Brightness isn't the problem. I never change it from default. These new 'airy' layouts are just plain harder to read.

Default brightness is probably brighter than minimum brightness (it is on Android, at least).

Lowering the brightness actually makes it worse. It has nothing to do with brightness and everything to do with contrast. The older you get, the more contrast you need.

If it's age, you're getting more farsighted, and need to go to the "increase text size" setting, which works considerably better than anything in iOS6

You might click "Increase text legibility".

I'm stoked for this ability for some relatives who's otherwise whip out reading glasses for email.