The Collaborative International Dictionary of English v.0.48:

Great White Way \Great White Way\
   Broadway, in New York City, in the neighborhood chiefly
   occupied by theaters, as from about 30th Street to about 50th
   Street; -- so called from its brilliant illumination at
   night.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

Great White Way
    n 1: a street in Manhattan that passes through Times Square;
         famous for its theaters [syn: Broadway, Great White
         Way]