Ballast

A Ballast is a large resistor that regulates the amount of electrical current in a circuit. Most ballasts are used for fluorescent lamps to regulate the current thru it, which might rise to a dangerous level and burn it out.

Ballast is also crushed stone used in railway tracks. See ballast tamper.

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  3 Magnetic Ballasts: the ballast on the top is a Rapid start ballast, while the lower two ballasts are preheat ballasts.
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  Electronic 4 lamp Ballast