I also have transition lenses in my prescription glasses. I can assure you they have darkened on more then one occasion. Often enough, in fact, the I bought a set of non-transition glasses for welding. It was quite a surprise the first time it happened. At first I thought maybe there was an issue with my helmet, but is has occurred with 3 different helmets. Gene
UV light is harmful to the eyes. The purpose of a welding lense is to block those harmful UV rays. This is why its recommended you watch solar eclipses through welding lenses - but I digress!
Transition eyeglass lenses are activated by UV rays. And in fact, they don't react much at all if you're in a car because the windshield also blocks most UV rays.
SO ...
If your glasses are transitioning behind your helmet it means that its less effective than a car windshield.
FWIW - I have a Lincoln and a 3M helmet - my glasses do not transition with either of them.
