Performance difference between VrayLight mesh and VrayLightMTL

[LudvikKoutny]

Hi,

I was wondering, is there any performance difference between using VRayLight set to mesh and VrayLightMTL? Say I have mesh made of about 30 thin and long polygons to be used as cove lighting. Is there any benefit of using VRayLight set to mesh over applying VrayLightMTL on that geometry?

Thanks.

[julianb]

Hey,
from what I know if you transform your geometry (the thin and long polygons in your case) into an actual light (by using the V-Ray Mesh Light icon) you get all the benefits of a light that you can tweak from the Modify panel in Max.
If you simply applied a VRayLightMtl to the thin and long polygons you will get just a few options in the material editor that you can change.
Also (and I might be wrong here)- I believe a mesh with a VRayLightMtl is more prone to cause things like fireflies (overexposed pixels) in your final render and then you have to fight that with other means.
If I were you I would just convert the geometry into a V-Ray light. You can always get your geometry back from the V-Ray light anyway.

[LudvikKoutny]

I actually observed nearly no difference (except for the unnecessarily more control provided by VrayLight) but I did not do any advanced testing, hence my question.

[Morne]

VRayLightMTL works in the GI element (not the VRayLighting element). So it will brighten up your GI, but not your Lighting channel. Something that should be considered depending on your comp needs. I find that brightening the GI renders quicker than brightening the Lighting channel.

Make sure you DON'T tick "Direct illumination" in the VRaylightMtl as this will just be a lot harder to clean up

[LudvikKoutny]

VRayLightMTL works in the GI element (not the VRayLighting element). So it will brighten up your GI, but not your Lighting channel. Something that should be considered depending on your comp needs. I find that brightening the GI renders quicker than brightening the Lighting channel.

Make sure you DON'T tick "Direct illumination" in the VRaylightMtl as this will just be a lot harder to clean up

Well, obviously the point is to be using direct illumination inside of VrayLightMTL, otherwise it won't be explicitly sampled light source, but just luminous surface picked up by GI without any smart sampling. What I am asking about here is difference between VRayLight set to mesh light and VrayLightMTL with Direct Illumination enabled.

It's not a lot harder to clean up by the way. It's beneficial depending on scenario. If you have huge but dim light source, then it would make more sense to keep it of. But if you have very small and strong light source that's quite away from the rendered surface, then there's no chance to get optimal result unless you turn direct illumination on.

[vlado]

If you are using the "direct illumination" option in a VRayLightMtl material, there is no performance difference between a VRayLightMtl and a mesh light.

Best regards,
Vlado

[LudvikKoutny]

If you are using the "direct illumination" option in a VRayLightMtl material, there is no performance difference between a VRayLightMtl and a mesh light.

Best regards,
Vlado

All I needed to know. Thanks!

[Morne]

It's not a lot harder to clean up by the way. It's beneficial depending on scenario. If you have huge but dim light source, then it would make more sense to keep it of. But if you have very small and strong light source that's quite away from the rendered surface, then there's no chance to get optimal result unless you turn direct illumination on.

Yes well you didn't mention direct illumination for VRayLightMTL in your 1st post, but you did mention cove lighting. Since cove lighting is basically indirect lighting (a hidden light), I would say VRayLightMtl with direct illumination off is the way to go in that scenario