The floodlights illuminating the upper 30 floors of the Empire State Building will be turned off from dusk until mid night from now to May 31 so that migrating birds returning north this spring will not be come confused and fly into the structure. In the fall, the lights again will be turned off from Sept. 15 to Nov. 1 for the south bound migration. The procedure was begun in 1955 at the urg ing of the National Audubon Society.