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Francis,

As I understand it polarizer pairs block a percentage of light dependent on the relative rotational angle between them from 0° to 90°. Neutral density filters are stacked to block the desired percentage of light. The Sun should appear comfortably dim when using either type of filtering (common sense?). Technical data should be provided with the product used.

Greg Rudzinski

The polarizer's working for visible light does not mean they will work for UV. I know welding filters have been tested for UV reduction (in part I inspect welding for a living). It strikes me that a polarizing filter works in a fundamentally different way than a regular filter and the effect may be frequency dependent, the effect may cut off at some frequency that is out of our range of vision. If it were a camera or some other sensor behind the filter, sure let's find out. I would want to see test data for UV reduction before risking my eyes.