The tail light features a Smart Light Sensor so it comes on automatically when it senses darkness. With 180 lumens ahead fanning out for 180 degree visibility and 100 lumens behind, you'll be spotted whether it's pitch dark or merely dusk. 24 LEDs per light disperse the beam evenly, to minimize the blinding effect on other riders and drivers while maximizing your chance of being seen. The Burner set runs for up to 60 hours between charges, giving you about a month of riding before you need to plug it in (depending on how much you ride).