Rechargeable 1500 Lumen Headlamp featuring Flex Fuel. The NEBO EINSTEIN Series is inspired by, obviously, Albert Einstein, who had a brilliant mind and a knack for innovation. He was fascinated by light and its many uses, and the EINSTEIN Series lights are inspired by his passion.After years of research and development, NEBO introduced the EINSTEIN 1500 FLEX a headlamp that embodies the spirit of adventure. With its low-profile, compact design, this headlamp is the perfect companion for any outdoor enthusiast.But don't let its small size fool you the EINSTEIN 1500 FLEX packs a powerful punch. With five different light modes, it's versatile enough to handle any situation. Never run out of light with the flex fuel feature, you can also power the light with two CR123A alkaline batteries.The EINSTEIN 1500 FLEX is also incredibly convenient. The USB-C rechargeable battery provides up to 18 hours of use, so you never have to worry about running out of power. And with its durable construction, you can trust that your headlamp will withstand the toughest conditions.