From our guide to finding the right size lighting, including for pendants ( http://bit.ly/1cuh1Fj):

For hanging pendants above an island or table, start with 28-34 inches above said table as a rough guideline, but make sure to consider the sight lines of the people in the room so no one gets glare in their eyes or runs the risk of hitting their head on the pendants! Mount a pendant every 2 feet or so above a kitchen island.

Hope this helps! Let us know if you need more advice.