Abstract: A light integrator having four parallelepipedal glass plates which have an identical width. Each plate has an inner side and an outer side with a length, as well as a first and a second longitudinal side and two end faces with a height, the plates are arranged relative to one another such that they enclose a parallelepipedal open cavity extending over the length, the glass plates being bonded to one another. The inner sides of the plates are subdivided into, in each case, a mirror-coated, optically active surface and an adhesive surface, and the inner side bearing with its adhesive surface of in each case one glass plate indirectly via adhesive against the first longitudinal side of another glass plate. The inner side of said glass plates have a groove running in a longitudinal direction and acting as an adhesive trap adjoining the optically active surface.