Optoelectronic components are frequently used to illuminate rectangular areas. For example, back-lighting apparatuses are known for flat screens, which have a plurality of optoelectronic components. However, the latter normally have a rotationally symmetrical emission characteristic. Homogeneous illumination of a rectangular area is not possible using optoelectronic components such as these since rotationally symmetrical beam cones cannot be superimposed, simply for basic mathematical reasons, in such a way that the area is illuminated homogeneously.
By way of example, if the components are arranged in a hexagonal grid in order to achieve an illumination intensity distribution which is as homogeneous as possible in a central area of the illuminated area, inhomogeneities occur at the edge of the illuminated area. The homogeneity of the illumination at the edge of the illuminated area can be improved by arranging the components in a rectangular grid. The homogeneity of the illumination in the central part of the area is then worse compared to the arrangement in the hexagonal grid, and the illumination intensity distribution has fluctuations which run on the same grid as the arrangement of the optoelectronic components.
In order to reduce these inhomogeneities, the components must be arranged at a very short distance from one another. The back-lighting apparatus therefore contains considerably more optoelectronic components than are required to achieve the desired light intensity.
Alternatively, the radiation can be output from a back-lighting apparatus through a diffuser plate with high reflectivity and low transmission. This forces multiple scattering to occur within the back-lighting apparatus, and increases the homogeneity of the output light, at the expense of efficiency. Additional optoelectronic components are then required in order to achieve the desired light intensity of the back-lighting apparatus.
In another procedure for reducing the inhomogeneities, the beam cones of the components are greatly widened by means of divergent lenses. The homogeneity which can be achieved in this way is, however, inadequate for many applications. Furthermore, this procedure places extremely stringent demands on the manufacturing tolerances and assembly tolerances.