. . . After all, the speed of light is 280,000 miles per hour.
Off the top of my head, it is 186,282 miles per SECOND in a vacuum (about .99 of that in air). There is a neat experiment involving some fascinating mathematics, a microwave oven, and a chocolate bar, if you want to verify that speed at home.
But I don't think it is the reaction time that affects your eye comfort. All auto-darkening helmets are fully dark in the UV and IR spectrum all the time. They just go dark in the visible spectrum. You will not be hurt if you forget to turn the helmet on and strike an arc for a second.
Eye strain is a funny thing. I suspect that the poor optical quality and distortion created by the cheap helmets is a large cause of it.
I know that with an HF helmet, I had a hard time distinguishing the puddle. The upgrade to a Speedglas was not only more comfortable, but greatly improved my welding, as I could now see what I was doing (I'm not praising Speedglas over Miller BTW. I've got two Speedglas helmets myself, and haven't even touched a Miller).
Thanks for the delay info. I had that incorrect. Your reading glasses must be different than mine. Mine center the 2 images, correct for astigmatism (not much, but everyone has some) and magnify at different factors depending on which eye. Now I know you can get prescription lenses for welding helmets.
But those aren't called cheaters, now are they? They are corrective lenses.
There are three kinds of lens corrections that you will typically see in a single lens:
Negative spherical correction. These will reduce the image size, and are the type of lens used to correct distance vision in a near-sighted person (like myself).
Positive spherical correction. These magnify the image, but also correct close up vision in a far-sighted person. This is the same correction used in reading glasses, and cheaters. It is also what a camera macro correction lens uses, and it not only magnifies, but also allows you to focus closer.
Cylindrical correction. This is used for astigmatism.
Cheaters are just like cheap drugstore reading glasses.
Prescription reading glasses made for your eyes will sometimes have different powers for each eye (if you need that), and will have the optical centers placed in front of your pupils (this greatly improves the image quality, since not all people have the same interpupillary distance).
Prescription reading glasses would also correct astigmatism (if you need it).
If you're TIG welding, you will often want to get closer to your work, then you would be to a book, so lots of people use a cheater lens to allow them to focus on what they're welding, even though they do not need reading glasses. Personally, I can still focus up to about 4" from my eyes, so a cheater really doesn't do me any good (so long as the torch is 2" from my helmet's lens, I can focus just fine, and closer than that, I'd be worried about melting plastic anyway).