Page History

 When rendering with V-Ray GPU, the Render Mode does not matter - Render Elements are generated and the rendering speed is the same in both the Volumetric and Volumetric Geometry modes.

Volumetric Options → Smoke Color → Volume Light Cache | Light Cache Speedup.

In general, for lower-resolution simulations, the Phoenix FD Light Cache will significantly speed up the rendering. As the resolution increases, the benefit from using the Phoenix FD Light Cache diminishes. If Volume Light Cache is disabled, try enabling it to check if that will speed-up the rendering. You can reduce the render times significantly by increasing the Light Cache Speedup setting. Increasing it from 0.9 to 0.99 to 0.999 should yield a big difference in render speed.

The Light Cache Speedup should be increased until artifacts start appearing in the rendered image. Grid Light Cache artifacts will look like voxel-sized dark and bright spots. They would also flicker in animation. Grid artifacts start appearing when a voxel does not get to cast enough shadow rays – this is usually related to the lighting setup – e.g. the illumination is too dim, there are too many grids in the scene, etc. If you see these artifacts, then your Light Cache Speedup is too high and you have to decrease it. If decreasing it to zero still does not help, disable the Light Cache.

Disable the Volume Light Cache option if:

1. Reducing the Light Cache Speedup option to zero does not help resolve artifacts in the smoke. If you see bright and dark voxels, this means the light cache speedup is too high. If you see pixel sized noise, then it's the sampling - you should adjust the V-Ray settings accordingly (e.g. increasing the Max Subdivs for the Bucket Sampler).
2. You are rendering an animation and you notice flickering which will not go away after reducing the Light Cache Speedup.
3. You are using Progressive rendering.
4. There are multiple grids in the scene - for a large number of grids in the same scene, disabling the Phoenix FD Light Cache might speed things up, as opposed to a single grid where it's best to keep it enabled.

All options under the Rendering roll-out are supported by V-Ray Adv (CPU).

The following options are not supported by V-Ray GPU:

1. Smoke Color → Scattering → Approximate & Approximate+Shadows - V-Ray GPU is significantly faster when using the Ray-Traced (GI Only) option. V-Ray Global Illumination should be enabled for this option to have any effect.
2. Smoke Color → Volume Light Cache. This option refers to the internal Phoenix FD Light Cache,  which is not related to the V-Ray Light Cache. It's a CPU-only feature that helps speed up Bucket rendering.
3. Fire → Fire Lights. All Fire Lights options are ignored when rendering with V-Ray GPU. Enable Global Illumination from the V-Ray Settings if you need the Smoke and/or the scene to be illuminated by the fire.