By Tom Gregg
Fluorescent lamps operate at 120 volts (we use 120 volts for this example). The ballast is a transformer/current limiting devise.
Example, on a 277 volt system the ballast reduces the voltage applied to the lamp to 120 volts.
The ballast has an ignition voltage much higher than the rated voltage to start a fluorescent lamp.
Example, a 2 lamp F96 ballast fires 750 volts (referred to as open circuit voltage) to ignite 2 F96 lamps, or a total of 16 feet of lamps. Once the lamps have started the ballast reduces the voltage to 120 volts for normal operation. The same is true for the F40 ballast except the ignition voltage is 250 volts to ignite 2 F40 lamps, or a total of 8 feet of fluorescent lamps. The F40 ballast also generates a 3-4 volt cathode heat.
At the point of ignition (like creating a spark) the cathode in one end of the lamp will sputter off emission past. This will cause a slight end darkening at one end which is normal. Like water, electricity will take the path of least resistance. When the resistance at one end of the lamp becomes to much the ignition point will move to the opposite end of the lamp, and slight end darkening will occur. From there it will move to the second lamp and continue the process till all 4 ends have a slight darkening. When all 4 ends have darkened it is time to replace the lamps. Any further operation of these lamps will begin to damage the ballast.
At the end of lamp life most of the emission coating has been depleted from the cathode. The cathode is still in tact at this point, but the ballast will over work itself trying to ignite, or keep the lamp operating and will eventually burn the cathode out.
Remember, you replace fluorescent lamps for the same reason you change oil in your car (you don’t want to damage the engine ). A ballast cost 12-17 times more than a fluorescent lamp, not including labor. Don’t run your fluorescent lamps to the point that they damage the ballast.
If a lamp is left in operation beyond the recommended relamp period, the ballast will heat up and destroy the power factor capacitor which changes all the ratings of the ballast. It will no longer operate at the designed voltage/amperage, and wattage. The ballast is damaged.
If a ballast heats up to the point that the thermalcouple disengages it from the electrical circuit (prevent a fire) the damage is already done.
The ballast is an auto transformer consisting of primary and secondary induction windings. The only insulation these coils of wire have is a thin coat of varnish. When the ballast over heats it burns off the thin coat of varnish allowing the windings to short out and drastically changing the electrical values of the ballast. When this happens the transformer action can become a step up transformer consuming a great deal more wattage and causing premature lamp failure.
- New lamps operated on a damaged ballast will experience short lamp life.
- Sever end blackening of 2-3 inches on one end of a fluorescent lamp is caused by a defective ballast.
- Broken or defect lamp holders, and loose electrical connections will cause the same problem. Remember the heat in the fixture will cause expansion that can decrease a positive electrical contact.
Normal end of life. Slight end darkening.
Abnormal end darkening, approximately 2- 3 inches in length
Problem, defective ballast.
Defective ballast will continue to prematurely burn out new lamps (weeks to Months).
Replace ballast, lamps, and defective lamp holders.
A word about Electronic Ballast
Electronic ballast are more efficient than the standard ballast. They are available in operating configurations of Rapid Start, and Instant Start. The benefits far out way the standard ballast with the new proven technology, energy savings, and reliability. Fluorescent lamp performance improves, both in light output, and life. Quick starts, no flickering, and the occasional noise (60 cycle hum) has been eliminated.
For more information and better lighting, contact your
Frank S. Johnson