Light integrator consisting of four identical, parallelepipedal glass plates (1) which are adhesively bonded to one another and which jointly enclose a parallelepipedal open cavity (6), wherein the inner sides (2) delimiting the cavity are subdivided into in each case a reflectively coated, optically active surface (2.1) and an adhesive surface (2.2), which includes a groove (7) running in the longitudinal direction and acting as an adhesive trap which adjoins the optically active surface (2.1), and the adhesive surface (2.2) of one glass plate (1) in each case bears indirectly via adhesive (9) on the first longitudinal side (4.1) of another glass plate (1).