I refer to days in Seattle when the sunlight is not obstructed by clouds. "Bright" days are much easier on the eyes. Much less squinting. I've been both places -- Seattle and So. Cal. -- long enough to know the difference. What part of any of this sounds silly?
I would say the part about bright days being easier on the eyes. I have actually LIVED in So Cal.(22 years), I am now living farther north than that (10 years). I have LIVED at a similar latitude parallel to Seattle (4 years), and I have even lived in the Northeast, farther north than Seattle. I have visited nearly every major city and state in the US.
I have never experienced this effect that you describe, nor have I ever heard anyone else describe such an effect, nor have I read anywhere of this effect.
I understand your reasoning, but the effect just isn't there at a perceptible level.
I lived in the Seattle area (Redmond) for seven years. Those "bright" days last for about 2 weeks in July :) Of course, when there is a sunny day in Seattle, it's the most beautiful place in the world. Snowcapped volcanoes in almost every direction. The only saving grace for the long, ugly winters is that you can go skiing in 45 minutes.
I always recommend to everyone I know (I live in north GA now) to go visit Seattle at least once in the summer. There's nothing like walking up Mt Rainier to the snow in the summer, seeing a Killer whale pod slide by the ferry, and the bald eagles. Quite a "wow" factor.