Think of photons as paint ball splats

Final gather





Turn down light



Turn up light GI photons





with fg we filled in some sports but it is still grainy



Let's look closer at our setup ...
We have a little corner setup of a plane and a L-Ext ...



The light is a Photometric Target Area light ... [as opposed to a mr Area Spot.] The combination of the ray trace shadows and an Area light is a win for soft shadows.



The multiplier is a nice way for a non-architect to adjust the light





Our units are generic, with 1 unit = 1 inch.

The number of photons per sample affects the "noisiness" of the render. A lower number is more noisy. A higher number is blurry, and longer to render.

A suggested number to start at is 100, but we are using the default 500 in this example.

Regarding max. sample radius ... photons need to overlap. If they are too small, and there aren't enough of them, they won't overlap. Setting this over 1.0 can be helpful.





This shows a render with 1000 FG ... a couple of minutes ...





Here we are trying agin to get some of the red into the walls ... FG is off

First we have sampling radius of 1.0 and 60,000 GI per light ...



Then increase radius to 2.0 and 600,000 photons per light





With FG on we can clearly see the effects of the GI below the pot as it reflects the red onto the gray floor.





If you go back and increase the energy multiplier of the light we see the red starting to spread ...





FG back on ...

The result is too "hot" or lively -- you can see the problem around the root of the handle -- but it is useful to see the effect of increasing the energy multiplier, which is not the same as the regular multiplier of a standard light. It is directly related to GI.

[I rendered out the FG version with GI off on the right, to dramatize the effect of the GI.]