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Q: Questions about Ultraviolet Radiation of the Sun ( No Answer,   6 Comments )
Subject: Questions about Ultraviolet Radiation of the Sun
Category: Science > Earth Sciences
Asked by: hassan30-ga
List Price: $10.00
Posted: 06 Mar 2006 08:43 PST
Expires: 05 Apr 2006 09:43 PDT
Question ID: 704229
As the best of knowledge, ultraviolet radiation of the sun (type A and
B) has no benefit to human body and causes premature aging, damage to
DNA and skin cancer. It is reflected from, almost, every thing ?
water, sand, buildings, etc. Ridiculously, it passes clouds and fog,
which means that in the time we think there is no problem in being
under the sky and may not take any action to protect ourselves from
the sun, it still harms us!

I would like to know whether the about information is true in the
light of the below questions.

1) What is the percentage of UV rays are reflected by the materials surrounding us?
2) In what percentage do UV rays pass clouds and fog?
3) Is there types of glass which UV rays cannot penetrate, or do in
small amounts? And are they used in buildings, cars, etc?
4) Do tinted glasses and Anti-glare films (used in cars and houses)
protect against UV rays?
There is no answer at this time.

Subject: Re: Questions about Ultraviolet Radiation of the Sun
From: siliconsamurai-ga on 06 Mar 2006 09:20 PST
Answering your many questions would take a lot of time and extensive
research so I?ll pass, but here is some helpful information.

Actually Vitamin D is a critical hormone. One kind of UV radiation
destroys Vitamin D-3 (essential for protection against melanoma) and
the other kind of UV radiation triggers Vitamin D-3 synthesis in the

Tinted and most glass filter out UV A which destroys Vitamin D 3. That
is thought to be the reason indoor workers are more likely to die of
melanoma than outdoor workers who are exposed to direct sunlight ?
this is true only of the survival rate ? excessive sun exposure almost
certainly causes melanoma (the most deadly skin cancer).
Subject: Re: Questions about Ultraviolet Radiation of the Sun
From: hassan30-ga on 07 Mar 2006 00:34 PST
You said UV A destroys vitamin D 3 while UV B helps the body to
synthesise it. So if glass filter out UV A, why are indoor workers
more likely to die from melanoma?
Subject: Re: Questions about Ultraviolet Radiation of the Sun
From: siliconsamurai-ga on 07 Mar 2006 07:42 PST
Sorry, typo, should have indicated most glass filters out UV B, letting through
UV A which destroys it.

BTW, I don't say it, clinical trials published by NIH and NCI say it.
Subject: Re: Questions about Ultraviolet Radiation of the Sun
From: knickers-ga on 15 Mar 2006 07:36 PST
Regarding above. You need to be aware that the names UVA and UVB are
just names that we put on specific parts of the electromagnetic
spectrum. UVB, which is wavelengths 290 to 315 nm, found in sunlight
when the sun is high enough above the horizon for UVB to penetrate the
atmosphere. UVA is 315 nm up to about 400nm. Above this visible light
starts. UVB is generally more dangerous because it has the shorter
more energetic wavelengths. However, in general most the UV spectrum
is absorbed by most common organic groups. If the UV radiation is of
sufficient intensity then it can cause these chemical bonds to
rupture. These chemical bonds are the same that are found in our
tissue. Hence UV damage to our skin and cells. It all depends on the
intensity and amount of exposure. Some UV generates good chemical
reactions and too much generates bad chemical reactions i.e. cell
Most Glass absorbs about 80% of the UV light. Hence you are not likely
to get any Tan or sunburn when behind most forms of glass or even
plastic sheet. But you do get very hot. Clouds and fog are far more
transparent to UV light. Even on a moderately cloudy day 60% of UV
light will reach the earths surface. You need to be aware that light
intensity and hence UV intensity varies considerable across the
surface of the earth. Hence on equivalent sunnys days Florida has
about 2.5 times the light power compared to London. The average is
about 1000W/m2. So a lot of sun energy. You can get special UV
transparent glass but this costs a fortune and is not used in normal
applications. Most coatings, filters or treatments will increas UV
absorption for the reasons I highlighted above and hence reduce UV
Regarding reflection. I am not sure of figures but it will depend
intirely on the nature of the surface. Generally you can say shiny
bright surfaces are better reflectors. If you want to test UV expsoure
of materials there are various test methods. Companies like offer accelerated testing of materials and can
simulate years of exposure of materials in a matter of weeks.
Subject: Re: Questions about Ultraviolet Radiation of the Sun
From: hassan30-ga on 28 Apr 2006 06:14 PDT
Thank you very much knickers-ga for your comment!
Subject: Re: Questions about Ultraviolet Radiation of the Sun
From: hassan30-ga on 19 May 2006 03:03 PDT
Thank you very much knickers-ga for your useful comment.

I have been looking in the web for more information about UA
radiation. There is another type of UV which is C. Its wavelength
ranges between 290 to 15 nm. Some lamps also produce UV.

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