An illumination system comprises a lightguide (12) having a plurality of light extraction features (LEFs); and a plurality of independently controllable light sources (11a, 11b, 11c). The LEFs have a preferred direction, with light that is incident on an LEF along the preferred direction of the LEF being extracted from the lightguide generally parallel to a reference plane, and light that is incident on an LEF not along the preferred direction of the LEF being extracted from the lightguide at an extraction angle to the reference plane, the extraction angle being related by a response function to an incidence angle between the light propagation direction and the preferred direction of LEF. The shape of the LEFs varies with distance from a reference point or respective reference point so that the response function becomes larger with increasing distance of the LEFs from the reference point.