Common Signs It’s Your Ballast and Not Your Bulbs

Updated 7/6/23 by Hannah Lee

All it takes is one flicker and you may begin to ask yourself, “Is my bulb about to go out?” While it’s possible your light bulb is at the end of its life, in the case of any light fixture with an external ballast or driver, the exterior hardware may be the primary culprit. Before blaming the light bulbs, it's important to know the common signs and causes of ballast failure.

What is a Ballast Anyway?

Used primarily in fluorescent lighting systems, a ballast is an electrical device designed to regulate electrical current. It allows the light to turn on and then continually regulates the current flowing through the fluorescent bulbs, ensuring proper voltage and stable light output. Fluorescent tube lights would overheat and burn out very quickly without a ballast to ensure they do not draw too much electricity.

Magnetic ballasts were usually included in any fixture that needed this kind of mechanism. However, newer technology has led to electronic ballasts becoming increasingly popular. Electronic ballasts are known to provide better power quality. Additionally, an electronic ballast is less likely than a magnetic ballast to produce a buzzing sound or allow visible flickering when turning on.

LED Drivers are another component you may encounter when troubleshooting light fixtures. They serve a similar function to magnetic or electronic ballasts, but are used in LED fixtures to convert the electrical current to the low voltage direct current LEDs require.

Signs of Ballast Failure

How do you know if a fluorescent lighting ballast or LED driver is toast? Most likely, you won't know right away. Watching for a few key signs of a faulty ballast will help you determine if it is the underlying cause. Common symptoms of a bad ballast or driver include dimming lights, a humming noise, rapid flickering, or changes in color.

When facing issues with any light fixture, you should check all of the components, including the light bulbs. You may need to remove the ballast cover to inspect the ballast. Obvious signs of a faulty ballast include burn marks, swollen casing, or (in the case of “ye old” magnetic ballasts) leaking oil.

If you’re still unsure if your ballast has bit the dust, you need to get your hands on a brand-new bulb and replace the current one. If the replacement lamp fails to light up, then 9 out of 10 times the ballast is the culprit.

Testing Ballast Function with a Multimeter

A multimeter set can help you tell if a ballast is bad by allowing you to test its function. A multimeter is an instrument designed to measure electric current (amps), voltage, and resistance (ohms). Most devices are digital, but some may be analog. They are user-friendly and versatile, making them a simple tool to test ballasts. Of course, proper safety precautions should always be taken when working with lighting fixtures and electricity.

Prior to testing ballasts with a multimeter, remove the ballast cover so you can access the input terminals. To check the voltage of a ballast, turn on the multimeter and select the appropriate voltage range. Place the probes on the input terminals or the leads connected to the ballast, ensuring they make adequate contact with the metal parts of the ballast's terminals. If the multimeter reads a voltage close to the rated voltage, it indicates your ballast is receiving adequate power. However, if there is no voltage or the reading is significantly lower than the rated voltage, there may be a problem with the electrical power supply or wiring.

Once you have confirmed the system is receiving power, you can test the resistance of the ballast. First, ensure that the electrical power to the fixture is off, and remove the ballast cover, if the ballast is not already exposed. To set up the multimeter, turn it on and select the ohm setting. Place the probes on the input terminals or the leads connected to the ballast.

If the ballast is still functioning properly, an analog multimeter has a needle that will sweep across the measuring scale to the right. If the ballast is bad, there will be no measurable resistance and the needle won’t move. For digital multimeters, the digital readout will typically read a “1” when it doesn’t measure resistance.

Using a multimeter successfully is often a test of your knowledge of electricity, the ballast specifications, and your analytical skills, making this option a bit more tricky.

Determining Why Your Ballast Failed

The environment surrounding the fixture is often the primary reason ballasts fail prematurely. Heat and moisture are enemies #1 and #2 to your ballast. Every ballast has an ambient operating temperature range and UL location rating. When it’s too hot or too cold, the ballast can burn up or fail to start your lamps at all. Excessive heat combined with prolonged condensation inside an electronic ballast can cause corrosion.

Some may suggest removing the parts of the ballast casing and cleaning the electrical board, which may work for those knowledgeable and experienced in working with electronic fixtures. However, if you are unable to put the electronic ballast back together, you will be looking for a new ballast. Not to mention potential safety concerns.

To avoid issues with your ballast due to heat and moisture, make sure the fluorescent light fixture has a ballast that is UL rated for its location, particularly if installed in damp or wet areas. The appropriate ballast should be able to handle the high and low temperatures of your local climate.

Lighting Tip: LED drivers often have shorter lifespans than LED arrays or fixtures. Compare light bulb and driver specifications before purchasing.

Causes of LED Driver Failure

When an LED driver fails, it will most likely just stop transmitting power to your LED bulbs. However, LED drivers tend to have a shorter lifespan than the LED arrays they are paired with. So, it is vital you look for signs of a failed LED driver before replacing LEDs.

A failing LED driver could send more power through your LEDs than they can handle (aka overdriving), causing them to overheat and ultimately frying your LED array.

An LED driver that is sending a very low amount of power, or excessively underdriving, will cause light quality and output to suffer. This can result in a fixture that produces inconsistent lighting or that never reaches full brightness, leading you to believe that bad bulbs are the cause of dim lights.

Similar to ballasts, LED drivers can suffer from heat and water damage. LEDs and their components are particularly susceptible to heat. The power a driver restrains produces heat and the resulting build-up can take a toll on the driver’s functionality.

LED drivers also have ambient operating temperature ranges. The efficiency of an LED driver is significantly affected when you exceed the recommended temperatures. Just like ballasts, not all LED drivers are damp or wet location rated so make sure the LED driver for your fixture is rated for rain or shine.

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