Re: Yellow tents and UV (was: outdoor gum demo)
Okay, I quoted that information, which came as a revelation to me, from one skin cancer site, and I figured that the skin cancer people should have a pretty good handle on UV. Since it corroborated my own observation, that my gum exposures in sun don't change noticeably from morning to afternoon, summer to winter, it made sense to me. But it was only one piece of information, and so when challenged, as I always do (wasting thousands of hours over the last ten years checking out assertions made on this list) I looked further. There doesn't seem to be a lot of available information on the subject, or maybe I'm not thinking of the right google terms, but what I've found is consistent with what I've already presented. Here's a couple of samples: "UVA rays persist all year round, even in the winter– unlike UVB rays. UVA rays exist from sunrise to sunset, even on cloudy days – unlike UVB rays. UVA rays pass through windows and glass - unlike UVB rays." La Roche lab site "There is relatively little fluctuation of UVA throughout the day and in different seasons of the year." Photodermatology, Osterwalder and Lim. Some of what I found doesn't look at UVA by itself but as a measure of its relative proportion to the total radiation, which varies in a way that would be wholly consonant with UVA staying fairly constant while UVB fluctuates: UVA is a much higher proportion of radiation in morning and evening hours, on cloudy days, and in winter, than at midday and in summer. Katharine On Apr 21, 2009, at 11:06 PM, Paul Viapiano wrote: Loris...
|