Overview:
I kept wondering why my character still has light on it, it has no illumination level, no glow, deactivated any lights, disabled IBL.

Tests:
1.Enabling/disabling GI in the toolbar either made it brighter or less bright.

2.Only when I disabled GI in the exclude effects area, the character was completely hidden in the dark and then the GI toggle in the toolbar finally made the character disappear in the dark but it should have already been dark with GI enabled.

Is this a bug or just the nature of the only way the GI shader will work?

Expected result:
I think GI should work in all light levels and if there is no light transmission enabled from any source ie; no self illumination or glow, no IBL, no lights etc then the subject should be completely unseen.

Repeatable steps (problem exists only in CC4)
1.Create a scene
2.Add character or prop
3.Disable lights
4.Set background to black
5.Disable IBL
6.Enable and disable GI from toolbar
7.While GI is enabled, open exclude effects and toggle GI for subject on and off.

Importance:

When creating a character, it's essential to see how the character looks in all lighting levels incase something is enabled that shouldn't be and to make sure the skin & hair, color, brightness, opacity & translucency is correct at different lighting levels.

Lastly, it seems the light level slider in both CC4 and iC8 doesn't provide a enough control to lower the light levels
unless you enable contrast on the light and lower fog transmittance! but there still should be more darkness levels especially for smoother gradual light animation in iC8.