Ballasts, such as those used in fluorescent lighting systems, prevent overheating by limiting the lamp's electrical current, according to Rensselaer Polytechnic Institute. Without a ballast, a lamp would not even be able to start.
Ballasts work as inductors to cause an equilibrium reaction inside the lamp, according to HowStuffWorks. In magnetic ballasts, which are the most simple type, the wire inside the ballast is coiled to amplify the magnetic field generated when electricity travels through the wire. This regulates a fluorescent lamp's electrical current. Other ballast designs use different methods to achieve the same functionality.
When a lamp that relies on gas is turned on, it relies on the ballast to prevent overheating. Electricity heats the filaments inside the bulbs, ionizing the gas. When gas is first ionized, the resulting electrical current spike would cause the lamp to fail if the ballast were not present to limit it, as explained by EngineersGarage.
The ballast also releases the energy it has stored, causing a surge that helps set up the electrical arc running through the gas. In some new fluorescent lamps, the ballast is designed to continuously channel electricity, making it possible for the lamp to rapidly switch on instead of requiring time to warm up.