I was reading this article where they describe implementation of "light probes" in Unity game engine.

Quote from that article:

The useful property of spherical harmonics encoded probes is that a linear interpolation between two probes would just be a linear interpolation of their coefficients.

I don't know how to do this with more then 2 probes?

If i use distance from object to probe as a weight, how can i do this with (let say) 4 nearest probes?

How do i sum up this weighted vectors into one/final?