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The global switches control various aspects of the renderer globally.

 

 

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||Render Setup window|| > V-Ray tab > Global switches rollout

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Light evaluation – Determines how lights are sampled in scenes with many lights.  For more information, see The Adaptive Lights example below.

Adaptive lights – Uses information from the Light cache to determine which lights to sample. If a Light cache is not used, uniform sampling is used. Depending on the scene, it can be faster than the Full lights evaluation and Uniform probabilistic lights mode.
Full lights evaluation – V-Ray goes through each scene light and evaluates it at each shading point. In scenes with many lights and lots of GI bounces, this leads to a lot of shadow rays being traced and rendering can become extremely slow. When GPU rendering, this introduces probabilistic light calculations but does not allow the Number of prob. lights to be set. Older V-Ray scenes with the Probabilistic Lights parameter disabled default to using this option.  For more information, see The Probabilistic Lights example below.
Uniform probabilistic
Light tree 1 – V-Ray randomly chooses the specified number of lights selects suitable finite light sources based on proximity and evaluates only those. Lower values make the rendering faster, but potentially more noisy. Higher values cause more lights to be computed at each shading point, thus producing less noise, but increasing render times. This option makes it possible to render images that would otherwise take a very long time, at the expense of possibly introducing more noise into the rendering. When GPU rendering, this introduces probabilistic light calculations. Previous V-Ray 3 scenes that had the Probabilistic Lights parameter enabled, default to using this option. For more information, see The Probabilistic Lights example below.This mode may speed up the Light Cache and Brute Force calculations for scenes with lots of lights. It can also reduce flickering due to missed light sources. 

Number of lights – Number of lights from the scene that are evaluated by V-Ray when the Light evaluation parameter is either Adaptive or Uniform Probabilisticis  set to Adaptive. To achieve a positive effect from probabilistic or adaptive light sampling, this value must be lower than the actual number of lights in the scene. Lower values make the rendering go faster, but the result is potentially more noisy. Higher values cause more lights to be computed at each hit point, thus producing less noise but increased render times. For more information, see The Probabilistic Lights example below.

Reflection/refraction – Enables or disables the calculation of reflections and refractions in V-Ray maps and materials.

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Example:

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Adaptive Lights

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Below is an example rendering of a scene with over 1000 spherical Area lights with the Cutoff threshold set to 0.0 (no cutoff). Both images were rendered with the Progressive image sampler for the same amount of time. When Full lights evaluation is used, the rendering is very noisy. When Uniform probabilistic mode is enabled and set to 8, the image is much cleaner as V-Ray is able to compute more GI rays, which are the main source of noise in this scene.

 

the default Bucket Image Sampler settings, using Brute Force/Light Cache GI engines. Only the Noise Threshold parameter was set to 0.001. Notice how the render time is reduced significantly in favor of the Adaptive Lights in comparison to Full Evaluation.

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Full lights evaluation

 

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Uniform Probabilistic (8 lights)

 

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Adaptive Lights; render time 26 mins

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Light Tree; render time 32 mins

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Full Evaluation; render time 38 mins

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3ds Max photometric scale – When enabled (the default), it aligns the VRayLight, VRaySun, VRaySky, and VRayPhysicalCamera to the photometric units used by 3ds Max and its photometric lights.

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Consistent lighting elements – When enabled, this option provides more accurate, artifact-free lighting render elements not dependant on light sampling. It also provides better support for Adaptive dome light. Please note, that this option is applicable to raw lighting render elements only when the corresponding normal and filter render elements are available (e.g., VRayRawGlobalIllumination = VRayGlobalIllumination / DiffuseFilter).

 

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Since V-Ray Next Update 1, some of the render elements are rendered differently than before. The Lighting render element now contains all direct diffuse illumination and the GI element contains all indirect diffuse illumination. Similarly, all direct reflections of lights now go to the Specular element and all indirect reflections go to the Reflection element.


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Previously this behavior depended on the sampling of the lights and not just on the type of the contribution. Some of the direct contributions that should be in the Lighting and Specular elements were written to the GI and Reflection elements instead. In both cases they compose back to Beauty correctly but the different types of contributions are now split between the elements more consistently.

This change makes the elements more consistent but it's also needed for preventing artifacts in these elements with the adaptive dome light (and possibly in the future with other adaptive lights).

The raw elements are affected only when the corresponding normal and filter elements are available, otherwise they're rendered as before. This is because the raw elements have to be derived internally from the corresponding normal elements in order to work with the consistent elements (f.e. VRayRawGlobalIllumination = VRayGlobalIllumination / DiffuseFilter).

There's an option to enable or disable the new behavior in the Consistent rollout under the V-Ray tab in the Render Setup window. The consistent elements are automatically enabled when the scene contains an adaptive dome light so they don't have artifacts. They are also enabled by default for new scenes. For V-Ray GPU they are always enabled without an option to disable them.

 

Footnotes

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    Since V-Ray Next, Update 2 the Uniform Probabilistic Lights evaluation method is replaced with the enhanced Light Tree evaluation method.