Arnold Mesh Light doesn't work

[mosssi]

Hi guys, I'm testing Arnold for Houdini and I noticed that mesh light doesn't work in any condition. So do you think there is a way to recreate a mesh light with Arnold light shader?

Thank you

[Juraj]

Hi, you should avoid lighting your scenes with emissive shaders. You will get loads of noise and bad GI. Check arnold docs.

I do not have htoa in front of me but I played with mesh lights in past and they worked perfectly. Check docs if you are setting up everything correctly. You can also use light shader on geometry mesh and get attributes to influence your lights color, intensity etc.

[mosssi]

43 minutes ago, Juraj said:

Hi, you should avoid lighting your scenes with emissive shaders. You will get loads of noise and bad GI. Check arnold docs.

I do not have htoa in front of me but I played with mesh lights in past and they worked perfectly. Check docs if you are setting up everything correctly. You can also use light shader on geometry mesh and get attributes to influence your lights color, intensity etc.

Thank you Juraj, I looked at those pages before and I think I did everything right but actually I'm trying to light my scene with fire that I have and I thought mesh light is the best way for lighting the scene (fire to poly). So what can I do to replace my fire because of the noise that you mentioned?

 

[Juraj]

Hi, I would stick to mesh light, find out why it does not work. Make sure that mesh light and source mesh geometry are both renderable.

Before convert your fire to rough mesh and sample heat / temp values onto points and then you can use blackbody shader inside your light shader.

[mosssi]

18 hours ago, Juraj said:

Make sure that mesh light and source mesh geometry are both renderable.

Hi Juraj and thanks again. yes I didn't now that both mesh and light should be visible to arnold, although I couldn't render a full emission mesh but I turned of camera ray on mesh and now I have just fire light.

18 hours ago, Juraj said:

Before convert your fire to rough mesh and sample heat / temp values onto points and then you can use blackbody shader inside your light shader.

and about what you said about sampling heat, I didn't get it exactly. do you mean that I should use a volume VOP and sample the heat or temperature onto some random points that I scattered inside the volume itself and use those points as fire source? if it is could you tell me how should I use points for lighting? thanks man

[Juraj]

Hi, glad that you got it working

If I remember correctly, you cannot use points for mesh light, you need actual polygons (I might be mistaken). So you can convery your fire geo to rouch mesh / scatter points and copy spheres onto them. After that use wrangle / VOP to sample temp/heat values and save them into point attribute.

After that you can use light shader inside your mesh light object. There you can use User Data Float / RGB to get that attribute and drive your light color and intensity (also try to use blackbody or alBlackbody from alShaders).

[mosssi]

Thanks man, you saved my day. I managed to do what you said and it's interesting in look but the noise is really expensive to reduce. So I will try using point lights and driving the intensity and color by area of the polygon flame or maximum of sampled heat attribute and see if it works properly.

[Juraj]

Glad I helped

Yes, you can get a lots of noise. But do not try to render everything in one pass. Do separate render pass with diffuse materials and this mesh light only. You can add it in comp as light is additive and you can set up your sampling to work more efficiently in this lighting scenario.

Another idea would be like you said scattering 50 point lights inside volume and sampling their intensities

[paranoidx]

Hi, it's been a long time and still I benefit from you share @Juraj 

Thank you, that's why forum always worth than Fb