“Be Seen. Run Longer.” The Nathan LightSpur Rx™ attaches to the back of your shoes for greater visibility in low light conditions. This Ragnar® approved device is the perfect travel essential for races that may require running in the dark. Features 3 modes. Perfectly tensioned to stay on shoes during high-impact motion. Contains a fixed Li-ion Polymer rechargeable battery with an 8+ hour continuous burn, and 16+ hours of strobe. USB power cord include. Fits shoes up to size 15. Provides LED visibility up to 2400 ft.