O.K. so we're not talking about Transitions lenses, right? Just regular glasses. Hey, could be that I'm really behind on new technology, but I did just recently buy a new pair of expensive glasses from UC Berkeley optometry center and darn it, I still need sunglasses. These lenses do nothing to block UV/UBF on their own, as far as I can tell. And I was told by staff that I needed uv/ubf sunglasses with these lenses.(Yeah yeah it's a marketing ploy etc.) I can't imagine anyone saying that climbers on snow, for example, can get by without sunglasses. But sunlight in summer at high altitude reflecting off granite is also potentially damaging. "Squinting" on a glacier won't cut it; nor at 10,00 feet in the summer. The proof: yes, it's anecdotal, but it sure feels a lot better when I put on uv/ubf sunglasses. So sure, no proof at all, just intuition.
Something tells me Bob will show me the contrary numbers. And I'm always wanting to learn.
I also grew up believing that car windows block UV/UBF rays. Not so.