> > Couldn't it be said that POV-Ray does support wavelength-dependant
> > scattering, but that it only works with three wavelengths (R,G,B), and
you
> > must specify the scattering for each one manually?
>
> eh! eh! good question! I'm also waiting for an answer...

Well. You *could* say that POV-Ray only supports three wavelengths for
scattering, but that would still not be entirely true. Wavelength-dependant
scattering implies that you can throw white light at an object, and it will
spit the entire spectrum of colored light out. POV-Ray, in no manner
whatsoever aside of using photons, does that. And if you have to manually
define the scattering for each wavelength by yourself, where is that true to
the concept of stating that POV-Ray scatters only three wavelengths?
Additionally, unless you use photons, the light isn't focussed and
refracted, which is what happens with wavelength-dependant scattering: while
passing through the air (notice the "while", it doesn't get refracted only
upon entry and exit as POV-Ray does it), the different wavelengths are
scattered differently. Hence the red sky on sundown, the light only gets
"bent" towards the viewer, straight lines of light would actually not reach
the viewer.

The only true thing about that is that you can do just about anything with
POV-Ray, given the time it might take to render a complex scene, but that
hardly proves that POV-Ray can do wavelength-dependant scattering.

If you're interested on the technical aspect: POV-Ray traces straight rays,
not curved rays, which would be required for proper wavelength-scattering.
Or, if curves aren't possible, to at least approximate the effect by
permitting rays only to a certain length, then recalculate if the direction
changes, and move onward. But then, the results aren't easily predictable
and may vary greatly in animations or when dealing with small-scale
turbulences.

-- 
"Tim Nikias v2.0"
Homepage: <http://www.nolights.de>

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