there is an emission object in the scene above (Sun), and one can see that sky is really shadeless
my .blend: test.blend.zip (130 KB)
>>note that actually sky is not a full sphere: the bottom of the sphere (the "under"ground part) is deleted
hmm! just noticed: with shadeless sky the bottom of the ground (the ground from the side where part of sphere is deleted) looks OK. If i merge the bottom of the sphere, so now it’s a closed area, then the ground from both top and bottom looks like on the “shadeless sky” image in the previous post.
So I see that my shadeless Sky-sphere:
a) kills all bouncing lighting (that is my Sun becomes much less powerfull inside shadeless object)
b) it also kills environment lighting, just like any other opaque closed object
To be honest, I should say that a) is something that is expected. But I didn’t expect b)… sad for me.
I suppose that now I have an idea of what is going on with such shadeless material in Cycles - there is no bouncing light from such material, and the Sky sphere kills environment light.
Now it’s easy to explain three images in the previous post:
diffuse sky - everything is OK, there are environment and Sun lighting
shadeless sky - environment lighting was killed by the Sky-sphere. There is also no bouncing light from the Sky, so the Sun looks much less powerfull and the Ground is almost black (and this is why the noise is so noticeable)
hidden sky object - environment lighting is OK, and there is no bouncing light from the Sky (there is no Sky), just like on shadeless sky image. But due to environment light, the Ground is OK
Thanks to all for help