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Contents of small neon glow lamps

Discussion in 'Lighting' started by [email protected], Mar 21, 2005.

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  1. Guest

    Hello all!

    I am curious to know how small neon glow lamps (NE-2, etc) are
    constructed. Clearly you start with a small glass tube, and fill it
    with neon. What pressure? Pure Ne or a mixture? I understand that
    some long neon tubes, as used with multi-kV transformers in signs, have
    a little mercury in them along with the gas... do little glow lamps have
    mercury? Then you need metallic electrodes - is a particular metal
    preferred? Finally, I know that electronic vacuum tubes often contain a
    "getter" to help get rid of any residual oxygen; is this done for glow

    For reference, the kind of lamp I am talking about looks like this
    and is maybe 1/4" (6 mm) diameter and anywhere from 1/2" to 1" (12
    to 25 mm) long.


    Matt Roberds
  2. Art

    Art Guest

    Highly probable a mixture of Ne and an inert material. Extremely simple in
    design, very probable at slightly above nominal atmospheric pressure. Highly
    probable no Hg within these items since they depend only on the ionization
    point of the Ne to "fire". Amazing, the Ne ionizes at a specific voltage
    [+ - a given %], and produces that nice reddish-orange glow. That fact has
    been used to produce oscillators based on the ionization voltage of these
    devices, also voltage regulation circuitry. Check out the 'How things work'
    web site. Should have much more information regarding these items.
  3. Yes or a mixture of neon and argon.
    I believe the pressure is about 20 Torr but am not sure. I disagree
    that the pressure is over an atmosphere.
    Pure Neon or neon plus argon.
    This is where this discussion gets really messy. There are "Neon"
    lamps and then again there are "neon" lamps. Let me try to explain.

    In my opinion, a Neon lamp contains Neon, at least as the active gas.
    Your Neon lamp is called a "glow" lamp because the electrodes are
    placed so close together that there is no positive column in the lamp
    and the light comes from the "cathode glow", which is one of the
    regions with high electric filed that exists close to every electrode.
    A Neon glow lamp is optimized to produce light from the cathode glow
    region of the discharge. Your Neon glow lamp has cold electrodes which
    create a higher electric field immediately in front of the cathode
    then would be created if you had hot thermionic cathodes and thereby
    increase the intensity of the cathode glow.

    In long lamps, be they neon or otherwise, most of the light comes from
    the positive column, not the cathode glow. In fluorescent lamps, most
    of the UV that hit the phosphor comes from the positive column. In
    those long thin "neon" lamps used for signs, virtually all the light
    you see comes from the positive column of the discharge.

    Now, the industry that makes Neon lamps with cold cathodes also make
    other cold cathode lamps of similar shape that may not contain any
    neon at all - and they call these "neon" lamps - so the terminology
    can get confusing.
    The ones that use phosphor may have some mercury to generate UV. The
    most common red-orange Neon glow lamps do not.
    Usually Nickel.
    Can be. Usually barium. An Italian company, SAES, makes barium getters
    for fluorescent and other types of discharge lamps. Of course, in
    fluorescent lamps, the phosphor acts as a great getter.
    Typical Neon glow lamp.

    Vic Roberts
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.
  4. I have heard 8 Torr, but do not know for sure myself.
    Based on what I see in my diffraction grating along with what I have
    heard before, it appears to me that:

    "High intensity" neon glow lamps (e.g. C2A/NE-2H, A1C/"mini NE-2H) have
    pure neon.

    "Standard intensity" neon glow lamps (e.g. A1A/NE-2, A1B/"mini NE-2",
    NE-51) have 99.5% neon .5% argon. The glow is dimmer but the lamps strike
    and operate at a lower voltage.
    Strangely, the "cathode/negative glow" is made more yellowish by the
    argon. It appears to me that in this particular glow, argon detracts less
    from the brightest yellow spectral line of neon than from other visible
    neon lines, and that the argon in this glow produces only infrared.
    In a lamp with a "positive column", the 99.5% neon .5% argon mixture
    glows usually hot pink to magenta in color, purpler at lower currents, and
    again dimmer than pure neon.
    Based on my experience with a diffraction grating, phosphored "neon"
    glow lamps - usually have a mixture of neon and xenon, sometimes a
    mixture of neon and krypton.
    I am referring to the ones around or under an inch long, having closely
    spaced electrodes, glowing without a positive column and generally having
    both leads on the same end. Otherwise the lamp is a different animal,
    typically a miniature cold cathode fluorescent lamp - and every one of
    those I ever saw the spectrum of have mercury. They also have an inert
    gas or inert gas mixture in addition to the mercury, and I have detected
    neon in some of them.

    - Don Klipstein ()
  5. TKM

    TKM Guest

    The cathode glow mode of operation makes it possible to use a neon glow lamp
    (such as the NE-2) as a fairly accurate volt meter. I have one such device
    that's about 40 years old. It's just a single-turn potentiometer calibrated
    in volts connected in series along with a fixed resistor to one lead of the
    glow lamp. Apply power and turn the pot until the lamp just fires and read
    the voltage on the scale.

    Terry McGowan
  6. Guest

    Thanks for all the replies! Besides the answers I got here, the
    Philips book at Mike's site * is the best reference I have found
    so far.

    Matt Roberds

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