Re: Sunscreen and UV

[maury <maury@WEBTEXAS.COM>]

I make extensive use in Texas summer of cheap roll-down shades outdoors

over exposed windows. They used to be cheap bamboo and last several

years. They are still cheap, but the UV exposure now seems to destroy

the strings and they do not last one summer anymore.



What should happen if I sprayed the strings with sunscreen?



I have reverted to sticking white adhesive shelf paper in many window

sections, (works great, but not very attractive) but if I buy some more

roll-down shades, I plan on trying sunscreen to see what happens. Have

also wondered about Armor-All or Nu-Vinyl solutions (used on car

interior plastic sufaces to fend off UV effects)

Maury          maury@webtexas.com

=====================================

RuthWeiner@AOL.COM wrote:



> In a message dated 8/3/02 1:10:48 PM Mountain Daylight Time,

> WesVanPelt@att.net writes:

>

>

>

>> I am wondering exactly how sunscreen blocks UV radiation. When you

>> put it on the skin, it "disappears" so it is transparent to visible

>> light. And the layer of sunscreen is quite thin. I read recently

>> that there are 5 or 6 different chemical compounds that can be used

>> as sunscreen.

>>

>> So, what is the mechanism that protects the skin from the effects of

>> UV? Does the mechanism include some reaction with the skin? Would

>> sunscreen spread on window glass to the same thickness screen out

>> the same fraction of UV as on the skin?

>

> The active ingredient in most sunscreens some derivative of

> para-aminobenzoic acid (PABA).  The sunscreen I use contains methyl

> p-amino benzoate.  These compounds absorb in the UV, not in the

> visible range, which is why they "disappear".  Window glass absorbs UV

> also, by the way.  The UV absorption of any compound depends on the

> amount of the compound present; in a colloidal suspension like

> sunscreen, it depends on the concentration. So yes, a layer of

> sunscreen on anything blocks UV to the same extent.

>

> In 1974 I judged a science fair in which we gave a prize in the senior

> division to a girl who had smeared various sunscreens with different

> active ingredient concentrations on plant leaves, and had measured the

> extent to which the sunscreen blocked photosynthesis.  She didn't get

> it QUITE right -- photosynthesis used light at the red end of the

> visible spectrum also -- but she had very much the right experimental

> idea, and her results were pretty dramatic.  (She also got the prize

> because the whole idea and execution was hers.  All too often the

> entry reflects the work of some scientist or engineer Mommy or Daddy.)

>

> Ruth Weiner, Ph. D.

> ruthweiner@aol.com



--

It is the soldier, not the campus organizer, who has given us the

freedom to demonstrate.                       Charles M. Province





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