Yes, blocks UV...
This item does indeed block UV rays. I know this because I can shine a 360-400nm light directly in to my transitionals  and they go dark, immediately. However, if these safety glasses are between the light and my transitional eye wear, no change what so ever. As we all know transitional eye wear is triggered by UV rays so I'm left with the conclusion that these glasses block UV at least in that wave length.<br /><br />Also, they fit on top of my glasses- so all around they work as intended for me.
Rating: 5 stars