in the following elements signal paths and beam paths which have the same meaning have been provided with the same reference characters in the figures and after they have been described once they will only be further mentioned in the further description insofar as is necessary for the understanding of the present invention fig1 shows a first embodiment with a single light source 10 the light emitted by source 10 is focussed to a parallel light beam by a means of focussing means 11 in this embodiment a spherical concave mirror 11a the focal point of which coincides with the position of the light source 10 and a lens 11b the focal point of which also coincides with the position of the light source 10 the parallel beam passes onto a means of polarization 13 which in this embodiment is a polarization beam splitter the beam splitter 13 divides the light beam 12 into an effective beam 12a and a complimentary beam 12b effective beam 12a has a first polarizing direction and passes to an element 14 which is to be illuminated such as an lcd display the complementary beam 12b has a second polarizing direction and is reflected onto a mirror 15 the complementary beam 12b is reflected back to the polarization beam splitter 13 by the mirror 15 and subsequently to the lens 11b the lens 11b focuses the deflected complementary beam 12b onto the light source 10 which in this embodiment example has a glass body with a rough surface the deflected complementary beam 12b is depolarized by passing through the rough surface thereby exhibiting components of the first polarization direction.