I have one HJC, Shoe and something else helmets. All are pretty old and don't come with any visors.
Anyone try these stick-on light sensitive films? Like transitions lens??
https://www.cyclegear.com/gear/pro-grip-light-sensitive-shield
While its not a horrible idea, it would suffer from my comments made earlier about the other kind of stick-on: Concerned that it would scratch, it doesn't cover the whole view area, might touch your nose, might introduce additional internal reflection layers, in the cold could have fog between the layers, and would be very concerned on installing it without ruining it.
Additional concerns- most photosensitive materials are triggered by UV, not by visible light. And many clear shields have UV protection built into them. If that is the case with yours, the add-on film might not darken, or darken as much as you want or expect. And on other shields (like mine), that have an anti-fog treatment on the inside, the stick-on adhesive might permanently damage the shield if it is removed later (so it could be a non-reversible test).
Of course, at $22, it is cheap enough to give it a try.