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OT:Incandescent "soft white" bulb coating?

Discussion in 'Electronic Basics' started by Bob Masta, Jan 21, 2005.

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  1. Bob Masta

    Bob Masta Guest

    Not exactly an electronics question, but I know some
    lighting gurus hang out here. (Google hasn't been any
    help so far.)

    What is the stuff used as the coating on typical
    incandescent "soft white" bulbs? I gather that
    the non-soft-white are simply acid etched on the
    inside of the envelope, but the soft white have
    a separate powder applied somehow. What
    is this stuff chemically? What makes it stick?
    (It seems pretty fragile if you touch it on a
    broken envelope piece.)


    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
  2. Dan Ritter

    Dan Ritter Guest

    All I know is that at least in flourescant lights they use different
    shades of colored phosphors. I would imagine it's the same stuff but I
    don't know.
  3. Doesn't stuck much... Even the broken pieces of filament swirled around
    inside the bulb scrape off the powder. Hopefully it is just some talc,
    gypsum, ...

  4. The two commonly used finishes inside are etched glass (frosted) and applied
    silica powder. As I said, the etched glass is known as 'inside-frosted' or
    simply 'frosted' and results in the appearance of a glowing ball of light within
    the globe. But silica powder is also used, and called 'soft-white' by most
    major manufacturers. Although this cuts output more than etched glass, it makes
    the entire bulb glow more evenly.

    I hope this helps some.

  5. Bob Masta

    Bob Masta Guest

    Thanks, Jon, this is exactly the sort of info I was
    hoping for. Any idea what makes the silica stay on the
    inside of the envelope?

    Thanks again!

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
  6. No, but I honestly haven't tried to fathom this in any detail. I don't either
    have theory or experimental data to suggest much to me.

    If you have a bulb to break open, see how well you can clean the substance off
    with your fingers or wet rag. If it all comes off easily, then it is probably
    surface tension and possibly some frosting on the inside to encourage that
    tension and the particles are probably "very, very tiny." Otherwise, maybe they
    "use something." But my bet would be that they would avoid depending on
    anything other than the silica -- the more that is added, the higher the cost
    (especially, as it is hard to find higher-temp materials and deal with
    outgasing, etc.) and the more dangerous it may be in the home, as well.

    But I just don't know.

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