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hydrogen gas spectral lamp question

Discussion in 'Electronic Design' started by Don Lancaster, Oct 15, 2012.

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  1. We picked up an outrageously expensive supposedly monochromatic light
    source that was intended to light up a 12 inch optical flat.

    It lights up ok, but I sort of expected to see a "pure orange" color.
    Instead it is white with a strong orange tint.

    Is this normal or did some helium leak out of the bulbs?

    What happens after their normal hundred hour lifetime?

    Replacement bulbs are likely to cost $1000 each.

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
  2. Owen Roberts

    Owen Roberts Guest

    They are broadband. Usually a high pressure sodium lamp or a low
    pressure mercury or helium lamp. Sounds like your missing a filter.

  3. Hi Don, I don't know about Hydrogen lamps. But we make a Rb lamp
    with Xenon as a 'starter' gas. I've been getting new quotes for the
    interference filter (IF), so I was just looking at the spectrum

    For Rb there are the two D lines at 795 and 780nm., and then a whole
    bunch of other peaks, mostly at longer wavelength. The IF has to pick
    off one of the D lines, and then the rest of the 'crud'.

    I've used the lamp with IF to look at 2" optical flats. (I had to use
    a CCD camera to see the 795 line... PITA.)

    George H.

  4. Its a lapmaster CP-1 intended for use with optical flats up to twelve inches

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
  5. Bill Sloman

    Bill Sloman Guest

    which tells you absolutely nothing about the lamp.

    I could have asked for more information

    but only at the expense of filling in a very long form.

    I suspect that they are charging the earth for a not-very-expensive
    lamp, and hope to be able to keep on ripping off the gullible by
    hiding the exact nature of wahtever it is they are selling.
  6. Bret Cannon

    Bret Cannon Guest

    "Don Lancaster" wrote in message

    Its a lapmaster CP-1 intended for use with optical flats up to twelve inches

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at

    I have no direct experience with these lamps, but the visible lines of
    atomic hydrogen are the Balmer series with wavelength of 656 nm, 486 nm, 434
    nm, etc.., but I don't know if the relative intensities of these lines are
    such that they would appear to be orange. I would guess that there should a
    small amount of H2 that is efficiently dissociated by the helium metastables
    produced by the discharge.

    Is there enough light to look for line structure by diffraction from a CD?

    Bret Cannon
  7. Martin Brown

    Martin Brown Guest

    Why would you expect orange? That would be a helium or sodium lamp.

    A hydrogen lamp typically looks pale pink like the red 656nm and blue
    486 lines with a hint of violet 434/410 some continuum and whatever
    other weak lines Penning mixture contributes - a CD spectrograph should
    easily show you what you have unambiguously. eg Structure/Spectra/HydrogenLampAndSpectrum.jpg

    If it doesn't show the hydrogen Balmer lines then it isn't hydrogen!

    Amateur astronomy filters are available that will isolate the cyan
    H-beta and red H-alpha lines pretty well. In fact for the latter
    colloidally coloured low pass glass will probably do the job.

    A helium plasma does look pinker shade orange.
    Why are you using Hydrogen as opposed to a much cheaper Sodium lamp?
  8. Owen Roberts

    Owen Roberts Guest

    Oh, I just looked at the web site. I've seen those. HP sodium lamp,
    no filter. Na lamps for that cost 35-100$ at McMaster Carr.

  9. Martin Brown

    Martin Brown Guest

    It should be a low pressure SOX sodium lamp. The doublet line isn't
    ideal but is plenty good enough for most optical engineering purposes. A
    12W lamp ought to be more than enough light they are incredibly
    efficient the big ones still hold the record in lumens/watt.

    These days I'd have thought a semiconductor laser and beamspreader or
    diffuser was more convenient and a better monochromatic light source.
  10. Glen Walpert

    Glen Walpert Guest

    Unfortunately this is normal.

    Same as any similar design low pressure gas discharge tube, evaporated
    electrode material traps gas on the tube walls and output gradually
    declines, but 100 hours is a ridiculously short lifetime. The lamp is
    essentially a neon sign folded into a regular grid instead of a sign and
    filled with an alternate gas mix, powered by an ordinary neon sign
    transformer, The far superior mercury lamp monochromatic illuminators
    are made the same way, and I know of some of them that ran almost 40
    hours per week for nearly a decade without any problematic loss of
    output; about what you would expect from a good neon sign.
    I have one of those that I got at an auction, only to recall after
    getting it home that a former employer once described it as a nearly
    unusable POS, speculating that a competitor sold it to their customers to
    prevent them from inspecting their parts, while lamenting the loss of the
    company which manufactured his large yellow-green mercury sources, which
    were large enough for his 14" flats and filtered to a single mercury
    line. I forget the exact wavelength, but when viewed from a practical
    ~20 degrees from perpendicular you saw 10 microinches per band to as
    close as you could read it (~1/20 band). It produced far more distinct
    bands than you will ever see with the lapmaster due to the the very low
    contrast you get from it's unfiltered output. Also, if you use the base
    of the lapmaster to support your work (as it is designed to be used) the
    heat from the transformer can cause significant workpiece and flat
    distortion. You can remove the lamp from the base to avoid this problem.

    Last time I looked Edmund was selling smaller filtered mercury line
    inspection illuminators, in a proper stand leaning ~20 degrees forward of
    vertical, for less than $1000 IIRC.

    For those not familiar with this method of inspection, you are looking at
    the reflection of a diffuse source from the entire surface of a polished
    work surface under the flat interfering with the reflection from the
    flat, so the source needs to be significantly larger than the flat and
    coherent over the length of the gap between flat and work (<.001") but
    preferably not coherent between the work and the top of the flat (~ 1" or
    more). After gently setting one side of the flat on the work and then
    lowering the other side onto the air film you can let go of the flat and
    wait for the air film to squeeze down to around a 10 band wedge, where
    band curvature (flatness) is most easily read.

    If I knew where to get the large mercury line filters I would get one and
    have a neon sign maker refill the tube in my lapmaster with mercury. But
    I wonder if you could do as well today by illuminating a sheet of ground
    glass or an LCD backlight diffuser with laser diodes at lower cost.
  11. Martin Brown

    Martin Brown Guest

    Presumably it just has to be good enough to isolate the wanted green
    line. One of the Schott colour glasses might do eg

    Or maybe Lee stage filters which are much cheaper. Jade #323 isn't far
    off. Hard part is removing 578 & trace sodium D-line output.
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