A retractable window covering for natural illumination of building interiors by redirecting the incident daylight at angles that promote its deeper penetration into the interior space. The window covering comprises an optically transmissive, flexible polymeric sheet having reflective surfaces incorporated into its material and configured to redirect at least a portion of light propagating through the sheet towards a desired direction. The window covering is operable from a closed to an open position so as to increase or decrease the amount of redirected and/or admitted light.