My bachelor's degree is in neurobiology and it would have been very interesting if this was reproducible in other people. Experiencing physical pain from visual stimuli (stimuli unrelated to light intensity, at least) is not something I've ever really heard of. You may have discovered the visual equivalent to the Brown Note.
I know in the past I felt pain while trying to say certain lies. I do not mean I felt uncomfortable, I mean I felt real pain. It is weird, but sometimes you can cause pain without a direct physical cause.
