A simple 'click' of the lens will power up 2 LEDs that pump out 4 lumens of beautiful, bright light that is even visible from the side of your bike for cross traffic. The silicone mounting strap makes it easy to install/remove and works on pretty much any bike frame from 15-35mm. Ingress protection rating or 'IP Rating' is a techy way to describe the level of water and dust-proofness a product has. This light meets the IP-65 Standard, which means it is totally protected against dust/grit and fully resists strong jets of water from all directions. Two CR2032 coin cell batteries are included and are super-easy to replace.