IBLs do kind of work in Superfly, but not the same way as they to in Firefly.

IBL is a trick to get ambient light into a scene without calculating indirect light, Superfly/Cycles always calculates indirect light, it does not know this trick.So an IBL will just be a different kind of Envsphere, just with different mapping. You cannot see this light, though, when you still have the construct ("Ground") visible, since it shadows the whole scene.

That's the main difference between an IBL in Firefly and in Superfly - Superfly always calculates shadows, but an IBL was built to provide ambient light and not be shadowed.

If you want the look an IBL gives, you need to render with Firefly.

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