Bob Hughes wrote:
> "Christoph Hormann" <chr### [at] gmxde> wrote in message 
> news:dcn984$3f2$1@chho.imagico.de...
> 
>>The transmission of light is nothing that makes sense to simulate in 
>>POV-Ray since it has no effect on the image POV-Ray renders (light itself 
>>isn't visible).  Therefore using emitting media for the glow and placing a 
>>spotlight at the end is the way to go.
> 
> 
> I don't think I can debate you on that, especially since I'm not sure what 
> you meant by "no effect on the image", but never say never. Not sure what 
> all Anthony knows about fiber optics but I know only enough to describe it 
> to people with no knowledge of it in the first place. ;)
> 
> As I might have said elsewhere already, I was once able to get a simulated 
> fiber optic cable made in POV and at least partially succeeded (maybe). It 
> was done by using photons and reflection on the inside of an S-shaped 
> sphere_sweep. I think it is total internal reflection effect, I believe, 
> that is the operative factor IRL. Meaning, the boundary of the tube with the 
> air is supposed to cause the light to stay within the tube walls because of 
> a specific limiting angle whereby light only reflects instead of breaks 
> through.
> 
> My test scene wasn't very good for anything as I recall, and I was counting 
> on faking it with reflection, not refraction. I'm not good enough with 
> photons to be sure if it really works or not anyway. I guess there would be 
> trouble due to how the photons are designed to map out into the scene, not 
> very sure of anything about it though. Probably was never designed to bounce 
> around inside of curving tubes.
> 
> Sure hope you can manage to do something with your idea, Anthony. I just 
> found the test scene I had done and rendered it as-is. Only got a bunch of 
> red spots everywhere, mostly at the ground beyond the opposite end of the 
> tube. Probably wouldn't help to see the scene yourself, it's basically just 
> a narrow spotlight close to one end of that sphere_sweep (hollowed out with 
> a smaller twin), which then has refraction and reflection including 
> interior_texture.
> 
> I just looked for info about TIR and fiber optics and there's mention of 
> critical angles for the light entering the tube and the bends in the tube. 
> Gets beyond me but this one web page allows for calculating the critical 
> incidence angle for different ior, if you're interested.
> 
> http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/totint.html
> 
> Bob
> 
> 
Hi Bob,

	I don't really know that much about them, only what a quick google 
search could tell me.

	That being said, I did find out that the coating layer has a lower IOR 
than the fiber core.  This is explained by that link you posted. When 
passing through one medium strikes a medium with a lesser IOR, "the ray 
is bent away from the normal." Thus, the angle of reflection will be 
greater than the incident angle. (I can picture this.  That doesn't mean 
that I completely understand it.)

	I do however see Christoph's point about max_trace_level.

	Thanks for the link.

Regards,

A.D.B.

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