> 1) point light source with "fading_distance" and "fade_power",
>    but found out, that the light in far distance gets a
>    constant level, NOT completely dark! So the pillars are
>    visible even in infinity. I even tried a darker light.
>
> 2) I added an ambient light with:
>       global_settings { ambient_light rgb<0.1, 0.1, 0.1> }
>    which (to my astonishment) DARKENS the whole scene.
>    However the floor in close distance is too dark now.

It seems that you're not aware that there is a default ambient light
setting. The default for the global_settings ambient_light setting is rgb
<1,1,1>. This is multiplied by each object's ambient light setting, which is
set in the object's texture's finish and has a default of rgb <0.1, 0.1,
0.1>. That means that by default, even without any light sources, all
objects will show at 1/10 their intensity.

In order to remove this ambient light and start from pure blackness, you can
set the default ambient light value for all objects like this:

#default {finish {ambient 0}}

Since you seem to want your light sources to be completely in charge of the
lighting, you may also want to set diffuse to 1 (the default is 0.6) so that
the incoming light color is multiplied by the full color of the object's
pigment (as opposed to just 60% of it):

#default {finish {ambient 0 diffuse 1}}

Though doing so is not necessary to create blackness.

> 3) I added a spotlight pointing to the bottom of the
>    camera position.
>    However objects in close distance give wrong shadows now.
>    And the radius and falloff is difficult to find off, because
>    when touching near objects, the light cone should not be visible
>    on vertical structures.

I'm not quite clear what you're saying here.

 - Slime
 [ http://www.slimeland.com/ ]

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