Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Fluorescent Bulbs and Power Bills

  1. Apr 12, 2008 #1
    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...
  2. jcsd
  3. Apr 12, 2008 #2


    User Avatar

    Staff: 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.
  4. Apr 13, 2008 #3
    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?
  5. Apr 15, 2008 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    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.
  6. Apr 15, 2008 #5
    What about running power/energy? "40W" fluorescent bulb doesn't mean it consumes 40 Joules/sec does it?
  7. Apr 15, 2008 #6


    User Avatar

    Staff: Mentor

    Yes, that's exactly what it means.
  8. Apr 16, 2008 #7
    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?
  9. Apr 16, 2008 #8


    User Avatar

    Staff: Mentor

    Well hold on - often for marketing purposes the box a compact fluroescent lists both the actual power usage and the incandescent equivalent light output.
    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.
  10. Apr 16, 2008 #9
    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...
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Fluorescent Bulbs Power Date
Detecting fluorescence via CW or pulsed LEDs Jun 11, 2016
Is CFL an inductive load? Jan 10, 2015
How do fluorescent tubes light up with radio waves? Feb 29, 2012
Mercury gas in fluorescent lights Aug 31, 2010
Fluorescent bulbs Jan 16, 2010