>>>Objects being in separate light groups still cast shadows for all
>>>lights.
> 
>>Here's why: the shadow is caused by the object the shadow is cast
>>across, which is lit by all lights.  When the tracer looks up how much
>>light is falling on the shadowed object, it doesn't need to know about
>>the light-groups that some other object (which happens to be in the way
>>of the light) is using.
>>
>>So, you need to put the shadowed object in a complementary light-group
>>or something instead.
> 
> Sorry, I am not sure I understand what you mean... er rather : I am sure I
> do not understand... :'-( Could you explain a bit more ?

Hmmm...  First recall that POV-Ray, like all other tracers, shoots rays 
from the camera, not from the light sources.  When these rays hit an 
object, it then shoots rays *towards* each light source to see if it's 
in shadow or not.

These shadow rays don't care whether the object they intersect happens 
to be part of a light-group or not.  They only care if the object the 
camera-ray hit was in the correct light-group.

Remember, a shadow is just an absence of light.  The shadow falls across 
a different object than the one you put in the light-group.  It is this 
shadowed object that needs to have the correct lights attached to it.

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