Could be an auto lens: they look gold (or purple, depending on the angle).
Advantages -- some are shade adjustable, otherwise, you can actually see what you're pointing the torch at without having to flip the helmet up and down all the time.
Thanks for that. They're not very expensive at all. Might get one to use if I have any "lying on your back" MIG to do -- the Speedglas has a very fragile shell and really isn't up to taking heavy hits from molten metal!