ballast lamp - normal incandescent lamp used as a ballast resistor, current limiter, alarm, or to stabilize a discharge lamp, a. ballast resistor - a resistor inserted into a circuit to swamp or compensate changes, e.g. those arising with temperature fluctuations. One similarly used to swamp the negative resistance of an arc or gas discharge. Also known as ballast tube. b. ballast resistor - a resistor manufactured from material having a large positive temperature coefficient of resistance. It is constructed so as to have a substantially constant current over a range of voltage and with a circuit to absorb small changes in the applied voltage and stabilize the current in the circuit. One consisting of a resistor seated in an evacuated or gas-filled envelope of glass or metal is called a ballast lamp.