[Jewelry making - Article 00825] - Re: [Orchid] Infrared light

[Mike Aurelius]

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    Donna - Ok, I can see what they are doing, although I do not totally
    agree with the way they are calculating the shade number. 

    As I mentioned in my previous note, one of the key factors in
    determining the shade number is the maximum visible light
    transmission, which for a shade 5 is 3.16%. What I believe that
    Gentex is doing is modifying the typical welders filter curve (which
    looks like a standard distribution curve) in such a way to transmit
    light centered in the orange/yellow wave bands (560 to 600 nm) and
    lowering the transmission in the rest of the visible light bands to
    achieve the overall 3.16% visible light transmission. There is
    nothing wrong or illegal or anything with doing this, and it does
    achieve the purpose of allowing "more" light through the filter
    (actually, the more "brilliant" colors), however, for metal working,
    you really want to cut the yellow sodium flare at 575 nm, not enhance
    it (this is what a didymium filter does). The standard welders filter
    peaks at about 536 nm, so what they have done is shifted the
    transmission spectrum towards the IR by about 50-60 nm. 

    I have nothing against Gentex, as I said they are a well-known
    company with a good reputation. However, I don't personally believe
    that this particular filter is a good thing. The yellow flare that
    comes from sodium burning off is distracting and annoying and all
    this filter does is allow more of it to pass through. 

Anyway, that is my $0.02.

Mike Aurelius
 

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