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fluorescent light problem

Discussion in 'Misc Electronics' started by Michael, Jul 21, 2003.

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  1. Michael

    Michael Guest

    Two fluorescent fixtures in two bathrooms of my mother's house seem to
    be possessed. Both are
    integral parts of medicine cabinets and are 20 years old, as is the
    house. Eight or nine
    years ago one light started acting up: when the wall switch was flipped
    ON, sometimes the tube would come on only dimly while other times it
    would come on fully. When ON dimly, the tube could be made to come on
    fully by touching a finger to the metal cabinet. New tubes exhibited
    the same symptom and behavior. Two years ago I replaced the ballast and
    that seemed to fix the problem; it didn't fail to fully fire in several
    dozen ON/OFFs. But last winter that same fixture started acting up in
    the same old way, and last week a second, identical fixture in another
    bathroom followed suit. Mom is on the war path, demands satisfaction.
    But I don't know what else I can do. Ripping out the two medicine
    cabinets and installing ones that have incandescent lights is definitely
    a non-starter.

    What are common causes of "fizzling" fluorescents? Are "hot" and
    "return" swapped? Should the metal cabinet be solidly
    grounded?...insulated from ground? I'm in NY and fixtures are in NH, so
    I can't check what the actual case is.

    Finally, is there a more appropriate NG for this query?


  2. I can't answer all your questions but can suggest that corrosion of the
    contacts is a possibility. Also, I have found that the contacts lose their
    tension. Touching the cabinet? That's strange ... I'll be curious to see
    if you get any replies about that!
  3. Tom Biasi

    Tom Biasi Guest

    Hi Michael,
    Since its the bathroom I would bet on the corroded contacts.
    Sometimes even the slightest coupling to ground or AC Hum will cause a
    borderline lite to come on.
    Next time you see one flickering run your finger up and down the tube and
    see what happens.
  4. It is possible you have a poor ground or neutral connection.


    Chip Shults
    My robotics, space and CGI web page -
  5. Michael, the symptoms that you describe are characteristic of a
    fluorescent light housing that is not properly grounded. You may want
    to check the grounding on these fixtures.

    Harry C.
  6. By coincedence, the new ballast transformers were defective, or there
    was some type of electrical problem. A knowledgable electrician should
    have been able to work this out for you.

    Jerry Greenberg
  7. Michael

    Michael Guest

    Yup ... I forgot to add that touching the glass tube also causes the
    tube to come on fully.

    I used to have old circular fluorescent on the ceiling in my own kitchen
    and in cold weather it would do the come-on-dim thing. Reaching up with
    a metal broom handle and touching the glass tube made it fire. I
    finally ripped the thing out.
  8. Michael

    Michael Guest

    Possible, I guess, but I did try to make good connections by
    continuously rotating the tube for about half a minute. Did that just
    to make sure ..... in desperation, because I never did like or trust the
    contacts in fluorescent tube sockets.
  9. Michael

    Michael Guest

    I'll definitely check ground connections next time I visit home. Since
    touching the metal cabinet around the light has an effect, it seems
    likely that the cabinet does *not* have a solid ground. I don't
    understand though why two lights - one upstairs and one downstairs -
    worked fine for about 10 years.
  10. 1. Are the ballasts 2-bulb ballasts? Especially "trigger start" ones?

    If one bulb glows dimly and the other one does not glow at all and you
    tried new bulbs:

    a) The fixture needs to be grounded. Failure to start due to lack of
    grounding is often inconsistent and may vary seasonally. If touching a
    bulb or the fixture helps, then chances are the problem is lack of proper

    b) A hot-neutral reverse may cause this.

    c) Check the voltage across the two contacts in each socket - it should
    be around 9 volts.

    d) Try twisting the bulbs around for better contact. If this fixes it,
    then you will have to clean the contacts in the sckets with fine
    sandpaper or get new sockets (lampholders). It may be easier to cut new
    lampholders from a ballast that has them or from the cheapest new fixture
    you can find than to find a supplier that sells just a few of them.

    e) Make sure you have the proper wattage bulb for the ballast. Nowadays
    2-foot (and worse still 4-foot) fluorescent bulbs come in different

    Same story if both bulbs are out.

    If all bulbs glow dimly then the problem is almost certainly not
    improper grounding or hot-neutral reverse.

    2. Bulb glows dimly with a single bulb trigger start ballast: By far the
    most likely explanation is poor contact with one pin, or maybe with one
    pin on each end of the bulb, or broken connection that results in lack of
    that roughly 9 volts across the pins on each end.

    3. Both bulbs glow a little dim but not very dim, and/or flicker rapidly
    in unison, or alternate between normal brightness and dim or dim/flickery
    in unison, and the bulbs are known good:
    Some 2-bulb trigger start ballasts, especially for 20 watt bulbs, are
    marginal in design. Try a different brand of bulb. Be sure you have the
    proper wattage bulb.

    4. If the fixture has starters:

    Voltage measurements across the two contacts of each socket will be
    meaningless and ideally read zero but could be anything depending on the
    impedance of your voltmeter.

    Try replacing the starters, although bad starters usually cause symptoms
    other than the ones you described.
    Bad starters can cause rapid degradation of good bulbs and bad bulbs can
    cause bad extra wear on good starters.

    5. Try reading: (Sam Goldwasser's F-lamp FAQ) (my troubleshooting guide)

    - Don Klipstein ()
  11. In strange static-assisted cases, try cleaning the bulbs. In a few
    areas especialy coastal areas, a very fine salty film on the bulbs may, at
    times of higher humidity, mess up the electric field distribution within a
    bulb that is trying to start.
    This is almost certainly not the explanation if all bulbs are glowing
    dimly rather than any bulbs not glowing at all.

    - Don Klipstein ()
  12. Michael

    Michael Guest

    So much good stuff. Enough to keep me reading for quite a while. I
    have a good feeling that what I need to know is in there somewhere.
    Many thanks, Don.
  13. Dan Fraser

    Dan Fraser Guest

    Many florescent fixtures need to be grounded to fire properly. Two wire
    fixtures need the correct wire connected to the neutral and hot. If they
    are reversed, they will be hard to start. That you can touch yours and
    have them start indicates you may indeed have a reversed hot and

    Dan Fraser

    From Costa Mesa in sunny California
    949-631-7535 Cell 714-420-7535

    Check out my electronic schematics site at:
    If you are into cars check out
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