[TheForge] IR vs UV

[Mike Porter]

Bruce,
All good points, and no disagreement from this end. The government also 
agrees with you, which is shown in the tighter restrictions on UV than IR 
for ANSI filter shade ratings.

So, why don't I speak more about UV? There are three reasons, which are 
listed below in order of increasing importance:
(1) UV is much more generally recognized as dangerous.
(2) UV, even UVC, is easily blocked.
(3) IR is much harder to deal with effectively without ruining your view in 
the process.
Mike P.

----- Original Message ----- 
From: "Bruce Freeman" <freemab222 at yahoo.com>
To: "theforge" <theforge at mailman.qth.net>
Sent: Sunday, February 12, 2006 1:07 AM
Subject: [TheForge] IR vs UV


> Mike,
>
> Like I said, I did NOT research the topic of IR before
> I spoke up, and I still have not done so.  I
> appreciate your contributions on this issue.
>
> Your most salient point about IR is that it does not
> provoke a response - pupil contraction - of the eye,
> the way visible light does.
>
> But what I really mean to convey is the incredible
> difference the wavelength of light makes to its
> effect.  It is NOT just a matter of energy difference.
> The effect of some amount of IR energy to an equal
> amount of UV energy is the difference between no
> effect at all and blindness.  (NOT to say IR can't
> lead to blindness - it just takes a LOT more IR energy
> to do it.)  The reason is the means by which these
> different energies work.
>
> IR is "infra red" radiation - light of longer
> wavelengths (lower energy) "below" visible (i.e., red
> - the longest visible wavelenght) light.  When IR
> strikes matter, it causes molecular vibration, and
> little else.  Molecular vibration is heat, plain and
> simple.
>
> UV is "ultra violet" radiation - light of shorter
> wavelengths (higher energy) "above" visible (i.e.,
> violet- the shortest visible wavelenght) light.  When
> UV strikes matter, it causes electrons in most
> materials to be promoted to higher energy
> orbitals.(Kinda like Earth suddenly jumping into Mar's
> orbit.  This works on the atomic level, not on the
> solar system level.)  When this happens, the molecule
> becomes a lot more reative.  It may break apart, or
> react with something else.  If this molecule is part
> of YOU, this is not good news.
>
> Visible light is somewhere between these.  One of the
> reasons it is visible is that it can cause electron
> promotion like UV.  But it is so much less energetic
> that the usual result is the electron just drops back
> down and reemits the colored light.
>
> Now, these are NOT absolute regions of the spectrum,
> but they are useful generalizations.  My real point is
> that IR is qualitatively different from UV, and
> there's no need to be AS worried about it as we are
> about UV.
>
> Looking at your typical forge fire is really no more
> harmful than staring at a wood fire.  Yes,  parts of
> that forge fire ar much hotter than the wood fire, but
> those parts typically are beneath the top layer.  Be
> concerned, but not overly concerned.  Be aware of the
> possible problems, but don't exaggerate them.
>
> Bruce
> NJ
>
>
>
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