Filter – 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 might produce artifacts near corners if the light cache is noisy. You can use the Pre-filter setting to decrease the noise. This option works best if the light cache is used for secondary bounces only, or for testing purposes.
Nearest – 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 – 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 that the units used depends on the Scale parameter.