I've never had a double ligero, but my tobacconist says the Double Ligeros are the only cigar he smokes that can knock him on his ass, and he smokes 5 cigars each day, at least.
Ligero is a designation given to leaves on the upper part of the plant. I want to say the LFD ligeros use filler/binder from the lower primings of the ligero section, while the double ligeros use only the highest primings of the ligero.