vray lights cause weird spots

[Kitchensink]

Hi guys,

I'm sure there is a simple explanation for this but I just can't seem to figure it out. When I try to create a natural looking lampshade effect, the combination of a vray sphere light and a lampshade made with a vray 2-sided material seems to give the best looking and most realistic effect. The problem ( as seen in the image below ) is that it will generate these perfectly round light spots on surrounding geometry. Sometimes many and sometimes only a few but it will always do it. We have tried bumping up settings of the materials, the render settings, and the light itself but it does not seem to work.


Any ideas?

Thanks for any help you can send my way.

[vlado]

They look like reflective caustics from the metallic base of the lamp; do you have reflective GI caustics enabled or disabled?

Best regards,
Vlado

[Kitchensink]

seeing spots?

Thanks for the reply. I do not have the reflective caustics checked ( refractive is however ) but to test your theory I changed the lamp base material to a matte color and the spots went away. That being said, it obviously has something to do with the combination of the vray sphere light and the reflective material properties it is reacting with. If the reflective GI caustics is not checked then what else do you think it could be?

[Kitchensink]

got it!

OK, I think we found the problem. The wall material has a small amount of blurry reflection on it. The reflective subdivision of the wall material was set at the default 8 with interpolation checked on to speed render time. If we uncheck interpolation, the spots will go away. It will also go away if we keep interpolation on but bump the subdivisions up to 32 or 64. It seems as though the light is bouncing off the highly polished chromes legs and then hitting the wall but the wall does not have enough samples to deal with it properly. Does this sound like a plausible answer to anyone?


Thanks.

[vlado]

I see; this can be the reason then. Since the wall is glossy, some of the reflected rays may bounce off the metal stand and hit it under an angle to produce a hilight. Since this happens only very rarely, and the hilights are very bright, you get them spots.

Best regards,
Vlado