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Single frame – Computes a new light cache for each frame of an animation.
Fly-through
– Computes a light cache for an entire fly-through animation, assuming that the camera position/orientation is the only thing that changes. The movement of the camera in the active time segment only is taken in consideration. Note that it may be better to set Scale to World for fly-through animations. The light cache for the entire animated sequence is computed only at the first rendered frame and is reused without changes for subsequent frames.
From file
– The light cache is loaded from a file. The light cache file does not include the prefiltering of the light cache; prefiltering is performed after the light cache is loaded, so that you can adjust it without the need to recompute the light cache.
Progressive path tracing – The light cache algorithm is used to sample the final image progressively. For a discussion of this mode, see the Progressive Path Tracing With V-Ray tutorial.  

File – Specifies the file name to load the light cache from, when the Mode is set to From file. Please note that you can also load a light cache by dragging and dropping a .vrlmap file directly in your viewport. Just be aware that doing so loads it for usage immediately, turning GI on, changing its Secondary engine to Light cache and its Mode to From file.

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Fancy Bullets
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  • For flickering due to an animated camera, for short camera moves, an easy fix is to enable the Use camera path option. To remove flickering for longer camera moves where the camera is the only animated part of the scene, precalculate the light cache using Fly-through mode and then use the saved cache for the entire animation.
  • For interior renders or other complicated lighting situations, increasing the light cache Subdivs parameter will make the light cache smoother and more accurate; values around 2000 or 3000 typically work well.
  • The Retrace option helps to reduce light leaks and flickering. For animations, a value of 8.0 works well.
  • Prefiltering also smooths the light cache and reduces flickering. A Pre-filter value of 20 works well.

 

Following the above, some suggested settings could look like this:

For animations where the only moving object is the camera, enable the Use camera path option, or precalculate the light cache for the entire animation using the Fly-through mode.

For animations with moving objects and/or moving camera:

Fancy Bullets
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  • If the camera is moving at relatively small distances (f.e. within a single room of an interior render), enable the Use camera path option.
  • Set the Subdivs parameter to 3000, Sample size to 0.01, Prefilter enabled and Prefilter samples to 20, Retrace enabled and Retrace threshold to 8.0.

 

Notes

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Fancy Bullets
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  • Do not set the Adaptive amount in the Global DMC rollout to 0.0 when using the light cache, as this will cause excessive render times.
  • Do not apply perfectly white or near-white materials to the majority of the objects in the scene, as this will cause excessive render times. This is because the amount of reflected light in the scene will decrease very gradually and the light cache will have to trace longer paths. Also avoid materials that have one of their RGB components set to maximum (255) or above.
  •  If you want to use the light cache for animation, you should choose a large enough value for the Filter size in order to remove the flickering in the GI.
  • There is no difference between light caches computed for primary bounces (direct visualization) and for secondary bounces. You can safely use light caches computed in one of these modes for the other.
  • Similar to the photon map, you can get "light leaks" with the light cache around very thin surfaces with substantially different illumination on both sides. Sometimes it might be possible to reduce this effect by assigning different GI Surface ID's to the objects on both sides of the thin surface (see the Object settings window); the effect can also be reduced by decreasing the Sample size and/or the filtering.
  • The Light Cache calculation cannot be distributed among several machines for distributed rendering.
  • An alternative way of loading a light cache is by dragging and dropping a .vrlmap file directly in your viewport. Just be aware that doing so will load it for usage immediately, turning GI on, changing its Secondary engine to Light cache and its Mode to From file.

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