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<div class=Section1>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>This comment comes from a physicist, so I
may be more critical that the average bear.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>To begin with, antireflective coatings
have been around for a long time. The trick with antireflective coatings is as
follows:</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal style='margin-left:.5in;text-indent:-.25in'><font size=2
color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'>(1)<font size=1 face="Times New Roman"><span style='font:7.0pt "Times New Roman"'>
</span></font></span></font><font size=2 color=navy face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:navy'>Even if the material
(e.g. low iron glass) absorbs ~1% of the light incident on it, at the “boundary”
between the air and glass, light will be reflected due to a “mismatch in
the index of refraction”. This reflection depends on the angle of
incidence, and depends on the polarization of the light (direct sunlight is
unpolarized).</span></font></p>
<p class=MsoNormal style='margin-left:.5in;text-indent:-.25in'><font size=2
color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'>(2)<font size=1 face="Times New Roman"><span style='font:7.0pt "Times New Roman"'>
</span></font></span></font><font size=2 color=navy face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:navy'>For example a 3 mm (1/8”)
thick sheet of low iron glass will average 89% transmittance and 8% reflectance
of “solar energy” (over that part of the spectrum that Si solar
cells are most sensitive). If a single layer is used, the material used for the
antireflective coating has to have an index of refraction that is half way
between 1.0 (air) and glass (~1.45) or 1.23 and be 110 nm thick. Although not a
perfect match, MgF2 (index equal to 1.38) is commonly used. Teflon is an
excellent coating but it is easily scratched and difficult to apply in films as
thin as 110 nm.</span></font></p>
<p class=MsoNormal style='margin-left:.5in;text-indent:-.25in'><font size=2
color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'>(3)<font size=1 face="Times New Roman"><span style='font:7.0pt "Times New Roman"'>
</span></font></span></font><font size=2 color=navy face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:navy'>Coating the glass has to
be tightly controlled and I doubt this would work as a DIY project.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>So I am pretty sure that this coated glass
would improve the transmission, but I am very skeptical about it protecting
underlying glass and I would be very surprised if it more scratch resistant
that regular float glass. On the contrary, I would expect the coated glass to
require special handling and be LESS environmentally robust.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<div>
<p class=MsoNormal><font size=3 color=navy face=Arial><span style='font-size:
12.0pt;font-family:Arial;color:navy'>- Peter</span></font></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt'>Peter T.
Parrish, Ph.D., President<br>
California Solar Engineering, Inc.<br>
820 Cynthia Ave., Los Angeles, CA 90065<br>
CA Lic. 854779, NABCEP Cert. 031806-26<br>
<a href="mailto:peter.parrish@calsolareng.com"><font size=1><span
style='font-size:9.0pt'>peter.parrish@calsolareng.com</span></font></a> <br>
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
</span></font></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt'> </span></font></p>
</div>
<div>
<div class=MsoNormal align=center style='text-align:center'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabindex=-1>
</span></font></div>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <b><span style='font-weight:
bold'>On Behalf Of </span></b>Keith Cronin<br>
<b><span style='font-weight:bold'>Sent:</span></b> Saturday, December 05, 2009
10:09 AM<br>
<b><span style='font-weight:bold'>To:</span></b> RE-Wrenches<br>
<b><span style='font-weight:bold'>Subject:</span></b> [RE-wrenches]
Antireflective coatings</span></font></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> </span></font></p>
<div>
<div>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:black'><a
href="http://www.ecmag.com/?fa=article&articleID=10827">http://www.ecmag.com/?fa=article&articleID=10827</a></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:black'> </span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:black'>Do any of you have any comments on the
efficacy of these types of products?</span></font></p>
</div>
</div>
</div>
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