What reflects UV radiation more: stratus clouds or cumulus clouds? Interested in this since I sometimes look down on the clouds in the plane, and wonder if some of the reflected UV-A radiation might damage my eyes.
According to the below albedo rating diagram (percentage is reflection of incident radiation) cumulus cloud is the greater total spectrum reflector so it will reflect more UV that equivalent stratus formations.



Do note that water vapour does however absorb the vast majority of UV (≈100nm) that it intercepts as we can see in this diagram:

So overall cloud UV reflectance will be quite low.