Severi Salminen wrote:
> Glass has about 4% reflection coefficient when angle of incidence is 0.
> I guess this 4% holds true both when entering glass and exiting it?

It's more complicated than that in reality. Light doesn't reflect from 
the surface of the glass. It reflects inside the glass. It only seems 
like it reflects from the surface because different paths that reflect 
at different depths in the glass cancel out. A piece of glass the proper 
thickness has no "surface reflection" at all, and a half wavelength 
thicker and it has 16% reflection. So, technically speaking, there's no 
"reflection off the back" at all - it's just that the math works out to 
make it look like there is. (And I have no idea where I left the book I 
have that explains the math well enough to indicate whether the math 
works out to make it look like a 4% reflection off the back, too. ;-)

(Similarly, a mirror reflects all over its surface, but only the paths 
where incidence = reflection don't tend to cancel out. Diffraction 
gratings and holograms take advantage of this, for example.)

I mean, if you're talking about "physically-accurate" tracing. :-)

-- 
   Darren New / San Diego, CA, USA (PST)
     "That's pretty. Where's that?"
          "It's the Age of Channelwood."
     "We should go there on vacation some time."

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