An electrical ballast is a device intended to limit the amount of current in an electric circuit. Ballasts vary greatly in complexity. They can be as simple as a series resistor as commonly used with small neon lamps or light-emitting diodes (LEDs). A more complex type is one that uses reactance. Losses in the ballast due to its resistance and losses in its magnetic core may be significant, on the order of 5 to 25% of the lamp input wattage. Practical lighting design calculations must allow for ballast loss in estimating the running cost of a lighting installation. Prior to 1980 in the United States, PCB-based oils were used as an insulating oil in many ballasts to provide cooling and electrical isolation. Older buildings (including schools and commercial operations) will often have PCB ballasts in their fluorescent lights even today because the ballast will work a longer than the bulb. he U.S. Environmental Protection Agency (EPA) today released guidance recommending that schools take steps to reduce potential exposures to PCBs from older fluorescent lighting fixtures. The guidance, part of EPA’s ongoing efforts to address potential PCB exposures in schools, is based on evidence that the older ballasts contain PCBs that can leak when the ballasts fail, leading to elevated levels of PCBs in the air of schools that should not represent an immediate threat but could pose health concerns if they persist over time.