A ballast is the device needed to energize fluorescent lamps during operation. In all fluorescent lighting systems, the ballast provides the proper voltage to start the lamp and then regulates the electric current flowing through the lamp to stabilize output.
There are two types of ballast, electromagnetic and electronic. For several years electricians have been installing the electronic ballast when an electromagnetic ballast fails. However, the clear advantage of electronic ballasts has led to the decision in some buildings to make a complete change-over, even though the existing electromagnetic ballasts may still be functioning. Most electronic ones do not make any noise.
Vibration of electromagnetic field causes the humming noise. You can dampen it by making sure it's in the housing tight. You may be getting some noise from the housing itself, as the vibration from the ballast occurs. Also, try changing the bulbs, it may be trying to regulate with a bad bulb, or vice/versa as the ballast may be going bad. Perhaps you are specifying in the wrong wattage bulb? Just a thought.
reply »