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UV nail lamps for EPROM

Discussion in 'Electronic Design' started by Bud Finley, May 18, 2007.

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  1. They probably mean the main strong shortwave UV wavelengths of
    low pressure mercury vapor.
    The 365-366 nm cluster of mercury spectral lines does go through most
    glass well, and is a weak but slightly significant spectral feature of
    fluorescent lamps. Exception: Triphosphor lamps (including most compact
    fluorescents) of color temperature rating 3500K or higher usually in my
    experience have a blue-emitting phosphor ingredient that utilizes that UV
    wavelength.

    Maybe silver chloride responds to the 404.7 nm violet wavelength of
    mercury, or has slight response to the violet-blue 435.8 nm wavelength of
    mercury that is strongly present in the light from fluorescent lamps.

    http://coolcosmos.ipac.caltech.edu//
    cosmic_classroom/classroom_activities/ritter_bio.html

    indicates silver chloride reacting to visible blue and violet light as
    well as to UV.

    http://photography.about.com/library/weekly/aa011402b.htm

    also indicates ability of blue and violet visible light as well as UV to
    cause silver chloride to do its photochemical reaction.

    Both of these note Ritter discovering UV via its great ability to cause
    the photochemical reaction in silver chloride.
    A lot of fluorescent lamps have phosphor coatings that do not absorb
    longwave UV.

    - Don Klipstein ()
     
  2. Mike Monett

    Mike Monett Guest

     
  3. The Phantom

    The Phantom Guest

    The coating is not opaque even to visible. Shine a flashlight through a
    fluorescent tube and you will notice that visible light passes through.
    Long wave ultraviolet does also.

    If you go to Home Depot, or some such place, you can buy one of those
    horribly inefficient "black light" bulbs that is really an incandescent
    bulb with an envelope made of Wood's
    glass(http://en.wikipedia.org/wiki/Black_light). Break the bulb so you
    have some pieces of the Wood's glass to play with. Get a piece of
    something that is highly fluorescent, like one of those bright orange price
    labels on some item of food. Hold up a piece of Wood's glass to an
    ordinary visible fluorescent tube (compact fluorescents work), and let
    whatever comes through the Wood's impinge on the label. The label will
    fluoresce. You may have to make a shield of a piece of cardboard with a
    hole in it so most of the visible isn't shining in your eyes, but the piece
    of Wood's glass covers the hole, through which whatever is transmitted
    shines on the label. Actually, blue light, such as from a blue LED will
    also fluoresce the label, but the Wood's glass filters out most of the blue
    and passes primarily long wave UV. The fact that the label fluoresces
    indicates that some long wave UV is emitted by the fluorescent tube.

    A good test of the reaction of silver chloride to various colors of light
    would be to use several ultra-bright LED's, say, orange, yellow, green, and
    blue. Shine them on the silver chloride. The good thing about using these
    light sources is that they are pseudo-monochromatic. There is a narrow
    emission band, and no out of band energy to confuse the results.
     
  4. Mike Monett

    Mike Monett Guest

    Thanks. I'm surprised that an ordinary incadescent gives off any UV.
    Actually, my goal was to make a poor man's absorption analyzer to
    measure the concentration of silver ions in a solution. Adding salt
    converts the ions to insoluble silver chloride, and the density of
    the dispersion indicates the ion concentration:

    Ag(+) + OH(-) + Na(+) + Cl(-) --> AgCl(ppt) + NaOH

    I was looking for a light source that would not decompose the silver
    chloride to silver metal and chlorine gas during the measurement.
    After the measurement is complete, I plan to illuminate the solution
    with UV and measure the absorption of the silver metal particles to
    see if that gives any useful information:

    2AgCl + 2UV --> Ag(s) + Cl2(g)

    It looks like infrared or a plain red led may work for the initial
    measurement, especially if I keep the intensity very low. This
    produced a pleasant several days of research on lock-in detection
    methods, and a very interesting SPICE analysis of two of the most
    common methods. It looks like a simple inverter driving a CMOS SPDT
    switch will do the job quite nicely. Most sources indicate the
    inverter needs 0.1% or 0.05% resistors to get good balance, but the
    SPICE model shows the inverter balance doesn't have to be perfect
    and it will still give good results.

    Thanks for your interesting post.

    Regards,

    Mike Monett
     
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