How do I Diagnose Ballast Issues?

A small box inside the light fixture contains a circuit known as ballast that limits the flow of electrical current to a fluorescent light bulb. The life span of ballast diminishes when a one or more conditions remain unresolved. Attend to faulty ballast as soon as you can to reducing humming or buzzing. Use a process of elimination to diagnose and confirm the existence of malfunctioning ballast.

A buzzing fluorescent light signals ballast trouble.
  1. Turn the light switch off. Use a stepladder and screwdriver to remove the light diffuser from the fixture. A ladder will allow you to reach the lens of the fixture. Use the screwdriver for removing screws that fasten the diffuser to the fixture.

  2. Conduct a temperature check if the lamp refuses to turn on. Most ballasts require a temperature of 50 degrees or higher. When the temperature of the room drops below that number, the ballast may not function.

  3. Listen for a sound coming from the light fixture. Noise can come from a loosely mounted ballast. Check for and eliminate rattles and vibrations. Check the tightness of all the elements within the fixture. When a ballast makes an excessively loud buzzing or humming sound, it may need replacing.

  4. Use a voltage meter to check the voltage in your electrical line if the ballast cycles continuously. Replace the ballast when the meter indicates sufficient power in the line for ballast operation.


  • Exercise caution when handling a ballast. Do not touch any oil leaking from the ballast. The oil contains chemicals that may burn or irritate unprotected skin.

About the Author

Truell Bliss retired from the restaurant and hospitality industry after almost a lifetime of service. An officer in the American Culinary Federation, he earned his dietary manager certification and progressed into positions as chef instructor, chef manager, dining services operations manager and finally, director of food service.