It's a light about the size of a golf ball. It has a silicone rubber strap to attach to handlebars, etc. It runs on button batteries (2), not rechargeable, so they're easy to find even when you're out and about. Please refer to the last photo for brightness. It has 3 modes: flashing, fast flashing, and constant on. I bought it from a Chinese online shopping site, but I ordered too many, so I'm selling the extras.