Hi I'm gonna go off about eyes for a bit cuz I LIVE for the glow in Tenno eyes when they're added. So...
Coryn's eyes are at a constant 35% glow-
Backroom and in the Cathedral.
Like that's at 35% compared to Isaah being at a natural 50%
(im sorry he got that very wide eyed stare)
So.. there's 2 ways to me their eyes react. Emotions and Lighting.
In the backroom, it's obvi to see there's a bit of a difference between the two. Isaah got a bit more intensity to his while Coryn is a bit dim. In the dark is what's horrifying cuz that shit is BRIGHT.
Isaah's especially because of being at that natural 50%.
Here's a bit of a scale from 100% - 0% eye glow based off how I like to see it.
High brightness to the point the veins are visible - 50 - 100%
This is for more darker areas with little to no light or just total darkness (applies to both brothers)
As for emotions. This kind of brightness is more for high intense emotions be it overwhelming happiness, anger/rage, or if startled.
"Normal" brightness usually adheres to Coryn with his eyes being at 35%, yet this'll also scale to 45% if: neutral, accepting, or content. In Coryn's case, his eyes tend to have a bit of a "pulse" to them if he's around loved ones (Hex, Arthur, Isaah, Umbra).
Lower brightness will be more visible in the pupils than the iris (25 - 30%). This'll be like if they're outside and the sun is beating down. I have tested this via backroom when the sun was coming in, and all I could see was just the glow in the pupil. Emotion wise, this is for more if tired/exhausted, fearful, bored, or upset.
Now if it's 0 - 10% glow? This is mainly for if asleep to leave just that "normal" look eyes have without any sort of glow. But if there's mild glow? He's just waking up it's ok..... Or if he's dying. That's the oop option lol.
And yes both boys' eyes are like that without any sort of glow and it's wild. But imagine that with just the pupils glowing? Yeah that's the lower brightness in a nutshell.
Anyway! This has been me rambling (ha) about eyes n whatnot cuz I love the idea of the eye glow reacting to emotions or lighting.