None of the lights with Usb ports are useful for anything other than providing an emergency charge for a phone or running a GPS unit at 5V 500mA = 2.5W. You can get a lot of power out of a dynohub, up to 10W , but it costs money to do so. Probably the highest output device so far is the Forumslader, from Germany, it has a lot of trickery so it can maximise the efficiency of the hub at low speeds like you'd find touring, but it's not cheap!