[TheForge] IR vs UV

[Bruce Freeman]

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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