The invention relates to a transparent substrate comprising, on its surface, a light-diffusing array comprising at least 10 juxtaposed sub-gratings of parallel lines of features, said features being separated by domains with a refractive index differing from that of the features, each sub-grating comprising at least 20 repeated successive identical features equally spaced apart with a period p, said period varying non-monotonically from one edge of the sub-grating array to the other. This substrate redirects the light without iridescence in a daylighting application.