In my mid teens, as a weekend project, my dad decided I needed to learn how to weld. Surprisingly, by Sunday afternoon I'd moved through MIG/MAG and was making passable attempts at joining bits of aluminum together with a TIG welder. Teenagers learn fast, and my dad was an ex-pro who built bike frames
for track cyclists out of various exotic materials back in the day. The reason he left for a less lucrative job was that back in the 60's it was assumed you were trading your eyesight for money*. This changed fairly rapidly with the development of welding helmets.
What problems do these solve? Well most commonly, welding metal is using enough electrical current to liquify metals, adding bits, then hopefully they're joined together when you let them cool. The problem lies with the electric current which is so intense it creates an arc, superheated plasma that emits light all the way from UV through the visible spectrum to infra red**. This light is bright, roughly as bright as looking at the sun. The UV and IR are big problems here, they're invisible so your iris wont close, you wont blink or turn away to protect yourself. But these can be filtered out very effectively with common plastics like the polycarbonate in cheap safety glasses.
The super bright visible light can be solved by a very aggressive tint. But then for all the time you're not actively welding it's like navigating the workshop in eclipse glasses. It occurs to me that we could solve that problem by simply upgrading the workshop lighting so that everything is about as bright as the sun/welding arc all the time. This will get expensive however***. Competing with the sun often is. But we can do it for a very small slice of the optical spectrum.
An optical filter that does this is called a "band-pass". You could choose a slice of the spectrum, say from 505-515nm (green) and coat a whole polycarbonate face shield. How they do this is essentially magic to me. Then, take an array of very powerful 510nm LEDs and light up the work area. Now, you can see perfectly, albeit only in green, all the time and when you strike the welding arc, it will only be about twice as bright - well within the eye's ability to adapt.
This is, in almost every way, inferior to the auto-darkening LCD screen helmets available for modest sums.
*It turns out it was probably your lungs unless you took the precaution of filtering the welding fumes though a Marlboro.
** in fact most of the electromagnetic spectrum is possible. The reason Manchester University put the Jodrell Bank radio telescope installation deep into the Cheshire countryside is that the trams/trolleys using overhead electrical pickups would generate huge RF interference. Someone should check if the WOW! signal wasn't just someone tack welding a new antenna mount or something.
***and upset the optical telescope people