in 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 , the outlet area is limited by four rectilinear sides , of which two each meet in one of the corners of the outlet area , and , in one or two corners , the sides meeting therein converge at right angles while , in the other corners , the sides meeting therein converge at an angle , which is not equal to 90 °.