Or just reflect..... The sun puts off UV light. Actually, as I recall, the sun puts off radiation, some in the form of what we call light, some of it is visible by us and some is not, because it is in wave length's our eyes can't detect, but other eyes can.
Some materials reflect certain of the waves, and we see that as colors. Some do not tend to reflect wave length's in the UV spectrum, or at least not well, others do it a lot. We can't detect those colors, but other eyes can.
I guess I need to ask the question.... why now ? We have known of this problem with some materials for years.... So they are all selling us a line of clothing that nothing can see, except for that blinking light on our face ?
So what ELSE am I supposed to not believe / trust anymore ?
ChuckC