-> safesun.com is a commercial site selling a UV detector tool for personal use 
-> it tells you how much UV you have been exposed to... 
  
What sort of UV? 
  
Some years ago, I has a basal cell carcinoma - a kind of skin cancer 
which, fortunately, is easily and reliably cured. The doctor told me 
that it had probably been caused by a bad sunburn I'd had when I was a 
teenager, some 40 years earlier. She warned me to watch out for other, 
similar lesions, and also to wear plenty of sunscreen. And she told me 
that the sunscreen should be one that contains "Parsol 1789" (its 
chemical name is Butyl Methoxidbenzoylmethane) which is an ingredient 
that screens out a particular band of UV wavelengths that do a lot of 
harm to the skin and that are not absorbed by the ingredients in many 
sunscreen lotions. Even though these other lotions may have good SPF 
(sun protection factor) numbers, cutting down the overall UV by factors 
of 30 or more, they don't do much good at preventing skin cancer. In 
fact, they can be counter-beneficial, since they prevent the skin from 
becoming tanned, and therefore allow even more of the most harmful UV 
to get through. 
  
UV isn't just a single thing. It's a spectrum of wavelengths that have 
different effects on the skin. So its intensity can't be adequately 
described with a single number. 
  
                           dow 
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