Read up on the guidelines of using UV to treat water.
I have read the medical docs and this is what I have found.
UV-A is not effective against all organisms. The SODIS system doesn't make sense and I suspect it is not very successful. I wouldn't rely on it.
Steripen uses UV-B which does not penetrate clear plastic or glass. It reflects off the surface.
This explains why you don't go blind by looking at the bottle while using a Steripen.
Look it up.
And as stated, there is a reason why beer bottles are tinted. Beer(and food) in clear bottles goes bad much quicker from bacteria growth when exposed to sunlight. I won't go into the biology as to why.
You can look this up as well.
One of the guidelines of using UV-B to treat water is to avoid direct sunlight for long periods after treating.
The Steripen docs even mention this fact.

