Is it more efficient to turn off older fluorescent lights or leave them on?

Question

We are trying to be more energy efficient at work and have been trying to get folks to turn off the lights in areas that aren't used constantly (like bathroom, library, break room). However, our maintenance person told us that the ballasts in our fluorescent lighting are old and it actually takes more energy to turn the lights on/off than to just leave them on. Now, I thought that modern bulbs had overcome this, but everything I read talks about the bulbs, not the ballasts. How does the age of the ballasts effect the energy consumption? Perhaps I'm showing my ignorance about the mechanics of light fixtures, but I'd like to understand how it works if anyone out there can enlighten me (to be honest I'm not exactly sure what a ballast even is). Is our maintenace person right? I'd really like to see some supporting evidence as well (scientific or unbiased studies/links if possible).

Answer 1

Here's how I answered a similar question a few days ago in regards to compact flourescent lights, but even the bigger bulbs have a linear result:

QUESTION:  "How much power does it take to start a low energy light bulb? Someone told me they need so much energy to?

power up when first switched on that it is cheaper to leave them on than to keep turning them off and on, as you would do normally.

Sounds dubious to me."

ANSWER:  "So little for the single CFL, or even a bank of 5 or 6 CFLs, that your electric meter isn't even sensitive enough to measure it.

Just for the sake of putting numbers to this let's make a few ridiculously generous assumptions:

$0.50 per kilowatt-hour

50 watt CFL bulb

CFL bulb using 200% of rated power for 12 seconds in order for the bulb to ignite to full fluorescence.

Operating the bulb for one hour would cost $0.025 cents

(50W) / (1000W per kW) * (50 cents per kWh) * (1 hour)

The turning on of the light would cost $0.00016

(100W) / (1000W per kW) * (50 cents per kWh) * (12 seconds) / (3600 seconds/hour)

It would cost 15000 times more to leave the light on for one hour versus turning it off and back on this hypothetical situation. You'd have to flip the switch off-on 15000 times in one hour to cost the same as leaving it on. Good Luck!

In actuality electric prices are closer to 15 cents per kWh, CFLs only use about 125% of rated wattage to ignite and only take less than 2 seconds to ignite.

In summary, turn off the light when you are not using it."

EDIT - Flouresent bulbs operate on a higher voltage than 120 Volts, generally in the range of 300-700 volts.  Ballasts have low wattage step-up transformers to raise the voltage and an ignitor circuit to heat the elements on the ends of the bulbs and vaporize the medium inside of the bulb, that in turn flouresces the phosphor coating and emits a light.  Once there is a current flow through the bulb the ignitor drops out and the ballast just operates as a transformer.

Older Magnetic ballasts have inductive coils that draw more energy during both the lamp ignition and during the operation of the lamps.  Modern electronic ballasts use almost as much energy during the ignition but a lot less during operation and will generally ignite the lamp faster.  The older ballasts also produce more heat.

The only way to tell what kind of ballast you have is to visibly look at the ballast.  The nameplate gives it away.

Answer 2

That's a load of bull, unless the light will only be off for a minute or 2 maybe.

Answer 3

Your maintenance man is the real ignoramus.  It's one thing to not know, it's quite another to claim you do when you don't.

The extra energy used to start a fluorescent light is about equal to a few seconds of operation.

There is an issue with the life of the bulbs and ballast though.  The life of both will be shortened if they are cycled often but the energy savings will overcome this in most circumstances.