The resistance from the extra 2 ft of wire would be minute, and hard to measure. Also the difference in brightness will be impossible to tell even though there will be a difference (not visible to the human eye). You can take any 2 lightbulbs, and they will never illuminate the exact same just from minute differences during the manufacturing process (even if they came off the same assembly line). Your thinking too much. You can cut 2 ft of wire, and then use the same yard stick to cut another 2 ft. They will not be exactly the same length. One will be thousandths of a millimeter off from the other.