Refraction problem with irrmap and lightcache

[ruud3dv]

The floor looks way too bright when seen through the glass.

Glass material: fully refractive, affect shadows is on, IOR 1.6, fresnel reflections on, max depth for refraction set to 16.
There are only two other materials, light and darkgray, both nonreflective.
Lighting: VraySun and VraySky
GI: irrmap as primary and lightcache as secondary, lightcache retrace on and store direct light off

During GI calculation all looks fine, both lightcache and irradiance map show normal brightness for the floor seen through the glass, but when rendered it's too bright.

When using BF and Lightcache for GI the result is fine.
Didn't find any coplaner faces.

Using Vray 3.10.03 on Max 2015 x64, Win7 x64.

[ruud3dv]

Found the problem: irradiance preset was set to Low (-3/-2). For some reason the only way to render properly with these settings would be to enable 'Check sample visibility' but that about doubles the rendertime in this case.

With irradiance map set to Medium it renders fine, and only takes a bit longer for the irradiance map calculation.

Is this normal/expected behavior?

[Macker]

Is that not just the reflection of the brightly lit floors externally?

[ruud3dv]

Nope, to clarify here's a render with a darker gray for the surroundings.
In the first post you can see in the RawRefraction that the floor is much brighter than the walls, while they have the exact same light grey material.

But this is strange: when the reflection of the glass is disabled, the problem does not occur.

[ruud3dv]

I've attached a simple test scene showing the problem.
Now: if you render a region close around the problem area, the problem is gone.. probably due to more samples being forced through the glass...

[ruud3dv]

Finally found it!!
Irradiance map 'Sample lookup' was set to 'Overlapping (very good/fast)'. When set to 'Density-based (best)' the glass renders perfectly!
I must have accidentally changed this setting at some point, it was always set to Density based.

[svetlozar.draganov]

Glad to hear you sorted it out.
Let us know if it happens again.