I was curious about how Norbert Kern's light & shadows lighting 
environment compares to my 4th prefab render rig's outdoor setting, so I 
wrote a couple of scenes to illustrate them.

Image nkern-light+shadows2.jpg uses Norbert's lighting setup, including 
his sky, his radiosity setting, and the finish he posted.  The colors 
used were:

   Gray sphere:          srgb 0.5
   Green sphere:         CHSV2RGB (<115, 0.65, 0.08>) / 0.6
   Post:                 CHSV2RGB (<23, 0.75, 0.12>) / 0.6
   Yellow-green sphere:  CHSV2RGB (<92, 0.8, 0.12>) / 0.6
   White sphere:         srgb 1
   Brown square:         CHSV2RGB (<23, 0.75, 0.12>) / 0.6
   Green square:         CHSV2RGB (<91, 0.80, 0.18>) / 0.6

I had previously derived the greens and the brown from photographs I 
took of grass, leaves, and soil.  I calibrated the colors against 96% 
white paper, decreasing the assumed paper luminance very slightly due to 
its age.

The rc3-nkern-ltshad-e*-2.jpg images used my 4th prefab render rig.  The 
following colors were used, with the diffuse finish values applied 
directly to the objects:

   Gray sphere:          srgb 0.5                      diffuse 0.6
   Green sphere:         CHSV2RGB (<115, 0.65, 0.08>)  diffuse 1
   Post:                 CHSV2RGB (<23, 0.75, 0.12>)   diffuse 1
   Yellow-green sphere:  CHSV2RGB (<92, 0.8, 0.12>)    diffuse 1
   White sphere:         srgb 1                        diffuse 0.6

I used these radiosity settings:

   radiosity
   { count 200
     error_bound 0.5
     normal on
     Radiosity_Pretrace (0.8, 2) // posted in p.b.s-f
     recursion_limit 2
   }

In addition, the render rig automatically supplies radiosity { media on 
}, because the sky is fog based.

The lighting is not so straightforward, since the render rig creates its 
own black box environment, but since I wrote it, I can give some 
specifics.  The dirt and grass have these colors with diffuse 1:

   Dirt:   CHSV2RGB (<23, 0.75, 0.12>)
   Grass:  CHSV2RGB (<91, 0.80, 0.18>)

The rig uses rgb <1.038, 0.989, 0.956> for the direct sunlight.  The 
sky, disregarding the clouds, contributes about 1/8 the luminance of the 
direct sun; this is the best amount I could determine for a Sun at 45°. 
(I positioned the Sun at Norbert's 47°, but I haven't gone through the 
trouble of programming dynamic sky colors into my render rig, and the 2° 
shouldn't make that much difference.)  I did not take aerosols into 
account, and I presumed that my sources were measured at low turbidity. 
And if you know me, you don't need to ask about the assumed_gamma.

The exposure figure is a multiplier for the sunlight and sky colors.

Since all renders used radiosity with POV-Ray 3.7, any ambient settings 
were moot.

As you can see, my sky is considerably lighter than Norbert's, resulting 
in lower contrast.  However, Norbert's scene is in a heavily forested 
area, which naturally lends itself to dark shadows.  When I look 
outside, my instinct tells me that the sky should be lighter than I have 
made it, but for the time being, I am trusting scientifically measured 
numbers over my non-linear vision.  It should be noted that since blue 
is a low luminosity color, that 1/8 figure is lower than the flux ratio.

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