Having no mass, photons always travel at speed of light, even when they
go through transparent objects. They are absorbed and emitted several
times before they escape the material. The collective effect of billions
of them in a beam is as they travel slower than c. This collective
behavior is correctly described by Maxwell's equations. Individual
photons are better described by quantum mechanics.  This
collective behavior is what is simulated in povray, the behavior of
beams of light
 best described by Maxell's eqs.

Alberto

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