is different from the distance between the centers of the adjacent illumination groups. For example, a different orientation can be realized if the adjacent illumination groups are rotated with respect to one another regarding their principal direction of radiation. 
         [0019]    Each illumination group of a backlighting arrangement pursuant to the invention has a plurality of semiconductor light sources in the same arrangement. This forms the backlighting arrangement from an arrangement of illumination groups of the same kind. Semiconductor light sources, for example, can be semiconductor chips, organic luminescent polymers, individual LEDs, or OLEDs. 
         [0020]    Illumination groups can also be made by assembling a plurality of LEDs into a common illumination group. 
         [0021]    According to a preferred embodiment, at least two of the semiconductor light sources provide different colors or different color contributions. 
         [0022]    According to another preferred embodiment, each illumination group has at least one red light-emitting semiconductor light source, at least one green light-emitting semiconductor light source, and at least one blue light-emitting semiconductor light source. 
         [0023]    In the case of semiconductor chips that serve as semiconductor light sources, the illumination groups can be individual radiation-emitting semiconductor components, wherein each semiconductor component has a plurality of semiconductor chips. In particular, the illumination groups can be so-called “multichip LED packages.” These are LED components that comprise a plurality of semiconductor chips. These semiconductor chips can have different emission spectra, for example red (R), green (G), and blue (B). Such multichip packages are sold, for example, by the OSRAM company under the trade name 6-Lead Multitopleds. By way of example, they have three semiconductor chips, each with a red, a green, and a blue emission spectrum, and six electrical contacts. 
         [0024]    Another embodiment of the invention provides that the illumination groups are arranged in a regular grid arrangement. A regular grid arrangement in this case brings about homogeneous lighting of the entire surface. 
         [0025]    For homogeneous backlighting, another advantageous embodiment of the invention provides that the regular grid arrangement contains planar grid structure types of a group that in turn includes hexagon, rhombus, rectangle, or parallelogram. The individual illumination groups then are each seated on the corners of the corresponding grid structure types. 
         [0026]    According to a particular variant, the illumination groups are arranged on at least one carrier. The entire backlighting arrangement can also be arranged on one common carrier. However, it is also possible for each individual illumination group, or a plurality of them, to be arranged on separate carriers. 
         [0027]    According to another advantageous embodiment, the carrier is of strip-shaped design. Individual or multiple illumination groups can thus be arranged on strip-shaped carriers. The backlighting arrangement can then be formed by arranging a plurality of these strip-shaped carriers next to one another. Each two adjacent strips of identical structure in this case, for example, can be rotated by 180° from one another with regard to the principal direction of radiation of their illumination groups. The adjacent strips are thereby oriented antiparallel to one another. 
         [0028]    Another advantageous embodiment provides that each two adjacent illumination groups are rotated by a given angle, particularly by 90° with respect to one another, relative to an imaginary axis along their principal directions of radiation. If this embodiment, in addition, is arranged in a rectangular grid, it can be achieved that each illumination group of the backlighting arrangement has two adjacent illumination groups oriented differently, in each case within their own rows and columns. This reduces edge effects of inhomogeneous color mixing. 
         [0029]    Another advantageous embodiment provides that two adjacent illumination groups in each case are rotated with respect to one another by 180° relative to an imaginary axis along their principal direction of radiation. This embodiment allows simple assembly of the backlighting arrangement, with improved color mixing at the same time. 
         [0030]    Another advantageous embodiment of the backlighting arrangement provides that illumination groups are placed next to one another in rows in the same orientation on a strip-shaped carrier, and the illumination groups are lined up next to one another during construction of the backlighting arrangement, with two identical adjacent illumination group strips being antiparallel to one another in each case. 
         [0031]    Another advantageous embodiment provides that the illumination groups are arranged on a carrier consisting of a printed circuit board. All popular printed circuit boards are feasible here, but especially including metal-core boards, which have good thermal conductivity. 
         [0032]    Another advantageous embodiment of the backlighting arrangement provides that the semiconductor light sources of the backlighting arrangement, which have the same emission spectrum, are controllable separately. In this way, color tint effects in the image can be produced, particularly when using the backlighting arrangement in combination with a flat picture screen. 
         [0033]    Another advantageous embodiment of the backlighting arrangement provides that the semiconductor light sources of the particular illumination groups are individually controllable. In this way, if individual semiconductor light sources fail, undesirable inhomogeneous color effects can be reduced or avoided by suitable electronic readjustment. 
         [0034]    An illumination device has a backlighting arrangement as described above and an optical element. Optimized color homogeneity can beneficially be produced with the illumination device pursuant to the invention. 
         [0035]    It is expedient for the optical element to be arranged relative to the backlighting arranged so that light emitted by the backlighting arrangement passes through the optical element. 
         [0036]    According to a preferred variant, the illumination device is a display device. In this case it is especially preferred for the optical element to have properties that provide information. In particular, the optical element can be an LCD (Liquid Crystal Display). 
         [0037]    According to an alternative variant, the illumination device is a lighting device. In this case, the optical element can have light-mixing or light-aligning properties. 
         [0038]    A diffuser, for example, is especially suitable as an optical element with light-mixing properties. The diffuser is primarily characterized by the fact that it has at least one surface for the passage of light that scatters diffusely, which may be roughened, or a diffusely scattering volume area with added scattering particles, for example. 
         [0039]    A BE (Brightness Enhancement) film, particularly a prismatic film, can also be used as an optical element with light-aligning properties. A BE film, for example, can have prismatic structures arranged linearly. These cause light coupled into the film from a bottom face to be partially reflected. The transmitted portion is restricted to a relatively small flare angle. The BE film essentially represents a filter that transmits light in a narrow angle around the principal direction of radiation, and reflects the rest of the radiation. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0040]    Other benefits, preferred forms of embodiment, and refinements of the invention are described below in combination with the examples of embodiment explained in  FIGS. 1 to 5 . The figures show: 
           [0041]      FIG. 1  a schematic representation of a first backlighting arrangement pursuant to the invention, 
           [0042]      FIG. 2  an embodiment of a second backlighting arrangement pursuant to the invention, 
           [0043]      FIG. 3  another embodiment of a third backlighting arrangement pursuant to the invention, 
           [0044]      FIG. 4  another embodiment of a fourth backlighting arrangement pursuant to the invention, 
           [0045]      FIG. 5  schematic representations of a backlighting arrangement already described for backlighting a surface, 
           [0046]      FIG. 6  a schematic cross-sectional view of a first embodiment of an illumination device pursuant to the invention, 
           [0047]      FIG. 7  a schematic cross-sectional view of a second embodiment of an illumination device pursuant to the invention. 
       
    
    
       [0048]    In the examples of embodiment and the figures, identical elements or elements with identical action are given the same reference symbols. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0049]    The illustrations of the backlighting arrangements in the figures are of schematic nature. The elements in the figures therefore do not correspond to reality, but are shown symbolically to be able to make the functioning of the arrangements more understandable. 
         [0050]    In the backlighting arrangement  1  of  FIG. 1 , little or no interfering color edge occurs. A red-emitting semiconductor component  22   c , a green-emitting semiconductor component  22   b , and a blue-emitting semiconductor component  22   a  alternately face the dashed line of the edge  23 . This alternating color sequence comes into existence because each two adjacent illumination groups of the same construction  21   a ,  21   b , each having a red-emitting semiconductor component  22   c , a green-emitting semiconductor component  22   b , and a blue-emitting semiconductor component  22   a , are arranged turned by 180° with respect to one another relative to their principal directions of radiation. 
         [0051]      FIG. 2  shows a schematic representation of a second advantageous embodiment of the invention. In this special form of embodiment, each illumination group contains a radiation-emitting semiconductor component with three radiation-emitting semiconductor light sources. In this embodiment, these are a blue-emitting semiconductor chip  42   a , a green-emitting one  42   b , and a red-emitting one  42   c . The illuminations groups are arranged so that the illumination groups in a column of the rectangular grid arrangement all have the same orientation. However, the illumination groups  41   a ,  41   b  of adjacent columns are all turned by 180° relative to an imaginary axis parallel to the principal direction of radiation compared to those of the adjacent column. In other words, every other column of illumination groups is arranged antiparallel to its adjacent column. This improves the color homogeneity over the entire surface. Illumination groups pursuant to the invention are not limited, of course, to such multichip packages, but comprise all types of arrangements of radiation-emitting semiconductor components. 
         [0052]    The edge  43  of the backlighting arrangement  1  shown with dashed zig-zag lines means that embodiments pursuant to the invention are not limited to a number of sixteen illumination groups, but can be expanded by more illumination groups in any directions, depending on the application. Similarly to  FIG. 1 , an alternating color sequence of semiconductor light sources occurs at the horizontal edges of the backlighting arrangement  1 . 
         [0053]      FIG. 3  shows a third backlighting arrangement  1 . In this special embodiment, each illumination group contains a radiation-emitting semiconductor component with three radiation-emitting semiconductor chips. In this example of embodiment, they are a blue-emitting, a green-emitting, and a red-emitting semiconductor chip  52   a ,  52   b , and  52   c , respectively. Adjacent illumination groups are turned by 90° from each other. In other words, four successive illumination groups  51   a ,  51   b ,  51   c ,  51   d  of a column and/or of a row do not have the same orientation. This can minimize color inhomogeneities both at the edge  53  of the backlighting arrangement  1  and over the entire surface of the backlighting arrangement  1 . 
         [0054]    However, embodiments are not reduced only to the angles of 180° or 90° already mentioned. Variations in the arrangement can optionally assume any rotational angle relative to the direction of radiation of the illumination groups. However, a uniform variation of the rotational angle of successive illumination groups is preferred. In the arrangement shown in  FIG. 3 , each illumination group has a maximum of two adjacent illumination groups that have the same orientation. 
         [0055]    The dashed zig-zag edge shown of the backlighting arrangement  1  makes it clear that the embodiment is not limited to a number of sixteen illumination groups, but can be expanded in any directions by additional illumination groups, depending on the application. Similarly to  FIG. 1 , an alternating color sequence of semiconductor light sources occurs at the horizontal and vertical edges  53  of the backlighting arrangement  1 . For this and for all other embodiments, the illumination groups used are not limited to multichip packages. In particular, illumination groups can also have the form of a combination of a plurality of individual semiconductor light sources, for example such as LEDs. The illumination groups are also not limited just to the arrangement of semiconductor light sources in groups of three, but they can contain any number of semiconductor light sources. The emission spectra of illumination groups pursuant to the invention are also not limited exclusively to the colors red, green, and blue, but can instead comprise all colors. 
         [0056]    Another advantageous embodiment is shown in  FIG. 4 . In this case, the orientation of the illumination groups corresponds essentially to that shown in  FIG. 3 . In each case, a blue-emitting, a green-emitting, and a red-emitting semiconductor chip  62   a ,  62   b , and  62   c  are combined in a multichip package to make up an illumination group  61   a ,  61   b ,  61   c . The backlighting arrangements  1  of  FIGS. 3 and 4  differ principally in that two adjacent columns of the backlighting arrangement  1  are displaced vertically from one another in each case. This creates a backlighting arrangement  1  with an arrangement of illumination groups in a type of hexagonal grid. This makes it possible to achieve a larger illumination density, with color homogeneity improved over similar backlighting arrangements at the same time. 
         [0057]    The discussions corresponding to those for  FIG. 3  apply appropriately to the zig-zag dashed edge  63  of the backlighting arrangement  1  of  FIG. 4 . 
         [0058]    However, backlighting arrangements pursuant to the invention are not limited just to hexagonal or rectangular grids; they can also comprise rhombic or parallelogram grid structures. Illumination groups arranged in a grid structure mean principally arrangements in which the illumination groups lie on the grid points of a regular grid. 
         [0059]    In another embodiment, the semiconductor light sources and/or the individual illumination group arrangements can be controlled separately by means of a control. For example, the contrast in given image areas can be increased by adjusting the light intensity with such a control. The tint of the emission of the backlighting arrangement can also be varied by varying the light intensity of the individual semiconductor light sources with the same emission spectrum. If individual light sources or illumination groups fail, the change of emission brought about by the failure can be corrected. 
         [0060]    The illumination device  11  shown in  FIG. 6 , for example, has a backlighting arrangement  1  like that described in connection with  FIG. 2 , and an optical element  10 . 
         [0061]    The backlighting arrangement  1  comprises a plurality of semiconductor light sources  42   a  and  42   b  that are arranged on a carrier  12 . The carrier  12 , for example, can be a printed circuit board. A blue semiconductor light source  42   a  and a green semiconductor light source  42   b  are components of an illumination group  41   b.    
         [0062]    The illumination groups  41   b  are arranged on the carrier  12  so that the emitted light passes through the optical element  10 . 
         [0063]    In the case illustrated, the illumination device  11  is a display device, wherein the optical element  10 , which is an LCD, has the property of providing information. 
         [0064]    There is a liquid crystal  14  between a first substrate  13   a  and a second substrate  13   b , with an electrical field being applied to the liquid crystal  14  to display information. 
         [0065]      FIG. 7  shows an illumination device  11  with a backlighting arrangement  1  and an optical element  10 , with the illumination device  11  serving as a lighting device. The optical element  10  can have light-mixing or light-aligning properties. The optical element  10  is preferably a BE (Brightness Enhancement) film with a suitable structure, for example a prismatic array or an array of inverse CPCs (Compound Parabolic Concentrators). 
         [0066]    The invention is not limited by the description with reference to the examples of embodiment. Instead, the invention comprises any new feature and any combination of features, which includes in particular any combination of features in the Patent Claims, even if this feature or this combination itself is not specified explicitly in the Patent Claims or examples of embodiment.