The ones I'm using this year are significantly lighter than the ones I used last year. Obviously it affects the weight and FOC but at the ranges I shoot at deer, I had no ill effects whatsoever. I would imagine if you shoot out to 35-40 yards or beyond, then yes, it could cause flight problems. The Lumenoks only add 18 grains to my arrows, and while it is all on the back of the arrow, I have seen no negative effects out to 35 yards so far. They are the bomb when shooting in the woods though, especially at dusk/dawn. No second guessing where your arrow hit (or missed).