> Imagine you are standing in a hothouse. The glass is painted white but lets 
> sunlight pass through in a diffused way. How can you simulate this in 
> POV-Ray? I have been experimenting in several directions but the results are 
> totally different from what I want. Anybody an idea how to solve this?
> Alternatively, how do you simulate sunlight passing through a piece of white 
> cloth? With objects standing in the way casting shadows that you can see on 
> the other side?
> 

I know of two ways to do that.

The cheapest in terms of computation time is to use the keyword 
double_illuminate. In a way, it allows the light to go through your 
object, and to influence radiosity computation, for example. You get to 
view shadows cast by objects on the layer as well. But it can cause 
problems if you need to view the layer from the outside and from the inside.

The other, more physically faithful way is to use a thin layer of 
scattering media, with a very high density. It's difficult to get right, 
though, because you'll probably need to tweak the media parameters to 
get a good looking surface that renders in a reasonnable time.

In both cases you need radiosity to have a lighting inside the hothouse 
from the sun...

Hope this helps

-- 
Vincent

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