When you need to light a scene with light emitting objects, the worst case scenario is when you have a VDB object. With global illumination, your scene will work but the effect will be very expensive to render.
One of our clients needed to render cannon fire effects and thus illuminate the scene with each explosion flash. They found a trick to replace the global illumination effect by area lights dynamically textured by renders of the VDB sequences, and they dramatically reduced the render time with similar results.
In this video, I’ll show you this technique based on Clarisse’s ability to use a live render as texture. You’ll see how a small render of VDB explosion could be used to texture an area light. Thanks to this tip, you’ll get similar results, compared to a GI light, with faster render times!
The same technique can be used for a lot of tricky lighting scenarios, like indirect interior lighting.
Here is a reconstruction of the setup, using a simplified geometry.