On 18 Aug 2004 19:19:13 +0100 (BST), David Damerell
<
[email protected]> wrote:
>Pat Lamb <[email protected]> wrote:
>>David Damerell wrote:
>>>Patrick Lamb <[email protected]> wrote:
>>>>My wife makes fun of my "farmer's tan." Parts of my body regularly
>>>>covered by clothes, like a t-shirt, are pale, while uncovered parts of
>>>>my body are tan (or red, depending on the week). Why do you think I'm
>>>>pale? I think it's because a shirt of any type blocks the sun.
>>>I think everyone knows this. The question is, _why_ does this happen,
>>>given that measurements suggest the results would be otherwise?
>>Faulty measurement equipment? Faulty measurement technique?
>>I don't really know, don't really care.
>
>Perhaps then you should shut up, and let the people who _are_ interested
>discuss it without pointless interruptions.
I do hope this wasn't supposed to be a snappy comeback. Rather than
displaying your intellect, it displayed your density. Mine was a
pointed comment in a pointless discussion.
The starting point of this thread was an allegation that white cotton
t-shirts have a rather low SPF equivalent. Two posters, further down
the thread, report single instances of sunburn through such a t-shirt.
The overwhelming majority of people wearing t-shirts don't get burned.
Therefore, the alleged low SPF is cast into doubt.
I could offer speculation, and perhaps more intelligent speculation
than most, about why the observed protection of t-shirts exceeds the
reported low value. However, that would be strictly speculation.
Nobody's come forth with enough information to make this an
intelligent discussion yet.
If you want to flap your gums (or fingers), continue as you were. If
you'd prefer to have a discussion which might result in something
useful, start asking or answering some good questions, such as:
(1) What kind of t-shirt are we talking about? Brand? Areal
density, before and after washing?
(2) Was a calibrated UV meter being used to test the absorbance?
(3) What waveband was tested?
(4) Did the experimental setup account for backscatter?
(5) If we're going to talk about the two anecdotal instances where
sunburn occurred through the t-shirt, we need information about the
t-shirt in question (was it a beefy Hanes t or a thin, cheap shirt?)
and information from which we can deduce likely UV radiation levels,
including time of year, time of day, latitude, and relative humidity
levels. Similar information would be useful for all negative reports.
So decide. Either inject some level of rigor or admit we're all idly
chatting.
BTW, either way, I think it's reasonable to ask for more details about
where the data came from. If the discussion is just over, "Will I get
sunburn wearing a white t-shirt?" it can't be answered just from
experiential data and some magazine's counterclaim. That question
can't be answered without the answer to my question (1), above. If
you want to get down to details and learn some facts, you'd still need
the same information.
Pat
Email address works as is.