The fact that bright light can still annoy you just shows that there is an upper limit (and there is a lower one too, obviously) -- not that it doesn't work.
You’re absolutely right. I didn’t intend to imply that excessively bright stimuli (such as when the ground is snow or concrete or sand and the sun is directly overhead), couldn’t be too bright even when adapted as far as possible.
What I meant (and should have stated more precisely/clearly, not using the word “only”) was rather that, at the intensity of an iPad screen, adaptation should make any hurting stop. The iPad screen is several orders of magnitude dimmer than the brightest sunny days. Light adaptation takes us pretty darn far.
The fact that bright light can still annoy you just shows that there is an upper limit (and there is a lower one too, obviously) -- not that it doesn't work.