When you plug it in, the light is off, but the button is lighted so you can see where the button is in the dark. The button is not visible in the photo, it is on the left side of it which is the back side of the light opposite the lens. You would have to reach down to the position of the light to turn it on or to switch to low setting. It also have a flash setting that I never use.

There are lots of USB powered lights from Asia on Ebay, the others might be wired differently, the one I showed is the only one I am familiar with.

A bit off topic, but I decided to quit mounting a light on my S&S bike when i tour on it. Since I almost never use a light on that bike when touring, installing and later removing the light on the bike was a hassle since I had to remove the light to pack the bike in the S&S case. Thus, for touring on that bike I switched to the light in the photo. I leave that light in my handlebar bag in the rare event that I need it. I can run it off of a powerbank that i also keep in the handlebar bag.