so far the most common approaches are: irradiance map, light cache, photon mapping (+ final gathering)
I understand how photon mapping works
I understand a little about light cache "it is noted that it is similar to photon mapping, but instead of light vertices, it stores camera vertices" , but here comes the question of "how does it estimate spectrum at any location?" in other words, it doesn't use photon density, so how does it work.
about irradiance map, I see it is similar to "targeted" brute force, so it targets sharp edges "points of interest" with higher density, and estimates irradiance at these points from hemi sphere subdivisions
all of the above is my understanding, it may be correct or totally wrong, so if some one may clarify these stuff to me this would be appreciated
, + any other well known biased methods "I totally understand other methods like PPM, VCM"