VrayMeshLights extreme long render times

[peprgb]

Hi,

I was having really high render times in a simple scene so started finding the problem...

I have 4 Cylinders as VrayMeshLights, with 32 subdivs for these lights the times goes very very high. Every single bucket is rendered slow, not only those from the are of lights (yes, i guess this is because the lights affects all the scene.

Using max 2012, Vray 2.4.03, really low render settings.

times:

1_ VrayMeshLights OFF: 3min 12seg
2_ VrayMeshLights ON 8 Subdivs: 5min 27seg
3_ VrayMeshLights ON 32 Subdivs: 1hour....

[joconnell]

Pop up a sample rate pass but I'd be almost inclined to use 4 area lights to make a long strip box instead of the cylinders.

[peprgb]

Here Sample rates, more green dots on the 32 Subdivs but almost same thing. On the RGB of course we see more shoft shape.

Yes, putting area lights the results is almost the same, and no problems with high subdivs.

Thanks,

[joconnell]

Righty - so it seems like your AA is doing pretty much all the work here - it actually looks like quite low settings overall.

Could you stick up:

-Your aa min and max
-Do you have "use dmc threshold" wicked on or off, beside your aa min / max? If so what number is in there?
-Stick up the reflection subdivs you're using on floor, ceiling and wall materials?
-What GI method are you using?
-Also could you put up a reflection pass, MTL glossiness pass, a raw lighting and a way global illumination pass?

Just trying to find what's really noisy in the scene.

The light coming from the left of the scene - what's that from?

[Svetlozar Draganov]

Is it possible to attach a simplified version of your scene - just the walls / floor / ceiling / lights and screen/cover object which hides mesh-lights.
Thank you very much in advance.

[peprgb]

The red colors are high AA? so then is doing in all the scene, this is the problem, these 2 lights affects every bucket being soooo slong rendering.

The floor hasn't any reflection and there is only one Vray Dome light, i cant understand the problem, thus, the problem is on high subdivs of VrayMeshLight, but dont understand how this is affecting sooooo drastically.

The settings are low,
- AA Adapt. DMC 1-2
- "use dmc threshold" is ON (being 0,01 the DMC Sampler Noise thr.)
- GI: IRR (Low, 35 hs-20int)+LC/500 Sub)

Will save the channels you are asking, but i dont think there would be so much there...

[peprgb]

Is it possible to attach a simplified version of your scene - just the walls / floor / ceiling / lights and screen/cover object which hides mesh-lights.
Thank you very much in advance.

For sure, here is attached, the thing is curious because with another really similar scene i almost dont have differences in render times with 8 or 32 subdivs on the VrayMeshLIghts.

Try rendering with 8 subdivs and 32 subdivs (they are 2 separated mesh lights, but attached the problem was there too).

Thanks,

file is max 2012

[joconnell]

Hmm - if I render that scene I get pretty much nothing but black aside from a portion of light in the bottom left?

[peprgb]

Uoppss, i guess this is for the missing HDRI, try putting Dome mult. to 30 or so...

thank you!!

[joconnell]

There're a lot of things in that scene using plugins and textures I don't have, will try something with a flat grey shader but it's not going to be totally accurate to your scene!

[peprgb]

Thanks joconnell, well the HDRI was not the problem so dont understand the issue with black scene (i unticked "Use texture" amd is rendering fine with 1.4 Mult)

Yep, im using MultiTexture and MightyTiles (but this one was changed for a yellow/white VrayMtl).

[Svetlozar Draganov]

For sure, here is attached, the thing is curious because with another really similar scene i almost dont have differences in render times with 8 or 32 subdivs on the VrayMeshLIghts.

Try rendering with 8 subdivs and 32 subdivs (they are 2 separated mesh lights, but attached the problem was there too).

Thanks,

file is max 2012

Thank you very much for the attached file.

I think I found what cause this excessive render times - it is some strange combination from Dome Light , Mesh Lights and DMC Sampler.

The first suspicions option was activated Double Side in Mesh Lights - since they are cylinders this is not needed and with only this OFF I got around 30% faster render times.
The other very strange connection was between Dome Light and Mesh Lights - if I increase Mesh Light Subdivisions from 8 to 32 the whole image calculates much slower even on the areas not illuminated by Mesh lights , which made me think that the problem is not in the Mesh Lights but in the Dome Light. When I increased Dome Light subdivisions to 32 - the render us much faster and with less noise.
The next change was in DMC Sampler - I changed it to 1 / 6 / 0.02 - this gives me good quality / speed ratio.
And finally I decrease light intensity from Dome Light and Mesh Lights a bit - because Vray doesn't like overexposured spots.

With these tweaks render time from 5min 20 sec (original scene with Mesh Light subd=32 ) went to 34s with almost the same quality.
debug_alto07.zip

[peprgb]

Woww really weird thing!! saving your comments if the case, for the future.

Thank you very much!!