The Sanibel Island lighthouse is very easy to find once you arrive on Sanibel.  If coming from the Causeway approach to the island, you just make a left at the 4 way stop sign as you enter the island.  This road is named Periwinkle way.  Follow Periwinkle until it ends and you have arrived at the lighthouse.  The lighthouse sits on the Eastern end of the island closer to the causeway bridge and opposite end of the island from Captiva Florida