the 400nm is the longest of the high energy wavelengths of light
that the lenses help to block. Here’s a good chart that shows where
on the spectrum that wavelength falls:
Deep purple light, which is the shortest wavelength most people can
actually see, is about 400 nm, so they are saying that they will
protect you from the ultraviolet emissions (wavelengths shorter than
400nm). Polycarbonate is inherently good at stopping UV - coatings,
tints, or additives to the polycarbonate can help even more with
The wavelength of the energy emitted from a torch or hot object is
directly proportional to its heat. Ultraviolet light comes from HOT
stuff, 4500+ degrees F (oxy acetylene, TIG welders, plasma torches).
Since Oxyacetylene burns at 3840 C (about 6000 F) it definitely is
emitting some UV. Those of us using oxyacetylene a lot should
definitely consider some UV blockers as well as some visible light
blockers, there is a lot of energy that falls into the visible light
spectrum that is not really good for you either. These glasses say
they stop sodium flare (bright purple, that’s why the tint) which is
high energy visible light that comes mainly from working glass:
One of the big problems with UV and other invisible radiation (I
work around fairly high power lasers) is that those wavelengths
bounce quite nicely. The glasses we wear when a big laser is
unshuttered are full on nerd herd… big bulbous wraparounds, because,
while clip-on lenses are useful, especially for small, very bright
oxyacetylene flames like from a smith mini torch, they may be a
partial answer because they only stop the light that is right in
front of you, not the stuff that might bounce in from the sides!
Welders run into that more than we do, because their flare is SO
BRIGHT and bounces off of everything in the vicinity - ask the
welder who has a sunburn on the back of his neck from working with a
white wall behind him!
on the other end of the spectrum…
Infrared (IR) is mainly just felt as heat. If you feel heat on your
skin, your eyes are getting it too, but unfortunately your eyes don’t
have nerves that are sensitive to heat to tell you about it.
Most of the infrared heat from your torch radiates at right angles
to the flame - expanding cylinders of heat, and it doesn’t bounce
around as much as UV does. Usually we as jewelers don’t heat really
big objects, but we DO get really close to our work sometimes… to
see what we are doing.
(geek 7x24, jeweler wannabe)