@Override
        public int compare(Light l1, Light l2) {
            if (l1.lastDistance < l2.lastDistance)
                return -1;
            else if (l1.lastDistance > l2.lastDistance)
                return 1;
            else
                return 0;
        }
This assumes lastDistance have been computed in a previous step.
jme3-core/src/main/java/com/jme3/light/LightList.java