Wireless Sensor Networks (WSNs) use geographic routing to deliver measurement data to one or more sink nodes. In employing geographic routing data packets are forwarded along approximate geodesic (shortest) paths, WSNs distribute the forwarding task unevenly between nodes. Nodes closest to the data sinks, or the geographic centre of the network coverage area and nodes at the periphery of void areas carry significantly more traffic. Consequently, their batteries deplete at a faster rate than the remaining nodes, causing void areas to form and grow, thus decreasing the overall network lifetime below a theoretically attainable period. We propose a routing protocol inspired by the propagation of light-rays in graded-index media aiming to extend the overall network lifetime with minimal, local co-ordination overheads only.