What American city or part of the country is known for having the purest sun light?

Question

What American city or part of the country is known for having the purest sun light?

Answer 1

It all comes from the same Sun. It's all equally "pure," whatever that means.

Answer 2

Purest sunlight?  What would that be?  Every part of the earth receives basically the same sunlight.  Sometimes clouds are in the way, or other atmospheric interference, or sometimes pollution, but it's all the same light.

Now if you meant clearest air, that would probably be Alaska or (taking .American in it's more geographic meaning) northern Canada.