It took me forever to find something other then just conjecture on the effectiveness of UV filters. It would seem a pretty logical thing for filter manufacturers to publish their transmissions graphs but it doesn’t seem like any of them do (forum posting suggest B + W will provide them on request).

Here is an actual test of UV filters.

Note that the B + W has the best visible light transmission and is available with a multi-coating. Looks like a good lens protector to me although it’s pretty worthless as a UV filter.