# Fluorescent Bulbs and Power Bills

## Main Question or Discussion Point

I think this question is straightforward:

Fluorescent lighting requires several hundred to several thousand volts to startup right?
Shouldn't this increase your energy bill at the end of the month if your always supposedly trying to 'save' power by turning off lights as often as possible?

I've heard power companies don't charge you for 'reactive' power which is what starts up the fluorescent lighting? In which case the bulbs are more efficient.

Or is it more efficient to leave the bulbs running longer than switching them off...

Related Electrical Engineering News on Phys.org
russ_watters
Mentor
Power is voltage times amperage. They use a high voltage and a low amperage.

Modern fluorescents don't take very long to start, so it is better to turn them off when not in use.

So its that simple? They use a very small startup current, and I assume a very low operating current? Are the startup and operating currents the same?

Also, how do dimming fluorescent bulbs work - are they just varying the current through them?

Redbelly98
Staff Emeritus
Homework Helper
Power is voltage times amperage. They use a high voltage and a low amperage.
And energy (what you pay the electric company for) is
time x voltage x current

The short startup time also makes for an insignificant startup energy.

What you DO pay for, with frequent restarts, is shorter bulb life. For a standard 40W fluorescent tube, lifetime is reduced 1 or 2 hours for each start. I'm not sure what the number is for CFL's. When I'll be away from the room for just a few minutes, I'll leave the lights turned on.

And energy (what you pay the electric company for) is
time x voltage x current

The short startup time also makes for an insignificant startup energy.
What about running power/energy? "40W" fluorescent bulb doesn't mean it consumes 40 Joules/sec does it?

russ_watters
Mentor
What about running power/energy? "40W" fluorescent bulb doesn't mean it consumes 40 Joules/sec does it?
Yes, that's exactly what it means.

Ok so I guess the difference between a fluorescent 40W bulb and a filament 40W bulb is the luminous output right?

Also, in my house i can only have 1 or 2 fluorescent bulbs per room of say 4 bulbs. Having more than that causes the extra bulbs not to light up. Does anyone have any ideas? I was thinking too much startup power was being drawn?

russ_watters
Mentor
Ok so I guess the difference between a fluorescent 40W bulb and a filament 40W bulb is the luminous output right?
Well hold on - often for marketing purposes the box a compact fluroescent lists both the actual power usage and the incandescent equivalent light output.
Also, in my house i can only have 1 or 2 fluorescent bulbs per room of say 4 bulbs. Having more than that causes the extra bulbs not to light up. Does anyone have any ideas? I was thinking too much startup power was being drawn?
That makes no sense. Does the same thing happen if you have incandescents? It sounds like you have a wiring problem. No, it doesn't have anything to do with startup power: startup power is whatever the lamp wants to take or else the circuit breaker will trip. A circuit has no way to regulate its amperage besides tripping the breaker.

But you may want to get yourself a voltmeter with a clamp-on ammeter.

You asked about dimming fluorescents earlier - I don't know how they work, but I do know that if you use a non-dimming fluorescent on a dimmer switch, you will kill the bulb.

That makes no sense. Does the same thing happen if you have incandescents? It sounds like you have a wiring problem. ...

But you may want to get yourself a voltmeter with a clamp-on ammeter.
I know that doesn't make sense, the same thing does not happen with incandescents - I can run all 4 of 4 bulb sockets with incandescents but only 2 of 4 with fluorescents. I've tried unscrewing 1 of the 4 incandescent bulbs then running 3 fluorescents but that didn't work.

I guess the electrician who did the house must have done something dodge...