~Nitecore says~ 

The NU21 lightweight rechargeable headlamp is the perfect companion for runners and outdoorsmen alike. Its unibody optical lens system is specifically designed for reflecting a uniform and soft light that can emit a max brightness of 360 lumens that can reach up to 63 yards, making it perfect for night running and route finding. The NU21 offers versatility with four brightness modes, as well as emergency SOS and beacon. Alternatively, switch to the dual red LEDs and protect your night vision or for a long-lasting signal light. Its ultra-low standby power consumption provides a 365-day ready experience while its highly efficient constant current circuit guarantees a comfortable visual experience.