It would not slow things down much in simple scenes, but could boost them up in cases like interiors. So maybe it would be a good idea for dome lights to be generally sampled twice more. Corona for example, has global sampling multiplier for all light sources set to 2 by default. Generally, I think that the problem is the dome light by default is not sampled enough, and with universal settings + global subdivs approach, there is no way to increase for DomeLight specifically. It is something I've already reported here: but it did not get much attention.

I tested that hypothesis by removing curtains and instead narrowing down the window opening: V-Ray for 3ds Max V-Ray for 3ds Max :: Issues If this is your first visit, be sure to check out the FAQ by clicking the link above. Not an issue of 2sided mtl but rather that DomeLight is generally inferior to Corona's IBL when sampling deeper interior scenarios. Now, I suspect that this is related to something I've reported some time ago. The slight brightness difference is due to the slight differences in CoronaSky vs VraySky, non the less it's not nearly as much different to attribute to such performance difference. This is V-Ray 3.40 with 100% defaults at 1 minute:ДЄnd this is Corona 1.5 with everything default except time limit changed from 0 to 1 minute: I've made very similar scene from scratch to avoid possibility of trying to debug a scene from inexperienced user who flipped some obscure switch somewhere, and yet I was able to reproduce the behavior: There is no reason V-Ray should not be able to handle such cases better without need to tweak settings or introduce things like denoiser to cover the problem up.

I do not think the point here is to get down to tweaking of all sorts of parameters, but rather that Corona simply seems to handle this (in archviz quite common) case a bit better by default.

Curtain material vray 3ds max