I've read some interesting stuff in this sub about color blindness, watching eclipses, tracking things with your eyes, etc.

But I don't know much about how your eye processes intensity. What is the mechanism that transforms an amount of light to a brain signal(?) then a physical response? I was unsurprised to find, anecdotally, that when I squint, my discomfort in bright light lessons. I was surprised to find that closing one eye seems to lessen my discomfort as well. ( I would have thought one eye would still be telling my brain "hey it's uncomfortable")

Do we, humans, have response outside the usual visible range? Do other animals have any non-visible response to intensity? (I.e. maybe they don't need to see something, but being aware or alerted to something is enough for a defense mechanism.) Is the intensity response a function of frequency? Can the intensity response become dulled or heightened? Is this linked with eye damage?

Just thinking about this has led me to think about all sorts of related eye questions, but I have tried to keep the ones here just intensity related.