Many have asked how this was done. To get the skirt to fly out like this, Whitney Sue did Pirouettes (spun on her toe) and on about the 2nd or 3rd turn I would snap. It took 26 tries to get this one! The lights flash at 1/1200th sec so they stopped the skirt.
Here are 22 of the 26 tries! Click to enlarge thumbnail strip and to see the GIF animation by Erich Mangl! http://www.pbase.com/erichmangl