Magnetic ballast is a type of ballast that uses a magnetic core to regulate the voltage of a fluorescent light. Magnetic ballasts are the simplest type of ballast and have been in use for many years. Their great advantage is their robustness. Built from rugged materials, they can withstand exposure to electric system transients and fluctuations, as well as extremes of heat and cold. Their efficiency has been continuously improved, so that it may be worthwhile, in terms of energy and money, to replace older ballasts (as well as fluorescent tubes) with new ones.