Light control window covering and method and apparatus for its manufacture

A light-control window covering comprising:

• a first sheet of sheer material, and a second sheet of sheer material spaced apart from the first sheer sheet of material;
• a plurality of vanes having a first face and a second face, a center region and a first and a second longitudinal margin, the first face of each vane being ultrasonically welded to the first and second sheets of sheer material along the respective first and second longitudinal margins, each vane having a single permanent crease;
• the vanes being movable from a light-passing position in which the center region of each vane is substantially perpendicular to the first and second sheets of sheer material, to a light-blocking position in which the center region of each vane is substantially parallel to the first and second sheets of sheer material, the second longitudinal margin of each vane being folded over and adjacent the center region of each respective vane in the light-blocking position, and the vanes being spaced from one another such that in the light-blocking position the first longitudinal margin of one vane overlaps the second longitudinal margin of an adjacent vane.