[Radiance-general] under water light fixtures

[Gregory J. Ward]

Hi Christoph,

John is right.  If you want to see the light beam in the water, the  
mist material is for you.  Follow the examples and stop the mist  
volume right before the light source, and preferably just inside the  
walls and water surface of your pool.  List the underwater light  
source(s) in your mist's string arguments.  You should specify a high  
scattering albedo (probably 0.97 0.99 0.99) and a fairly high H-G  
constant (0.85 or so).

The water surface needs to be a dielectric as Ignacio indicates.  If  
you apply a texture for a natural wavy appearance, you will see the  
distorted bottom of your pool and the scattered beam of your source,  
but you will be missing caustics from the water's surface on the pool  
bottom and the surroundings above water, as Radiance doesn't know how  
to calculate those properly.  Even without a texture, you won't get  
proper illumination of the bottom from lights above, I'm afraid.  The  
best you can hope for is sky contributions from the ambient calculation.

Attached is an example description of a 10 by 5 meter pool with two  
(diffuse) lights.

-Greg

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> From: "Reinhart, Christoph" <Christoph.Reinhart at nrc-cnrc.gc.ca>
> Date: November 6, 2006 12:25:06 PM MST
>
> Dear Radiance colleagues:
>
> One of my students is interested in modeling an under-water light  
> fixture for a swimming pool in Radiance. I have modeled a water  
> surface in the past, but I am not sure how to model light traveling  
> through water. I vaguely recall hearing that to do so one must  
> model the water volume as a dielectric. Could anybody explain to me  
> how this is done? An example file would be very much appreciated.
>
> Christoph