An optical element, e.g. based on a diffractive Fresnel lens, having suppressed or reduced chromatic aberration under non-monochromatic light and/or enhanced directional homogenisation in its angular irradiation characteristics, comprises a plurality of optical zones (10, 20), wherein each zone comprises at least one homogenising noise-introducing feature. In embodiments the at least one homogenising noise-introducing feature comprises one or more zonal displacement features, e.g. ripples (20′, 20″) and/or one or more zonal modulation features, e.g. one or more patterning features (30).