material setting 'use irradiance map' causes big differences in render results

[mw@a2studio]

Hi there, I'm having the following problem.

My scene consists of a studio setup in the shape of a bowl, a character, and 1 vray sphere light set on 'affect diffuse' only, and 'store with irradiance map' on.
GI: irradiance map and light cache. Max 2012 vray 2.40.04.
The scene renders quiet slow, and i managed to figure out this was because of the material on the studio setup. The option 'use irradiance map' was unchecked, see left side. With the checkerbox on i get the result on the right. Not only is the result way brighter, we can also see an edge where the studio setup start to go upward.
How come there is such a great difference with this option on/off? And is there a way to fix this?

[DanielBrew]

Hi and welcome to the forum,

When you rendered your scene with 'use irradiance map' unchecked for your bowl material the GI will have been calculated using brute force for the objects with that material applied. However, if your light is set to 'store with irradiance map' it will be excluded from lighting those objects so they will render much darker.

[mw@a2studio]

Hi Daniel,

Thanks for the quick reply. Your explanation sounds very reasonable
But i'm still confused why the soft edge of the bowl is much more visible with the one, and almost invisible with the other technique. So not only will those object render much darker, which they do, but they are also lit differently?

[DanielBrew]

But i'm still confused why the soft edge of the bowl is much more visible with the one, and almost invisible with the other technique. So not only will those object render much darker, which they do, but they are also lit differently?

It's difficult to say without seeing your scene but I expect it is because in the darker render the bowl is lit by the environment light which is diffuse and lights unoccluded surfaces very evenly. In the lighter render the bowl is lit predominantly by the sphere light. So the lighting will be more directional and depend on the light's position.

[svetlozar.draganov]

If you could attach the scene that would be great.
Like DanielBrew mentioned it is difficult to predict why the result is different without knowing how the scene is set up.

[mw@a2studio]

Thanks Daniel!
Like Svetlozar Draganov said, maybe it's more helpfull to upload the scene, so here it is.

[DanielBrew]

@mw@a2studio

I've changed your sphere light into a dome and the lighting is much more even. I've changed to the render settings as well but only so I could see the result more quickly.
scene.zip

[mw@a2studio]

Wow, great result, and it renders really fast. Thanks a lot!
Did you only tweaked the irradiance map parameters as far as render settings go?

[DanielBrew]

Did you only tweaked the irradiance map parameters as far as render settings go?

I don't think I changed anything else other than the resolution is a quarter of the original.

[mw@a2studio]

Ok. Thanks again, you've been a great help!
Cheers