Ballast Definition
A light ballast, which is sometimes referred to as control gear, is an essential component of certain types of light fixtures, including HID (high-density discharge) and fluorescent fixtures. If you’ve ever turned on a fluorescent light and heard a low hum or buzz, this is the sound of the ballast switching on.
A ballast regulates the current that flows through the bulb (sometimes referred to as a tube or lamp). Your home’s main power supply provides a much higher current than is needed to power certain types of bulbs, but a ballast lowers the current to the optimal operating level. Also, some lamps require a greater current at the time they are switched on and shortly thereafter, and a lower current after they have been operating for a while. Some ballasts can work with a dimmer that allows you to adjust the brightness of the light.
A ballast is often used with lighting fixtures in a commercial application. For a helpful overview of other types of commercial lights, see Choose the Best Commercial Lighting for the Space.
Light Tube and Ballast Compatibility
Some ballasts don’t work with some light tubes or lamps. You need to match a ballast to the tube type and size, the number of tubes in the fixture and the voltage of the fixture. Information in the product specifications and on the ballast label can help you determine the type of tube lamp and fixture a ballast is compatible with.
All tube lights have a size designation or shape code comprised of the letter “T” followed by a number, which is the diameter of the tube measured in eights of an inch. Match the ballast to the size of the existing tubes in the fixture.
For example:
- T5 = 5/8-inch diameter
- T8 = 1-inch diameter
- T12 = 1-1/2-inch diameter
On a ballast label, you can often find key information about:
- The ballast type (magnetic or electronic)
- The supported lamp type (fluorescent vs. HID)
- The number of tubes the ballast supports
- The input voltage the ballast supports
- A list of compatible tube lights
Some ballast labels also include a simple wiring diagram.
120 volts is the most common voltage for home fixtures. In some cases home workshops and garages with heavy-duty power tools might require higher voltages. Single-volt ballasts work with only one voltage. Multi-volt ballasts adjust to a range of voltages.
Types of Light Ballasts
While there are ballasts for HID lights, fluorescent light ballasts are the most common for the homeowner. There are two types: magnetic and electronic ballasts. Magnetic ballasts are no longer manufactured, so you’ll mostly see a magnetic ballast on older fixtures.
Electronic ballasts employ a more advanced technology to regulate the current flowing through fluorescent bulbs. They’re also smaller than magnetic ballasts and operate at a greater level of efficiency, which allows them to produce light with less flickering and noise. There are several start types. When replacing a ballast, it’s best to use one with the same start type.
Instant-Start Ballasts
Instant-start ballasts turn on tubes immediately by delivering a high-voltage burst of electricity that energizes the filaments and gas inside the tubes. This design saves energy but can shorten the lifespan of the bulb. This factor makes instant-start ballasts better for commercial or industrial installations where the light fixtures won’t be switched on and off frequently.
Rapid-Start Ballasts
Rapid-start ballasts preheat the bulb electrodes to help the light turn on quickly. They require a bit more time to illuminate the bulb and use more power than instant-start ballasts but can allow better bulb life. These ballasts are suitable for fixtures in locations where the ambient temperature is higher than 50 degrees Fahrenheit.
Programmed-Start Ballasts
Programmed-start ballasts use a constant low-voltage current to keep the tube electrodes preheated. When the light turns on, a higher voltage current is employed. This ballast design is not as energy efficient as the instant-start variety, but it prolongs the life of the lamp, making it a better choice for installations where the lights will be switched on and off many times a day, for example with lights that have motion-activated sensors.
In addition to standard fluorescent ballasts, there are compact fluorescent light (CFL) ballasts.
LED Light Ballasts
While you might hear the term LED light ballast, LED tube lamps don’t actually use ballasts. Instead, an LED uses a device known as a driver to regulate the amount of current the tube receives in an LED light fixture.
However, Type A LED tube lights, also known as plug-and-play LEDs, work with most existing fluorescent fixtures and ballasts. Type A/B LED tube lights, or hybrid LEDs, work with most fixtures that have a ballast installed, as well as fixtures where the ballast has been removed. Type B LED tube lights won’t work in a fixture wired with a ballast. The fixture must be rewired so the current goes directly to the light sockets, but this helps improve compatibility with the fixture and uses less energy.
Always defer to the LED tube manufacturer’s specifications to ensure an LED tube works with your fixture and ballast.
There are a couple of ways to identify a magnetic ballast in an older fixture:
- The ballast should be labeled as magnetic or electromagnetic.
- Cellphone video of a light with a magnetic ballast shows bars across the light, due to the low frequency of flicker the ballast creates.
Note that LED tubes typically don’t work with a magnetic ballast.
How to Tell if a Ballast Needs Replacing
Here are some typical things you may notice if your magnetic ballast is malfunctioning:
- The light constantly flickers.
- You hear a constant buzzing or humming noise.
- The light takes longer than usual to start.
- The light becomes noticeably dimmer.
How to Test a Ballast
If you notice any of the above warning signs that you may need a ballast replacement, you can test the ballast using a multimeter, a useful tool that measures electrical current. See Choose the Best Electrical Testers and Meters for help choosing a multimeter.
Although the instructions for testing a ballast may vary depending on the ballast type and your multimeter, here is a general overview for testing a ballast:
- Turn off the power to the light fixture at the breaker box, and test to ensure the power is off. Then remove the casing and the bulb.
- Disconnect the ballast and examine it carefully. If you notice any burn marks, you should replace the ballast.
- If the ballast doesn’t appear to be damaged, follow the manufacturer’s instructions for your multimeter to test the wiring. This will involve touching the multimeter probes to specific wires to see if a current can flow through. For more information, see How Do I Use a Multimeter? If no current is detected, it’s time to replace the ballast.
Always follow local electrical codes. Some electrical work requires a licensed electrician. Disconnect the power to any component you’re testing and carefully follow the manufacturer’s safety recommendations for any testers. If you’re not sure of the proper safety procedures or you don’t understand the wiring you’re working with, call a professional.
Key Points to Know About Light Ballasts
A working ballast helps ensure your fluorescent lights turn on when you flip the switch and work without flickering. Here’s what you need to remember when shopping for a fluorescent light ballast:
- A ballast controls and reduces the current to a level suitable for the light tube or lamp.
- Fluorescent ballasts are the most common type in a home.
- LED light tubes don’t require ballasts, but you can find LEDs that work in fixtures with or without ballasts.
- Modern ballasts are electronic models, but older fixtures might have magnetic ballasts.
- Instant-start ballasts turn lights on quickly and use less energy, but rapid-start and programmed-start ballasts extend the lifespans of the tubes.
- A flickering or humming fluorescent light might mean it’s time to replace a ballast.
Shop Lowes.com for fluorescent light ballasts that work with different sizes of lights different light fixtures. If you’re not sure which ballast you need, visit your local Lowe’s and talk to a Red Vest associate. They can help you choose the right ballast for your lights or help you find compatible LED tube lights that work with your fixture.
Light Ballast FAQ
Use the answers to these questions about fluorescent lights and ballasts to know when a ballast needs to be replaced and how to find the right ballast for your light.
What Type of Ballasts Do I Need for LED Lights?
LED light tubes don’t use ballasts. If you’re replacing fluorescent bulbs with LED tube lights, pay attention to the LED tube type. Type A LEDs work in many fixtures with an existing ballast. Type B LEDs require the fixture to be rewired so the current doesn’t run through the ballast. Type A/B LEDs can work in a fixture with a ballast or one where the ballast has been removed.
Why Do My Fluorescent Lights Flicker and Hum?
While there are several possible reasons for flickering and humming, malfunctioning ballasts or tubes are common causes. A malfunctioning ballast can provide unstable current to a light, causing it to flicker. A flickering fluorescent light can also be a sign that the tube needs to be replaced. A loose ballast or an older magnetic ballast can cause a fixture to hum.
Can I Replace a Magnetic Ballast With an Electronic Ballast?
Yes, in most cases you can replace an older magnetic fluorescent ballast with an electronic ballast. However, rewiring of the fixture is necessary. This might require an electrician and you need to make sure the new ballast is compatible with the type, size and number of light tubes in the fixture.
Can I Replace a Ballast on My Own?
You can change a ballast as a DIY (do-it-yourself) project if you have the technical knowledge and experience with the necessary safety procedures for working with electricity. However, some ballasts can be complicated to wire, so it’s always best to hire a professional electrician if you are not confident of your abilities.