With regard to selecting good sunglasses, as far as I know, there are the following methods.

1. See label and find "Bloc UV 99%, 100% or upto 400nm
2. Darkness doesn't guarantee blocking hamful lights.
3. Expensive one doesn't mean the best quality one.
4. Big frame is good because any hamful light can be blocked at any angle.

Do you agree with me or would you add some more?
:)