And so on a sunny day, a highly photosensitive individual may not be able to walk through at all and would have to literally close their eyes to walk through, they mostly squint to keep as much light away from the eye as possible.

This describes me perfectly. Ever since I was a kid I was very sensitive to bright sunlight - and we got lots of it in Cyprus. Even sunglasses weren't of much help in school (where they weren't allowed) or when the sunlight was so bright it seemed to enter from the sides. This often led to avoidance of sports and other very outdoorsy activities. Cos my options were either walk around with my eyes closed, or else let tears run down my face, and no male kid wants to be seen crying!