how to improve mesh light quality and reduce noise

[dfk1976]

When creating a mesh light of for example a plane geometry I could make following observations:

-increasing the plane geometry mesh segments increases the noise of the mesh light in the rendering result
-decreasing the plane geometry mesh segments decreases the noise of the mesh light in the rendering result

In the render settings -> Global DMC rollout -> Use local subdivs is disabled so how can you increase the subdivs for the mesh lights because these settings are grayed out in the mesh light settings therefore?

The only way I could imagine were to increase the -> Image sampler (Antialiasing) rollout -> Min shading rate to a higher value.

So, chaosgroup people, would this be your recommendation too? Or could there be a new option / could you add a new option to override the subdivs specifically for the vray mesh lights for example in the light properties or in the mesh light rollout itself, even if the Min shading rate is disabled?

Regards.

[^Lele^]

Mesh lights (and vraylightMtl with direct illumination active) are a notoriously hard problem to solve, so it's normal they are noisier than standard lights, and will need more samples to clear up.

The only way I could imagine were to increase the -> Image sampler (Antialiasing) rollout -> Min shading rate to a higher value.

EDIT: I read MIN AA.
Theory says you should raise MAX subdivs instead.
That's the thing about the adaptive, unified sampler: if given room (read, max subdivs), it will concentrate more work where it's needed, and *only* there.
Raising MSR will raise slack per camera ray, making final render time to convergence higher (in all but the simplest of scenarios.).

In the render settings -> Global DMC rollout -> Use local subdivs is disabled so how can you increase the subdivs for the mesh lights because these settings are grayed out in the mesh light settings therefore?

Please don't do this.
Turning back on individual nodes' subdivs is counter to the efficiency the adaptive sampler offers by default, and will lead to (loads!) more overall work (both at nodes' default subdivs, and with old-school subdivs settings for shaders and lights.).
It'll also make your scene much harder to debug.

Feel free to poke back if something isn't clear.

[dfk1976]

To understand it better what I want to ask:

I don't want to go back to the "old vray times" where you had to setup all subdivs of materials, lights etc. and adaptive image sampler settings.

So in vray (I think since version 3) the new sampling method was introduced where you could set the parameter Use local subdivs to disabled. And with this setting vray takes care of the image sampling. From my understanding when setting Min shading rate to higher values normally you should get better results for DOF, glossiness, area shadows, light sampling etc.. And here I want to know if vray could have a separate setting only for the mesh lights which can improve the mesh light quality. The goal should be that you can set a value for Min shading rate for DOF, glossiness, area shadows, light sampling and a separate shading rate for the mesh light sampling (override the mesh light subdivs).

Do you understand what I mean?

[^Lele^]

I do understand, it's a good idea in principle, but it falls in the same category as the MSR itself, in terms of how sampling is done and eventual slack.
I have been told some better sampling strategy will soon (ish!) be implemented, and that will take care of the noisier mesh lights, without user intervention.

[jacksc02]

lele This new sampling strategy sounds interesting!