Illumination device for a screen with at least two operating modes

An illuminating apparatus intended for a display screen and operable in at least two operating modes B1 and B2 for illuminating one of two, and/or at least one operating mode B3 for simultaneously illuminating both, at least partially disjoint angular ranges W1 and W2, comprising:

• a backlight unit of planar extension, which, in a first alternative, radiates light into the restricted angular range W2 and, in a second alternative, radiates light into a restricted angular range W2a, not congruent with W2,
• a plate-shaped light guide that is situated in front of the backlight unit, as seen in a viewing direction, and features outcoupling elements on at least one of the large surfaces and/or within its volume, wherein the light guide is transparent to at least 70% of the light originating from the backlight unit,
• light sources arranged laterally on at least one of edge of the light guide,
• wherein a number of outcoupling elements per unit area and their extension are chosen so that the light guide, on at least 50% of its area, scatters at most 25 percent, preferably at most ten percent, of the light penetrating its large surfaces by more than ten degrees, whereby, at least in operating mode B2, the light radiated by the backlight unit into a restricted angular range W2 or W2a, when it passes the light guide, is scattered not more than slightly outside the angular range W2 or W2a,
• wherein a distribution of the outcoupling elements, on at least one of the large surfaces and/or within the volume of the light guide, is specified to the effect that light radiated by the light sources into the light guide and coupled out of the light guide by the outcoupling elements is radiated into a restricted angular range W1a, while at least 50% of an amount of light coupled out of the light guide is coupled out in a direction away from the backlight unit,
• wherein, in the first alternative, the restricted angular range W1a corresponds to the restricted angular range W1, and wherein, in the second alternative, the light coupled out of the light guide into the restricted angular range W1a is imaged by one or several optical layers situated, as seen in the viewing direction, in front of the plate-shaped light guide in such a way that it is finally radiated into the restricted angular range W1, and wherein, in the second alternative, the one or several optical layers deflect the light originating from the backlight unit in such a way that it is finally radiated into the restricted angular range W2, and
• wherein:
• i:
• is in operating mode B1, the light sources are switched on and the backlight unit is switched off;
• ii:
• in operating mode B2, the backlight unit is switched on and the light sources are switched off;
• iii:
• in operating mode B3, both the light sources and the backlight are switched on.