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Store direct light - when this option is on, the light cache will also store and interpolate direct light. This can be useful for scenes with many lights and irradiance map or direct GI method for the primary diffuse bounces, since direct lighting will be computed from the light cache, instead of sampling each and every light. Note that only the diffuse illumination produced by the scene lights will be stored. If you want to use the light cache directly for approximating the GI while keeping the direct lighting sharp, uncheck this option.

Show calc. phase - turning this option on will show the paths that are traced. This does not affect the calculation of the light cache and is provided only as a feedback to the user. This option is ignored when rendering to fields - in that case, the calculation phase is never displayed.

Adaptive sampling - when this option is on V-Ray will store additional information about the incoming light for each light cache sample, and try to put more samples into the directions from which more light is coming. This may help to reduce the noise in the light cache, particularly in the case of caustics.

Use camera path - when this option is on V-Ray will calculate the light cache samples for the entire camera path, instead of just the current view, in the same way as this is done for the Fly-through mode. This is useful when rendering animations with moving objects where the camera also moves and the light cache needs to be in Single frame mode. In this case, setting the Use camera path option on will help to reduce any flickering, as the GI sample positions on static geometry will not change.

Reconstruction Parameters

These parameters control how the light cache is used in the final rendering, after it has been calculated.

Prefilter - when this is turned on, the samples in the light cache are filtered before rendering. Note that this is different from the normal light cache filtering which happens during rendering. Prefiltering is performed by examining each sample in turn, and modifying it so that it represents the average of the given number of nearby samples. More prefilter samples mean a more blurry and less noisy light cache. Prefiltering is computed once after a new light cache is computed or loaded from disk.

Prefilter samples - this parameter controls the number of samples taken during prefiltering.

Filter Type - this determines the type of render-time filter for the light cache. The filter determines how irradiance is interpolated from the samples in the light cache.

• None - no filtering is performed. The nearest sample to the shaded point is taken as the irradiance value. This is the fastest option, but it may produce artifacts near corners, if the light cache is noisy. You can use pre-filtering (see below) to decrease that noise. This option works best if the light cache is used for secondary bounces only or for testing purposes.
• Nearest - this filter looks up the nearest samples to the shading point and averages their value. This filter is not suitable for direct visualization of the light cache, but is useful if you use the light cache for secondary bounces. A property of this filter is that is adapts to the sample density of the light cache and is computed for a nearly constant time. The Interpolation samples parameter determines how many of the nearest samples to look up from the light cache.
• Fixed - this filter looks up and averages all samples from the light cache that fall within a certain distance from the shaded point. This filter produces smooth results and is suitable for direct visualization of the light cache (when it is used as the primary GI engine). The size of the filter is determined by the Filter size parameter. Larger values blur the light cache and smooth out noise. Typical values for the Filter size are 2-6 times larger than the Sample size. Note that Filter size uses the same scale as the Sample size and its meaning depends on the World Scale check box.

Interpolation Samples - when the Filter Type is set to Nearest this parameter determines how many of the nearest samples to look up from the light cache.

Filter Size - when the Filter Type is set to Fixed this parameter determines the size of the filter. The units of the value is determined by the state of the World scale parameter.

Use light cache for glossy rays - if this option is on, the light cache will be used to compute lighting for glossy rays as well, in addition to normal GI rays. This can speed up rendering of scenes with glossy reflections quite a lot. 

Depth - this parameter determines the length of the light paths to be traced. It is important to note that even though in Light cache the depth is limited, due to the recursive nature of this method there will be longer paths in the end result.

Use retrace threshold - when enabled, this option improves the precision of the global illumination in cases where the light cache will produce too large error. This is especially obvious with the Use light cache for glossy rays option, or near corners where light leaks might be possible because of the light cache interpolation. For glossy reflections and refractions, V-Ray dynamically decides whether to use the light cache or not based on the surface glossiness and the distance from it so that the errors due to the light cache are minimized. Note that this options may increase the render time.

Retrace threshold - specifies a threshold for the distance.