How do I know when my Tahitian limes are ripe and ready to use

Limes are actually harvested before they are ripe, most will turn yellow if you leave them on the tree. Look for fruit which is a lighter green, smooth and slightly soft when gently squeezed. The best way to check is to harvest one, cut it open and give it a try. Keep in mind that they will not ripen further once they are harvested.