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How does light bouncing work in unreal?

I’ve been experimenting coming over from mental ray, vray and so many other off-line renders throughout the years.

One thing I’m trying to grasp in several test levels in unreal is that light bouncing seems a little different. I’m getting results I’m not used to.

In an example shot below. It appears these shadows are pitch black despite default sun + sky, 10 light bounces and 10 indirect light bounces. This happens both with CPU and GPU lightmass.

(ignore the bright gap with the ground)

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The same scene, but interior, we have this;

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Obviously with white walls (diffuse white set to .7) we have far more light bounce and zero black shadows. However I wondering, is light bounce in unreal different in that it more relies on the colour of the material it’s bouncing off from than the intensity of the GI from the sky itself?

I noticed dark floor will result in dark ceilings but walls will not get this colour wash. I’ve struggled to get good GI in scenes with black floors.

Do default settings need to be tweaked to get a more physical based sky which we see in VRay, Arnold etc?

If I increase the Sky strength it doesn’t really do anything but throw out the balance of the Sun’s intensity.

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