Relatively flat illumination devices are known in the art and are for instance described in U.S. Pat. No. 7,025,482 and U.S. Pat. No. 7,181,378.
U.S. Pat. No. 7,025,482 describes a light guide member and an illuminating device which are able to efficiently uniformly irradiate illumination light to only an area requiring illumination. Therefore, a reflection face is constructed by reflection stripes such as many grooves, etc. widened in a concentric circle shape. Light from a light source unit is widened toward this entire reflection face without irregularities by a diffusing portion such as a reflection prism, etc. Thus, only the range actually requiring the illumination can be illuminated without irregularities, and visibility of the illumination range using a front light is raised.
U.S. Pat. No. 7,181,378 describes apparatuses, and methods for manufacturing such apparatuses, to convert a first distribution of an input radiation to a second distribution of output radiation. The apparatus can be defined in some embodiments by generating a two-dimensional representation of three active optical surfaces including calculating a segment of first, entry and second surfaces based on first second, and third generalized Cartesian ovals, respectively, and successively repeating the calculating of the segments of the first and second surfaces, and rotationally sweeping the two-dimensional representation about a central axis providing a three-dimensional representation. In some embodiments, portion of the first and/or second surfaces can be totally internally reflective (TIR). This document especially describes a folded-optics apparatus comprising a body that receives light, the body comprising first, second and third surfaces; the third surface defining a cavity, and at least a portion of the third surface is refractive; the second surface extending generally radially away from the cavity, and the second surface comprising a reflective region; and at least a first portion of the first surface provides internal reflection folding and at least a second portion of the first surface provides refractive transition between the body and an exterior of the body.
Further, WO2008047278 describes a luminaire comprising a light guiding layer and a plurality of LEDs, which LEDs are accommodated in at least one hole arranged in the light guiding layer, for emitting light into the light guiding layer. The light guiding layer further comprises at least one out-coupling structure, for coupling the light out of the light guiding layer.