Most average curling games do not use curling stones with lights equipped. Almost any time you see curling stones with lights, it’s at a big tournament like the Olympics. In curling, there is a line called the hog line, players must release the handle of a curling stone before crossing the hog line for the stone to be considered in play. A green light on the curling rocks indicates that the handle was released in time, and a red light indicates that it was not released on time.