Yep, that’s pretty much it. I presume that thick cloud layers would pretty much block the UV and thin layers would do pretty much zip zilch nada. Is there some sort of rule of thumb that could be used? I’ve never really noticed enough to be able to have my own internal law. Having just come off a week on the beach, I still couldn’t tell if I was more or less susceptible to rayburn when the sun went behind the clouds. Anyone have the real straight dope? xo, C.