With regulated circuitry, Princeton Tec's Quad can run on alkaline or lithium batteries. Four Ultrabright LEDs illuminate the darkest conditions with a wide flood beam. With a low battery indicator, a separately molded battery tray and high grade materials, the Quad is a popular headlamp for paddling and general outdoor use.Regulated Output: Princeton Tec lights feature regulated LEDs with a sophisticated regulating circuit that maintains constant brightness as long as the batteries have sufficient voltage. Through the Regulated Output period constant brightness, the light will maintain a certain level of lumens depending on the setting. Following this duration, the light will continue to work, though it will function at a lower lumen output. Lights without Regulated Output will begin dimming slowly from the onset, and will continue to dim until the battery is exhausted. They will not maintain a constant lumen output like that of Regulated Lighting.