A device for generating a quadrangular illuminating field, having a light mixing rod, which has a quadrangular cross-section as well as a quadrangular inlet area and a quadrangular outlet area, and guides light coupled in via the inlet area to the outlet area, in order to generate therein the quadrangular illuminating field, said outlet area being limited by four rectilinear sides, of which two each meet in one of the corners of the outlet area, wherein, in one or two corners, the sides meeting therein converge at right angles and, in the other corners, the sides meeting therein converge at an angle, which is not equal to 90°.