What is a ballast?

In the lighting industry, a ballast is responsible for controlling the flow of energy into the lamp itself. Ballasts can be wired onto an existing fixture or incorporated into its design, but the function is the same either way – make sure the flow of electricity into the lamp is safe enough to handle.

Several types of lighting require ballasts to properly operate, including fluorescent, metal halide and high-intensity discharge lamps (HIDs). LED lights use a driver, which is similar to a ballast and also modulates the flow of electricity into the diode. Incandescent and halogen lamps do not require a ballast because electrical flow is regulated by the filament inside the lamp. It’s this resistance that generates illumination.

What does a ballast do for a lighting system?

A ballast acts like a control valve for a fixture. Much like a control valve regulates the flow of water or gas through a pipeline, a ballast regulates the flow of electricity into the lamp. There are two reasons why many lighting solutions cannot do without this functionality.

1. Ballasts prevent damage to the lamp – Without a ballast in place, it wouldn’t take long for a fluorescent tube or metal halide become damaged beyond operation. A ballast prevents dangerous levels of current from reaching the lamp and frying sensitive components.

2. Ballasts provide an initial kick to switch the light on – Ballasts increase voltage to the system upon startup, as this provides the initial current needed to turn the light on. Once on, ballasts modulate the current so that it flows steadily into the system.

What types of ballasts are available for lighting?

There are a lot of ballasts available on the market, as they need to be matched up to the fixture’s electrical requirements. However, they can be sorted into two primary categories, including:

Magnetic ballasts

Magnetic ballasts represent older lighting technology, but they are still a preferred option in many projects, as they last a long time and cost less than electrical ballasts. However, magnetic ballasts are heavy, weighing around 4 pounds on average. This can pose a challenge during installation. Magnetic ballasts are also responsible for the familiar “hum” that we associate with fluorescent and HID lights, so they are a better fit for exterior projects. Some magnetic ballasts, called F-cans, do run quieter, though, and can be incorporated into interior systems.

Electronic ballasts

Electronic ballasts utilize solid state circuitry instead of a magnetic core to control current. Compared to magnetic ballasts, electronic ballasts weigh less and are silent, so they are a popular choice inside buildings. They are more expensive upfront, but electronic ballasts are more efficient than their magnetic counterparts, so the additional cost can be mitigated in the long run. Due to their enhanced efficiency, electric ballasts are rapidly replacing magnetic models in most settings.

Those are the two primary ballast technologies, but some models are built with additional features (related to lamp startup) that make them particularly useful in some situations. Here are a few examples:

  • Instant start – Instant start ballasts deliver a greater burst of current to the lights they are tied to. This means the lights switch on instantly, but the added current is hard on the lamp and can reduce its lifespan. This isn’t a problem if the ballast is tied to lights that will only be switched on a couple times a day, which is often the case in office and commercial settings. Given the nature of an instant start ballast, it’s highly recommended that these ballasts not be used with occupancy sensors. Doing so could quickly burn the lamp out.
    Instant start ballasts are also prized for their energy efficiency, as they are most efficient ballasts while in operation. This is another reason why instant start models are typically used with lights that are left on for extended periods of time.
  • Dimming ballast – A dimming ballast allows for precise control over the lamp’s output, as the fixture’s intensity can be adjusted up or down as needed. This is a popular feature in ballasts installed in residential buildings, as well as museums, galleries and theatres.
  • Rapid start – A rapid start ballast is designed for lights that are switched on and off frequently, like those found in kitchens and in residential and commercial bathrooms. Instead of sending a burst of current to the lamp, rapid start ballasts gradually increase flow, which is easier on the lamp and will prolong its life. While they aren’t as energy efficient as instant start ballasts, they can be safely paired with occupancy sensors.
  • Programmed rapid start – A programmed rapid start ballast also gently ramps up flow into the lamp. On top of that, though, a programmed rapid start ballast can also heat up the lamp before it is switched on.
    Lights are sensitive to thermal conditions and will deteriorate faster if operating in low temperatures. With a programmed rapid start ballast, the lamp is heated to a point where the fixture can operate without compromising its long-term durability.

What is the difference between a ballast and an LED driver?

LED technology does not use conventional ballasts, though some LED technologies are built with an internal driver that is compatible with some ballasts.

An LED driver performs the same function as a ballast, in that it controls the flow of electricity into the light. That’s not all, though, because unlike most other lighting technologies, LEDs require low voltage DC current to function. An LED driver converts the high voltage AC current that most places provide into usable DC current. An LED driver, then, is just as critical to an LED lighting system as a ballast is to other forms of lighting.

When most people think of lighting, they think of the lamp itself and how it looks. There’s a lot more to a lighting system, though, and one of the most important components is the ballast. With the ability to safely meter out current as needed, ballasts and drivers are the heartbeat of a lighting solution.

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