I decided to fit an LED in the head of my costume that will provide light behind the "Vision Bar" (the robot equivalent of eyes). A hole is poked (or drilled) towards the top of the head on the front face. I then seated the LED in the hole. After that I tape an AA battery pack inside the head. I then wire one end of the battery pack to LED and the other to a switch, keeping in mind the fact that the current can only flow in one direction through a diode. A wire is then run from the switch to the LED. Please note that the wire-LED connection is crimped to keep it from failing.