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Dimming flourescents

Discussion in 'Electrical Engineering' started by Jimmie, Mar 30, 2005.

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  1. Jimmie

    Jimmie Guest

    Recently installed some of thse flourescent bulb replacements. They work
    great but they will not dim.They are at full brigtness no matter what the
    setting of the dimmer is. What I expected was that the light would suddenly
    come on as I turned it on at somewhere less than full on and go off before I
    reached full off. They come on at full brightness with the dimmer just
    barely on. My question, Am I saving eletricity by operating at nearly off
    postion, doing damage to lamp, doing damage to the dimmer?

  2. Ken

    Ken Guest

    I always thought that fluorescent bulbs were gas and required a minimum
    voltage to conduct. How do they dim a fluorescent bulb? Thanks.
  3. John Gilmer

    John Gilmer Guest

    It takes a little more engineering but it's quite possible to "dim" a
    fluorescent lamp.

    I don't know how "they" really do it, but a way to "dim" would be just to
    replace a 40 watt ballast with a 20 watt ballast. The bulb would still
    "see" the voltage needed to start but would only get HALF the current.

    Likewise, it's possible to over drive a fluorescent lamp. Just replace a
    40 watt ballast with something larger.
  4. Bud

    Bud Guest

    Dimming ballasts vary the current through the tube; the voltage is
    substantially constant. Dimming ballasts keep the filaments at the end
    of the tubes at full voltage while the arc current is lowered. One of
    the problems with a non-dimming ballast is the filament voltage is
    'dimmed' also.

  5. Ken

    Ken Guest

    Ah, I did not think of limiting the current! Don't these lamps flicker
    if they reduce the current? Or do they simply dim?
  6. In many cases, it is done by rapidly chopping the current.
    Actually, triac phase control dimmers can be used (and used
    to be), but it's a bit more complicated than dimming a
    filament lamp.
    They will flicker because when the current drops below a certain
    level, there's not enough electron/ion bombardment to keep the
    filaments hot enough to conduct into the gas fill by thermionic
    emission. By separately heating the filaments, this problem is
    resolved. Actually, running at reduced tube current without
    separately heating the filaments, even before it's low enough
    to cause flicker, will wear out the electron emitting coating on
    the filaments much faster than running at the correct power
    rating, contrary to what one might imagine.
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