Patent ID: 8087799

Claim:
An illumination means, comprising: a single annular segment defining an opening between ends of the single annular segment and the ends being operatively arranged for receiving an edge area of a wafer, the single annular segment including: a plurality of light sources formed as light-emitting diodes arranged on the annular segment; a housing, wherein the plurality of light sources are arranged on a board inside the housing; and, a reflective element arranged inside the housing such that light emitted from the plurality of light sources does not impinge perpendicularly on an upper edge area, a lower edge area and a front area of the wafer, and wherein the plurality of light sources are arranged opposite the reflective element inside the housing; wherein the housing comprises: the single board shaped as the single annular segment; a cover arranged opposite the upper edge area, the lower edge area and the front area of the wafer, said cover in the shape of the single annular segment; and, a window arranged to allow the passage of the light from the light sources therethrough and wherein first and second lids are arranged to close the housing at respective end areas of the housing, each of said end areas being the ends of the single annular segment and the window includes a diffusely scattering optical element and/or a diffractive optical element for beam shaping; and, wherein a beam path of the light emitted by the plurality of light sources is parallel to the upper edge area and the lower edge area of said wafer when the wafer is received by the annular segment.