Le 2022-10-25 à 19:49, neri-engineering a écrit :
>> Ah, this makes sense.  I will try that.  The strange behavior I'm seeing is
>> consistent with your explanation.
> 
> I got it.  The snippet below works as expected.  The 'emission' is because I'm
> using radiosity and want the shadow cast onto the floor to be a tad less dark,
> 'diffuse' limits how bright the floor is.  Thanks for the help

You should not use emission for that purpose. What you do actually mean 
that the floor is a source of illumination. Don't take bad habits.
The purpose of emission is to have some object actually emit light. It 
allow the creation of scenes where there are no light_source to get 
illuminated.
With radiosity, you need an environment outside the visible part of the 
scene.

For a room, that normally mean having all the walls and ceiling present. 
That way, the light bouncing off the other walls and ceiling will 
illuminate the areas that are in the shadow from regular lights.
Make the ceiling white or light grey as most of the ceilings are. Use 
recursion_limit 2 or 3.
For outdoor scenes, that's done with a sky_sphere or a huge sphere 
surrounding the scene.

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