<P> An electrical ballast is a device placed in line with the load to limit the amount of current in an electrical circuit . It may be a fixed or variable resistor . </P> <P> A familiar and widely used example is the inductive ballast used in fluorescent lamps to limit the current through the tube, which would otherwise rise to a destructive level due to the negative differential resistance of the tube's voltage - current characteristic . </P> <P> Ballasts vary greatly in complexity . They may be as simple as a resistor, inductor or capacitor (or a combination of these) wired in series with the lamp; or as complex as the electronic ballasts used in compact fluorescent lamps and high - intensity discharge lamps . </P>

A(n) ____ is not a type of fluorescent ballast