I actually saw an interesting design for a lighthouse with a rotating light on youtube. The rotation was achieved by sticky pistons arranged in a complete circle around a central light source. The pistons opened and closed in a sequence, which gave the lighthouse a rotational effect from a distance. The ingenious part of the construction was that it used a minecart to activate the motion. The minecart was on a closed circular track underneath the light, powered so that it ran infinitely even when empty. The track had detection rails dispersed at regular intervals, and those rails activated the pistons above, so the rotational effect of the light itself matched the path of the minecart going around and around in circles.