Abstract:
An illumination unit for planar illumination is described. The illumination unit includes a light source and a waveguide plate, the waveguide plate being provided with mounting possibilities for the light source, various optical filters, electronics boards, and a liquid-crystal cell.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an illumination unit. 
     BACKGROUND INFORMATION 
     An illumination unit for planar illumination is already known from the related art. Such an illumination unit is used, for example, in the liquid-crystal display (LCD) of the firm Toshiba with the type designation TFD 50 W 30. The LCD has a supporting frame in which the different components, such as the liquid-crystal cell, light guide of the illumination unit, lamp for the illumination unit, reflectors for the illumination unit, as well as the control electronics are mounted. Because the design is composed of many components, considerable expenditure of energy is necessary to assemble the LCD. 
     SUMMARY 
     The arrangement according to the present invention has the advantage that the assembly of the LCD requires considerably less time, and is therefore more cost-effective. 
     A further advantage is that the components of the LCD can be manufactured at a lower cost per unit. 
     Finally, a further benefit is that the illumination unit of the present invention allows a modular design of the liquid-crystal display which appears easy to automate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 : shows a front view of an illumination unit in accordance with an example embodiment of the present invention. 
     FIG.  2 : shows a rear view of an illumination unit accordance to the present invention. 
     FIG.  3 : shows a side view of an illumination unit according to the present invention. 
     FIGS.  4  and  5 : show detail drawings for mounting the lamp of an illumination unit according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows the front view of an illumination unit according to the present invention. The illumination unit has a base plate  19  which is made of transparent or slightly diffusive material. The basic form of base plate  19  is that of a flat, rectangular cuboid having two short end faces  22  and  23 , two long end faces  24  and two top surfaces  25  and  26 , the first top surface  25  having a slightly raised, surrounding rim which is designed as a retaining frame  7 . The two long end faces  24  have a depression  11  which has a rectangular cross-section and extends from first top surface  25  to second top surface  26 . The first, short end face  22  is provided with a cutout  5  whose width and depth are so dimensioned that a cable, ribbon cable or conductor strip can be run through cutout  5  from first top surface  25  to second top surface  26 . Arranged on first top surface  26 , in each of the corners between a long end face and a short end face, is a fixing pin  6  formed as a cylindrical body which is approximately perpendicular to the first top surface. Running along short end faces  22  and  23  are two slits  8  which are approximately perpendicular to the top surfaces and interconnect them. The length of the slits is selected such that they are as long as possible, but do not connect the long end faces, and do not jeopardize the structural stability of base plate  19 . A lamp is mounted in each of the two depressions  11 , the lamp having an elongated, cylindrical shape and its longitudinal axis running in a direction parallel to the longitudinal axis of base plate  19 . Also located in depression  11 , on the side of lamp  9  facing away from base plate  19 , is a reflector  10 . A line AA′ defining the sectional plane for the sectional drawing depicted in FIG. 3 is drawn in between two of depression pins  6 . 
     FIG. 2 shows a rear view of the illumination unit depicted in FIG. 1, identical component parts being provided with identical reference numbers. Again, a base plate  19  having a basic rectangular form is shown, the second top surface  26  being visible in the rear view. Cutout  5  can be seen in the first short end face; the two end faces  24  have one depression  11  each. One lamp  9  and one reflector  10  each are mounted in depression  11 . The two slits  8 , which were already visible in FIG. 1, run between the mutually opposing corners of depression  11 . Slits  8  divide base plate  19  into a mounting zone  3  and a waveguide zone  1 . In this context, the area of base plate  19  located between the two slits  8  is designated as waveguide zone  1 , while the expression mounting zone  3  refers to the remaining areas of base plate  19 . The drawing shows four mounting bore holes  2  in the corners of second top surface  26 . 
     FIG. 3 depicts a cross-section through the illumination unit, shown in FIGS. 1 and 2, along intersection line AA′ shown in FIG.  1 . Again, identical component parts are provided with identical reference numbers. Base plate  19  has an approximately rectangular cross-section, the first top surface  25 , second top surface  26  and both long end faces  24  being shown as intersection lines. An elevation, i.e., the retaining frame, is provided at the edge of first top surface  25 . Two fixing pins  6  are also shown on first top surface  25 . Light emitted by lamp  9  is now either irradiated directly into base plate  19 , or is coupled into base plate  19  with the aid of reflector  10 . The light coupled into base plate  19  is reflected at the cut surfaces of slits  8  which, if desired, can be polished or provided with a reflective coating for this purpose. Furthermore, the light, which spreads in a direction approximately parallel to the top surfaces, is totally reflected at them. Due to these reflection effects, the light remains restricted mainly to waveguide zone  1  of base plate  19 . Portions of the light conducted in waveguide zone  1  are not totally reflected at first top surface  25 , but rather are emitted. Therefore, the material for base plate  19  is selected such that it has a slightly light-diffusing effect; however, other physical arrangements, such as the structuring of one or both top surfaces with prisms, as described in the German Patent Application No. 96 52 209.9, are also conceivable. By providing depressions  11 , it is possible to mount lamps  9  and reflectors  10  in the same base plate  19  which also has waveguide zone  1 . To make a liquid-crystal display using the illumination unit according to the present invention, the various required filters can be placed on top surface  25  in the form of films. For this purpose, the films should have an approximately rectangular form, with dimensions which are selected such that they are smaller than the inside dimensions of retaining frame  7 . It is also possible to provide the films with four circular holes which are arranged in such a way that the films can be supported with the assistance of fixing pins  6 . A liquid-crystal cell, composed of two glass panes with the liquid crystal situated in between, is then placed on fixing pins  6  above the film. The external dimensions of the liquid-crystal cell are selected in such a way that it is held against retaining frame  7 , free from play and strain. Usually, a liquid-crystal cell has an electrical connection in the form of a flexible strip having imprinted electric conductors. This flexible strip can be run through cutout  5  to the back side, and folded there onto second top surface  26 . An electronics board and, optionally, a rear cover can also be secured on second top surface  26  with the aid of fixing bore holes  2 . 
     The exemplary embodiment shown in FIGS. 1 through 3 can easily be adapted to other designs of lamps  10 , for example, an L- or U-shaped lamp, or even to a different number of cylindrical lamps. In particular, allowance is also made to furnish a depression  11  only on one long end face of base plate  19 , and to mount a single bar-shaped lamp. In this case, it is also advantageous to apply a reflecting coating to the second long end face opposite of the lamp. 
     It is also conceivable and provision is made for using massive mirror (reflector) elements, particularly of metal or metallic layers, to limit waveguide zone  1 , instead of using slits  8  which are relatively easy to produce. To this end, after producing a massive base plate  19 , it is possible to provide slits in base plate  19 , a mirror then being inserted and secured in the slits. If base plate  19  is produced using a casting process, for example, reaction casting, injection molding or pressure die casting, then it is also possible to first introduce the mirror into the casting mold, and then cast around with the material for base plate  19 . 
     It is further possible for slits  8  to pass right through, so that they interconnect two mutually opposing depressions  11  or end faces. In this case, however, it is necessary that the first top surface and the second top surface not be interconnected. 
     It is also possible and allowance is made for making the depth of slits  8  greater where they are at a greater distance from the lamp, since in this manner, the light is homogenized within the waveguide zone. 
     A particularly simple possibility for mounting the lamp in the base plate is shown in FIG.  4 . To this end, starting from a short end face, base plate  19  is provided with a bore hole  20  having a diameter which is somewhat greater than the outside diameter of lamp  9 , and running in a direction parallel to long end face  24  and to the upper surface. Lamp  9  is supported in this bore hole  20 . Additionally, the long end face can now be rounded off, so that instead of a long end face, rounding  15  results. Rounding  15  can then ideally be used for placing a mirror. 
     It is also possible and provision is made for selecting the lamp mounting shown in FIG. 4, without providing base plate  19  with depression  11 . If, in this case, the long end face is replaced over its entire length by the rounding, then a mirror  15  can also be produced by vapor-depositing a reflecting material on rounding  15 . 
     A further exemplary embodiment is shown in FIG.  5 . FIG. 5 again shows the top view of a first short end face  22  of a base plate  19 . Starting from first short end face  22 , base plate  19  is provided with a bore hole  20  running in a direction approximately perpendicular to first short end face  22  and approximately parallel to long end face  24 . Again, a lamp  9  is inserted into bore hole  20 . A reflective coating  18 , made, for example, of vapor-deposited metal, is applied on the body of lamp  9 . Reflective coating  18  covers approximately half or two thirds of the surface area of the cylindrical form of lamp  9 , so that light can emerge from the lamp only in the direction of waveguide zone  1  of base plate  19 . Due to this reflective coating  18  applied to lamp  9 , the outlay required for assembling the illumination unit and a liquid-crystal display mounted on it is further reduced.