Bright spots with VRayBlend Material

[AltoR]

Hi

On a very simple archviz scene lit by a VRay Sun and VRaySky, some weird bright spots appear on a metalic part of the building. The shader of this part is a simple VRayBlend material composed of 2 VRayMtl with some glossy reflections in it (subdivs 70) with a Falloff map as mask. Render settings are set quite high (Irr map Hsph 140, LC 2200, Adaptive DMC 4/12, noise threshold 0.003).
Render time is 3mn11s.
If I replace the VRayBlend Mtl by a simple VRayMtl with same glossy reflections and same subdivs (70), render time drops to 0mn31s (!) and weird bright spots disappear ... So it seems to be an issue with the VRayBlend Mtl ... but I have no idea on how to solve it.

Can someone help me please ?

Thank you in advance

[tashko.zashev]

Hi,

Can you post a stripped down version of this scene, in order to reproduce this issue quickly?
Thank you in advance.

[AltoR]

Here is attached a simplified version of the scene. I checked: the bug still happens. In fact, the bug seems to happen because of the glass material instead of the VRayBlend one like I first thought: when I hide the glass panes, it renders fine, no more bright spots on the metal. When glass panes are visible, here comes the bug again. My glass material is a very simple VRayMtl so ... I still don't understand ...

[tashko.zashev]

Thank you for posting the scene file Altor.

Basically these bright spots are caustics, which are produced by the IRR map calculations ( "Reflective" GI caustics option in the IRR map parameters is checked).
They are actually a indirect light that is reflected from the window glass and appeared over the metallic part. So usually this option should be Off, especially when use V-Ray Sun that produces very high intensity specular reflections.

For more information about this option you can check the Spot3d (http://www.spot3d.com/vray/help/200R..._params_gi.htm)
I hope this helps you.

[AltoR]

OK I understand now.
Thank you so much for your support and have a good day