I noticed a cousin, on my wife's side, with an incandescent MagLite this weekend. I am not sure if it is a 3 D or 4 D size. At any rate, I am looking at this as an opportunity. Now I am NOT looking for suggestions for exotic stuff that can only be purchased online in this particular case, but I am looking for whatever the lowest common denominator is. That is to say, what does Wal-Mart carry in the way of LED upgrades that will work on a 3 or 4 D MagLite?