Specifies a minimum for how many nearby values to interpolate. For example, set this value to three. If we are shading a point and can only find two nearby previously computed values in the cache, then it forces the computation of a new value at the current point, and the final irradiance at that point is a blend of all three values. So it tends to smooth out the shading. Increasing this value improves render quality at the expense of render time.