An illumination optical unit for EUV projection lithography guides illumination light to an illumination field, in which a lithography mask can be arranged. A facet mirror with a plurality of facets guides the illumination light to the illumination field. Respectively one illumination channel which guides an illumination light partial beam is predetermined by one of the facets. Exactly one illumination channel is guided over respectively one of the facets. The illumination optical unit is configured so that, at any time and at any point in the illumination field when the illumination optical unit is in operation, any pairs of illumination light partial beams guided over different illumination channels are incident on this illumination field point at times of incidence, the time difference of which is greater than a coherence duration of the illumination light.