We put a spotlight on our robot...a cheap $14 unit from Walmart. We only used the LED and reflector from the spotlight. The custom circuit consists of a LM7805 voltage regulator and 3.6 Ohm 5 Watt series resistor, and it also uses a Spike relay. The relay is controlled by a relay output on the roborio.
http://www.simple-electronics.com/20...regulator.html
in case you don't know how to figure the resistance and wire up this type of custom circuit.