I have a nice little USB light which has no off switch, it is 'on' for the duration of being plugged in.

My question is, is there a way of disabling the USB port so as to turn off the light while it is still plugged in? Preferably, this could be done from the command line, but if it's possible at all that would be really cool regardless. I use Mac and Linux, but am interested to learn if this is possible in any OS, or if physical hardware prevents usage like this.