LCD materials will often spec a minimum storage temperature and a minimum operating temperature. Modern LCD materials might be rated for storage temperatures down to -40 before they are permanently damaged while their operating temperature may only be freezing or higher.
From direct experience, I know that the auto-darkening function can noticably slow down when you actually try and use them in low temperatures.
I was doing some outdoor welding last winter on an object too large to fit in the garage, and I noticed that as my helmet started getting colder, there would be an increasingly annoying brief visible flash at the time of striking the arc due to the time for the helmet to auto-darken getting slower and slower. Also, I would notice when the arc was stopped, the helmet would stay dark for a noticable moment.
The thing to remember about auto-darkening helmets is that the bulk of the eye-safety is unrelated to the darkening function. The UV and IR filtering is always in place assuming you have not removed the seemingly clear piece of glass that is the UV&IR filter.
Yes, intense enough visible light can hurt your eyes, but since intense visible light tends to constrict your pupils, or make you close your eyes, blink, or squint, its not as dangerous as the invisible UV and IR.
- Rick