system
Given the following post, respond as if you're commenting on Reddit:
human
Why does closing one eye help the pain when it's really bright out?

Shouldn't it be equally bright in each eye?
gpt
You "feel" bright light when the iris contracts and makes your pupils small. This is why photophobia is a common symptom of corneal abrasion and viral keratitis, and why browache results from pilocarpine drops that force the pupil to shrink.

When you cover one eye, you reduce the stimulus to pupil constriction. The pupils still constrict (even in the closed eye) but the stimulus isn't as intense, so the response is not as "painful".