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When a fluorescent lamp is to be operated on dc which of the following additional device must be incorporated in the circuit?

  • When a fluorescent lamp is to be operated on DC, an additional device that must be incorporated in the circuit is a Ballast resistor.
  • The Ballast resistor is connected in series with the fluorescent lamp to limit the current that flows through the lamp. In AC circuits, the voltage across the lamp reverses polarity 100 to 120 times per second.
  • This rapid change in voltage allows the ballast in an AC circuit to be an inductive coil that opposes the flow of current, limiting it to the desired level.
  • However, in DC circuits, the voltage is constant, and an inductive ballast will not function as intended.
  • Therefore, a ballast resistor is used in DC circuits to provide the necessary resistance to limit the current flow through the lamp.