@Michaelab

I suppose U used BB's sphere in your picture and reduced the light intensity to create "night". Am I right?

OK, night.
BB's sphere is a diffuser-emitter (he probably has a better explanation for it, but I like to keep things simple).
The sphere works best with a Sky texture on it. And it simulates 'air light diffusing" to help with real IDL calculations.

Most downloadable sky textures are bright day sky textures.
At night however, the sky is not bright, but dark.

So you will have to darken the sphere, or darken the textures, to create a night environment.

As I look at our picture?
The figure is darker but the environment stayed bright as in a day situation.

Darken the sphere, or darken the sky texture you had put on the sphere to get "night light" IDL calculations.

BB himself surely has other tricks up his sleeve. :-)

 

 

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