A cardiac ablation instrument includes a catheter body and a tear-shaped balloon that is connected to the catheter body. The instrument further includes a radiant energy emitter that is axially movable within a central lumen of the catheter body. A radiant energy transparent body surrounds the energy emitter and includes a plurality of illumination fibers disposed circumferentially about the energy emitter. A detector communicates with a contact sensing element and is configured to determine an amount of at least one color component of the reflected light The amount of the at least one color component being indicative of contact between the balloon and a target tissue site.