Can't get rid of light leaks - any suggestions?

[rkuerbitz]

Dear community,
I am having trouble getting rid of light leaks in my rendering of a certain project. Following some other forum suggestions, I pinned down the problem to Light Cache (it will render good with only Brute force GI). As you can see, the leaks affect walls and a roof object
I already tried the following:
- rasing subdivisions to 6000 (from 2000)
- raising leak prevention to 1
- putting a "isolation" object inside the wall and the roof
... and I still get these light leaks.

I use the most current version of vRay Next with 3ds Max 2019.

I now have less leaks, but they still are there! Do any of you have any suggestions? Any help would be very much appreciated. Thanks in advance!
Ralf

[Miro]

Can you share the scene to support@chaosgroup.com so we can take a look?

[glorybound]

Just by looking at your image, those lights seem really bright. Are you using real work camera and light settings?

[rkuerbitz]

Dear Bobby,

yes I am using real world camera and lights (IES). Howver the screenshot has changed exposure (x1,7) in the vray frame buffer. I did send a stripped-down file still showing the symptoms to chaosgroup.

[rkuerbitz]

Well, to close this thread and maybe help other searching: chaosgroup support provided the solution:

We've seen something similar a couple of times before on random scenes. In the light cache settings, if you turn off Retrace or set Leak prevention to 0.0 the leaks should go away.
Can you confirm it's the same on your end?

So, in this case, the leak prevention parameter does just the opposite...

[^Lele^]

Leak prevention defaults at 0.8 for good reasons.
Return it to its default, instead of 1.0 as you had it, and see if that creates the leaks.
Turning it off is NOT suggested.

[rkuerbitz]

Hi Lele, I know turning off leak prevention is not suggested. But Miroslav from chaosgroup took my scene and gave me this suggestion (see italic text). It worked for me. (I did have the leaks with 0.8 which was my default start).

[^Lele^]

Ah ok then, i won't comment further on the rest of the LC settings if support has had a look: if turning LP off seems viable to you, so be it.
I'd still try and reset the LC settings, and use those as they are, changing what we suggest as allowed: namely subdivs and retrace amount.
If those settings leak, then we can think of it as an issue with V-Ray, otherwise it's got more to do with setup, so turning LP off only compounds the miseries, if it removes the splotches in the very specific case.