Ah, the miracles of modern science. Bet this stuff protects against nuclear fallout.....now gimmee my 6 bladed razor.....
SNAKEOIL!!!!!!!
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I knew it was coming- SPF 100
Ah, the miracles of modern science. Bet this stuff protects against nuclear fallout.....now gimmee my 6 bladed razor.....
SNAKEOIL!!!!!!!
Order of Kilopi
Is that an American or European sun factor?
From what I remember it's like percent/proof for alcohol, US uses numbers that are twice as large to describe the same thing.
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Reductionist and proud of it.
Being ignorant is not so much a shame, as being unwilling to learn. Benjamin Franklin
Chase after the truth like all hell and you'll free yourself, even though you never touch its coat tails. Clarence Darrow
A person who won't read has no advantage over one who can't read. Mark Twain
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So SPF99 would be OK, but SPF100 is snakeoil?
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I'm in need of some SPF150 or so; you know, stuff that actually sucks out some of the sun's effects that are already in your skin. I burnt the heck out of my shoulders working in the yard this weekend.
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I just saw a commercial for SPF 100 this morning. I couldn't help but remember an umbrella for a patio table being rated as SPF30. How is that even possible?
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Ah, I see (maybe). SPF is not a percentage. So SPF150 wouldn't give you negative tanning. AFAIK it is a ratio (or a factor, even): SPF100 means that after 100 hours in the sun, you will have had the equivalent of 1 hour of unprotected exposure.
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Why not? The danger is that a lot of people assume that umbrellas or clothing have a very large (infinite?) SPF. I saw something about studies of infant clothes that showed they had a very low SPF (maybe less than 10?). So even witht their skin covered they could get burned.Originally Posted by closetgeek
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Because there's a large amount of scattered sunlight from the rest of the sky, so even if you don't get the direct sunlight there's still a lot of UV hitting your skin.
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Reductionist and proud of it.
Being ignorant is not so much a shame, as being unwilling to learn. Benjamin Franklin
Chase after the truth like all hell and you'll free yourself, even though you never touch its coat tails. Clarence Darrow
A person who won't read has no advantage over one who can't read. Mark Twain
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Ah. Drats. Then the gooey aloe mess I've been using will have to do. It doesn't seem to be doing anything other than making my shoulders smell like aloe and menthol though. The annoying part was that I actually thought to put on some sunscreen (I usually don't. Melanoma be damned), but the stuff we had was a few years old and I suspect even new it wouldn't have worked that well (It was 'rated' as SPF50, but it was a spray and very watery).
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No, SPF 100 is that you will not burn until exposed to 100 times the sunlight required to produce a burn if unprotected. It is not the most objective of measures. It also only relates to UVA. There are proscriptions in some countries as to the highest SPF rating that can be assigned.
http://en.wikipedia.org/wiki/Sunscreen
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That is a better definition than mine which (among other problems) assumed a constant level of exposure for 100 hours.
UVB, surely?It also only relates to UVA.
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And these come out differently because the sun moves in the sky: other things being equal (which they often aren't) you get a bigger cumulative UV dose around noon than you do at other times of the day.No, SPF 100 is that you will not burn until exposed to 100 times the sunlight required to produce a burn if unprotected.
Grant Hutchison
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"These" what?
True: exposure risks dramatically change throughout the day, but since SPF is a ratio, there is no fixed amount of exposure that the computation needs to depend on.
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These two things I quoted in my post: Strange's "after 100 hours in the sun, you will have had the equivalent of 1 hour of unprotected exposure"; and DrRocket's "you will not burn until exposed to 100 times the sunlight required to produce a burn if unprotected".
Grant Hutchison
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I wasn't sure, which is why I asked. Overall, those comments discuss the ratios, so do you not agree with my post?
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I agree with your post. Do you not agree with mine?
Grant Hutchison
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The point is that 100 hours in the sun does not equate to 100 times as much sunlight, since the amount of sunlight varies over time.
__________________________________________________
Reductionist and proud of it.
Being ignorant is not so much a shame, as being unwilling to learn. Benjamin Franklin
Chase after the truth like all hell and you'll free yourself, even though you never touch its coat tails. Clarence Darrow
A person who won't read has no advantage over one who can't read. Mark Twain
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I wasn't sure what you were trying to get at. I agreed with your post, but didn't see how it applied to SPF. So I put in my 2 cents.
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Coincidentally, 2 cents provide very good sun coverage, albeit over a very small surface area.
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Sun coverage maybe, but did you ever try to pick up anything metal that's been sitting in the hot sun? Ouch, a different kind of burn.
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Because the "100" in SPF100 means a 100-fold increase in UV dose, which does not convert to a 100-fold increase in sun-exposure time. These two things are different. That's why Dr Rocket pointed out the correct interpretation of the "100", and why Strange was happy with the correction.
Grant Hutchison
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Yes; Being that his comment was unspecified, I automatically took it as 100x equal exposure and didn't even take it as an issue. It's kind of hard to stay in the sun for 100 hours unless you're at the poles.
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Well, just a bit inside the polar circle. Easy enough to get sunburned in the Arctic and Antarctic.
Grant Hutchison
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That is what I meant. But, oh no, DrRocket the Big Mathematician just has to come along and get all picky about the details
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Yes; another clarification on the unspecified and/or shortened version "poles".
I've heard that. Combination of longer total exposure and clearer skys I would assume.
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And snow, which reflects UV. Worst sunburn I ever had was under my chin after a day crossing snow and ice at high latitudes.
Grant Hutchison
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Water used to do it to us. Growing up we had a boat at the local lake (mud-hole, but that's what passes for a lake 'round here), so we'd be out on the water for hours at a time two or three days a week.
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Some people cope just fine:
I think this whole 100 bit is like that bull about "wind chill factor" one hears these days on weather reports. If you want to sell something (e.g. a weather report or sun blocker), come up with a way to be able to use totally absurd numbers which can somehow be justified when challenged.
Ahh, marketing. My favorite.
Established Member
Would you not expect that down parka to provide some protection ?
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That'll teach you Brits about the dangers of keeping your chin up.
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