Ballast may mean something that improves stability
- Track ballast (gravel or cinders) forms the railroad or railway track-bed on which sleepers (ties) and track is laid. The ballast allows for proper drainage and minimizes frost heaving.
- Ship's ballast (water, sand, rocks, or bricks) is used to weight a ship down when it has very little cargo (though water may contain invasive species of pests).
- An electromagnetic lamp ballast uses electromagnetic induction to provide the proper starting and operating electrical condition to power a fluorescent lamp, neon lamp or HID lamp. The electromagnetic ballast used in an electric circuit limits the current flow to the lamp. It does not change the frequency of the power; the connected lamp illuminates on each half-cycle of the mains power so it flickers at 100 Hz (for most of the world) and 120 Hz (for those portions of the world that use 60 Hz mains power; see alternating current). Some ballasts that connect to two or more lamps vary the phase relationship between the multiple lamps to mitigate the flicker of the lamps. These ballasts are often called lead-lag ballasts because the current in one lamp leads the mains phase and the current in the other lamp lags the mains phase.
- An electronic lamp ballast uses solid state electronic circuitry to provide the proper starting and operating electrical condition to power a fluorescent lamp, neon lamp or HID lamp. Electronic ballasts are generally smaller and lighter, function cooler and more efficiently than electromagnetic ballasts. Electronic ballast usually change the frequency of the power from the standard mains frequency to 20,000 Hz or higher, substantially eliminating the stroboscopic effect associated with fluorescent or high-intensity discharge lighting. They are often based on inverter/converter style power supplies, rectifying the input power and then chopping it at a high frequency, much like the first part of a switched-mode power supply.