The vision penalty from helmets is presumably because it obscures your vision. When it’s dark it’s harder to see further – why would those two penalties stack together?
Narrow sight of view(full helm) should has nothing to do with brightness/darkness of the environment, right? So can they stack?
Actually they shouldn’t stack. Instead the highest penalty applies. If your helmet allows you to see 3 tiles, but the darkness obscures everything withing two tiles, you can only see 2 tiles ahead.
On the other side, darkness and a full helmet increases the overall difficulty to see stuff. I think, if I had to fight in the dark with a closed helmet, I would completely loose my orientation.
