Hi, I have a scene with fireworks and would like the sparks to light up the smoketrails. So far, it seems I can only light up my volumetrics with lights, not with an emissive material on the particles. Is that a Houdini limitation? Or am I missing a setting somewhere?

ATM, I can get my result only by instancing lights to the particles, which gets very slow when I'm emitting tons of particles, and doesn't transfer all the relevant point attributes (size/brightness/alpha) to the lights.

Thanks,
Jasper

I think only a point (particle) cant emit. It needs some prims (faces) so maybe tiny boxes or tedraeder with an emissive material could do the job.

But i think you should probably “fake” this by building some sort of geo from the particles or some selection of your particles especially if it is a ton of particles…

Hi Olaf, I don't see any result from any geo with emissive material. Am I missing something somewhere?

Hi, I wanted to look into this for future reference and put together a quick scene to investigate.

I'm not sure this will be much help for your needs but it may provide some options to explore. As you can see from the images and hip file, enabling Emission Illuminates Objects won't affect the volume but using a Geometry Light will.

I'm sure there must be better methods so I've posted hoping to gain some more knowledge.

Rob

Did you increase volume level above 0? Volumes aren't any different than diffuse surfaces in this regard. If the ray limit is 0, no rays are sent into the scene.

Edit:
This is definitely broken. I did a test with nonzero volume limit, to no effect.

Edit2:
Enabling PBR allows emission to effect volumes with volume limit 1.

OOoh, that's it - volume limit was on zero, thanks jsmack!

-Jasper

It's probably because emission is indirect light (?), so raising volume limit above 0 makes sense. If you want direct light I guess geometry light is the way to go.