BALLAST FOR FLOURESCENT LAMP

[lquadros]

What is the exact function of a ballast in a flourescent lamp? Is there a high inrush current?
We turn off these lamps at work during 10min. breaks as a power conservation measure. Then again 30 min. during lunch. Do you think 10 min or 30 min. switch off is really helping us? What about the life of the lighting unit by doing so?

That makes me think also about leaving transformers 10 to 30 KVA during weekends and between shifts. Will it help us to save by eliminating core losses on these?

Thanks in advance for your answers.

 

[Ed MacLaren]

Re: BALLAST FOR FLOURESCENT LAMP

The ballast has several functions in a typical fluorescent fixture.

1. Step-up the branch circuit voltage high enough to ionize the lamp filling gas and start the lamp current flowing.

2. Provide sufficient impedance to prevent the lamp current from exceeding the design value. The lamp has negative impedance (runaway)characteristics. It's impedance drops as the filling gas is ionized.

3. Most ballasts include a power-factor correction capacitor.

4. Most two-lamp ballasts provide for sequence starting.

Do you think 10 min or 30 min. switch off is really helping us? What about the life of the lighting unit by doing so?

Turning off fluorescent lights more frequently does decrease the rated lamp life (usually lamp life ratings are based on a minimum of three hours on). However, leaving the light on all the time means that it will reach those rated lamp life hours that much sooner. Typically turning the lamps off will give you longer time between lamp changes.

The best way to figure out the answer is to determine the crossover point. This point is where the savings in electrical energy begin to outweigh the cost of decreasing the life of the lamp. It depends on your local electric rates, but I've heard that crossover point is something like 15 to 20 minutes.

What that means is that if you are going to be gone from the room for more than 20 minutes, turn it off. If you are only going to be gone for a few minutes leave it on.

Ed

[ February 17, 2004, 02:13 PM: Message edited by: Ed MacLaren ]

 

[spsnyder]

Re: BALLAST FOR FLOURESCENT LAMP

Another thing to consider are the type of ballasts you have. If you have Instant Start (IS) ballasts they will be more efficient when on, but starts have a much more adverse effect on the lamp life. Rapid Start (RS) ballasts are not as sensitive to starts, but aren't quite as efficient when running.