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What is a Lighting Ballast?

By J. Dellaporta
Updated May 17, 2024
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A lighting ballast is a piece of equipment required to control the starting and operating voltages of electrical gas discharge lights. Examples of gas discharge light sources include fluorescent and neon lights and high-intensity discharge (HID) lamps. The term lighting ballast can refer to any component of the circuit intended to limit the flow of current through the light, from a single resistor to more complex devices.

A lighting ballast is necessary to operate discharge lights because they have negative resistance, meaning they are unable to regulate the amount of current that passes through them. A lighting ballast must be used to control current flow; otherwise the light could fail. Small light sources can use passive components, which require no additional power to operate, as ballasts. An example would be a series resistor that limits the flow of current across its terminals. For high-powered lights, however, a resistor would waste a large amount of electricity, so a more complex lighting ballast is required.

An electromagnetic lighting ballast uses electromagnetic induction to provide the starting and operating voltages of a gas discharge light. Inside each is a coil of wire and an electromagnetic field that together transform voltage. Some also include an igniter for high-power applications.

Electromagnetic ballasts limit the flow of current to the light but do not change the frequency of the input power. The lamp then illuminates on each half-cycle of the power source. This is why many fluorescent and neon lights visibly flicker. Since the light illuminates on half-cycles, the rate of flicker is twice the frequency of the power source, meaning the light will flicker at 100Hz or 120Hz. A lead-lag lighting ballast can minimize flicker when connected to two lamps by alternating the flow of current to them: one leading the frequency of the input power and the other lagging behind it.

A more modern type of lighting ballast is electronic instead of electromagnetic. An electronic lighting ballast uses solid state circuitry to transform voltage, but unlike electromagnetic ballasts, can also alter the frequency of power. This means that an electronic lighting ballast can greatly reduce or eliminate any flicker in the lamps. Because it uses solid-state circuitry instead of magnetic coils, it is also more efficient and therefore runs cooler.

Because of their greater efficiency and ability to reduce flicker, electronic ballasts are more popular than electromagnetic ballasts, and are often used to replace them. A few applications, however, require an electromagnetic lighting ballast, such as ballasts that must preheat or ballasts for extremely high output lamps.

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Discussion Comments
By anon338196 — On Jun 12, 2013

Can we use fluorescent lamps without ballast? If we can, then please provide me the methodology.

By anon327153 — On Mar 26, 2013

Just wondering if anyone out there can tell me how to recover the copper windings in a ballast? I'm into recycling and trying to up the money I get for these as is. I know they are filled with a tar substance and being environmentally savvy, burning is out of the question. Any helpful suggestions would be welcome.

By anon209186 — On Aug 25, 2011

Just wondering if ballast were installed in vehicles. My Acura Cl's low beams are not working and it has nothing to do with the bulbs.

By anon137883 — On Dec 29, 2010

how do you check a ballast when light doesn't work?

By anon98631 — On Jul 23, 2010

no the lamp will burn out or explode if not used with the correct control gear. a hid lamp (high intensity discharge lamp) works on a ballast and igniter system. using the incorrect lamp puts pressure on the ballast and it eventually burns out, thus causing the circuit to trip. It will cost you more in the long run.

By anon83322 — On May 10, 2010

What is considered "high-powered lights"? I have some neon lights in my garage. how would I know if a ballast is required or if a resistor would do?

By anon76031 — On Apr 08, 2010

could i just use a transformer instead of a ballast to run my hid sodium lamp? cheers

By anon60608 — On Jan 14, 2010

I would try to match the number on the ballast to the bulb, for example, a 159 bulb to a 159 ballast for long lasting life. Otherwise you will be changing bulbs every other day. --Elbows

By anon47636 — On Oct 06, 2009

I have got a 400W high pressure sodium that isn't working. The bulb is new so how can I find out if it is the ballast or the ignition?

By anon39162 — On Jul 30, 2009

my neon lights turn on and then off but won't turn on again unless I jiggle the bulb. I assume the light bulbs are functioning, but do I have a ballast problem? Thanks.

By anon37552 — On Jul 20, 2009

hi thanks for your explanation. just wanted to know if a 600w bulb or below would work on a 1000w ballast the light bulb will be the same high pressure sodium or metal halide (HID)

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